04.Eclipse下Ndk开发（以文件拆分合并为例模拟一下开发过程，参考文件加密的过程）

(创建于2017/12/6)

1.工具类PatchUtils

package com.ren.ndk_file_patch;

public class PatchUtils {
    
    static{
        System.loadLibrary("ndk_file_patch");
    }

    public native static void diff(String path,String path_pattern,int count);
    
    public native static void patch(String path_pattern,String merge_path,int count);
}

2.生成的头文件 com_ren_ndk_file_patch_PatchUtils.h

/* DO NOT EDIT THIS FILE - it is machine generated */
#include 
/* Header for class com_ren_ndk_file_patch_PatchUtils */

#ifndef _Included_com_ren_ndk_file_patch_PatchUtils
#define _Included_com_ren_ndk_file_patch_PatchUtils
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_ren_ndk_file_patch_PatchUtils
 * Method:    diff
 * Signature: (Ljava/lang/String;Ljava/lang/String;I)V
 */
JNIEXPORT void JNICALL Java_com_ren_ndk_1file_1patch_PatchUtils_diff
  (JNIEnv *, jclass, jstring, jstring, jint);

/*
 * Class:     com_ren_ndk_file_patch_PatchUtils
 * Method:    patch
 * Signature: (Ljava/lang/String;Ljava/lang/String;I)V
 */
JNIEXPORT void JNICALL Java_com_ren_ndk_1file_1patch_PatchUtils_patch
  (JNIEnv *, jclass, jstring, jstring, jint);

#ifdef __cplusplus
}
#endif
#endif

3.编写的c文件 ndk_file_patch.c

#include "com_ren_ndk_file_patch_PatchUtils.h"
#include 
#include 
#include 
#include

#define LOGI(FORMAT,...) __android_log_print(ANDROID_LOG_INFO,"renzhenming",FORMAT,__VA_ARGS__);
#define LOGE(FORMAT,...) __android_log_print(ANDROID_LOG_ERROR),"renzhenming",FORMAT,__VA_ARGS__);

long get_file_size(const char *path){
    FILE *fl = fopen(path,"rb");
    //把与fp有关的文件位置指针放到一个指定位置。
    //文件指针定位到文件末尾，偏移0个字节 
    fseek(fl,0,SEEK_END);
    //函数用来获取文件读写指针的当前位置,对于二进制文件，则返回从文件开头到结尾的字节数。
    return ftell(fl);
}

JNIEXPORT void JNICALL Java_com_ren_ndk_1file_1patch_PatchUtils_diff
  (JNIEnv *env, jclass jclz, jstring path_jstr, jstring path_pattern_jstr, jint file_num){

    //转换文件路径
    const char *path = (*env)->GetStringUTFChars(env,path_jstr,NULL);
    const char *path_pattern = (*env)->GetStringUTFChars(env,path_pattern_jstr,NULL);

    //得到分割之后的所有文件路径

    //申请一段连续的内存空间（一个数组）保存所有分割的文件地址
    char **patches = malloc(sizeof(char*)*file_num);

    int i = 0;
    for(;iReleaseStringUTFChars(env,path_jstr,path);
    (*env)->ReleaseStringUTFChars(env,path_pattern_jstr,path_pattern);
}

/*
 * Class:     com_ren_ndk_file_patch_PatchUtils
 * Method:    patch
 * Signature: (Ljava/lang/String;Ljava/lang/String;I)V
 */
JNIEXPORT void JNICALL Java_com_ren_ndk_1file_1patch_PatchUtils_patch
  (JNIEnv *env, jclass jclz, jstring path_pattern_jstr, jstring merge_path_jstr, jint file_num){
    //字符串转换
    const char *merge_path = (*env)->GetStringUTFChars(env,merge_path_jstr,NULL);
    const char *path_pattern = (*env)->GetStringUTFChars(env,path_pattern_jstr,NULL);
    //得到分割后的子文件路径列表
    char **patches = malloc(sizeof(char*)*file_num);
    int i = 0;
    for(;iReleaseStringUTFChars(env,merge_path_jstr,merge_path);
    (*env)->ReleaseStringUTFChars(env,path_pattern_jstr,path_pattern);
}

4.Android.mk文件

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := ndk_file_patch
LOCAL_SRC_FILES := ndk_file_patch.c
LOCAL_LDLIBS := -llog   //使用了log，需要引入

include $(BUILD_SHARED_LIBRARY)

5.开始拆分合并

public class MainActivity extends Activity {
    private String SD_CARD_PATH;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        SD_CARD_PATH = Environment.getExternalStorageDirectory().getAbsolutePath();
    }
    
    public void diff(View view){
        String path = SD_CARD_PATH +File.separatorChar+ "2.mp4";
        String path_pattern = SD_CARD_PATH +File.separatorChar+ "2_%d.mp4";
        PatchUtils.diff(path, path_pattern, 2);
        System.out.println("拆分完成");
    }
    public void patch(View view){
        String merge_path = SD_CARD_PATH +File.separatorChar+ "2_new.mp4";
        String path_pattern = SD_CARD_PATH +File.separatorChar+ "2_%d.mp4";
        PatchUtils.patch(path_pattern, merge_path, 2);
        System.out.println("合并完成");
    }
}

6.注意添加权限，6.0动态申请