3 linux下jni的使用

一 配置linux环境并测试

1 java环境 http://www.jianshu.com/p/e5d8b62aed89 2 linux怎么跑跑java程序 2.1 错误代码 文件名与类名要相同

public class HelloWorld { public static void main(String args[]) { System.out.println("HelloWorld"); } }

2.2 正确代码

public class hello_java{ public static void main(String args[]) { System.out.println("HelloWorld"); } }

2.3 效果

root@52acd6c79e97:/home/huxiang_j/work/jni/java/test_java_hello_world_3_10# vim.tiny hello_java.java root@52acd6c79e97:/home/huxiang_j/work/jni/java/test_java_hello_world_3_10# javac hello_java.java hello_java.java:1: error: class HelloWorld is public, should be declared in a file named HelloWorld.java public class HelloWorld { ^ 1 error root@52acd6c79e97:/home/huxiang_j/work/jni/java/test_java_hello_world_3_10# vim.tiny hello_java.java root@52acd6c79e97:/home/huxiang_j/work/jni/java/test_java_hello_world_3_10# !javac javac hello_java.java root@52acd6c79e97:/home/huxiang_j/work/jni/java/test_java_hello_world_3_10# ls hello_java.class hello_java.java root@52acd6c79e97:/home/huxiang_j/work/jni/java/test_java_hello_world_3_10# java hello_java HelloWorld

二 linux下使用jni来实现java对c++的调用

1 创建文件目录

[hx133330@e69d19429.et15sqa /home/hx133330/work/jni] $cd TestNativeCode/src/com/wwj/nativecode/ [hx133330@e69d19429.et15sqa /home/hx133330/work/jni/TestNativeCode/src/com/wwj/nativecode] $ls TestNativeCode.java

2 编写TestNativeCode.java文件

//3 send abc return cba dll path package com.jni.demo; public class JNIDemo { //定义一个本地方法 public native void sayHello(); public native String changeString(String src); // public native void setInt(String src); public static void main(String[] args){ //调用动态链接库 System.loadLibrary("nativeCode"); JNIDemo jniDemo = new JNIDemo(); jniDemo.sayHello(); System.out.println(jniDemo.changeString("abcd")); } }

3 利用javac生成.class类文件

root@52acd6c79e97:/home/huxiang_j/work/jni/TestNativeCode# javac src/com/wwj/nativecode/TestNativeCode.java -d bin

4 利用javah生成.h头文件（找不到类的错误可以参考我前一篇博客）

root@52acd6c79e97:/home/huxiang_j/work/jni/TestNativeCode/bin# javah com.wwj.nativecode.TestNativeCode

5 编译.so文件

编写source.cpp

#include<iostream> #include<string> #include"com_wwj_nativecode_TestNativeCode.h" using namespace std; JNIEXPORT void JNICALL Java_com_wwj_nativecode_TestNativeCode_sayHello (JNIEnv *env, jobject jj){ cout<<"hello world"<<endl; }; JNIEXPORT jstring JNICALL Java_com_wwj_nativecode_TestNativeCode_changeString (JNIEnv *env, jobject jj, jstring js){ const char * str_in = env->GetStringUTFChars(js,false); string tem1,tem2; tem1 = str_in; tem2.assign(tem1.rbegin(),tem1.rend()); cout<<"tem1:"<<tem1<<" tem2:"<<tem2<<endl; const char * str_out = tem2.c_str(); jstring rt = env->NewStringUTF(str_out); return rt; };

然后利用g++编译成.so动态库

g++ -I$JAVA_HOME/include/ -I$JAVA_HOME/include/linux -shared -fPIC -o libmyjni.so source.cpp

并将这个so文件放到类的目录，这里即为bin目录，并改名为nativeCode，供后面java调用。 6 将.so添加到java.library.path环境变量中（根据自己情况修改）

export LD_LIBRARY_PATH=/home/huxiang_j/work/jni/TestNativeCode/bin/ root@52acd6c79e97:/home/huxiang_j/work/jni/TestNativeCode/bin# export LD_LIBRARY_PATH=/home/huxiang_j/work/jni/TestNativeCode/bin/

How to add .so file to the java.library.path in Linux http://stackoverflow.com/questions/16227045/how-to-add-so-file-to-the-java-library-path-in-linux

未添加会报错，错误如下：

Exception in thread "main" java.lang.UnsatisfiedLinkError: no nativeCode in java.library.path at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1867) at java.lang.Runtime.loadLibrary0(Runtime.java:870) at java.lang.System.loadLibrary(System.java:1122) at com.wwj.nativecode.TestNativeCode.main(TestNativeCode.java:8)

7 运行结果

root@52acd6c79e97:/home/huxiang_j/work/jni/TestNativeCode/bin# java com/wwj/nativecode/TestNativeCode hello world tem1:abcd tem2:dcba dcba