Java 多线程断点下载文件 - 军军小站|张军博客

基本原理：利用URLConnection获取要下载文件的长度、头部等相关信息，并设置响应的头部信息。并且通过URLConnection获取输入流，将文件分成指定的块，每一块单独开辟一个线程完成数据的读取、写入。通过输入流读取下载文件的信息，然后将读取的信息用RandomAccessFile随机写入到本地文件中。同时，每个线程写入的数据都文件指针也就是写入数据的长度，需要保存在一个临时文件中。这样当本次下载没有完成的时候，下次下载的时候就从这个文件中读取上一次下载的文件长度，然后继续接着上一次的位置开始下载。并且将本次下载的长度写入到这个文件中。

个人博客：

http://hoojo.cnblogs.com

http://blog.csdn.net/IBM_hoojo

email: hoojo_@126.com

一、下载文件信息类、实体

封装即将下载资源的信息

package com.hoo.entity;

/**

* function: 下载文件信息类

* @author hoojo

* @createDate 2011-9-21 下午05:14:58

* @file DownloadInfo.java

* @package com.hoo.entity

* @project MultiThreadDownLoad

* @blog http://blog.csdn.net/IBM_hoojo

* @email hoojo_@126.com

* @version 1.0

*/

public class DownloadInfo {

//下载文件url

private String url;

//下载文件名称

private String fileName;

//下载文件路径

private String filePath;

//分成多少段下载，每一段用一个线程完成下载

private int splitter;

//下载文件默认保存路径

private final static String FILE_PATH = "C:/temp" ;

//默认分块数、线程数

private final static int SPLITTER_NUM = 5;

public DownloadInfo() {

super ();

}

/**

* @param url 下载地址

*/

public DownloadInfo(String url) {

this (url, null, null, SPLITTER_NUM);

}

/**

* @param url 下载地址url

* @param splitter 分成多少段或是多少个线程下载

*/

public DownloadInfo(String url, int splitter) {

this (url, null, null, splitter);

}

/***

* @param url 下载地址

* @param fileName 文件名称

* @param filePath 文件保存路径

* @param splitter 分成多少段或是多少个线程下载

*/

public DownloadInfo(String url, String fileName, String filePath, int splitter) {

super ();

if (url == null || "" .equals(url)) {

throw new RuntimeException( "url is not null!" );

}

this .url = url;

this .fileName = (fileName == null || "" .equals(fileName)) ? getFileName(url) : fileName;

this .filePath = (filePath == null || "" .equals(filePath)) ? FILE_PATH : filePath;

this .splitter = (splitter < 1) ? SPLITTER_NUM : splitter;

}

/**

* function: 通过url获得文件名称

* @author hoojo

* @createDate 2011-9-30 下午05:00:00

* @param url

* @return

*/

private String getFileName(String url) {

return url.substring(url.lastIndexOf( "/" ) + 1, url.length());

}

public String getUrl() {

return url;

}

public void setUrl(String url) {

if (url == null || "" .equals(url)) {

throw new RuntimeException( "url is not null!" );

}

this .url = url;

}

public String getFileName() {

return fileName;

}

public void setFileName(String fileName) {

this .fileName = (fileName == null || "" .equals(fileName)) ? getFileName(url) : fileName;

}

public String getFilePath() {

return filePath;

}

public void setFilePath(String filePath) {

this .filePath = (filePath == null || "" .equals(filePath)) ? FILE_PATH : filePath;

}

public int getSplitter() {

return splitter;

}

public void setSplitter( int splitter) {

this .splitter = (splitter < 1) ? SPLITTER_NUM : splitter;

}

@Override

public String toString() {

return this .url + "#" + this .fileName + "#" + this .filePath + "#" + this .splitter;

}

}

二、随机写入一段文件

package com.hoo.download;

import java.io.IOException;

import java.io.RandomAccessFile;

/**

* function: 写入文件、保存文件

* @author hoojo

* @createDate 2011-9-21 下午05:44:02

* @file SaveItemFile.java

* @package com.hoo.download

* @project MultiThreadDownLoad

* @blog http://blog.csdn.net/IBM_hoojo

* @email hoojo_@126.com

* @version 1.0

*/

public class SaveItemFile {

//存储文件

private RandomAccessFile itemFile;

public SaveItemFile() throws IOException {

this ( "" , 0);

}

/**

* @param name 文件路径、名称

* @param pos 写入点位置 position

* @throws IOException

*/

public SaveItemFile(String name, long pos) throws IOException {

itemFile = new RandomAccessFile(name, "rw" );

//在指定的pos位置开始写入数据

itemFile.seek(pos);

}

/**

* function: 同步方法写入文件

* @author hoojo

* @createDate 2011-9-26 下午12:21:22

* @param buff 缓冲数组

* @param start 起始位置

* @param length 长度

* @return

*/

public synchronized int write( byte [] buff, int start, int length) {

int i = -1;

try {

itemFile.write(buff, start, length);

i = length;

} catch (IOException e) {

e.printStackTrace();

}

return i;

}

public void close() throws IOException {

if (itemFile != null) {

itemFile.close();

}

}

}

这个类主要是完成向本地的指定文件指针出开始写入文件，并返回当前写入文件的长度（文件指针）。这个类将被线程调用，文件被分成对应的块后，将被线程调用。每个线程都将会调用这个类完成文件的随机写入。

