java 文件分割及合并

文件分割与合并是一个常见需求，比如：上传大文件时，可以先分割成小块，传到服务器后，再进行合并。很多高大上的分布式文件系统（比如：google的GFS、taobao的TFS）里，也是按block为单位，对文件进行分割或合并。

看下基本思路：



如果有一个大文件，指定分割大小后（比如：按1M切割）

step 1：

先根据原始文件大小、分割大小，算出最终分割的小文件数N

step 2:

在磁盘上创建这N个小文件

step 3:

开多个线程（线程数=分割文件数），每个线程里，利用RandomAccessFile的seek功能，将读取指针定位到原文件里每一段的段首位置，然后向后读取指定大小（即：分割块大小），最终写入对应的分割文件，因为多线程并行处理，各写各的小文件，速度相对还是比较快的。

 

合并时，把上面的思路逆向处理即可。

 

核心代码：

分割处理：

/**
* 拆分文件
* @param fileName 待拆分的完整文件名
* @param byteSize 按多少字节大小拆分
* @return 拆分后的文件名列表
* @throws IOException
*/
public List<String> splitBySize(String fileName, int byteSize)
throws IOException {
List<String> parts = new ArrayList<String>();
File file = new File(fileName);
int count = (int) Math.ceil(file.length() / (double) byteSize);
int countLen = (count + "").length();
ThreadPoolExecutor threadPool = new ThreadPoolExecutor(count,
count * 3, 1, TimeUnit.SECONDS,
new ArrayBlockingQueue<Runnable>(count * 2));

for (int i = 0; i < count; i++) {
String partFileName = file.getName() + "."
+ leftPad((i + 1) + "", countLen, '0') + ".part";
threadPool.execute(new SplitRunnable(byteSize, i * byteSize,
partFileName, file));
parts.add(partFileName);
}
return parts;
}

private class SplitRunnable implements Runnable {
int byteSize;
String partFileName;
File originFile;
int startPos;

public SplitRunnable(int byteSize, int startPos, String partFileName,
File originFile) {
this.startPos = startPos;
this.byteSize = byteSize;
this.partFileName = partFileName;
this.originFile = originFile;
}

public void run() {
RandomAccessFile rFile;
OutputStream os;
try {
rFile = new RandomAccessFile(originFile, "r");
byte[] b = new byte[byteSize];
rFile.seek(startPos);// 移动指针到每“段”开头
int s = rFile.read(b);
os = new FileOutputStream(partFileName);
os.write(b, 0, s);
os.flush();
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
合并处理：

/**
* 合并文件
*
* @param dirPath 拆分文件所在目录名
* @param partFileSuffix 拆分文件后缀名
* @param partFileSize 拆分文件的字节数大小
* @param mergeFileName 合并后的文件名
* @throws IOException
*/
public void mergePartFiles(String dirPath, String partFileSuffix,
int partFileSize, String mergeFileName) throws IOException {
ArrayList<File> partFiles = FileUtil.getDirFiles(dirPath,
partFileSuffix);
Collections.sort(partFiles, new FileComparator());

RandomAccessFile randomAccessFile = new RandomAccessFile(mergeFileName,
"rw");
randomAccessFile.setLength(partFileSize * (partFiles.size() - 1)
+ partFiles.get(partFiles.size() - 1).length());
randomAccessFile.close();

ThreadPoolExecutor threadPool = new ThreadPoolExecutor(
partFiles.size(), partFiles.size() * 3, 1, TimeUnit.SECONDS,
new ArrayBlockingQueue<Runnable>(partFiles.size() * 2));

for (int i = 0; i < partFiles.size(); i++) {
threadPool.execute(new MergeRunnable(i * partFileSize,
mergeFileName, partFiles.get(i)));
}

}

private class MergeRunnable implements Runnable {
long startPos;
String mergeFileName;
File partFile;

public MergeRunnable(long startPos, String mergeFileName, File partFile) {
this.startPos = startPos;
this.mergeFileName = mergeFileName;
this.partFile = partFile;
}

public void run() {
RandomAccessFile rFile;
try {
rFile = new RandomAccessFile(mergeFileName, "rw");
rFile.seek(startPos);
FileInputStream fs = new FileInputStream(partFile);
byte[] b = new byte[fs.available()];
fs.read(b);
fs.close();
rFile.write(b);
rFile.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

为了方便文件操作，把关于文件读写的功能，全封装到FileUtil类：
package com.cnblogs.yjmyzz;

import java.io.*;
import java.util.*;
import java.util.concurrent.*;

