Eclipse中使用JNI調用C++ build的dll

Eclipse中使用JNI調用C++ build的dll

- Uper

最近想寫個從java程序中調用C++生成的dll的工具.  在網上搜索一些帖子，大概過程如下：

1. 建立自己的JAVA 類，該類帶有一個or多個native聲明的方法

2. 使用javac，生成.CLASS 文件

3. 使用javah，生成*.H文件

4. 根據*.H文件完成C++的dll

5. copy該dll到class所在的folder下

6. 使用java運行該application 即可.

但是當我把相關內容移到eclipse上時， 總是throw exception:java.lang.UnsatisfiedLinkError異常，後發現是我的*.h文件生成有問題。

下面把我的過程描述一下，以便參考:

Eclipse side

1. Create java class named SWIFTAlianceCASmfTest with function of declared native

      package test.cs.web;
      import java.lang.*;
      public class SWIFTAlianceCASmfTest{
            public native static int calculate(int addone);
            public static void main(String arg[]){
            try{
            SWIFTAlianceCASmfTest objTest = new SWIFTAlianceCASmfTest();
            int add1 = 3;
            int add2 = SWIFTAlianceCASmfTest.calculate(add1);
            System.out.println("The result is "+add2);
            }catch(Exception ex){
                  System.out.println("The result is "+add2);
            }  
            } 
            static {
                System.loadLibrary("mycalculate");  
            }
      }

2. Save it and eclipse will build and generate class file SWIFTAlianceCASmfTest.class in folder ../WEB-INF/CLASSES/test/cs/web/

3. Go to the folder ../WEB-INF/CLASSES/

Execute command javah -jni test.cs.web.SWIFTAlianceCASmfTest

 Note: test.cs.web is package name and not lose it.

 The file test_cs_web_SWIFTAlianceCASmfTest.h will be generated. Refer to below:

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

#include <jni.h>

/* Header for class test_cs_web_SWIFTAlianceCASmfTest */

 

#ifndef _Included_test_cs_web_SWIFTAlianceCASmfTest

#define _Included_test_cs_web_SWIFTAlianceCASmfTest

#ifdef __cplusplus

extern "C" {

#endif

/*

 * Class:     test_cs_web_SWIFTAlianceCASmfTest

 * Method:    calculate

 * Signature: (I)I

 */

JNIEXPORT jint JNICALL Java_test_cs_web_SWIFTAlianceCASmfTest_calculate

  (JNIEnv *, jclass, jint);

 

#ifdef __cplusplus

}

#endif

#endif

 

4. C++ side: According to head file test_cs_web_SWIFTAlianceCASmfTest.h, build dll named mycalculate.dll using VC and implement function Java_test_cs_web_SWIFTAlianceCASmfTest_calculate(,,)

.cpp

#include "jni.h";
#include "test_cs_web_SWIFTAlianceCASmfTest.h";

 

JNIEXPORT jint JNICALL Java_test_cs_web_SWIFTAlianceCASmfTest_calculate
(JNIEnv *env, jclass obj, jint nAdd1)
{
 return (nAdd1+nAdd1);
}

 

.def

LIBRARY LIB
EXPORTS
Java_test_cs_web_SWIFTAlianceCASmfTest_calculate @ 1

 

In VC tools, include the path of files jni.h & jni_md.h in JDK install directory.

 

5. Eclipse side: copy mycalculate.dll to folder ../WEB-INF/CLASSES/

Set Eclipse VM arguments: -Djava.library.path=<the position of mycalculate.dll located in> fgdsf

6. Run Java application in Eclipse and it will return result:The result is 6

 

以上有2點需要注意：

1. don't forget the package name when you generate head file by tool javah

2. the path of dll file and path of running command javah make is correctly.