神马文学网Beginning JNI with NetBeans? C/C Pack 5.5, Part I
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Beginning JNI with NetBeans™ C/C++ Pack 5.5, Part I
Contributed and maintained byDmitry LipinandKirill Sorokin.
The tutorial will guide you through the creation of a sampleapplication which uses JNI to execute some native code written inthe C programming language. For the Java™ part of the application youwill use NetBeans™ IDE 5.5; for the C part - NetBeans™ C/C++ Pack5.5.
You will start off by creating a simple Java project, adding a nativemethod to it and then implementing this method in C usingNetBeans C/C++ Pack 5.5.
This is the first part of the tutorial that covers the creation of a sampleJNI application in the Microsoft® Windows®operating system.
Expected duration: 30 minutes
Prerequisites
This tutorial assumes you have some basic knowledge of, orprogramming experience with, the following technologies:
Java programming language
C programming language
NetBeans IDE
Software Required for Tutorial
Before you begin, you need to install the following software onyour computer:
J2SE Development Kit (JDK™) 5.0 (download)
NetBeans IDE 5.5 (download)
NetBeans C/C++ Pack 5.5 (download)
Cygwin (download)
Notations Used in Tutorial
- the JDK installation directory
- the Cygwin installation directory.
- directory that contains the Java project you create
Tutorial Exercises
Exercise 0: Installing and Configuring Tutorial Environment
Exercise 1: Setting Up General Java Application Project
Exercise 2: Setting Up C/C++ Dynamic Library Project
Exercise 3: Building and Running Application
Exercise 0: Installing and Configuring Tutorial Environment
This exercise will guide you through the process of installing andconfiguring the required software. While the installation of JDK,NetBeans IDE and NetBeans C/C++ Pack is pretty trivial, Cygwinrequires special attention.
After you install the software, some minor changes to the systemconfiguration should be applied.
Downloading and Installing Cygwin
Download and run the Cygwin installer from http://www.cygwin.com/setup.exe.
At the Choose Installation Type page, select Install From Internet, and click Next.
At the Choose Installation Directory page, define the settings appropriate for your system, then click Next.
At the Select Local Package Directory page, define the directory which Cygwin installer will use as its cache directory, and click Next.
At the Select Connection Type page, choose the type of Internet connection you have, and click Next.
At the Choose Download Site(s) page, select a mirror which is closest to your location, and click Next.
At the Select Packages page, select at least these packages: gcc-core, gcc-g++, gdb, and make. You can select other packages as well but these are required for the tutorial.
Figure 1
Figure 2
Figure 3
Click Next. The Cygwin installer proceeds with the download and configuration of the selected packages.
Configuring System
Add the\bin directory path to the PATH environment variable value.
Running the Software
Start the NetBeans IDE.
Setting Up General Java Application Project
The goal of this exercise is to create and configure the Java partof the JNI application you will be developing. You will create anew Java application project, initialize its main class and add anative method to this class.
Creating General Java Application Project
Choose File > New Project. Under Categories, select General. Under Projects, select Java Application, and click Next.
Figure 4
Under Project Name, enter HelloWorld.
Change the Project Location to any directory on your computer (hereinafter, this directory is referred to as).
Leave the Create Main Class checkbox selected and accept the default value for the corresponding text field.
Figure 5
Leave the Set as Main Project checkbox selected, and click Finish.
The IDE creates the/HelloWorld project folder.
Editing Main Class Source
To open the Main class source in the editor, right-click the Main class node, and choose Open from the context menu.
Replace the body of the main method with the following: new Main().nativePrint();
Wait till the newly entered line gets underlined with a red wave. Press Alt - Enter and choose the Create method nativePrint() in helloworld.Main line from the drop-down list.
A compilation error was caused by referencing a non-existing method in Step 2 above and the IDE automatically proposes a fix for this problem.
Figure 6
Edit the nativePrint() method. Delete the contents of the method and add the native keyword to the method signature. So the method now should look like this: private native void nativePrint();
The native keyword indicates that the method has an implementation located in an external native library, thus the code is going to compile correctly. However at runtime the library location is not clear. Refer to theConfiguring the Java Project section below for details.
Press Ctrl - F11 to clean and build the project.
The project should build successfully.
Creating Native Library Header File
Switch to the console and navigate to the directory.