/**
* 文件处理辅助类
*
* @author yjmyzz@126.com
* @version 0.2
* @since 2014-11-17
*
*/
public class FileUtil {

/**
* 当前目录路径
*/
public static String currentWorkDir = System.getProperty("user.dir") + "\\";

/**
* 左填充
*
* @param str
* @param length
* @param ch
* @return
*/
public static String leftPad(String str, int length, char ch) {
if (str.length() >= length) {
return str;
}
char[] chs = new char[length];
Arrays.fill(chs, ch);
char[] src = str.toCharArray();
System.arraycopy(src, 0, chs, length - src.length, src.length);
return new String(chs);

}

/**
* 删除文件
*
* @param fileName
* 待删除的完整文件名
* @return
*/
public static boolean delete(String fileName) {
boolean result = false;
File f = new File(fileName);
if (f.exists()) {
result = f.delete();

} else {
result = true;
}
return result;
}

/***
* 递归获取指定目录下的所有的文件（不包括文件夹）
*
* @param obj
* @return
*/
public static ArrayList<File> getAllFiles(String dirPath) {
File dir = new File(dirPath);

ArrayList<File> files = new ArrayList<File>();

if (dir.isDirectory()) {
File[] fileArr = dir.listFiles();
for (int i = 0; i < fileArr.length; i++) {
File f = fileArr[i];
if (f.isFile()) {
files.add(f);
} else {
files.addAll(getAllFiles(f.getPath()));
}
}
}
return files;
}

/**
* 获取指定目录下的所有文件(不包括子文件夹)
*
* @param dirPath
* @return
*/
public static ArrayList<File> getDirFiles(String dirPath) {
File path = new File(dirPath);
File[] fileArr = path.listFiles();
ArrayList<File> files = new ArrayList<File>();

for (File f : fileArr) {
if (f.isFile()) {
files.add(f);
}
}
return files;
}

/**
* 获取指定目录下特定文件后缀名的文件列表(不包括子文件夹)
*
* @param dirPath
* 目录路径
* @param suffix
* 文件后缀
* @return
*/
public static ArrayList<File> getDirFiles(String dirPath,
final String suffix) {
File path = new File(dirPath);
File[] fileArr = path.listFiles(new FilenameFilter() {
public boolean accept(File dir, String name) {
String lowerName = name.toLowerCase();
String lowerSuffix = suffix.toLowerCase();
if (lowerName.endsWith(lowerSuffix)) {
return true;
}
return false;
}

});
ArrayList<File> files = new ArrayList<File>();

for (File f : fileArr) {
if (f.isFile()) {
files.add(f);
}
}
return files;
}

/**
* 读取文件内容
*
* @param fileName
* 待读取的完整文件名
* @return 文件内容
* @throws IOException
*/
public static String read(String fileName) throws IOException {
File f = new File(fileName);
FileInputStream fs = new FileInputStream(f);
String result = null;
byte[] b = new byte[fs.available()];
fs.read(b);
fs.close();
result = new String(b);
return result;
}

/**
* 写文件
*
* @param fileName
* 目标文件名
* @param fileContent
* 写入的内容
* @return
* @throws IOException
*/
public static boolean write(String fileName, String fileContent)
throws IOException {
boolean result = false;
File f = new File(fileName);
FileOutputStream fs = new FileOutputStream(f);
byte[] b = fileContent.getBytes();
fs.write(b);
fs.flush();
fs.close();
result = true;
return result;
}

/**
* 追加内容到指定文件
*
* @param fileName
* @param fileContent
* @return
* @throws IOException
*/
public static boolean append(String fileName, String fileContent)
throws IOException {
boolean result = false;
File f = new File(fileName);
if (f.exists()) {
RandomAccessFile rFile = new RandomAccessFile(f, "rw");
byte[] b = fileContent.getBytes();
long originLen = f.length();
rFile.setLength(originLen + b.length);
rFile.seek(originLen);
rFile.write(b);
rFile.close();
}
result = true;
return result;
}

/**
* 拆分文件
*
* @param fileName
* 待拆分的完整文件名
* @param byteSize
* 按多少字节大小拆分
* @return 拆分后的文件名列表
* @throws IOException
*/
public List<String> splitBySize(String fileName, int byteSize)
throws IOException {
List<String> parts = new ArrayList<String>();
File file = new File(fileName);
int count = (int) Math.ceil(file.length() / (double) byteSize);
int countLen = (count + "").length();
ThreadPoolExecutor threadPool = new ThreadPoolExecutor(count,
count * 3, 1, TimeUnit.SECONDS,
new ArrayBlockingQueue<Runnable>(count * 2));

for (int i = 0; i < count; i++) {
String partFileName = file.getName() + "."
+ leftPad((i + 1) + "", countLen, '0') + ".part";
threadPool.execute(new SplitRunnable(byteSize, i * byteSize,
partFileName, file));
parts.add(partFileName);
}
return parts;
}

