Android Jni层调用应用层(Java)的方法

android的应用层java能够调用jni层的函数,那么jni层也做了能够调用应用层java的方法,其实这个东西还真的涉及程序的编译原理方面的,不过这个直接说就是利用了反射,之前见过最多的是java反射java类中的方法,我的博客中还专门写了一份手稿介绍java反射的使用,jni层调用应用层的java,通过是动用了反射的原理,反射出来给jni层使用,所以可想而知,反射的能量是巨大的.

下面给出一个使用:

<1> : 新建android工程,工程树如下:

<2> : durianutils.h和durianutils.c两个文件参考前面博客中的,没有做任何修改.

durianjniusingjava.c :

#include "durianutils.h"
#include "durianjniusingjava.h"

static const char* classname="com/durian/jniusingjava/lib/DurianJniUsingJava";
JNIEXPORT jint JNICALL Java_com_durian_jniusingjava_lib_DurianJniUsingJava_DurianAdd(JNIEnv *env, jobject jobj, jint ab, jint cd){

	LOGI("ab : %d cd : %d",ab,cd);

	jclass clazz=(*env)->FindClass(env,classname);
	jmethodID appMethod=(*env)->GetMethodID(env,clazz,"DurianSum","(II)I");

	jint ret=(*env)->CallIntMethod(env,jobj,appMethod,ab,cd);

	LOGI("ret : %d",ret);

	return ret;
}

durianjniusingjava.h :

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

#ifndef _Included_com_durian_jniusingjava_lib_DurianJniUsingJava
#define _Included_com_durian_jniusingjava_lib_DurianJniUsingJava
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_durian_jniusingjava_lib_DurianJniUsingJava
 * Method:    DurianAdd
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_durian_jniusingjava_lib_DurianJniUsingJava_DurianAdd
  (JNIEnv *, jobject, jint, jint);

#ifdef __cplusplus
}
#endif
#endif

我感觉只要熟悉反射,这个东西很容易就写出来了.

<3> : 运行结果:

下面增加获取字符串 :

/**  
* @Title: DurianJniUsingJava.java
* @Package com.durian.jniusingjava.lib
* @Description: TODO
* @author zhibao.liu from durian organization
* @date 2015-12-28 上午11:24:07
* @version V1.0  
*/
package com.durian.jniusingjava.lib;

/**
 * @ClassName: DurianJniUsingJava
 * @Description: TODO
 * @author zhibao.liu Freelancer
 * @email warden_sprite@foxmail.com
 * @date 2015-12-28 上午11:24:07
 *
 */
public class DurianJniUsingJava {

    public int mParams=102;
    private String mMessage="zhibao.liu";
    
    public native int DurianAdd(int a,int b);
    public native int DurianSub(int a,int b);
    public native int DurianField();
    
    public int DurianSum(int a,int b){
        return a+b;
    }
    
    public static int DurianDul(int a,int b){
        if(a>=b){
            return a-b;
        }else{
            return b-a;
        }
    }
    
    static{
        System.loadLibrary("durianjni");
    }
    
}

增加一个

private String mMessage="zhibao.liu";

然后调整durianjniusingjava.c:增加部分如下:

JNIEXPORT jint JNICALL Java_com_durian_jniusingjava_lib_DurianJniUsingJava_DurianField
  (JNIEnv *env, jobject jobj){

	const char *str;

	jclass clazz=(*env)->FindClass(env,classname);
	jfieldID mfield=(*env)->GetFieldID(env,clazz,"mParams","I");
	jint mf=(*env)->GetIntField(env,jobj,mfield);

	LOGI("field mf : %d",mf);

	(*env)->SetIntField(env,jobj,mfield,5231);

	jfieldID msfield=(*env)->GetFieldID(env,clazz,"mMessage","Ljava/lang/String;");
	jstring msg=(*env)->GetObjectField(env,jobj,msfield);

	str=(*env)->GetStringUTFChars(env,msg,NULL);
	LOGI("field string : %s",str);

	return mf;
}

重新编译,运行结果如下:

.............

下面修改获取参数的值,然后修改参数的值:

(*env)->SetIntField(env,jobj,mfield,5231);

调整一下应用层的:

mDurianJniUsingJava=new DurianJniUsingJava();
        int sum=mDurianJniUsingJava.DurianAdd(12, 32);
        int sub=mDurianJniUsingJava.DurianSub(12, 32);
        int ret=mDurianJniUsingJava.DurianField();
        Log.i(TAG,"sum : "+sum +" sub : "+sub+" ret : "+ret +" mParams : "+mDurianJniUsingJava.mParams);

运行结果,增加一行log:

其他的类型一次类推.

下面代码增加了静态变量的获取.

上面工程源代码:

http://pan.baidu.com/s/1c1vTQ1M