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JAW User Guide

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1. class MouseEventHandler public WindowHandler public MouseEventHandler JNIEnv env jobject obj protected virtual bool wantMsg UINT uMsg virtual bool evMsg HWND hWnd 20 UINT uMsg WPARAM wParam LPARAM 1Param private void sendMouseMessage int message int x int y 3 endif In addition to reporting the mouse events in the implementation of MouseEventHandler the native window can be dragged by pressing the left mouse button To realize this feature we register WM MOVE and move the window to its new position with SetWindowPos MouseEventHandler cpp include MouseEventHandler h Jf sesesesssesesesse SELEETOF s esse seseeeseseseeeeeseseneses WindowHandler selectWindowHandler JNIEnv env jobject obj int select return new MouseEventHandler env obj sesesesssesese se class MouseEventHandler Constructor initialize base class MouseEventHandler MouseEventHandler JNIEnv env jobject obj WindowHandler env obj te Select which windows message will call evMsg bool MouseEventHandler wantMsg UINT uMsg return uMsg WM CREATE WM_LBUTTONDOWN WM LBUTTONUP WM_LBUTTONDBLCLK WM MOVE WM PAINT WM_DESTROY Event procedure Return false if message is handled by this procedure true to invoke DefWindowProc bool MouseEventHandler evMsg HWND hWnd UINT message WPARAM wParam LPARAM lParam 21 s
2. you fill the buffer with write lt type gt methods e g for characters writeChar A writeChar B writeChar C writeChar D writeChar E ys 3 readBuf transfers the given number of data or all available data from the JNIBuffer to the Java array e g readBuf 2 requests 2 elements from the JNIBuf fer If less than 2 elements are available only these are transferred to the Java array readBuf returns the number of elements actually transferred Since we have 5 characters in the JNIBuffer we get 2 and the oldest two characters A and B are transferred Since the JNIBuf fer is implemented as circular FIFO buffer its head pointer is advanced for two elements Java accesses the transferred elements through value 0 and 47 value 1 Fig 1 5 illustrates this process of course the empty fields are not really empty but contains invalid data Since JNIBuf isa circular buffer there is never a memory overflow When the buffers fills up an overflow flag is set and subseguent data are lost The state of this flag may be requested and reset by isBufOverflow writeChar writeChar writeChar writeChar writeChar readBuf 2 A B Java Buffer JNIBuffer Fig 2 5 JAW FIFO buffer JNIBuffer of size 18 In the next example you learn how this works We use a low cost interface USB AD12 from BMC http www bmcm de but
3. Implement ExitListener public void notifyExit nh destroy System exit 0 private void displayEvent Switch evt case NativeMouse 1Press report LeftButtonDown x y break case NativeMouse 1Release report LeftButtonUp x y break case NativeMouse 1DClick report LeftButtonDoubleClick x y break private void report String msg int x int y System out println msg at gt x y y public static void main String args new JawEx4 The callback method mouseEvent has 3 integer parameters the first is a code for the event type the other are the coordinates x and y where the event occurred We strongly advice against long lasting code in any callback because they may happen in a rapid succession It is much better to copy the values to instance variables and to wake up a sleeping Java thread that performs the more lengthy operation of displaying the values in the console window In the C project named mouseevent we declare the class MouseEventHandler Like before in order the image file rose bmp to be loaded the resource file MouseEvent rc must be part of the project MouseEvent rc ROSE BITMAP DISCARDABLE rose bmp The interface MouseEventHandler h is very simple MouseEventHandler h ifndef MouseEventHandler h define MouseEventHandler_h __ include jaw h Jf seseseseeesee class MouseEventHandler
4. Initializing Creating task OK Open channel OK Start task OK Getting data 1 0 004796481290760823 v 2 7804447419857858 V 3 4744458173444919 V 4 9949466238635214 V 5 5562710230507104 v 6 893065662563023 V 7 291095691077576 V 8 6074705342558098 V 9 8218023957636458 V 10 4 597450656458669 V 11 5 077127870309539 v 0 1 L 2 2 3 3 3 Fig 2 3 Output from JawEx6 when the input voltage varies slowly 2 5 2 Porting contAcquireNScan When the sample rate exceeds 1000 Hz reading and processing each single data with a timer is not suitable Entire blocks of data should be transferred from a acquisition module to a fast buffer often implemented with DMA The module hardware and the driver software must be designed accordingly as it is the case with NI modules and the NI DAOnx software The sample program contAcguireNScan from the NI DAOnx distribution shows how to proceed With JAW it is rather simple to port the functionalities to Java For lack of space the original code is not show here Like a two channel oscilloscope the application shows two input signals from the ADC at a sampling rate of 5 kHz sampling period 0 2 ms in a simple graphics window using GPanel from the package ch aplu util Most of the ideas comes from the previous example and are not explained again We still initialize step by step and display the results in the title bar of the graphics window A single data
5. min JNIVar lt double gt _exposedObj min get max JNIVar lt double gt _exposedObj max get NIDAOAcguirelScan NIDAQAcquirelScan delete chan if taskHandle 0 DAQmxBaseStopTask taskHand1e DAQmxBaseClearTask taskHandle int NIDA0AcguirelScan invoke int val Returns 0 if successful 1 if error Switch val case 0 Create task DAQmxErrChk DAQmxBaseCreateTask 8taskHandle break case 1 Open channel DAQmxErrChk DAQmxBaseCreateAIVoltageChan taskHandle echan T DAQmx_Val_RSE min max DAQmx_Val_Volts NULL break case 2 Start task DAOmxErrChk DAO0mxBaseStartTask taskHandle break case 3 Get data DAOmxErrChk DAQmxBaseReadAnalogF64 taskHandle pointsToRead timeout DAQmx_Val_GroupByChannel amp data samplesPerChan 36 amp pointsRead NULL JNIVar lt double gt _exposedObj value set data break case 4 Sleep Sleep period break return 0 Error if DAQmxFailed error DAQmxBaseGetExtendedErroriInfo errBuff 2048 if taskHandle 0 DAQmxBaseStopTask taskHand1e DAQmxBaseClearTask taskHandl1le if DAQmxFailed error JNIString exposedObj errorDescription setMBCS errBuff return 1 return 0 If everything goes well the values of a slowly varying voltage from the ADC is displayed every second Fig 2 3 37 FJ Java Input Output Console Iof x
6. block burst contains 200 values of each channel and is retrieved from the native buffer by calling invoke 5 We must ensure that this call is repeated every 200 0 2 ms 40 ms on average in order to avoid any buffer 38 overflow When the system is heavily loaded by other processes this value can be exceeded for a while without loosing any data or getting incorrect values In order to terminate the application properly an ExitListener is implemented so that notifyExit is called when the close button of the graphics window is hit In notifyExit all necessary cleanup operations are done JawEx7 java ContAcquireNScan from NIDAQmx distribution Acquire faster varying analog data and display on GPanel For demonstration with NI USB 6008 interface connect a first signal at terminals 2 and 32 GND and a second signal at terminals 5 and 32 GND both in range 10 10V import java awt Color import ch aplu util import ch aplu jaw public class JawEx7 implements ExitListener Transfer variables private String channel Dev1 ai10 Dev1 ai1 AIO amp AI1 private double min 10 Measuring range 10 10V private double max 10 private double sampleRate 5000 0 Samples per seconds private long samplesPerChannel 200 Samples per burst private String errorDescription new String Verbose error report private double data new double 2 int samplesPerChannel Data per
