Java中JNI的使用详解第六篇:传参之引用数据类型的使用

3种引用类型

• 类class

• 接口interface

• 数组array

基本数据类型的传递

第一步： 编写java

public class HelloWorld{

    Mclass mclass=new Mclass();

    static {
        System.loadLibrary("native");
    }
    
    public native String getString(String str);
    public native int[] getArray(int[] arr);
    public native void say(Minterface minter);
    public native void classSay(Mclass mclass);

    public static void main(String[] args) {
        final HelloWorld world=new HelloWorld();
        
        int[] arr={1,2,3,4,5,6};
        System.out.println(world.getString("I AM CLASS"));
        
        for (int mem : world.getArray(arr)) {
            System.out.println(mem);
        }

        world.say(new Minterface(){
            public void say(){
                world.mclass.say();
            }
        });
        world.classSay(world.mclass);

    }   
}

class Mclass{
    public void say(){
        System.out.println("I AM CLASS");
    }   
}

interface Minterface{
    void say();
}  

第二步： 编译、获取，更改JNI头文件名

$ javac HelloWorld.java
$ javah HelloWorld
$ mv HelloWorld.h  HelloWorld.c

第三步完成JNI文件的编写

#include 

JNIEXPORT jstring JNICALL Java_HelloWorld_getString
  (JNIEnv * env, jobject job, jstring jstr)
  {
    const char *str;
    str=(*env)->GetStringUTFChars(env,jstr,NULL);
    if (str==NULL)
    {
        return NULL;
    }
    printf("C received : %s\n", str);
    return jstr; 
 }

 
JNIEXPORT jintArray JNICALL Java_HelloWorld_getArray
  (JNIEnv * env, jobject job, jintArray arr){
     jint *carr; 
     jint i= 0; 
     carr = (*env)->GetIntArrayElements(env, arr, NULL); //推荐使用
     if (carr == NULL) { 
         return arr; /* exception occurred */ 
     } 
     for (i=0; i<6; i++) { 
         printf("num : %d\n", i); 
     } 
     (*env)->ReleaseIntArrayElements(env, arr, carr, 0); 
     return arr; 
  }

JNIEXPORT void JNICALL Java_HelloWorld_say
  (JNIEnv * env, jobject job, jobject pramjob){

   printf("%s\n", "java is called by HelloWorld_say  : ");

    jmethodID mid  = NULL;

    //1.获取对应的class 
    jclass cls = (*env)->GetObjectClass(env,pramjob);
    //2.获取对应的方法  
    //c语言是获取方法的id  
    mid = (*env)->GetMethodID(env,cls,"say","()V");
    //3.执行方法 
    (*env)->CallVoidMethod(env,pramjob,mid);

  }


JNIEXPORT void JNICALL Java_HelloWorld_classSay
  (JNIEnv * env, jobject job, jobject pramjob){
      printf("%s\n", "java is called by classSay  : ");
      jmethodID mid  = NULL;
       //1.获取对应的class 
      jclass cls = (*env)->GetObjectClass(env,pramjob);
      //2.获取对应的方法  
      //c语言是获取方法的id  
      mid = (*env)->GetMethodID(env,cls,"say","()V");
      //3.执行方法 
      (*env)->CallVoidMethod(env,pramjob,mid);
  }

第四步： 编译、设置程序共享库位置

$ gcc HelloWorld.c -shared -fPIC -o libnative.so -I /usr/lib/jvm/java-7-openjdk-amd64/include/
$ export LD_LIBRARY_PATH=.

第五步： 执行、打印成功！

C received : I AM CLASS
I AM CLASS
num : 0
num : 1
num : 2
num : 3
num : 4
num : 5
1
2
3
4
5
6
java is called by HelloWorld_say  : 
I AM CLASS
java is called by classSay  : 
I AM CLASS