Java调用C++示例-优快云博客

本文链接：https://blog.youkuaiyun.com/bench88/article/details/4168286

本文介绍如何通过Java Native Interface (JNI) 实现Java应用程序调用C++项目的方法。主要内容包括定义Java本地类、创建C++ DLL以及在Java中使用该DLL。

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谭炳超

For web development, we need to use Java app to call C++ project. We can use JNI to realize this requirement.

As the above diagram show, we have C++ PROJECT PAG that uses C++ to develop the functions. At the web interface, we use Java to develop the web function.

Because different compilers have different methods to rename function .So we cannot use C++ Project by Java directly.

In order to realize the call between JAVA and C++, we have to define a project in Java IDE as JAVA NATIVE CLASS PAG. The JAVA Native Class announces all class includes the main functions provided C++ PROJECT.

Main steps:

1. Write JAVA Class the have native announce. We call it JAVA NATIVE CLASS PAG.

2. Use javac or IDE(JBuilder,eclipse)to compile Java class

3. Use javah to create suitable head files

4. Create a JAVA,C++ PROJECT in VC6 to output a dll. The project will realize the head files

5. Write a main function to use the native class.

I give out a simple example:

1.TestJniClass

1. TestJniClass include two files: TestJniClass.java and MakeVFile.java.

· MakeVFile.java code :

package cellcom;

public class MakeVFile

{

public static void main(String[] args)

{

TestJniClass jdes=new TestJniClass();

int a= jdes.EraseMedia(111);

int b=jdes.Test666(2222);

System.out.println("result1 = "+a);

System.out.println("result2 = "+b);

}

· TestJniClass.java code:

package cellcom;

public class TestJniClass

{

static{System.loadLibrary("JniDll");}

public native int EraseMedia(int index);

public native int Test666(int index);

}

I put two files in D:/cellcom.

Use cmd : D:/>javah -verbose -d d:/cellcom -classpath ; cellcom.TestJniClass

To create cellcom TestJniClass.h.

TestJniClass.h code:

/* DO NOT EDIT THIS FILE - it is machine generated */

#include <jni.h>

/* Header for class cellcom_TestJniClass */

#ifndef _Included_cellcom_TestJniClass

#define _Included_cellcom_TestJniClass

#ifdef __cplusplus

extern "C" {

#endif

* Class: cellcom_TestJniClass

* Method: EraseMedia

* Signature: (I)I

JNIEXPORT jint JNICALL Java_cellcom_TestJniClass_EraseMedia

(JNIEnv *, jobject, jint);

* Class: cellcom_TestJniClass

* Method: Test666

* Signature: (I)I

JNIEXPORT jint JNICALL Java_cellcom_TestJniClass_Test666

(JNIEnv *, jobject, jint);

#ifdef __cplusplus

}

#endif

They all are C style function. When java loadLibrary("JniDll"),it can know how to call them. C style functions do not rename function in dll.

2.JniDLL Project

We create a dynamic-link library project in VC6.

Add cellcom_TestJniClass.h to project.

Add create cellcom_TestJniClass.cpp to realize the function.

Add system path ：change VC的tools/options/directories

settings, add the follow paths:

%java_home%/includeI

%java_home%/include/win32

At this project, we can call other C++ function.

At last, compile this project and give out a JniDll.dll.

3.Use JAVA Native class

create a project in eclipse as test1.

Put the JniDll.dll in the project folder. We can use it .

Use JNI

1.TestJniClass

2.JniDLL Project