我參加了CSDN博客之星評(píng)選，如不雅在以前的一段時(shí)光里陽(yáng)光小強(qiáng)的博客對(duì)你有所贊助，在這里欲望能投上您寶貴的一票，天天都可以投一次：http://vote.blog.csdn.net/blogstar2014/details?username=lxq_xsyu#content

一、什么是JNI

JNI是Java Native Interface的縮寫（Java本地調(diào)用），Java法度榜樣中的函數(shù)可聲調(diào)用Native說話寫的函數(shù)（一般指的是C/C++編寫的函數(shù)），Native說話寫的函數(shù)可聲調(diào)用Java層的函數(shù)。

二、為什么要有JNI

Java說話的跨平臺(tái)是因?yàn)樵诓缓掀脚_(tái)上可以運(yùn)行Java虛擬機(jī)，而虛擬機(jī)是跑在具體平滔喔贍，而本質(zhì)上Java是經(jīng)由過程JNI技巧實(shí)現(xiàn)的跨平臺(tái)，很多基層的模塊在Java說話出生之前已經(jīng)有了比較優(yōu)良的實(shí)現(xiàn)，為了避免反復(fù)造輪子所以我們要應(yīng)用JNI技巧來應(yīng)用已有的模塊。
[img]http://img.blog.csdn.net/20150104210435843?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZGF3YW5nYW5iYW4=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center

三、Mac OS上的情況搭建

在這里解釋一下Max OS上的所需情況搭建，Windows和Linux的請(qǐng)搜刮相干材料。
1、安裝JDK(此處省略）。
2、安裝ADT(Android Develop Tools),包含SDK和ADT插件,下載地址：http://pan.baidu.com/s/1o6OBIHG
3、安裝Xcode可以去蘋不雅市廛下載安裝（免費(fèi)）。
4、安裝Apache ANT(下載地址：http://ant.apache.org/bindownload.cgi）具體安裝過程可以參考：http://blog.csdn.net/song_hui_xiang/article/details/14315529
5、安裝GNU Make(默認(rèn)已經(jīng)安裝，所以不消安裝）可以應(yīng)用 make -version敕令驗(yàn)證是否安裝。
6、安裝NDK(下載地址：http://pan.baidu.com/s/1i3l5L8T），解壓后在用戶根目次下新建文件.bash_profile然后添加如下兩行（設(shè)備情況變量，可以臨時(shí)不設(shè)備）。

export ANDROID_NDK_HOME=/Users/lixiaoqiang/Documents/install_tools/ndk/android-ndk-r10c
export PATH=${PATH}:${ANDROID_NDK_HOME}

留意：后面的地址是你解壓后的目次
關(guān)于膳綾擎部分開辟對(duì)象扼要介紹：
1、Apache Ant,是一個(gè)將軟件編譯、測(cè)試、安排等步調(diào)聯(lián)系袈溱一路加以主動(dòng)化的一個(gè)對(duì)象，大年夜多用于Java情況中的軟件開辟。
2、NDK是Android原生開辟對(duì)象包，可以支撐C/C++等原生編程說話開辟Android應(yīng)用，它供給頭文件、庫(kù)和交叉編譯對(duì)象鏈。

四、第一個(gè)示例法度榜樣

轉(zhuǎn)載請(qǐng)解釋出處：http://blog.csdn.net/dawanganban
1、為eclipse指定NDK路徑
[img]http://img.blog.csdn.net/20150104212549675?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZGF3YW5nYW5iYW4=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center
2、導(dǎo)入Android NDK中的示例代碼（導(dǎo)入hello-jni工程），做過Android開辟的同伙應(yīng)當(dāng)很熟悉，這里就不煩瑣了。
[img]http://img.blog.csdn.net/20150104212738236?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZGF3YW5nYW5iYW4=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center
3、向項(xiàng)目中添加原生支撐
項(xiàng)目——>右擊——>Android Tools——>Add Native Support
該項(xiàng)目其實(shí)已經(jīng)包含了一個(gè)原生項(xiàng)目，所以這一步可以跳過，我們直接Finish持續(xù)。
4、插上手機(jī)（模仿器太慢了，建議應(yīng)用真機(jī)）運(yùn)行項(xiàng)目。在C/C++界面視圖我們可以看到如下信息

