Android平台Native开发与JNI机制详解

个人认为下面这篇转载的文章写的很清晰很不错. 注意Android平台上的JNI机制使用包括Java代码中调用Native模块以及Native代码中调用Java模块.

http://www.ophonesdn.com/article/show/263

众所周知，OPhone平台上的应用开发主要基于Java语言，但平台完全支持且提供了一定的Native开发能力（主要是C/C++），使得开发者可以借助JNI更深入的实现创意。本文主要介绍OPhone平台的JNI机制和Native模块开发与发布的方法。

/* A native method that is implemented by the
 


   * 'hello-jni' native library, which is packaged
 


   * with this application.
 


   */
  



  public
 
native
 String  stringFromJNI();  

/* A native method that is implemented by the
     * 'hello-jni' native library, which is packaged
     * with this application.
     */
    public native String  stringFromJNI();

#include <string.h>  



#include <jni.h>  


jstring  


Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env,  


                                                 jobject thiz ) {  


        return
 (*env)->NewStringUTF(env, 
"Hello from JNI !"
);  



}  

#include <string.h>
#include <jni.h>
jstring
Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env,
                                                 jobject thiz ) {
        return (*env)->NewStringUTF(env, "Hello from JNI !");
}

static
 {  



    System.loadLibrary("hello-jni"
);  



}  

static {
        System.loadLibrary("hello-jni");
    }

TextView tv = 
new
 TextView(
this
);  



tv.setText( stringFromJNI() );  


setContentView(tv);  

TextView tv = new TextView(this);
    tv.setText( stringFromJNI() );
    setContentView(tv);

package
 com.example.hellojni;  



public
 
class
 SayHello {  



        public
 String sayHelloFromJava(String nativeMsg) {  



               String str = nativeMsg + " But shown in Java!"
;  



               return
 str;  



        }  


}  

package com.example.hellojni;
public class SayHello {
        public String sayHelloFromJava(String nativeMsg) {
               String str = nativeMsg + " But shown in Java!";
               return str;
        }
}

jstring helloFromJava( JNIEnv* env ) {  



       jstring str = NULL;  


       jclass clz = (*env)->FindClass(env, "com/example/hellojni/SayHello"
);  



       jmethodID ctor = (*env)->GetMethodID(env, clz, "<init>"
, 
"()V"
);  



       jobject obj = (*env)->NewObject(env, clz, ctor);  


       jmethodID mid = (*env)->GetMethodID(env, clz, "sayHelloFromJava"
, 
"(Ljava/lang/String;)Ljava/lang/String;"
);  



       if
 (mid) {  



              jstring jmsg = (*env)->NewStringUTF(env, "I'm born in native."
);  



              str = (*env)->CallObjectMethod(env, obj, mid, jmsg);  


       }  


       return
 str;  



}  

jstring helloFromJava( JNIEnv* env ) {
       jstring str = NULL;
       jclass clz = (*env)->FindClass(env, "com/example/hellojni/SayHello");
       jmethodID ctor = (*env)->GetMethodID(env, clz, "<init>", "()V");
       jobject obj = (*env)->NewObject(env, clz, ctor);
       jmethodID mid = (*env)->GetMethodID(env, clz, "sayHelloFromJava", "(Ljava/lang/String;)Ljava/lang/String;");
       if (mid) {
              jstring jmsg = (*env)->NewStringUTF(env, "I'm born in native.");
              str = (*env)->CallObjectMethod(env, obj, mid, jmsg);
       }
       return str;
}

LOCAL_PATH := $(call my-dir)  



include $(CLEAR_VARS)  


LOCAL_MODULE    :=  hello-jni  


LOCAL_C_INCLUDES :=  $(LOCAL_PATH)/include  


LOCAL_SRC_FILES   :=  src/call_java.c \  


                                          src/hello-jni.c   


include $(BUILD_SHARED_LIBRARY)  

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE    :=  hello-jni
LOCAL_C_INCLUDES :=  $(LOCAL_PATH)/include
LOCAL_SRC_FILES   :=  src/call_java.c \
                                          src/hello-jni.c 
include $(BUILD_SHARED_LIBRARY)