7. burst End of native variables private NativeHandler nh private int time 0 private int maxTime 2000 ms private double dt 1000 0 sampleRate ms private GPanel p new GPanel 0 maxTime min max private volatile boolean isRunning false private double offset8 4 y offset of AIO private double offsetl 4 y offset of AI1 private String title NI ADC x maxTime 10 ms div y max min 10 V div public JawEx7 p title Initializing drawCoordinateSystem p addExitListener this 39 nh new NativeHandler c myjni nidaqc release nidagc dll this if isError nh invoke 0 return if isError nh invoke 1 return if isError nh invoke 2 return if isError nh invoke 3 return if isError nh invoke 4 return p title title int pointsRead Number of samples in one burst int oldTime 0 double oldEndData0 double oldEndDatal isRunning true while isRunning 0 0 while time lt maxTime Get data block by block pointsRead nh invoke 5 if pointsRead 0 p title Error while reclaiming data isRunning false break Draw signal AIO p color Color red p move oldTime oldEndData0 for int 1 0 1 lt pointsRead 1 p draw time i dt data 2 i offset0 oldEndData0 data 2 pointsRead 1 offset0 Draw signal AI1 p color Color green p move oldT
8. establish by calling the C function selectWindowHandler JNIEnv env jobject obj int select This is the only relict of JNI In the body of this function a user provided C class here called MyWindowHandler must be instantiated that is derived from WindowHand ler The JNI parameters env and obj are used to initialize WindowHandler They are never seen in the user code any more select is used to distinguish more than one class in the same C project This concept shields the user from most of the internal mechanism of JNI For simplicity the invocation of C methods is exclusively performed by NativeHandler s method int invoke int tag where the parameter tag is used to select one of several C methods The data transfer between Java and C is mainly done through Java instance variables In some simple cases the return value of invoke or callbacks may be used instead Because the access to instance variables are based on C templates this mechanism is particularly simple and omits ugly type casts between JNI and C data types Different overridden constructors of NativeWindow provide different native behavior In the most simple situation only the path of the native DLL is passed In order to give C read and write access to instance variables of a Java class its reference is passed to the constructor or expose is called As the word suggests this operation exposes even private instance variables to the C code that may acc
9. if you do not have this module you can define define simulation and the programs runs in a simulation mode 48 The module USB AD12 has 16 analog input channels 12 bits SV single ended one output Channel 12 bits and 4 digital I O channels The function library is freely available from the manufacture s homepage search machine with keywords libad4 sdk It contains the DLL libad4 dll and its import library libad4 lib The USB driver called install drivers lt version gt exe must be installed separately Like in the previous example the acguired data are displayed in a simple graphics window GPanel from package ch aplu uti1l A native timer that runs in a native high priority thread requests a new voltage value every 20 ms In the title bar of the graphics window we show the number of remaining data elements in the JNIBuffer Because this number can exceed 100 when the system is heavily loaded you realize the need of a native FIFO buffer In the reading loop we call readBuf 1 and transfer only one element if one is available JawEx8 java import ch aplu jaw import ch aplu util public class JawEx8 implements ExitListener Native variables private String device usb ad private int period 20 ms private int maxTime 10000 ms private double range 5 5V End of native variables private NativeHandler nh private GPanel p new GPanel 0 maxTime range range public JawEx
10. 0 0 pointsToRead 1 chan exposedObj channel getUTF8C min JNIVar lt double gt _exposedObj min get max JNIVar lt double gt _exposedObj max get samplesPerChan JNIVar lt __int64 gt _exposedObj samplesPerChannel get sampleRate JNIVar lt double gt exposed0bj sampleRate get 43 Timing parameters strcpy clockSource OnboardClock Data read parameters pointsToRead int32 samplesPerChan NIDAQContAcquireNScan NIDAQContAcquireNScan delete chan if taskHandle 0 DAQmxBaseStopTask taskHand1le DAQmxBaseClearTask taskHandl1le i int NIDAQContAcquireNScan invoke int val Returns 0 if successful 1 if error Switch val case 0 Create task DAQmxErrChk DAQmxBaseCreatelask amp taskHandle break case 1 Open channel DAQmxErrChk DAQmxBaseCreateAIVoltageChan taskHandle ehant ekin DAQmx_Val_RSE min max DAQmx_Val_Volts NULL break case 2 Configure internal clock DAQmxErrChk DAQmxBaseCfgSampClkTiming taskHandle clockSource sampleRate DAQmx_Val_Rising DAQmx_Val_ContSamps samplesPerChan break case 3 Allocate buffer 44 DAOmxErrChk DAQmxBaseCfgInputBuffer taskHandle 200000 break case 4 Start task DAQmxErrChk DAQmxBaseStartTask taskHand1e break case 5 Acquire data JNIArray lt double gt jary _exposedObj data double data jary get DA
11. 8 p addExitListener this nh new NativeHandler c myjni bmc release bmc d1l1l this double values new double 1 Array of 1 double nh createBuf values JNIBuffer with default bufSize nh startThread Start high priority thread int time 0 while true int nbPending nh countBuf Show number of pending data on heavily loaded systems if time gt 0 amp time 200 0 p title Buffer Count nbPending Read exactly one element from buffer if nh readBuf 1 1 49 if time 0 p clear drawCoordinateSystem p move time values 0 else p draw time values 0 time period if time gt maxTime time 0 Sleep 1 ms if few pending data in order to decrease CPU load substantially if nbPending lt 2 Console delay 1 private void drawCoordinateSystem double xspan maxTime 10 vor ime 1 98 1 S 198 13 p line i xspan 10 1 xspan 10 double yspan 2 range 10 Tor ime 1 OF 1 lt 195 iar p line 0 range i yspan maxTime range i yspan public void notifyExit nh destroy System exit 0 public static void main String args new JawEx8 We will not waste CPU time when no elements are ready to be transferred Therefore we put the Java thread to sleep for 1 ms if the number of available elements is less than 2 Because we read a new value every 20 ms and the JNIBuf
12. AQContAcquireNScan private int invoke int tag Task parameters int32 error TaskHandle taskHandle char errBuff 2048 int32 16 Channel parameters const char chan float64 min float64 max Timing parameters char clockSource 128 uInt64 samplesPerChan float64 sampleRate Data read parameters int32 pointsToRead int32 pointsRead 42 float64 timeout pe tendif The implementation is scarcely different from the previous example and should be self explanatory by consulting the original code of AcquireNScan c We just point out how easy it is to fill the Java array by calling invoke 5 You simply get the array pointer with JNIArray lt double gt jary _exposedObj data double data jary get and pass it to DAQmxBaseReadAnalogF 64 for filling the Java array NIDAQHandler cpp National Instruments NI DAQmx Prototype contAcquireNScan c from distribution of NI DAQmx include NIDAOHandler h define DAQmxErrChk functionCall if DAQmxFailed error functionCall goto Error jf seseseseseseses SELECTOP sseseseseeeseseseeeseseseeeses WindowHandler selectWindowHandler JNIEnv env jobject obj int select return new NIDAQContAcquireNScan env obj ff seeeseseseeeee es class NIDAQContAcquireNScan NIDAQContAcquireNScan NIDAQContAcquireNScan JNIEnv env jobject obj WindowHandler env obj samplesPerChan 1 timeout 1
