NDK学习笔记-文件的拆分与合并
文件的拆分与合并在开发中经常会用到，上传或是下载的时候都有这样的运用
文件拆分的思路
将文件大小拆分为n个文件
那么，每个文件的大小就是等大小的
如果文件大小被n除不尽，那么就使用n+1个文件来拆分
最后一个文件的大小就是整除不尽的那一部分数据
文件合并的思路
将拆分出来的全部文件胺顺序读取
挨个数据写入到指定文件中
所有文件数据写入完毕
那么合并就完成了
代码实现
布局文件（activity_main.xml）
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="拆分"
android:onClick="mDiff" />
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="合并"
android:onClick="mPatch"/>
</LinearLayout>
主活动文件（MainActivity.java）
import java.io.File;
import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.widget.Toast;
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 mDiff(View v) {
String path = SD_CARD_PATH + File.separatorChar + "test.mp3";
String path_pattern = SD_CARD_PATH + File.separatorChar + "test_%d.mp3";
Utils.diff(path, path_pattern, 3);
Toast.makeText(MainActivity.this, "···拆分完成···", Toast.LENGTH_SHORT).show();
Log.d("cj5785","···拆分完成···");
}
public void mPatch(View v) {
String path_pattern = SD_CARD_PATH + File.separatorChar + "test_%d.mp3";
String path_merge = SD_CARD_PATH + File.separatorChar + "test_merge.mp3";
Utils.patch(path_pattern, path_merge, 3);
Toast.makeText(MainActivity.this, "···合并完成···", Toast.LENGTH_SHORT).show();
Log.d("cj5785","···合并完成···");
}
}
工具类文件（Utils.java）
public class Utils {
/**
* 拆分
* @param path 原始文件路径
* @param path_pattern 拆分文件路径
* @param count 拆分个数
*/
public native static void diff(String path, String path_pattern, int count);
/**
* 合并
* @param path_pattern 拆分文件路径
* @param path_merge 合并文件路径
* @param count 拆分的文件个数
*/
public native static void patch(String path_pattern, String path_merge, int count);
static {
System.loadLibrary("NdkFilePatch");
}
}
JNI头文件（com_cj5785_ndkfilepatch_Utils.h）
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_cj5785_ndkfilepatch_Utils */
#ifndef _Included_com_cj5785_ndkfilepatch_Utils
#define _Included_com_cj5785_ndkfilepatch_Utils
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: com_cj5785_ndkfilepatch_Utils
* Method: diff
* Signature: (Ljava/lang/String;Ljava/lang/String;I)V
*/
JNIEXPORT void JNICALL Java_com_cj5785_ndkfilepatch_Utils_diff
(JNIEnv *, jclass, jstring, jstring, jint);
/*
* Class: com_cj5785_ndkfilepatch_Utils
* Method: patch
* Signature: (Ljava/lang/String;Ljava/lang/String;I)V
*/
JNIEXPORT void JNICALL Java_com_cj5785_ndkfilepatch_Utils_patch
(JNIEnv *, jclass, jstring, jstring, jint);
#ifdef __cplusplus
}
#endif
#endif
JNI头文件实现（NdkFilePatch.c）
#include <stdlib.h>
#include <stdio.h>
#include <Android/log.h>
#include "com_cj5785_ndkfilepatch_Utils.h"
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,"cj5785",__VA_ARGS__)
//获取文件大小
long get_file_size(char const *path)
{
FILE *fp = fopen(path,"rb");
fseek(fp,0,SEEK_END);
long size = ftell(fp);
fclose(fp);
return size;
}
//拆分
JNIEXPORT void JNICALL Java_com_cj5785_ndkfilepatch_Utils_diff
(JNIEnv *env, jclass jcls, jstring path_jstr, jstring path_pattern_jstr, jint file_num)
{
//文件路径
const char *path = (*env)->GetStringUTFChars(env,path_jstr,NULL);
const char *path_pattern = (*env)->GetStringUTFChars(env,path_pattern_jstr,NULL);
