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：

 1 public class CallNativeDemo {
 2     native void func();
 3 
 4     native double add(double a, double b);
 5 
 6     public static void main(String[] args) {
 7         System.loadLibrary("Main");
 8         CallNativeDemo callNativeDemo = new CallNativeDemo();
 9         callNativeDemo.func();
10         System.out.println(callNativeDemo.add(1,2));
11     }
12 }

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：

 1 /* DO NOT EDIT THIS FILE - it is machine generated */
 2 #include <jni.h>
 3 /* Header for class CallNativeDemo */
 4 
 5 #ifndef _Included_CallNativeDemo
 6 #define _Included_CallNativeDemo
 7 #ifdef __cplusplus
 8 extern "C" {
 9 #endif
10 /*
11  * Class:     CallNativeDemo
12  * Method:    func
13  * Signature: ()V
14  */
15 JNIEXPORT void JNICALL Java_CallNativeDemo_func
16   (JNIEnv *, jobject);
17 
18 /*
19  * Class:     CallNativeDemo
20  * Method:    add
21  * Signature: (DD)D
22  */
23 JNIEXPORT jdouble JNICALL Java_CallNativeDemo_add
24   (JNIEnv *, jobject, jdouble, jdouble);
25 
26 #ifdef __cplusplus
27 }
28 #endif
29 #endif

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

 1 #include <jni.h>
 2 #include <stdio.h>
 3 /*
 4  * Class:     CallNativeDemo
 5  * Method:    func
 6  * Signature: ()V
 7  */
 8 extern "C"{
 9 JNIEXPORT void JNICALL Java_CallNativeDemo_func
10 (JNIEnv *env, jobject job){
11     printf("hello world! by java and C++n");
12 }
13 
14 /*
15  * Class:     CallNativeDemo
16  * Method:    add
17  * Signature: (II)V
18  */
19 JNIEXPORT jdouble JNICALL Java_CallNativeDemo_add
20   (JNIEnv *env, jobject job, jdouble a, jdouble b){
21 
22       return a+b;
23 }
24 }

5.使用locate／find 查询jdk位置.

locate jdk

6.编写Makefile文件.

 1 #makefile
 2 
 3 .SUFFIXES: .o.cpp
 4 .PHONY:    clean
 5 .PHONY: start
 6 
 7 
 8 JDKLIB =/home/gongxijun/java/jdk1.7.0_40/include
 9 CC =g++
10 SRC =Main.cpp
11 OBJS =$(SRC:.cpp =.o)
12 OS = libMain.so
13 
14 .PHONY: start
15 start: $(OBJS)
16     $(CC) -shared -fpic -I $(JDKLIB) -I $(JDKLIB)/linux -o $(OS) $(OBJS)
17 .o.cpp:$(SRC)
18     $(CC) -g -Wall $@ -c $<
19 .PHONY: clean
20 clean:
21     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