13. AWT windows Native windows may have interesting properties missing in Java like semi transparency In the next example you create a window with selectable transparency level It contains an BMP image As usual you start writing the Java application JawEx3 java JawEx3 java import ch aplu jaw import javax swing JOptionPane public class JawEx3 public JawEx3 NativeHandler nh new NativeHandler c myjni trans release trans d1ll Path of DLL Transparent window Window title 10 20 Window position 260 200 Window size NativeHandler WS EX TRANSPARENT Window style String valueStr int value while valueStr null valueStr JOptionPane showInputDialog null Transparency 0 100 Native Window Transparency JOptionPane QUESTION MESSAGE try value Integer parseInt valueStr if value lt 0 value gt 100 throw new NumberFormatException catch NumberFormatException ex continue nh showWindow value nh destroy System exit Q public static void main String args new JawEx3 We use one of the overloaded constructors of NativeWindow that defines the most important window properties When executing JAW registers a window class using the Win32 API function RegisterClassEx and creates a window with the given OR combination of style flags with the API function CreateWindow These flags are declar
14. AnalogIn wantThreadMsg UINT uMsg return uMsg WM_THREADSTART WM_TIMER WM_THREADSTOP 52 void AnalogIn evThreadMsg HWND hwnd UINT message WPARAM wParam LPARAM 1Param Runs in JNIThread and not in the normal application thread define ID TIMER 1 double value static double time 0 Switch message case WM THREADSTART SetTimer 9 ID TIMER period TIMERPROC NULL break case WM TIMER ifdef simulation value range exp 0 0004 time sin 0 005 time time period if time gt maxTime time 0 else int32 t channel 1 uint32 t data ad discrete in adHandle AD CHA TYPE ANALOG IN Channel 0 data Interprete data as 32 bit 2 s complement and convert to volts value range int data double 0x80000000 endi f Copy to JNIBuffer writeDouble value break case WM THREADSTOP KillTimer 0 ID TIMER break When running the simulation the damped oscillation is shown In the title bar you find the number of available values in the JNIBuf waiting to be fetched by Java Normally this number is 0 or 1 but when the system is heavily loaded to do so start a big application 53 this number may increase over 100 Because all the stored values are fetched later on the curve is somewhat delayed but displayed without any error Fig 2 5 Buffer Count 0 OY x HELIST eet tt yet t tt tt pi tt tt A EA KA AK KA AK KK OKK E
15. BC Sending array to C C got array Te Z 33 Got back from C 10 20 30 28 25 Using realtime measurement modules from National Instruments National Instruments NI does not provide any support for Java programmers In their Knowledge Base NI suggests to use a JNI wrapper How can I access National Instruments drivers from Java Solution National Instruments does not currently provide language interfaces for Java It is possible however to access National Instruments drivers by making calls to the driver DLL Sun Java includes the Java Native Interface JNI which allows calls to be made to C DLLs from Java To utilize JNI with National Instruments drivers it is necessary to create a wrapper DLL for your driver DLL This wrapper DLL will comply with JNI naming requirements and perform the conversion from Java to C data types Consulting the sample programs written in C that are part of the distribution of NJ DAQmx and the NI DAOmx Function Reference JAW gives you the means to integrate the Nidag C library smoothly into you Java code First you need to download and install the distribution of NI DA Qmx Base You find it with a internet search machine and the keywords nidagmx download During the installation some DLLs are copied to the windows system32 folder amongst others nidagmxbaselv d11 On the native side we continue to use the development environment Microsoft Visual Studio 2008 Express Edition E
16. F8 string lt lt utf8str lt lt endl delete utf8str Release memory const wchar_t unicodestr JNIString _exposedObj str getUnicode int len int wcslen unicodestr char asciistr new char len 1 WideCharToMultiByte CP ACP 0 unicodestr 1 asciistr len 1 NULL NULL cout lt lt C got unicode string lt lt asciistr lt lt endl delete unicodestr Release memory delete asciistr ditto break case 1 LT const char cstr ABC A0U JNIString _exposedObj str setUTF8 cstr break case 2 cae const char cstr ABC AOU JNIString _exposedObj str setMBCS cstr break 27 case 3 Don t forget prefix L T const wchar t unicodeStr L ABC AOU JNIString exposedO0bj str setUnicode unicodeStr break case 4 JNIArray lt int gt jary _exposedObj ary int ary jary get cout lt lt C got array lt lt endl vor ide 1 Os 1 lt 838 1944 cout lt lt int ary i lt lt cout lt lt endl Write new values back to Java For Gnt d 0 lt 8 1 ary i 10 i 1 JNIArray lt gt destructor releases array here break return 0 The execution shows Sending string to C C got UTF8 string abc AnAqA C got MBCS string abc C got unicode string abc Got back from C UTF8 ABC Got back from C MBCS ABC Got back from C Unicode A
17. JAW User Guide Java API Wrapper Aegidius Pl ss www aplu ch jaw Content 1 Concepts 3 2 Installation of JAW and first sample application 5 2 1 Integration of third party non Java libraries teerseetoteteenesereerenese 9 2 2 Using tative Windows verses cece che ante hinted tia eer suns salke v teli e S NES 13 2 3 Callbacks using JNIMethod lt typep rseteneeeneeerneeteeneeereeeees 17 2 4 Transfer of string and array data cccecceecesccesecececcecseeeseeeeeeeeeeeeeeseeeseenseeeaeenaeeaes 24 2 5 Using realtime measurement modules from National Instruments 29 25 1 Porting acquire Scan niin ti k isi Sk anselseei A a 30 2 5 2 Porting contAcquireNScat ccccesescossssesesencnersosesavoussesvonencenvensnescesoseenseesensense 38 2 6 Data transfer using JN Buffer aii yesse a ae EEEa E Ea A E 46 3 Apendix Installation of Microsoft Visual Studio 55 l Concepts JAW is a frameworks with an underlying proxy pattern In JAW a Java class and its methods have a close correspondence to the native C class and their methods JAW uses but hides the JNI mechanism by defining two wrapper classes NativeHandler for Java and WindowHandler for C A typical JAW application uses an instance of NativeHandler and derives from WindowHandler No knowledge of JNI is required but a basic knowledge of C is necessary due to the fact that the user of JAW must edit and bui
18. Java code first In this context we consider Java as main and C as helper language JawEx1 java import javax swing JOptionPane import ch aplu jaw public class JniEx6 Native variables private int n 0 private double x Q public JniEx6 NativeHandler nh new NativeHandler c myjni jawsample release jawsample dll this Exposed object int rc JOptionPane YES OPTION int val 0 while rc JOptionPane YES OPTION rc JOptionPane showConfirmDialog null1 G SM sr fap p MS ego 5 vall 7 wall Jawlnc JOptionPane OK CANCEL OPTION JOptionPane INFORMATION MESSAGE if rc JOptionPane YES OPTION nh destroy System exit 0 Invoke native method val nh invoke val public static void main String args new JniEx6 As we will see the invocation of invoke calls the C method with the same name Next you develop the native Code using Visual Studio First create a new project with File New Project In the New Project dialog select Visual C Win32 in the Project Types section and Win32 Project in the Templates section Enter jawsample as project name and click OK The Win32 Application Wizard will open where you click Next As Application Settings choose DLL as Application type and Empty project as Addition options and click Finish The Solution Explorer pane will open In the icon bar change Debug to Release For the following steps w
19. KI Fig 2 5 JawEx8 in simulation mode 54 3 Apendix Installation of Microsoft Visual Studio Microsoft Visual Studio is a development suite for creating programs running under Microsoft Windows Several languages are supported essentially Visual Basic Visual C and Visual C All of them uses the same Integrated Development Environment IDE A promotion version Visual Studio Express Edition is available free of charge You find it with a internet search machine and the keywords Visual Studio Express Edition download Despite of the somewhat reduced functionality compared to the commercial versions lack of classes no resource editor etc it is fully adeguate for developing applications with the JAW framework For JAW only Visual C is needed After downloading and installing the Visual C part of Visual Studio you better test the installation by creating a sample application As everywhere on the world it is the Hello World that writes a greeting message to a console window Proceed as follows e Select File New Project A dialog appears e Select in pane Project types Win32 and in pane Templates Win32 Console Application Type in text field Name whatever you like e g HelloWorld and click OK e In the first dialog of the Win32 Application Wizard click Next Under Application Type select Console application and under Additional options Empty project Click Finish e In the Solution Explorer pane right click on Source Fi