//拆分完成后的子文件路径
char **patches = (char **)malloc(sizeof(char *) * file_num);
memset(patches, 0, sizeof(char *) * file_num);
int i = 0;
for(;i < file_num;i++)
{
patches[i] = (char *)malloc(sizeof(char) * 100);
memset(patches[i], 0, sizeof(char) * 100);
//子文件名称
sprintf(patches[i], path_pattern, i+1);
LOGI("patch path:%s",patches[i]);
}
//读取path文件，写入到file_num个文件中
int file_size = get_file_size(path);
FILE *fpr = fopen(path, "rb");
//文件大小能被整除
if(file_size % file_num == 0)
{
int part = file_size / file_num;
i = 0;
for(;i < file_num; i++)
{
FILE *fpw = fopen(patches[i], "wb");
int j = 0;
for(;j < part; j++)
{
fputc(fgetc(fpr),fpw);
}
fclose(fpw);
}
}else{
int part = file_size / (file_num - 1);
i = 0;
for(;i < file_num - 1; i++)
{
FILE *fpw = fopen(patches[i], "wb");
int j = 0;
for(;j < part; j++)
{
fputc(fgetc(fpr),fpw);
}
fclose(fpw);
}
FILE *fpw = fopen(patches[file_num - 1], "wb");
i = 0;
for(;i < file_size % (file_num -1); i++)
{
fputc(fgetc(fpr),fpw);
}
fclose(fpw);
}
fclose(fpr);
//释放malloc的空间
i = 0;
for(;i < file_num; i++)
{
free(patches[i]);
}
free(patches);
patches = NULL;
//释放资源
(*env)->ReleaseStringUTFChars(env,path_jstr,path);
(*env)->ReleaseStringUTFChars(env,path_pattern_jstr,path_pattern);
}
//合并
JNIEXPORT void JNICALL Java_com_cj5785_ndkfilepatch_Utils_patch
(JNIEnv *env, jclass jcls, jstring path_pattern_jstr, jstring path_merge_jstr, jint file_num)
{
//文件路径
const char *path_pattern = (*env)->GetStringUTFChars(env,path_pattern_jstr,NULL);
const char *path_merge = (*env)->GetStringUTFChars(env,path_merge_jstr,NULL);
//子文件路径列表
char **patches = (char **)malloc(sizeof(char *) * file_num);
memset(patches, 0, sizeof(char *) * file_num);
int i = 0;
for(; i < file_num; i++)
{
patches[i] = (char *)malloc(sizeof(char) * 100);
memset(patches[i], 0, sizeof(char) * 100);
sprintf(patches[i], path_pattern, i+1);
LOGI("patch path:%s", patches[i]);
}
FILE *fpw = fopen(path_merge, "wb");
i = 0;
for(; i < file_num; i++)
{
int file_size = get_file_size(patches[i]);
FILE *fpr = fopen(patches[i], "rb");
int j = 0;
for(; j < file_size; j++)
{
fputc(fgetc(fpr),fpw);
}
fclose(fpr);
}
fclose(fpw);
//释放malloc的空间
i = 0;
for(; i < file_num; i++)
{
free(patches[i]);
}
free(patches);
patches = NULL;
//释放资源
(*env)->ReleaseStringUTFChars(env,path_pattern_jstr,path_pattern);
(*env)->ReleaseStringUTFChars(env,path_merge_jstr,path_merge);
}
Android.mk文件
因为在C实现代码中使用了日志打印，所以要在Android.mk文件中，添加日志打印的依赖
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := NdkFilePatch
LOCAL_SRC_FILES := NdkFilePatch.c
LOCAL_LDLIBS := -lm -llog
include $(BUILD_SHARED_LIBRARY)
问题总结
- 在最开始的时候，日志无法打印，报错
ANDROID_LOG_INFO不存在，添加本地支持以后仍然不行，无论怎么折腾，依旧如此。无奈之下，重启eclipse，居然好了。后经查阅得知，这是NDK r9d存在的bug，按照stackoverflow一位回答者的建议，先clean项目，然后build就好了：
Cleaning the project and Project -> Build Project (I have Build Automatically disabled) recreated the .so library and all the symbols are now properly found
- 在拆分实现的时候，无论何种情况，得到的第最后一个拆分文件大小都为零，这里是因为在拆分的时候，大小的计算是基于字节大小的，故最后一个文件存储的大小是除数的字节数大小以下的一个值，很小。。。
