java调用c++函数的简单笔记

java使用jni调用c++动态库函数.

步骤：

１．编写java测试代码如下：

 public class CallNativeDemo {
     native void func();

     native double add(double a, double b);

     public static void main(String[] args) {
         System.loadLibrary("Main");
         CallNativeDemo callNativeDemo = new CallNativeDemo();
         callNativeDemo.func();
         System.out.println(callNativeDemo.add(1,2));
     }
 }

2. 使用javac　对代码进行编译：

javac CallNativeDemo.java

3.使用javah　生成CallNativeDemo.h头文件.

javah -cp . CallNativeDemo

生成的代码如下：

 /* DO NOT EDIT THIS FILE - it is machine generated */
 #include <jni.h>
 /* Header for class CallNativeDemo */

 #ifndef _Included_CallNativeDemo
 #define _Included_CallNativeDemo
 #ifdef __cplusplus
 extern "C" {
 #endif
 /*
  * Class:     CallNativeDemo
  * Method:    func
  * Signature: ()V
  */
 JNIEXPORT void JNICALL Java_CallNativeDemo_func
   (JNIEnv *, jobject);

 /*
  * Class:     CallNativeDemo
  * Method:    add
  * Signature: (DD)D
  */
 JNIEXPORT jdouble JNICALL Java_CallNativeDemo_add
   (JNIEnv *, jobject, jdouble, jdouble);

 #ifdef __cplusplus
 }
 #endif
 #endif

４．编写Ｍain.cpp文件,如果使用的是.c文件,去掉extern "C"{}

 #include <jni.h>
 #include <stdio.h>
 /*
  * Class:     CallNativeDemo
  * Method:    func
  * Signature: ()V
  */
 extern "C"{
 JNIEXPORT void JNICALL Java_CallNativeDemo_func
 (JNIEnv *env, jobject job){
     printf("hello world! by java and C++\n");
 }

 /*
  * Class:     CallNativeDemo
  * Method:    add
  * Signature: (II)V
  */
 JNIEXPORT jdouble JNICALL Java_CallNativeDemo_add
   (JNIEnv *env, jobject job, jdouble a, jdouble b){

       return a+b;
 }
 }

5.使用locate／find 查询jdk位置.

locate jdk

6.编写Makefile文件.

 #makefile

 .SUFFIXES: .o.cpp
 .PHONY:    clean
 .PHONY: start

 JDKLIB =/home/gongxijun/java/jdk1.7.0_40/include
 CC =g++
 SRC =Main.cpp
 OBJS =$(SRC:.cpp =.o)
 OS = libMain.so

 .PHONY: start
 start: $(OBJS)
     $(CC) -shared -fpic -I $(JDKLIB) -I $(JDKLIB)/linux -o $(OS) $(OBJS)
 .o.cpp:$(SRC)
     $(CC) -g -Wall $@ -c $<
 .PHONY: clean
 clean:
     rm -f $(OBJS)

7.使用make 编译Ｍakefile文件，生成.so动态库.

make Makefile 或者直接　make

８.运行java程序.

java -cp . -Djava.library.path=. CallNativeDemo

８.1结果如下：

hello world! by java and C++
3.0