**** Build of configuration Default for project HelloJni ****

/Users/lixiaoqiang/Documents/install_tools/ndk/android-ndk-r10c/ndk-build all 
Android NDK: WARNING: APP_PLATFORM android-19 is larger than android:minSdkVersion 3 in ./AndroidManifest.xml    
[arm64-v8a] Gdbserver      : [aarch64-linux-android-4.9] libs/arm64-v8a/gdbserver
[arm64-v8a] Gdbsetup       : libs/arm64-v8a/gdb.setup
[x86_64] Gdbserver      : [x86_64-4.9] libs/x86_64/gdbserver
[x86_64] Gdbsetup       : libs/x86_64/gdb.setup
[mips64] Gdbserver      : [mips64el-linux-android-4.9] libs/mips64/gdbserver
[mips64] Gdbsetup       : libs/mips64/gdb.setup
[armeabi-v7a] Gdbserver      : [arm-linux-androideabi-4.6] libs/armeabi-v7a/gdbserver
[armeabi-v7a] Gdbsetup       : libs/armeabi-v7a/gdb.setup
[armeabi] Gdbserver      : [arm-linux-androideabi-4.6] libs/armeabi/gdbserver
[armeabi] Gdbsetup       : libs/armeabi/gdb.setup
[x86] Gdbserver      : [x86-4.6] libs/x86/gdbserver
[x86] Gdbsetup       : libs/x86/gdb.setup
[mips] Gdbserver      : [mipsel-linux-android-4.6] libs/mips/gdbserver
[mips] Gdbsetup       : libs/mips/gdb.setup
[arm64-v8a] Compile        : hello-jni <= hello-jni.c
[arm64-v8a] SharedLibrary  : libhello-jni.so
[arm64-v8a] Install        : libhello-jni.so => libs/arm64-v8a/libhello-jni.so
[x86_64] Compile        : hello-jni <= hello-jni.c
[x86_64] SharedLibrary  : libhello-jni.so
[x86_64] Install        : libhello-jni.so => libs/x86_64/libhello-jni.so
[mips64] Compile        : hello-jni <= hello-jni.c
[mips64] SharedLibrary  : libhello-jni.so
[mips64] Install        : libhello-jni.so => libs/mips64/libhello-jni.so
[armeabi-v7a] Compile thumb  : hello-jni <= hello-jni.c
[armeabi-v7a] SharedLibrary  : libhello-jni.so
[armeabi-v7a] Install        : libhello-jni.so => libs/armeabi-v7a/libhello-jni.so
[armeabi] Compile thumb  : hello-jni <= hello-jni.c
[armeabi] SharedLibrary  : libhello-jni.so
[armeabi] Install        : libhello-jni.so => libs/armeabi/libhello-jni.so
[x86] Compile        : hello-jni <= hello-jni.c
[x86] SharedLibrary  : libhello-jni.so
[x86] Install        : libhello-jni.so => libs/x86/libhello-jni.so
[mips] Compile        : hello-jni <= hello-jni.c
[mips] SharedLibrary  : libhello-jni.so
[mips] Install        : libhello-jni.so => libs/mips/libhello-jni.so

**** Build Finished ****

這個(gè)過程其實(shí)就是在構(gòu)建原生組件并和Java應(yīng)用法度榜樣打包的過程。此時(shí)在我們手機(jī)上就可以看到一行文字
[img]http://img.blog.csdn.net/20150104220026008?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZGF3YW5nYW5iYW4=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center

五、項(xiàng)目構(gòu)造及重要目次介紹

[img]http://img.blog.csdn.net/20150104220319324?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZGF3YW5nYW5iYW4=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center
1、jni目次：包含原生組件的源代碼及描述原生組件構(gòu)建辦法的Make文件（Android.mk），該目次作為NDK構(gòu)建項(xiàng)目時(shí)的構(gòu)建目次。
2、libs目次：包含指定目標(biāo)平臺(tái)的自力子目次，在打包時(shí)該目次被包含在apk文件中。
3、obj目次：這是一個(gè)中心目次，編譯源碼后產(chǎn)生的目標(biāo)文件都保存在該目次下，我們最好不消拜訪該目次。

六、 實(shí)例工程解析

Android.mk的內(nèi)容如下

# Copyright (C) 2009 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := hello-jni
LOCAL_SRC_FILES := hello-jni.c

include $(BUILD_SHARED_LIBRARY)