20. MessageDialog null Could not start IrrKlang engine Fatal Error JOptionPane ERROR_MESSAGE nh destroy System exit 1 JOptionPane showMessageDialog null Press OK to start Trying to play audiofile JOptionPane INFORMATION MESSAGE nh startThread Start engine in high priority thread JOptionPane showMessageDialog null Press OK to stop Playing JOptionPane INFORMATION MESSAGE nh destroy System exit Q public static void main String args new JawEx2 Like before create a new project in Visual Studio named audio and add the new files AudioHandler cpp and AudioHandler h In the project properties add the irrKlang include folder in addition to the JAW include folder If you unpacked irrKlang in c irrKlang the folder is named c irrKlang include Append to the linker additional dependencies the irrKlang import library c irrKlang lib win32 visualstudiovirrKlang lib Copy the irrKlang DLLs irrKlang d1ll and ikpMP3 d11 to the home directory of the Java project in order to be loaded by AudioHandler d11 If you get an RuntimeException Can t load DLL these DLLs are not in the right folder The interface AudioHandler h declares the class AudioHandler Override WindowHandler s methods wantThreadMsg and evThreadMsg and declare the instance variables engine and audiofile AudioHandler h ifndef AudioHandler_h__ define AudioHandler_h__ in
21. QmxErrChk DAQmxBaseReadAnalogF64 taskHandle pointsToRead timeout DAOmx Val GroupByScanNumber data 2 int samplesPerChan amp pointsRead NULL return pointsRead return 0 Error if DAQmxFailed error DAQmxBaseGetExtendedErroriInfo errBuff 2048 if taskHandle 0 DAOmxBaseStopTask taskHandle DAQmxBaseClearTask taskHandle if DAQmxFailed error JNIString exposedObj errorDescription setMBCS errBuff return 1 return 0 When connecting two low frequency signal generators to the ADC module a graphics like fig 2 4 is displayed 45 Ani ADC x 200 ms div y 2 0 V div stopped Abb 2 4 Two channel oscilloscope with JawEx7 2 6 Data transfer using JNIBuffer In analogy to streams most drivers for typical measurement interfaces have three fundamental operations initializing open operation reading data from input ports writing data to output ports read write operations and releasing resources close operation If the distribution contains a DLL and its accompanying import library 46 lib and a documentation of the function calls is available with JAW you easily integrate these interfaces into Java without any knowledge of the cumbersome JNI If you do not have the import library you may create it from the DLL with a utility normally called implib A version of this tool is found in the distribution of the free Borland C compiler found with a internet se
22. Running g 1 Select the Physical Channel to correspond to where your signal is input on the DAQ device 2 Enter the Minimum and Maximum Voltage Ranges As Note For better accuracy try to match the Input Ranges to the i expected voltage level of the measured signal E Note Use the genVoltage example to provide a signal on your DAQ device to measure KS tepss ed 1 Create a task 2 Create an Analog Input Voltage Channel BS 3 Use the Read function to Measure 1 Sample from 1 Channel on the Data Acquistion Card Set a timeout so an error is returned if the sample is not returned in the specified time ha limit ki 4 Display an error if any 1 0 Connections Overview id Make sure your signal input terminal matches the Physical A Channel I O Control Recommended Use A Call the Read function FOR ROK include NIDAQmxBase h include lt stdio h gt define DAQmxErrChk functionCall if DAQmxFailed error functionCall goto Error int main int argc char argv Task parameters int32 error Q TaskHandle taskHandle 0 30 char errBuff 2048 X10 Channel parameters char chan Dev1 ai0 float64 min 10 0 float64 max 10 0 Timing parameters ulnt64 samplesPerChan 1 Data read parameters float64 data int32 pointsToRead 1 int32 pointsRead float64 timeout 10 0 DAQmxErrChk DAQmxBaseCreateTask amp taskHand1l
23. akes the inherited object reference and the name of the variable We call its methods get and set of the anonymous temporary object The following primitive types are supported bool signed char short int __int64 float double wchar_t e invoke reads the instance variables performs the increment operation and writes them back It also reads its parameter val and returns it incremented by one Since the signature of invoke is predefined only int parameters can be passed in this way With menu option Build Build Solution or F7 you create jawsample d11 in the folder c myjni jawsample Release No errors or warnings should occur With satisfaction we run JawEx1 with success 2 1 Integration of third party non Java libraries One of the main purpose for the development of JAW was the easy integration of non Java libraries into a Java application Sometimes the source code is available but most of the time only a dynamic library DLL together with its static import library are distributed In our next example we show how easy it is to integrate a given DLL in a Java program For the purpose of the demonstration we use the audio library irrKlang that you can download without charge from the internet using a search machine with the keyword irrklang The library is fine to play sound files in several formats such as wav mp3 ogg etc Moreover you can enrich the sound with several effect such as echo reverb distortion The librar
24. andler h _ define _ DataHandler_h__ include jaw h Jf seesesseseeeeases Class ATA DEMOS ss sessssssseesseesseess class DataDemo public WindowHandler public DataDemo JNIEnv env jobject obj WindowHandler env obj private int invoke int tag le endif As you see in the following implementation invoke 0 displays the transferred strings in a native console using cout invoke 1 invoke 2 and invoke 3 returns the strings using different character sets Because we selected the Multi Byte character set in the project s properties setMBCS returns accentuated characters correctly Since we used wchar_t setUnicode works fine too however setUTF8 fails With invoke 4 the Java integer array is transferred to C displayed in a console modified and returned back to Java where it is displayed again DataHandler cpp include DataHandler h include lt iostream gt using namespace std 26 WindowHandler selectWindowHandler JNIEnv env jobject obj int select ff Seeesessseseseses elass Datadag 2ososesososocesoeesooes int DataDemo invoke int val return new DataDemo env obj switch val case 0 const char charstr JNIString _exposedObj str getMBCS cout lt lt C got MBCS string lt lt charstr lt lt endl delete charstr Release memory const char utf8str JNIString _exposedObj str getUTF8 cout lt lt C got UT