Type the following:\bin\javah.exe -o HelloWorldNative.h -jni -classpath \HelloWorld\build\classes helloworld.Main A HelloWorldNative.h C header file is generated. It is required to provide correct function declaration for the native implementation of the nativePrint() method.
Switch back to the NetBeans IDE window.
Summary
In this exercise you created a new General Java ApplicationProject, specified its location and defined the package andname of the main class of the project. You also added a newmethod to the main class and marked it as a method having anative implementation. As a final step we created a C headerfile which is required later for the native library compilation.
Setting Up New C/C++ Dynamic Library Project
This exercise will lead you through the creation of thenative part of the sample application. You will create the C++Dynamic Library project and configure it to be able to build the JNIcode.
After the project has been set up, you will create theimplementation for the native method, you have declared earlier inthe Java part of the application.
Creating New C/C++ Dynamic Library Project
Choose File > New Project. Under Categories, select C/C++ Development. Under Projects, select C/C++ Dynamic Library, and click Next.
Figure 7
Under Project Name, type HelloWorldNative.
Under Project Location, type the same location as you entered for the General Java Application project,. The required value should be already there as the default value.
Accept the defaults for all other fields.
Figure 8
Leave the Set as Main Project checkbox selected. Then click Finish.
The IDE creates the/HelloWorldNative project folder.
Setting Project Properties
Right-click the project node and choose Properties from the context menu.
In the opened dialog box navigate to Configuration Properties > C/C++ > GNU C Compiler > General. Edit the values of the Additional Include Libraries properties. Set them to/include, /include/win32.
These settings are required to enable references to the Java jni.h library from your C code.
Note: If contains spaces, please ensure you embedded the path into quotation marks, otherwise you may experience build problems.
Figure 9
Navigate to Configuration Properties > C/C++ > GNU C Compiler > Command Line. Edit the value of the Additional Options property. Set it to -mno-cygwin -Wl,--add-stdcall-alias -shared -m32.
The -mno-cygwin option, enables building DLLs that have no dependencies on Cygwin own libraries and thus can be executed on machines which do not have Cygwin installed.
The -Wl,--add-stdcall-alias passes the --add-stdcall-alias option to the linker; without it, the resulting application would fail with the UnsatisfiedLinkError.
The -shared option tells the compiler to generate a DLL ( not an executable file).
-m32 tells the compiler to create a 32-bit binary. On 64-bit systems the compiled binaries are 64-bit by default , which causes a lot of problems with 32-bit JDKs.
Figure 10
Navigate to Configuration Properties > Linker > General. Edit the value of the Output property. Set it to dist/HelloWorldNative.dll.
The goal of this step is to simplify the path of the resulting DLL file, in order to make referencing it from Java easier for you.
Figure 11
Click OK.
The defined settings are saved.
Adding Header File
Copy the generated\HelloWorldNative.h header file to the C/C++ Library project directory, \HelloWorldNative.
In the Projects view, navigate to HelloWorldNative > Source Files. Right-click the Source Files node and choose Add Existing Item from the context menu. Point the IDE to the HelloWorldNative.h file.
The HelloWorldNative.h file appears under Source Files.
Implementing Method
Right-click the Source Files node and choose New > Add Empty C File from the context menu. Under File Name type HelloWorldNative, and click Finish.
The editor opens the HelloWorldNative.c file.
Figure 12
Edit the HelloWorldNative.c file by typing the following code: #include #include #include "HelloWorldNative.h" JNIEXPORT void JNICALL Java_helloworld_Main_nativePrint (JNIEnv *env, jobject obj) { printf("\nHello World from C\n"); }
Figure 13
Right-click the HelloWorldNative project node and choose Build Project.
The Output dialog box displays Build successful. Exit value 0.
Figure 14
Summary
In this exercise you created a new C/C++ Dynamic Library,specified its location and configured it to be able to buildJNI implementation of your Java method. You added the generatedheader file for the native method you have declared in the Javaapplication and implemented it.
Building and Running Application
In this exercise you will perform some final alterations to the Javapart of the application. This is required to ensure the Java part properly loads the nativelibrary you had compiled in the previous exercise. After that youwill compile and run the resulting application.
Configuring Java Project
Open the Main.java file in the editor.
Add the following initialization code: static { System.load("\\HelloWorldNative\\dist\\HelloWorldNative.dll"); }
Figure 15
Running Application
To set the HelloWorld Java project as the main project, right-click the project node and choose Set As Main Project from the context menu.
Press F6 to run the application.