有關(guān)Makefile的常識(shí)請(qǐng)參考我的另一篇博文：http://blog.csdn.net/dawanganban/article/details/38750151
第一行：Android.mk文檔必須以LOCAL_PATH變量的定義開首，my-dir是一個(gè)體系的宏定義，來定義源文件的目次地位。
第二行：Android構(gòu)建體系將CLEAR_VARS變量設(shè)置為clear-vars.mk片段的地位，更多片段的makefile文件請(qǐng)看ndk\build\core目次，如下：
[img]http://img.blog.csdn.net/20150104222306062?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZGF3YW5nYW5iYW4=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center
感化是清除除了LOCAL_PATH以外的LOCAL_<name>變量，如許可以避免沖突。
第三行：每一個(gè)原生組件被稱為一個(gè)模塊，LOCAL_MODULE變量用來給這些模塊設(shè)定一個(gè)獨(dú)一的名稱。
第四行：LOCAL_SRC_FILES變量定義用來建立和組裝這個(gè)模塊的源文件列表，用空格隔開。
第五行：指清楚明了build-shared-library.mk文件的保存地位，該片段包含了將源文件構(gòu)建成共享庫(kù)的須要過程。
下面我們來看看HelloJni.java

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.example.hellojni;

import android.app.Activity;
import android.widget.TextView;
import android.os.Bundle;


public class HelloJni extends Activity
{
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        /* Create a TextView and set its content.
         * the text is retrieved by calling a native
         * function.
         */
        TextView  tv = new TextView(this);
        tv.setText( stringFromJNI() );
        setContentView(tv);
    }

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

    /* This is another native method declaration that is *not*
     * implemented by 'hello-jni'. This is simply to show that
     * you can declare as many native methods in your Java code
     * as you want, their implementation is searched in the
     * currently loaded native libraries only the first time
     * you call them.
     *
     * Trying to call this function will result in a
     * java.lang.UnsatisfiedLinkError exception !
     */
    public native String  unimplementedStringFromJNI();

    /* this is used to load the 'hello-jni' library on application
     * startup. The library has already been unpacked into
     * /data/data/com.example.hellojni/lib/libhello-jni.so at
     * installation time by the package manager.
     */
    static {
        System.loadLibrary("hello-jni");
    }
}

大年夜膳綾擎可以看到調(diào)用了原生的stringFromJNI()辦法，應(yīng)用關(guān)鍵字native來通知Java編譯器，這個(gè)是用另一種說話實(shí)現(xiàn)的，再經(jīng)由過程加裝共享庫(kù)(static語(yǔ)句塊）hello-jni來告訴虛擬機(jī)原生辦法的具體實(shí)現(xiàn)。java.lang.System類供給了兩個(gè)靜態(tài)辦法，load和loadLibrary用來運(yùn)行時(shí)加載共享庫(kù)。下面我們來看看具體的實(shí)現(xiàn)。

#include <string.h>
#include <jni.h>

/* This is a trivial JNI example where we use a native method
 * to return a new VM String. See the corresponding Java source
 * file located at:
 *
 *   apps/samples/hello-jni/project/src/com/example/hellojni/HelloJni.java
 */
jstring
Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env,
                                                  jobject thiz )
{
#if defined(__arm__)
  #if defined(__ARM_ARCH_7A__)
    #if defined(__ARM_NEON__)
      #if defined(__ARM_PCS_VFP)
        #define ABI "armeabi-v7a/NEON (hard-float)"
      #else
        #define ABI "armeabi-v7a/NEON"
      #endif
    #else
      #if defined(__ARM_PCS_VFP)
        #define ABI "armeabi-v7a (hard-float)"
      #else
        #define ABI "armeabi-v7a"
      #endif
    #endif
  #else
   #define ABI "armeabi"
  #endif
#elif defined(__i386__)
   #define ABI "x86"
#elif defined(__x86_64__)
   #define ABI "x86_64"
#elif defined(__mips64)  /* mips64el-* toolchain defines __mips__ too */
   #define ABI "mips64"
#elif defined(__mips__)
   #define ABI "mips"
#elif defined(__aarch64__)
   #define ABI "arm64-v8a"
#else
   #define ABI "unknown"
#endif

    return (*env)->NewStringUTF(env, "Hello from JNI !  Compiled with ABI " ABI ".");
}

第一個(gè)參數(shù)JNIEnv是指向可用JNI函數(shù)表的接口指針，第二個(gè)參數(shù)jobject是HelloJni類實(shí)例的java對(duì)象。最后一句代碼是用c字符串創(chuàng)建UTF-8的Java字符串。