25. arch machine and the keywords free borland compiler In the next example we show the typical procedure to develop a Java application to acquire data from a measurement device Similar to the previous examples a class derived from WindowHandler is declared The constructor initializes opens the driver the destructor closes it For slow acquisition rates 1 Hz or lower we acquire single values by calling invoke and read the data back to Java via instance variables For the clocking a Java timer is used For faster acquisition rates to a maximum of 1000 Hz it is preferable to use a native timer that runs in a high priority native thread independent asynchronous of any Java thread In order to avoid overflows when the CPU is heavily charged the acquired data should be buffered in a native FIFO buffer called JNIBuf fer and not passed directly to Java Because the implementation of circular FIFO buffers is not straightforward JAW offers its own implementation as follows In your Java application create an array of the desired data type e g for characters char values new char 5 The size of this buffer is determined by the number of data that you want to transfer from C to Java in one junk but has nothing to do with the size of the native JNIBuffer You create the JNIBuffer that contains 18 elements with an instance nh of NativeHandler nh createBuf values 18 If you omit the size parameter a default of 1000 applies In C
26. atically deallocated by JAW when the destructor of JNIArray lt gt runs Array elements are read or set by using an array pointer that is returned for 24 all array types by the same method get Be aware that this pointer becomes invalid after the destructor is executed For the sake of a simple demonstration we transfer string and array data from Java to C and then back to Java JawEx5 java import ch aplu jaw public class JawEx5 Native transfer data block private String str abc private int ary 1 2 3 public JawEx5 NativeHandler nh new NativeHandler c myjni data release data dll this System out println Sending string to C nh invoke 0 nh invoke 1 System out println Got back from C UTF8 System out println str nh invoke 2 System out println Got back from C MBCS System out println str nh invoke 3 System out println Got back from C Unicode System out println str System out println Sending array to C nh invoke 4 System out println Got back from C TOr ime v Of S 38 14 System out print ary i nh destroy System exit Q public static void main String args 25 new JawEx5 The C project named data declares a class DataDemo that contains the only method invoke The interface DataHand1ler h is very simple DataHandler h ifndef DataH
27. ause the resource editor is not available in the current release of Visual Studio Express Edition trans rc must be created with the source editor or with any other text editor Fig 2 1 shows the semi transparent window dragged over some other application window valueStr JOptionPane skowInputDialog i null Transparency 0 100 Native Window Transparency JOptionPane QUESTION MESSAGE a Transparent window value IMGENSE if value throw ni catch Number or continue nh showWindsy Fig 2 1 Semi transparent window 2 Callbacks using JNIMethod lt type gt One of the well known features of JNI is calling Java methods from native code Such methods are often named callbacks With JAW creating callbacks is very simple because of the template JNIMethod lt type gt that is similar to JNIVar lt type gt The parameterless Java method me thodeName is invoked with JNIMethod lt type gt _exposedObj methodName call where type is the return type of methodName As explained before exposedObj is inherited from WindowHandler When the Java method has parameters the invocation from C is somewhat more complicated because it is necessary to include the signature of the parameter types in the order they are specified in the method s declaration As an example if we want to call the Java method void dolt int i double x char c from C we first declare dolt as JNIMethod lt void gt using th
28. clude jaw h include irrklang h using namespace irrklang a anh Glas Sm AUC MO nAnGIkCige TTT a class AudioHandler public WindowHandler public AudioHandler JNIEnv env jobject obj WindowHandler env obj protected virtual bool wantThreadMsg UINT uMsg virtual void evThreadMsg HWND hWnd UINT uMsg WPARAM wParam LPARAM 1Param private int invoke int tag ISoundEngine engine const char audiofile Ja tendif We mention some particularities in the implementation of Audiodandler invoke initializes the sound engine With a string template we get the path of the sound file from the Java instance variable An OR mask in ThreadMsg let you select which messages of the ThreadEventProc are really needed In addition to the non windows related WM_messages documented in the Win32 API documentation two extra messages WM THREADSTART and WM_THREADSTOP are sent when Java calls startThread or stopThread respectively evThreadMsg is called each time a message is sent All information about the message can be retrieved from its parameters evThreadMsg runs in a native thread so we play the sound file within this thead by calling play2D in the WM_THREADSTART section In the WM_THREADSTOP section that also runs when NativeHandler destroy is called the sound engine and the allocated string array are freed AudioHandler cpp Project properties Add irrKlang include directory Add library irrKlang l
29. e DAQmxErrChk DAQmxBaseCreateAIVoltageChan taskHandle chan DAQmx_Val_Cfg Default min max DAOmx Val Volts NULL DAQmxErrChk DAOmxBaseStartTask taskHandle DAQmxErrChk DAQmxBaseReadAnalogF64 taskHandle pointsToRead timeout DAQmx_Val_GroupByChannel amp data samplesPerChan amp pointsRead NULL printf Acquired reading f n data Error if DAQmxFailed error DAQmxBaseGetExtendedErrorInfo errBuff 2048 if taskHandle 0 DAQmxBaseStopTask taskHand1e DAOmxBaseClearTask taskHandle if DAQmxFailed error printf DAQmxBase Error s n errBuff return 0 As you see the initialization is done step by step We will maintain this process in the Java code by calling invoke with several different parameters The return value is used as error code means success 1 means failure Java can retrieve and display the description of the error from the String errorDescription The Java application uses a console window from the package ch aplu util JawEx6 java Prototype is AcguirelScan from NIDAQmx distribution Acquire analog data and display in modeless dialog For demonstration with NI USB 6008 interface Apply voltage 5V max at terminals 2 and 1 GND or attach 10 kOhm potentiometer at terminals 31 32 with potentiometer tap at terminal 2 Timed by API Sleep 31 import ch aplu jaw import ch aplu util public class JawEx6 implements ExitListen
30. e assume that the JAW includes are in c myjni include and the JAW library jaw Libisinc myjni Right click on Source Files and select Add New Item The Add New Item dialog will open Under Categories select Code and under Templates select C File Enter JawSampleHandler as name and click Add Right click on Header Files then select Add New Item Under Categories select Code and under Templates select Header File Enter JawSampleHandler as name and click Add It is important to modify some of the project properties by right clicking on the project name in the Solution Explorer Configuration Properties General Character Set Use Multi Byte Character Set C C General Additional Include Directories c myjni include Linker Input Additional Dependencies c myjni jaw 1lib Linker Debugging General Debug Info No Now edit the header file JawSampleHandler h in the usual C way of life JawSampleHandler h ifndef JawSampleHandler_h__ define JawSampleHandler_h__ include jaw h Jj eseeseseeereessee class JawSampleHandler class JawSampleHandler public WindowHandler public JawSampleHandler JNIEnv env jobject obj WindowHandler env obj 1 private int invoke int tag endif Remarks e The Class JawSampleHandler inherits from WindowHandler and has an empty constructor but initializes the base class with env and obj The only method is invoke with given