The program should execute correctly and the Output dialog box should say:
Hello World from C BUILD SUCCESSFUL (total time: 0 seconds)
Figure 16
Summary
In this exercise you made some final configuration steps andran the application to verify that the implementation of thenative method comes from the native C library.
Next Steps
You can download the sources for this tutorial fromhere.
You can use the following documents to get more information:
Getting Started With the NetBeans C/C++ Development Pack, the NetBeans C/C++ Pack 5.5 tutorial
Java Native Interface, the Java Native Interface 5.0 specification
Contributed and maintained byDmitry LipinandKirill Sorokin.
The tutorial will guide you through the creation of a sampleapplication which uses JNI to execute some native code written inthe C programming language. For the Java™ part of the application youwill use NetBeans™ IDE 5.5; for the C part - NetBeans™ C/C++ Pack5.5.
You will start off by creating a simple Java project, adding a nativemethod to it and then implementing this method in C usingNetBeans C/C++ Pack 5.5.
This is the first part of the tutorial that covers the creation of a sampleJNI application in the Microsoft® Windows®operating system.
Expected duration: 30 minutes
Prerequisites
This tutorial assumes you have some basic knowledge of, orprogramming experience with, the following technologies:
Java programming language
C programming language
NetBeans IDE
Software Required for Tutorial
Before you begin, you need to install the following software onyour computer:
J2SE Development Kit (JDK™) 5.0 (download)
NetBeans IDE 5.5 (download)
NetBeans C/C++ Pack 5.5 (download)
Cygwin (download)
Notations Used in Tutorial
Tutorial Exercises
Exercise 0: Installing and Configuring Tutorial Environment
Exercise 1: Setting Up General Java Application Project
Exercise 2: Setting Up C/C++ Dynamic Library Project
Exercise 3: Building and Running Application
Exercise 0: Installing and Configuring Tutorial Environment
This exercise will guide you through the process of installing andconfiguring the required software. While the installation of JDK,NetBeans IDE and NetBeans C/C++ Pack is pretty trivial, Cygwinrequires special attention.
After you install the software, some minor changes to the systemconfiguration should be applied.
Downloading and Installing Cygwin
Download and run the Cygwin installer from http://www.cygwin.com/setup.exe.
At the Choose Installation Type page, select Install From Internet, and click Next.
At the Choose Installation Directory page, define the settings appropriate for your system, then click Next.
At the Select Local Package Directory page, define the directory which Cygwin installer will use as its cache directory, and click Next.
At the Select Connection Type page, choose the type of Internet connection you have, and click Next.
At the Choose Download Site(s) page, select a mirror which is closest to your location, and click Next.
At the Select Packages page, select at least these packages: gcc-core, gcc-g++, gdb, and make. You can select other packages as well but these are required for the tutorial.
Figure 1
Figure 2
Figure 3
Click Next. The Cygwin installer proceeds with the download and configuration of the selected packages.
Configuring System
Add the
Running the Software
Start the NetBeans IDE.
Setting Up General Java Application Project
The goal of this exercise is to create and configure the Java partof the JNI application you will be developing. You will create anew Java application project, initialize its main class and add anative method to this class.
Creating General Java Application Project
Choose File > New Project. Under Categories, select General. Under Projects, select Java Application, and click Next.
Figure 4
Under Project Name, enter HelloWorld.
Change the Project Location to any directory on your computer (hereinafter, this directory is referred to as
Leave the Create Main Class checkbox selected and accept the default value for the corresponding text field.
Figure 5
Leave the Set as Main Project checkbox selected, and click Finish.
The IDE creates the
Editing Main Class Source
To open the Main class source in the editor, right-click the Main class node, and choose Open from the context menu.
Replace the body of the main method with the following: new Main().nativePrint();
Wait till the newly entered line gets underlined with a red wave. Press Alt - Enter and choose the Create method nativePrint() in helloworld.Main line from the drop-down list.
A compilation error was caused by referencing a non-existing method in Step 2 above and the IDE automatically proposes a fix for this problem.
Figure 6
Edit the nativePrint() method. Delete the contents of the method and add the native keyword to the method signature. So the method now should look like this: private native void nativePrint();
The native keyword indicates that the method has an implementation located in an external native library, thus the code is going to compile correctly. However at runtime the library location is not clear. Refer to theConfiguring the Java Project section below for details.
Press Ctrl - F11 to clean and build the project.
The project should build successfully.