/**
* 合并文件
*
* @param dirPath
* 拆分文件所在目录名
* @param partFileSuffix
* 拆分文件后缀名
* @param partFileSize
* 拆分文件的字节数大小
* @param mergeFileName
* 合并后的文件名
* @throws IOException
*/
public void mergePartFiles(String dirPath, String partFileSuffix,
int partFileSize, String mergeFileName) throws IOException {
ArrayList<File> partFiles = FileUtil.getDirFiles(dirPath,
partFileSuffix);
Collections.sort(partFiles, new FileComparator());

RandomAccessFile randomAccessFile = new RandomAccessFile(mergeFileName,
"rw");
randomAccessFile.setLength(partFileSize * (partFiles.size() - 1)
+ partFiles.get(partFiles.size() - 1).length());
randomAccessFile.close();

ThreadPoolExecutor threadPool = new ThreadPoolExecutor(
partFiles.size(), partFiles.size() * 3, 1, TimeUnit.SECONDS,
new ArrayBlockingQueue<Runnable>(partFiles.size() * 2));

for (int i = 0; i < partFiles.size(); i++) {
threadPool.execute(new MergeRunnable(i * partFileSize,
mergeFileName, partFiles.get(i)));
}

}

/**
* 根据文件名，比较文件
*
* @author yjmyzz@126.com
*
*/
private class FileComparator implements Comparator<File> {
public int compare(File o1, File o2) {
return o1.getName().compareToIgnoreCase(o2.getName());
}
}

/**
* 分割处理Runnable
*
* @author yjmyzz@126.com
*
*/
private class SplitRunnable implements Runnable {
int byteSize;
String partFileName;
File originFile;
int startPos;

public SplitRunnable(int byteSize, int startPos, String partFileName,
File originFile) {
this.startPos = startPos;
this.byteSize = byteSize;
this.partFileName = partFileName;
this.originFile = originFile;
}

public void run() {
RandomAccessFile rFile;
OutputStream os;
try {
rFile = new RandomAccessFile(originFile, "r");
byte[] b = new byte[byteSize];
rFile.seek(startPos);// 移动指针到每“段”开头
int s = rFile.read(b);
os = new FileOutputStream(partFileName);
os.write(b, 0, s);
os.flush();
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

/**
* 合并处理Runnable
*
* @author yjmyzz@126.com
*
*/
private class MergeRunnable implements Runnable { long startPos; String mergeFileName; File partFile; public MergeRunnable(long startPos, String mergeFileName, File partFile) { this.startPos = startPos; this.mergeFileName = mergeFileName; this.partFile = partFile; } public void run() { RandomAccessFile rFile; try { rFile = new RandomAccessFile(mergeFileName, "rw"); rFile.seek(startPos); FileInputStream fs = new FileInputStream(partFile); byte[] b = new byte[fs.available()]; fs.read(b); fs.close(); rFile.write(b); rFile.close(); } catch (IOException e) { e.printStackTrace(); } } }

}单元测试：
package com.cnblogs.yjmyzz;

import java.io.IOException;

import org.junit.Test;

public class FileTest {

@Test
public void writeFile() throws IOException, InterruptedException {

System.out.println(FileUtil.currentWorkDir);

StringBuilder sb = new StringBuilder();

long originFileSize = 1024 * 1024 * 100;// 100M
int blockFileSize = 1024 * 1024 * 15;// 15M

// 生成一个大文件
for (int i = 0; i < originFileSize; i++) {
sb.append("A");
}

String fileName = FileUtil.currentWorkDir + "origin.myfile";
System.out.println(fileName);
System.out.println(FileUtil.write(fileName, sb.toString()));

// 追加内容
sb.setLength(0);
sb.append("0123456789");
FileUtil.append(fileName, sb.toString());

FileUtil fileUtil = new FileUtil();

// 将origin.myfile拆分
fileUtil.splitBySize(fileName, blockFileSize);

Thread.sleep(10000);// 稍等10秒，等前面的小文件全都写完

// 合并成新文件
fileUtil.mergePartFiles(FileUtil.currentWorkDir, ".part",
blockFileSize, FileUtil.currentWorkDir + "new.myfile");

}
}