JNI 对象的操作

1.编写java程序,
1.1 

java 代码(Student.java)

 

/**
 *
 */
package jni;

/**
 * @author likun
 *
 */
public class Student {
    String name;
    int age;
    public Student(){

    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String toString(){
        System.out.println("Name:"+name+"  Age:"+age);
        return "Name:"+name+"  Age:"+age;
    }
}

 

java 代码(StuService.java)

/**
 *
 */
package jni;

import java.util.Iterator;
import java.util.List;

/**
 * @author likun
 *
 */
public class StuService {

    static {
        System.loadLibrary("student");
    }

    /**
     * 获得Student's List
     * @return
     */
    public static native List getStuList();

    /**
     * 返回Student对象
     * 非静态方法
     * @return
     */
    public  native Student getStudent();


    public static void main(String[] args) {
        StuService stuService=new StuService();
        stuService.getStudent().toString();

        List list=StuService.getStuList();
        for(Iterator ite=list.iterator();ite.hasNext();)
        {
            Student stu=(Student)ite.next();
            stu.toString();
        }


    }

}

声明native方法：如果你想将一个方法做为一个本地方法的话，那么你就必须声明改方法为native的，并且不能实现。
Load动态库：System.loadLibrary("student");

1.2 编译StuService.java 
javac -classpath . -d . jni/StuService.java

2.生成jni_StuService.h头文件
javah -classpath . -d . jni.StuService

cpp 代码(jni_StuService.h)

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

#ifndef _Included_jni_StuService
#define _Included_jni_StuService
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     jni_StuService
 * Method:    getStuList
 * Signature: ()Ljava/util/List;
 */
JNIEXPORT jobject JNICALL Java_jni_StuService_getStuList
  (JNIEnv *, jclass);

/*
 * Class:     jni_StuService
 * Method:    getStudent
 * Signature: ()Ljni/Student;
 */
JNIEXPORT jobject JNICALL Java_jni_StuService_getStudent
  (JNIEnv *, jobject);

/*
 * 构造Student对象
 * Method:    constructStudent
 * Signature: ()Ljni/Student;
 */
jobject constructStudent(JNIEnv *env ,int i);

#ifdef __cplusplus
}
#endif
#endif

3.在VC++环境中创建一个动态链接库的项目
3.1 File->new->Projects->Win32 Dynamic-Link Library
3.2 将jni_StuService.h加入Header Files
3.3 %root%\j2sdk1.4.2_10\include\jni.h 和%root%\j2sdk1.4.2_10\include\win32\jni_md.h加入Header Files
3.4 创建student.cpp,并实现 jni_StuService.h中的Java_jni_StuService_getStudent和Java_jni_StuService_getStuList的方法.

cpp 代码(student.cpp)

#include "jni_StuService.h"
/*
 * Class:     jni_StuService
 * Method:    getStuList
 * Signature: ()Ljava/util/List;
 */
 jobject JNICALL Java_jni_StuService_getStuList
     (JNIEnv *env, jclass)
 {
    /**************创建ArrayList 对象 start*****************/

    jclass class_ArrayList=env->FindClass("java/util/ArrayList");/* 获得Java类 */

    jmethodID construct=env->GetMethodID( class_ArrayList, "<init></init>","()V");/* 获得构造方法 */

    jobject obj_List =env->NewObject( class_ArrayList, construct, "");/* 创建java对象 */


    /**************创建ArrayList 对象 end *****************/

    /* 获得List的add方法 */
    jmethodID list_add=env->GetMethodID(class_ArrayList,"add","(Ljava/lang/Object;)Z");

    int i=0;
    while(i<3){

        jobject student=constructStudent(env,i);

        /* 调用List 的add方法 */
        env->CallObjectMethod(obj_List,list_add,student);

        ++i;
    }


    return obj_List;


 }


/*
 * Class:     jni_StuService
 * Method:    getStudent
 * Signature: ()Ljni/Student;
 */
JNIEXPORT jobject JNICALL Java_jni_StuService_getStudent
  (JNIEnv *env, jobject obj_this)
{
    return constructStudent(env,15);
}
/*
 * 构造Student对象
 * Method:    constructStudent
 * Signature: ()Ljni/Student;
 */
jobject constructStudent(JNIEnv *env,int i ){

    /**************创建Student 对象 start*****************/

    jclass class_Student=env->FindClass("jni/Student");/* 获得Java类   */

    jmethodID construct_Student=env->GetMethodID( class_Student, "<init></init>","()V");/* 获得构造方法 */

    jobject obj_Student =env->NewObject( class_Student, construct_Student, "");/* 创建java对象 */

    /**************创建Student 对象 end *****************/


    /**************创建属性ID***************************/

    jfieldID name = env->GetFieldID(class_Student,"name","Ljava/lang/String;");

    jfieldID age = env->GetFieldID(class_Student,"age","I");

    /**************创建属性ID end***************************/


    /**************给对象的属性赋值*************************/

    env->SetIntField(obj_Student,age,27+i);

    env->SetObjectField(obj_Student,name,env->NewStringUTF((char*)"likun35@163.com"));

    /**************给对象的属性赋值end *************************/

    return obj_Student;
}

4. 将生成的student.dll拷贝到\WINDOWS%root%\system32下面

5.运行StuService