31. e signature sequence IDC for int double char JNIMethod lt void gt doIt _exposedObj dolt IDC Then we pack the three parameters in a j value union which is declared as follows typedef union jvalue jboolean Zz jbyte jchar jshort jint jlong jfloat jdouble jobject jvalue a m nN In our example where we have three parameters of type int double char this becomes jvalue par 3 par 0 i 2 par 1 d par 2 c 3 1415 A The invocation is done with the method cal1 that takes the parameter par doIt call par In our sample application some of the mouse events from the native window are reported back to Java and displayed in a console redirected to a window from the package ch aplu util JawEx4 java import ch aplu util import ch aplu jaw public class JawEx4 implements ExitListener private int evt private int x private int y private NativeHandler nh public JawEx4 Console c new Console c addExitListener this nh new NativeHandler c myjni mouseevent release mouseevent dll this Move Window 10 20 258 184 NativeHandler WS POPUP NativeHandler WS VISIBLE System out println Click or drag image with left mouse button while true Monitor putSleep displayEvent Native call private void mouseEvent int evt int x int y this evt evt this x X this y y Monitor wakeUp
32. ed and documented in Nati veWindow The program is running in a loop and displays a modal dialog where the percentage of transparency may be entered Next you edit the interface of the class TransHandler TransHandler h ifndef TransHandler_h__ define TransHandler_h__ include jaw h Jif sesesesssesesesse class Wraishlamellelr s seceesseseeeeseee class TransHandler public WindowHandler public TransHandler JNIEnv env jobject obj protected virtual bool wantMsg UINT uMsg virtual bool evMsg HWND hWnd UINT uMsg WPARAM wParam LPARAM 1Param Je endif TransHandler overrides wantMsg and evMsg from WindowHandler Similar to wantThreadMsg and evThreadMsg the OR mask in wantMsg determines which messages sent to the WindowEventProc will call evMsg In this example we need WM CREATE and WM DESTROY that occur when the window is created and destroyed respectively and also WM PAINT that occurs each time the window must be repainted For details about the Win32 API you get many information from the internet using a search machine and the keywords windows api programming tutorial We should mention that evMsg runs automatically in a native thread that is completely decoupled from the JVM what makes the native window completely independent of the Java threads TransHandler cpp include TransHandler h include lt windows h gt If ssesessseeeses es SENEELOF sHesecessseseseasbesose
33. else System out println nStopped by user private void showError state State failed System out println nError errorDescription public void notifyExit switch state case failed nh destroy System exit 1 break case initializing Don t interrupt break case running state State quitting break 33 case guitting nh destroy 0 System exit 0 break public static void main String args new JawEx6 Once again the data transfer between Java and C is done with Java instance variables that can be accessed from both side We are careful to free all allocated resources by calling destroy when the program ends A state variable implemented as enum makes the program design simple Because we initialize step by step some variables must survive from one call of invoke to another Therefore we copy the passed values into C instance variables member variables You create a new C project named nidaq and code the header file NIDAOHandler h first where the original naming and formatting conventions are maintained NIDAQHandler h ifndef NIDAQHandler_h__ define _ NIDAQHandler_h__ include jaw h include NIDAQmxBase h Jf seeeeeseseaseess class NIDAOAcguirelScan class NIDAQAcquirelScan public WindowHandler public NIDAQAcquirelScan JNIEnv env jobject obj NIDAQAcquirelScan private int in
34. er Native transfer data block private String channel Dev1 ai0 DeviceID channel private double min 10 Input range min private double max 10 Input range max private double value Acquired data private String errorDescription Error report buffer private int period 1000 Measurement interval ms End of native transfer data block private NativeHandler nh new NativeHandler c myjni nidaq release nidaqg dl11 this Provide access by exposing private enum State failed initializing running quitting private volatile State state State initializing public JawEx6 Console c Console init c addExitListener this System out println Initializing System out print Creating task if mh invoke 0 1 showError return System out println OK System out print Open channel if nh invoke 1 1 showError return System out println OK System out print Start task if nh invoke 2 1 showError return System out println OK 32 System out println AnGetting data int nb 1 state State running while state State running if nh invoke 3 1 break else System out println Data 4 nb value V nh invoke 4 Sleep a while nb if state State running state State failed System out println nError while acquiring data
35. ess them without restrictions The NativeHandler s method startThread creates a native high priority thread The corresponding ThreadEventProc calls the user provided evThreadMsg in MyWindowHand Ler each time a Windows thread message is posted In addition to the standard Win32 API messages WM_THREADSTART and WM_THREADSTOP indicate the start and stop of the internal thread Because evThreadMsg runs in the native thread that is independent of the Java threads asynchronous operations may be performed like natively clocked acquiring data from a measurement interface A circular FIFO buffer is provided where C stores the acquired data while Java fetches them in its own thread that may be somewhat delayed due to heavy CPU load A distinct constructor of Nati veWindow creates a native window using the Win 32 API function CreateWindow with selectable window style Getting the windows messages from the corresponding WindowEventProc is very simple Override evMsg from WindowHandler in the user provided MyWindowHand Ler To enhance performance only user selected messages defined with an OR mask will call evMsg In order to make the native window independent of the JVM evMsg runs in a separate native thread that is completely hidden from the user code 2 Installation of JAW and first sample application In all our examples we assume Microsoft Visual Studio 2008 Express Edition English version as IDE to develop the native DLL A short in
36. fer may contain up to 1000 elements there is little risk for a buffer overflow when the system is busy 50 On the C side create a new project name bmc Consult the sample programs and the documentation distributed with Libad4 This gives you enough information how to write the code If you don t possess the ADC module just look at the parts that compile when simulation is defined First write BMCHandler h and declare the class Audioln BMCHandler h ifndef BMCHandler h define _ BMCHandler_h__ include jaw h include libad h I class AnalogiIn class AnalogIn public WindowHandler public AnalogIn JNIEnv env jobject obj AnalogIn protected virtual bool wantThreadMsg UINT uMsg virtual void evThreadMsg HWND hWnd UINT uMsg WPARAM wParam LPARAM 1Param private int period int maxTime double range int32 t adHandle tendif The constructor of AnalogIn fetches the Java variables and initializes the module with ad open On the other hand we release all resources in the destructor by calling ad close Remember that the constructor is executed when NativeHandler is instantiated und the destructor runs when destroy is called From chapter 2 we know the role of wantThreadMsg and evThreadMsg We use the occurrence of WM THREADSTART to call the API function SetTimer to setup a native timer with the given period We release its resources with Kil
37. ib irrKlang dll and ikpMP3 dll must reside in the Java class home directory include AudioHandler h l seeseaseseeseaeee SELEETOP a A A WindowHandler selectWindowHandler JNIEnv env jobject obj int select return new AudioHandler env obj Uf seeseaseseeseesee class Aueuomamedlsr s gt ss sessosssseso5ecs int AudioHandler invoke int val Get string from Java instance variable audiofile JNIString _exposedObj audiofile getUTF8 Start the sound engine with default parameters engine createIrrKlangDevice if engine return 1 Error starting the engine return 0 bool AudioHandler wantThreadMsg UINT uMsg return uMsg WM THREADSTART WM_THREADSTOP void AudioHandler evThreadMsg HWND hwnd UINT message WPARAM wParam LPARAM lParam Runs in the high priority native JNIThread Switch message case WM THREADSTART engine gt play2D audiofile break case WM THREADSTOP engine gt drop Delete engine delete audiofile Release allocated memory break After building audio d11 run the Java application JawEx2 When you click the OK button on the modal dialog box the sound starts playing until you click the OK button again 22 Using native windows In some situations a native window that displays text graphics or images and where the messages sent to its WindowEventProc are accessible is a better choice than Swing or