Creating Native Library Header File
Switch to the console and navigate to the
Type the following:
Switch back to the NetBeans IDE window.
Summary
In this exercise you created a new General Java ApplicationProject, specified its location and defined the package andname of the main class of the project. You also added a newmethod to the main class and marked it as a method having anative implementation. As a final step we created a C headerfile which is required later for the native library compilation.
Setting Up New C/C++ Dynamic Library Project
This exercise will lead you through the creation of thenative part of the sample application. You will create the C++Dynamic Library project and configure it to be able to build the JNIcode.
After the project has been set up, you will create theimplementation for the native method, you have declared earlier inthe Java part of the application.
Creating New C/C++ Dynamic Library Project
Choose File > New Project. Under Categories, select C/C++ Development. Under Projects, select C/C++ Dynamic Library, and click Next.
Figure 7
Under Project Name, type HelloWorldNative.
Under Project Location, type the same location as you entered for the General Java Application project,
Accept the defaults for all other fields.
Figure 8
Leave the Set as Main Project checkbox selected. Then click Finish.
The IDE creates the
Setting Project Properties
Right-click the project node and choose Properties from the context menu.
In the opened dialog box navigate to Configuration Properties > C/C++ > GNU C Compiler > General. Edit the values of the Additional Include Libraries properties. Set them to
These settings are required to enable references to the Java jni.h library from your C code.
Note: If
Figure 9
Navigate to Configuration Properties > C/C++ > GNU C Compiler > Command Line. Edit the value of the Additional Options property. Set it to -mno-cygwin -Wl,--add-stdcall-alias -shared -m32.
The -mno-cygwin option, enables building DLLs that have no dependencies on Cygwin own libraries and thus can be executed on machines which do not have Cygwin installed.
The -Wl,--add-stdcall-alias passes the --add-stdcall-alias option to the linker; without it, the resulting application would fail with the UnsatisfiedLinkError.
The -shared option tells the compiler to generate a DLL ( not an executable file).
-m32 tells the compiler to create a 32-bit binary. On 64-bit systems the compiled binaries are 64-bit by default , which causes a lot of problems with 32-bit JDKs.
Figure 10
Navigate to Configuration Properties > Linker > General. Edit the value of the Output property. Set it to dist/HelloWorldNative.dll.
The goal of this step is to simplify the path of the resulting DLL file, in order to make referencing it from Java easier for you.
Figure 11
Click OK.
The defined settings are saved.
Adding Header File
Copy the generated
In the Projects view, navigate to HelloWorldNative > Source Files. Right-click the Source Files node and choose Add Existing Item from the context menu. Point the IDE to the HelloWorldNative.h file.
The HelloWorldNative.h file appears under Source Files.
Implementing Method
Right-click the Source Files node and choose New > Add Empty C File from the context menu. Under File Name type HelloWorldNative, and click Finish.
The editor opens the HelloWorldNative.c file.
Figure 12
Edit the HelloWorldNative.c file by typing the following code: #include
Figure 13
Right-click the HelloWorldNative project node and choose Build Project.
The Output dialog box displays Build successful. Exit value 0.
Figure 14
Summary
In this exercise you created a new C/C++ Dynamic Library,specified its location and configured it to be able to buildJNI implementation of your Java method. You added the generatedheader file for the native method you have declared in the Javaapplication and implemented it.
Building and Running Application
In this exercise you will perform some final alterations to the Javapart of the application. This is required to ensure the Java part properly loads the nativelibrary you had compiled in the previous exercise. After that youwill compile and run the resulting application.
Configuring Java Project
Open the Main.java file in the editor.
Add the following initialization code: static { System.load("
Figure 15
Running Application
To set the HelloWorld Java project as the main project, right-click the project node and choose Set As Main Project from the context menu.
Press F6 to run the application.
The program should execute correctly and the Output dialog box should say:
Hello World from C BUILD SUCCESSFUL (total time: 0 seconds)
Figure 16
Summary
In this exercise you made some final configuration steps andran the application to verify that the implementation of thenative method comes from the native C library.
Next Steps
You can download the sources for this tutorial fromhere.
You can use the following documents to get more information:
Getting Started With the NetBeans C/C++ Development Pack, the NetBeans C/C++ Pack 5.5 tutorial
Java Native Interface, the Java Native Interface 5.0 specification
Beginning JNI with NetBeans? C/C Pack 5.5, Part I
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