编译C语言版本动态库

1. 编写JAVA类org.techshare.performance.NativeDemo.java，声明并调用native方法：

       public native int add(int x,int y);
   
       public static void main(String[] args) {
           System.load("/home/user/dev/cplusplus/PerformanceC/performance.so");
           NativeDemo bcd = new NativeDemo();
           int x =12;
           int y = 22;
           System.out.println(bcd.add(x,y));
       }

2. 通过javah导出头文件(导出文件名为org_techshare_performance_NativeDemo.h)：javah -classpath ./ -jni org.techshare.performance.NativeDemo

   /* DO NOT EDIT THIS FILE - it is machine generated */
   #include <jni.h>
   /* Header for class org_techshare_performance_NativeDemo */
   
   #ifndef _Included_org_techshare_performance_NativeDemo
   #define _Included_org_techshare_performance_NativeDemo
   #ifdef __cplusplus
   extern "C" {
   #endif
   /*
    * Class:     org_techshare_performance_NativeDemo
    * Method:    add
    * Signature: (II)I
    */
   JNIEXPORT jint JNICALL Java_org_techshare_performance_NativeDemo_add
     (JNIEnv *, jobject, jint, jint);
   
   #ifdef __cplusplus
   }
   #endif
   #endif

3. 创建C工程(可使用CodeBlock作为开发平台)

   1. 生成头文件org_techshare_performance_NativeDemo.h:  File – New – File – C/C++ Header – 填写org_techshare_performance_NativeDemo作为文件名 – 选择项目根目录
   2. 将第二步生成的文件内容拷贝至新创建的头文件中
   3. 生成C语言源文件：File – New – File – C/C++ source – org_techshare_performance_NativeDemo – 选择项目根目录
      1. .C文件中引入项目中创建的头文件
      2. 实现头文件中声明的方法

   #include "org_techshare_performance_NativeDemo.h"
   #include <stdio.h>
   JNIEXPORT jint JNICALL Java_org_techshare_performance_NativeDemo_add
     (JNIEnv *env, jobject obj, jint x, jint y){
       printf("Hello C world!\n");
       int res = x+y;
       printf("%d+%d=%d",x,y,res);
       return res;
   }

4. 编译动态库文件(前提是已安装JDK)：gcc -I /opt/jdk8u232-b09/include -I /opt/jdk8u232-b09/include/linux org_techshare_performance_NativeDemo.c -shared -fPIC -o performance.so

5. 执行JAVA方法