38. ies is specially suitable to add a sound background to game applications After downloading and unpacking you should take a short view to the distributed sample programs found in the example folder As you see there it s very easy to play a sound file Just create an instance of ISoundEngine ISoundEngine engine createIrrKlangDevice and start playing with engine gt play2D soundfile where soundf i le is the fully qualified path to the sound file As usual we begin on the Java side and write a simple application that displays a modal dialog using a JOptionPane where the user clicks the OK button to start playing Clicking the OK button in the next dialog terminates the application For the sake of simplicity the path to the sound file is hardwired in the Java code and read by the native code invoke 0 initializes the native sound engine und returns an error code 0 for success 1 for failure The sound engine needs to run in a native thread because the Java thread is blocked in the modal dialog This native thread is started with startThread JawEx2 java Use free audio library irrKlang from www ambiera com import javax swing JOptionPane import ch aplu jaw public class JawEx2 Native variable private String audiofile c scratch bamboleo mp3 public JawEx2 NativeHandler nh new NativeHandler c myjni audio release audio d1l1l this if mnh invoke 0 1 JOptionPane show
39. ime oldEndDatal for int 1 0 1 lt pointsRead i p draw time i dt data 2 1 1 offset1 oldEndDatal data 2 pointsRead 1 1 offset1 40 time pointsRead dt oldTime time if JisRunning break p clear drawCoordinateSystem oldTime 0 oldEndData0 oldEndDatal time 0 0 0 public void notifyExit if isRunning isRunning false p title title stopped else nh destroy System exit Q private void drawCoordinateSystem p color Color black double xspan maxTime 10 vor int 1 98 1 s 103 das p line i xspan 10 1 xspan 10 double yspan max min 10 ror mt 1 OR 1 lt gt 195 tia p line 0 min i yspan maxTime min i yspan private boolean isError int rc i pe 1 p title errorDescription nh destroy return true return false 41 public static void main String args new JawEx7 As usual create a new C project named nidaqc and write the code with the original C code at hand First write NIDAOHandler h which is very similar to the previous example NIDAQHandler h ifndef NIDAQHandler_h__ define _ NIDAQHandler_h__ include NIDAQmxBase h include jaw h class NIDAQContAcquireNScan class NIDAQContAcquireNScan public WindowHandler public NIDAQContAcquireNScan JNIEnv env jobject obj NID
40. l Timer when WM_TREADSTOP occurs On each timer event we get a WM_TIMER message Then we read a new value from the interface by calling ad_discrete_in or generate a value from a damped oscillation when running in simulation mode wri teDouble writes this 51 value into the JNIBuffer There is no need of a notification to the Java program because Java fetches the values in the JNIBuffer asynchronously in its own thread Accessing Java variables or invoking callbacks in evThreadMsg is not allowed because the native thread and the JVM are not synchronized BMCHandler cpp Must link with libad4 lib unless using simulation mode include BMCHandler h include lt math h gt define simulation seaseaseseeseosese SSe cto s eeseseseesmeseseeeseseseesees WindowHandler selectWindowHandler JNIEnv env jobject obj int select return new AnalogIn env obj class AnalogIn AnalogIn AnalogIn JNIEnv env jobject obj WindowHandler env obj const char driver JNIString _exposed0bj device getMBCS period JNIVar lt int gt _exposed0bj period get maxTime JNIVar lt int gt _exposedObj maxTime get range JNIVar lt double gt _exposed0bj range get ifndef simulation adHandle ad_open driver endif delete driver AnalogIn Analogin ifndef simulation if adHandle gt 0 ad close adHandle tendif bool
41. ld the native DLL with a C IDE typically with Microsoft s Visual Studio Features e Hides internal mechanism of JNI no native Java methods and no JNI C functions needed e Native code runs in a separate native high priority thread that is transparent to the user e Easy creation of visible or semi transparent native windows with simple access to its event loop by registering specific messages e Data transfer between primitive Java instance variables and C with templates eliminates type casts Data transfer between Java strings and array with C templates Support for Unicode MBCS and UTF 8 strings Callbacks of Java methods with C templates Native FIFO buffer for streaming data transfer from C to Java Designed to integrate third party DLL libraries into Java e g drivers for realtime measurement devices National Instruments Keithley etc Error handling by callbacks or returning error codes rather than throwing exceptions e Unnecessary to use javah to generate C header files Compared to plain JNI there are a few restrictions e No support of the Java invocation API dynamic creation of a JVM classes and methods e No support of data transfer via Java static fields e Only available for the Windows operating system On the Java side all JAW functionalities are provided through the library jaw j ar that contains the wrapper class Nati veHandLer While instantiating this class the link between Java and C is automatically
42. les and select Add New Item e In the dialog select in pane Templates C File und enter a name e g HelloWorld Click Add and the program editor will open Enter the following code HelloWorld cpp include lt iostream gt using namespace std void main cout lt lt Hello World lt lt endl e In the toolbar s list box that contains Debug select Release and compile link using the menu option Build Build solution e HelloWorld exe will be created in the subdirectory Release of the project folder Run it with the menu option Debug Start Without Debugging or Ctrl FS5 55 JAW uses the Win32 API and does not support the NET framework This makes it easy to create the DLLs with any other C compiler linker such as Borland C gcc etc If another compiler linker or an old version of VC is used it may be necessary to link with a slightly adapted version of jaw 1ib More information about availability of older or non VC versions of the JAW library is obtained from www aplu ch jaw 56
43. nglish version For NI DAQmx Base add the following items to the project properties e Configuration Properties C C General Additional Include Directories directory where is NIDAQmxBase h e g c nidaq include e Configuration Properties Linker Input Additional Dependencies fully qualified path of nidaqmxbase 17b e g c nidaq nidaqmxbase lib For our example we use the inexpensive NI module USB 6008 with the following features 8 analog input channels 12 bits max sample rate 10 kHz for 1 channel 2 analog output channels 12 bits 12 digital input output channels 32 bit counter After installing the NI DAOnx Base software the module is automatically recognized as new USB device 29 2 5 1 Porting acquire 1Scan In our next example we port the functionalities of the sample program acguirelScan c that is included in the NI DAQmx distribution from C to Java The application reads a single value from the analog input and displays it in a console window The original source is well documented if further information is needed consult the NI DAQmx Base C Function Reference found with an internet search machine Here is the code in the original formatting RR RRA ROA RR AR ORK AOR KAR KK ANSI C Example program acguirelScan c Example Category td AI Description i This example demonstrates how to take a single Measurement Sample from an Analog Input Channel Instructions for
