C_Cpp-C-JNI-NDK-Java

一.介绍

JNI(Java Native Interface)是Java提供的编程接口，通过JNIEnv指针,C/C++和java代码可以相互调用传递数据！NDK是Android开发C/C++工具集(代码库和编译工具),能将C/C++编程成不同平台(CUP/ABI)的so库jni.h文件位置:1.Android-ndk/platforms/android-版本/arch-arm/usr/include/jni.h2.JDK/include/jni.h

二.C/C++和Java数据类型映射

在jni.h中 typedef为C/C++类型定义别名,和java类型建立映射1.基本数据类型映射typedef unsigned char   jboolean;       /* unsigned 8 bits */typedef signed char     jbyte;          /* signed 8 bits */typedef unsigned short  jchar;          /* unsigned 16 bits */typedef short           jshort;         /* signed 16 bits */typedef int             jint;           /* signed 32 bits */typedef long long       jlong;          /* signed 64 bits */typedef float           jfloat;         /* 32-bit IEEE 754 */typedef double          jdouble;        /* 64-bit IEEE 754 */2.类对象映射2.1在C++中(全都继承于_jobject类)class _jobject {};class _jclass : public _jobject {};class _jstring : public _jobject {};class _jarray : public _jobject {};class _jobjectArray : public _jarray {};class _jbooleanArray : public _jarray {};class _jbyteArray : public _jarray {};class _jcharArray : public _jarray {};class _jshortArray : public _jarray {};class _jintArray : public _jarray {};class _jlongArray : public _jarray {};class _jfloatArray : public _jarray {};class _jdoubleArray : public _jarray {};class _jthrowable : public _jobject {};typedef _jobject*       jobject;typedef _jclass*        jclass;typedef _jstring*       jstring;typedef _jarray*        jarray;typedef _jobjectArray*  jobjectArray;typedef _jbooleanArray* jbooleanArray;typedef _jbyteArray*    jbyteArray;typedef _jcharArray*    jcharArray;typedef _jshortArray*   jshortArray;typedef _jintArray*     jintArray;typedef _jlongArray*    jlongArray;typedef _jfloatArray*   jfloatArray;typedef _jdoubleArray*  jdoubleArray;typedef _jthrowable*    jthrowable;typedef _jobject*       jweak;2.2在C中(没有类概念,全都是void*别名)typedef void*           jobject;typedef jobject         jclass;typedef jobject         jstring;typedef jobject         jarray;typedef jarray          jobjectArray;typedef jarray          jbooleanArray;typedef jarray          jbyteArray;typedef jarray          jcharArray;typedef jarray          jshortArray;typedef jarray          jintArray;typedef jarray          jlongArray;typedef jarray          jfloatArray;typedef jarray          jdoubleArray;typedef jobject         jthrowable;typedef jobject         jweak;

三.在java中调用C/C++函数

1.在java中定义native方法(C/C++函数接口)

package com.example;public class JavaDemo {     public native String getHello();}

2.实现C/C++函数接口

#include <stdio.h>#include <jni.h>// JNIEnv*封装很多java方法，jobject obj代表调用该函数的java对象jstring Java_com_example_JavaDemo_getHello(JNIEnv* env,jobject obj){    return (*env)->NewStringUTF(env,"hello...");}

3.使用NDK编译C/C++，生成libhello.so

在Android Studio编译C/C++https://developer.android.google.cn/studio/projects/add-native-code.htmlGoogle官方文档中国版, 专为中国开发者建的网站！

4.加载so库,调用C/C++函数

public class Main{    // 加载C/C++库libhello.so, 去除前缀lib    static{        System.loadLibrary("hello");    }    public void onCreate() {                new JavaDemo().getHello(); // 调用C/C++函数    }}

四.在C/C++中调用java方法

// 调用java方法, 把Java字符串解析为C语言字符串char* Jstring2CStr(JNIEnv* env, jstring jstr){    // 1.获取String类(java反射)    jclass clsstring = (*env)->FindClass(env,"java/lang/String");    // 2.获取String.getBytes方法(java反射)    jmethodID mid = (*env)->GetMethodID(env,clsstring, "getBytes", "(Ljava/lang/String;)[B");    // 3.调用getBytes方法(java反射),把java字符串变为字节数组jbyteArray    jstring strencode = (*env)->NewStringUTF(env,"GB2312");    jbyteArray barr= (jbyteArray)(*env)->CallObjectMethod(env,jstr,mid,strencode);    // 4.让jbyte*(char*别名) ba引用Java数组jbyteArray barr    jsize alen = (*env)->GetArrayLength(env,barr);    jbyte* ba = (*env)->GetByteArrayElements(env,barr,JNI_FALSE);    // 5.把Java端数组复制到本地内存(char*指向的)    char* rtn = NULL;    if(alen > 0){        rtn = (char*)malloc(alen+1);        memcpy(rtn,ba,alen);        rtn[alen]=0;    }    // 6.释放jbyte* ba对数组jbyteArray barr的引用, 好让java回收jbyteArray barr占用的内存    (*env)->ReleaseByteArrayElements(env,barr,ba,0);    return rtn ;}

简书: http://www.jianshu.com/p/52b3774fbe2b
CSDN博客: http://blog.csdn.net/qq_32115439/article/details/72567183
GitHub博客：http://lioil.win/2017/05/19/C_JNI_NDK_Java.html
Coding博客：http://c.lioil.win/2017/05/19/C_JNI_NDK_Java.html