44. signature and return type e We must include jaw h to get the JAW class declarations The implementation of JawSampleHandler defines the global function selectWindowHandler that is called when Java instantiates Nati veWindow JawSampleHandler cpp include JawSampleHandler h If sseeseestesessene SELECTO Os seesseseeeee seeeteseseeenes WindowHandler selectWindowHandler JNIEnv env jobject obj int select return new JawSampleHandler env obj Pf seesessseseeseesee class JawSampleHandler int JawSampleHandler invoke int val Read Java variables int n JNIVar lt int gt _exposedObj n get double x JNIVar lt double gt _exposedObj x get Perform operations val n x Write back Java variables JNIVar lt int gt _exposedObj n set n JNIVar lt double gt _exposedObj x set x return val Remarks e The global selector or dispatcher method selectWindowHandler creates an instance of our own class while passing the initialization values env and obj to the base class WindowHand ler It establishes the link between the C based JNI and C and provides the information about the JVM and the Java object that exposes its variables and methods The parameter select can be used to make a selection between several user defined classes It s not used in this example e We access the Java instance variables through template classes JNIVar lt type gt The constructor t
45. sssssoses WindowHandler selectWindowHandler JNIEnv env jobject obj int select return new TransHandler env obj ff seessesseeseseses class Wrainshlameller s se ssceesee eeeeseeee Constructor initialize base class TransHandler TransHandler JNIEnv env jobject obj WindowHandler env obj 19 Select which window messages will call evMsg bool TransHandler wantMsg UINT uMsg return uMsg WM CREATE WM PAINT WM_DESTROY Event procedure Return false if message is handled by this procedure true to invoke DefWindowProc bool TransHandler evMsg HWND hWnd UINT message WPARAM wParam LPARAM lParam static HBITMAP hBm NULL HDC hDC HDC hDCMem BITMAP bm PAINTSTRUCT ps switch message case WM_CREATE hBm LoadBitmap getInstance TEXT ROSE break case WM PAINT hDC BeginPaint hWnd amp ps hDCMem CreateCompatibleDC hDC SelectObject hDCMem hBm GetObject hBm sizeof bm amp bm BitBLt hDC 0 bm bmWidth bm bmHeight hDCMem 0 0 SRCCOPY DeleteDC hDCMem EndPaint hWnd amp ps return false case WM DESTROY DeleteObject hBm break return true In order to use the image file rose bmp as resource the resource file trans rc must be included in the project Both files must reside in the same folder as TransHandler cpp and TransHandler h trans rc ROSE BITMAP DISCARDABLE rose bmp Bec
46. stallation guide can be found in the appendix You download the latest JAW distribution from www aplu ch jaw and unpack it in any folder Copy jaw jar in your favorite jar folder e g c Xjars and include is as additional library to all Java projects Some applications need classes from the package ch aplu util For these samples copy aplu5 jar in c jars and include the jar file as additional library to the project Copy the static library jaw lib in some other folder e g c myjni create a subdirectory include and put all include files from the JAW distribution in c myjni include Our sample application shows how to pass the values of two instance variables to the native code where they are increased by one The modified values are read back by Java and displayed in a modal dialog We also demonstrate how to pass a value as method parameter to C and how to get the modified value back to Java by using the return value of the method call The native code is packed in the DLL j awample d11 which will be created later on The constructor of NativeHandler takes the fully qualified path to this DLL in order to load the native library The this reference passed to the constructor gives C read write access to all instance variables even if they are private Contrary to the JNI the qualifier native is not necessary to share values with the native code and there is no need to create a C header file using j avah We proceed top down and write the
47. tatic HBITMAP hBm NULL static int xPos static int yPos HDC hDC HDC hDCMem BITMAP bm PAINTSTRUCT ps switch message case WM CREATE hBm LoadBitmap getInstance TEXT ROSE return false case WM LBUTTONDOWN xPos LOWORD 1Param Relative coordinates yPos HIWORD 1Param sendMouseMessage LPRESS xPos yPos return false case WM LBUTTONUP sendMouseMessage LRELEASE LOWORD lParam HIWORD 1Param return false case WM LBUTTONDBLCLK sendMouseMessage LDCLICK LOWORD lParam HIWORD 1Param return false case WM MOUSEMOVE if wParam MK LBUTTON int xNew LOWORD 1Param Relative coordinates int yNew HIWORD 1Param int xDelta xNew xPos Displacement int yDelta yNew yPos _xXPos xDelta Absolute coordinates _yPos yDelta of upper left corner SetWindowPos hWnd HWND TOPMOST _xPos _yPos 0 0 SWP_NOSIZE SWP_SHOWWINDOW return false case WM PAINT hDC BeginPaint hWnd amp ps hDCMem CreateCompatibleDC hDC 22 SelectObject hDCMem hBm GetObject hBm sizeof bm amp bm BitBLt hDC 0 bm bmWidth bm bmHeight hDCMem 0 SRCCOPY DeleteDC hDCMem EndPaint hWnd 8ps return false case WM DESTROY DeleteObject hBm break return true void MouseEventHandler sendMouseMessage int message int x int y JNIMethod lt void gt mouseEvent _exposedObj mouseEvent III jval
48. ue par 3 par 0 i message par 1 i x pami min y mouseEvent call par For the callback we declare mouseEvent with the parameter signature III and invoke call with the three integers packed into par Fig 2 2 shows the native window dragged over the console window 23 java Input Output Console O x Click or drag image with left mouse button LeftButtonDown at x 107 y 30 LeftButtonup at x 107 y 30 Fig 2 2 Callback with mouse events 2 4 Transfer of string and array data In JAW we use the class JNIString to transfer strings between Java and the native code In C a string can be represented by a character array where the bytes are interpreted differently depending on the character set In Java strings are always coded in the Unicode character set When a Java string is transferred to C different get methods let you decide if characters are stored in the Multibyte Character Set MBCS the UTF 8 or the Unicode character encoding When calling get a character array of sufficient length is created that holds the transferred characters Do not forget to free the allocated memory with delete before the program ends The mechanism for transferring arrays of primitive types remains the same Template classes JNIArray lt type gt are used where type is one of wchar_t bool signed char short int _ int64 float double Depending on the JVM an internal buffer is created that will be autom
49. voke int tag int period Task parameters int32 error TaskHandle taskHandle char errBuff 2048 34 Channel parameters const char chan float64 min float64 max Timing parameters ulnt32 samplesPerChan Data read parameters float64 data int32 pointsToRead int32 pointsRead float64 timeout Je tendif In implementation NIDAOHandler cpp most of the original C program is copied There is no need to understand each detail We maintain the function call and error recovery using the macro DAOmxErrChk Instead of displaying the error message with printf we copy it into the string er rorDescription where it can be retrieved by Java NIDAQHandler cpp Must link with nidaqmxbase 1lib include NIDAOHandler h Pf serecesecsesessse SENEELTOF sasoeesssnseecssecseessssaseeass WindowHandler selectWindowHandler JNIEnv env jobject obj int select define DAQmxErrChk functionCall if DAQmxFailed error functionCall goto Error return new NIDAQAcquirelScan env obj Jf sesesssesseeessee class NIDAQAcquirelScan National Instruments NIDAQmx Prototype acguirelScan from distribution of NI DAQmx NIDAOAcguirelScan NIDAOAcguirelScan JNIEnv env jobject obj WindowHandler env obj samplesPerChan 1 timeout 10 0 pointsToRead 1 35 period JNIVar lt int gt _exposedObj period get chan JNIString exposed0bj channel getUTF8

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