三、单个线程下载文件

package com.hoo.download;

import java.io.IOException;

import java.io.InputStream;

import java.net.HttpURLConnection;

import java.net.MalformedURLException;

import java.net.URL;

import java.net.URLConnection;

import com.hoo.util.LogUtils;

/**

* function: 单线程下载文件

* @author hoojo

* @createDate 2011-9-22 下午02:55:10

* @file DownloadFile.java

* @package com.hoo.download

* @project MultiThreadDownLoad

* @blog http://blog.csdn.net/IBM_hoojo

* @email hoojo_@126.com

* @version 1.0

*/

public class DownloadFile extends Thread {

//下载文件url

private String url;

//下载文件起始位置

private long startPos;

//下载文件结束位置

private long endPos;

//线程id

private int threadId;

//下载是否完成

private boolean isDownloadOver = false;

private SaveItemFile itemFile;

private static final int BUFF_LENGTH = 1024 * 8;

/**

* @param url 下载文件url

* @param name 文件名称

* @param startPos 下载文件起点

* @param endPos 下载文件结束点

* @param threadId 线程id

* @throws IOException

*/

public DownloadFile(String url, String name, long startPos, long endPos, int threadId) throws IOException {

super ();

this .url = url;

this .startPos = startPos;

this .endPos = endPos;

this .threadId = threadId;

//分块下载写入文件内容

this .itemFile = new SaveItemFile(name, startPos);

}

@Override

public void run() {

while (endPos > startPos && !isDownloadOver) {

try {

URL url = new URL( this .url);

HttpURLConnection conn = (HttpURLConnection) url.openConnection();

// 设置连接超时时间为10000ms

conn.setConnectTimeout(10000);

// 设置读取数据超时时间为10000ms

conn.setReadTimeout(10000);

setHeader(conn);

String property = "bytes=" + startPos + "-" ;

conn.setRequestProperty( "RANGE" , property);

//输出log信息

LogUtils.log( "开始 " + threadId + "：" + property + endPos);

//printHeader(conn);

//获取文件输入流，读取文件内容

InputStream is = conn.getInputStream();

byte [] buff = new byte [BUFF_LENGTH];

int length = -1;

LogUtils.log( "#start#Thread: " + threadId + ", startPos: " + startPos + ", endPos: " + endPos);

while ((length = is.read(buff)) > 0 && startPos < endPos && !isDownloadOver) {

//写入文件内容，返回最后写入的长度

startPos += itemFile.write(buff, 0, length);

}

LogUtils.log( "#over#Thread: " + threadId + ", startPos: " + startPos + ", endPos: " + endPos);

LogUtils.log( "Thread " + threadId + " is execute over!" );

this .isDownloadOver = true;

} catch (MalformedURLException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

} finally {

try {

if (itemFile != null) {

itemFile.close();

}

} catch (IOException e) {

e.printStackTrace();

}

}

}

if (endPos < startPos && !isDownloadOver) {

LogUtils.log( "Thread " + threadId + " startPos > endPos, not need download file !" );

this .isDownloadOver = true;

}

if (endPos == startPos && !isDownloadOver) {

LogUtils.log( "Thread " + threadId + " startPos = endPos, not need download file !" );

this .isDownloadOver = true;

}

}

/**

* function: 打印下载文件头部信息

* @author hoojo

* @createDate 2011-9-22 下午05:44:35

* @param conn HttpURLConnection

*/

public static void printHeader(URLConnection conn) {

int i = 1;

while (true) {

String header = conn.getHeaderFieldKey(i);

i++;

if (header != null) {

LogUtils.info(header + ":" + conn.getHeaderField(i));

} else {

break ;

}

}

}

/**

* function: 设置URLConnection的头部信息，伪装请求信息

* @author hoojo

* @createDate 2011-9-28 下午05:29:43

* @param con

*/

public static void setHeader(URLConnection conn) {

conn.setRequestProperty( "User-Agent" , "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008092510 Ubuntu/8.04 (hardy) Firefox/3.0.3" );

conn.setRequestProperty( "Accept-Language" , "en-us,en;q=0.7,zh-cn;q=0.3" );

conn.setRequestProperty( "Accept-Encoding" , "utf-8" );

conn.setRequestProperty( "Accept-Charset" , "ISO-8859-1,utf-8;q=0.7,*;q=0.7" );

conn.setRequestProperty( "Keep-Alive" , "300" );

conn.setRequestProperty( "connnection" , "keep-alive" );

conn.setRequestProperty( "If-Modified-Since" , "Fri, 02 Jan 2009 17:00:05 GMT" );

conn.setRequestProperty( "If-None-Match" , "\"1261d8-4290-df64d224\"" );

conn.setRequestProperty( "Cache-conntrol" , "max-age=0" );

conn.setRequestProperty( "Referer" , "http://www.baidu.com" );

}

public boolean isDownloadOver() {

return isDownloadOver;

}

public long getStartPos() {

return startPos;

}

public long getEndPos() {

return endPos;

}

}

这个类主要是完成单个线程的文件下载，将通过URLConnection读取指定url的资源信息。然后用InputStream读取文件内容，然后调用调用SaveItemFile类，向本地写入当前要读取的块的内容。

四、分段多线程写入文件内容

package com.hoo.download;

import java.io.DataInputStream;

import java.io.DataOutputStream;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.net.HttpURLConnection;

import java.net.MalformedURLException;

import java.net.URL;

import com.hoo.entity.DownloadInfo;

import com.hoo.util.LogUtils;

/**

* function: 分批量下载文件

* @author hoojo

* @createDate 2011-9-22 下午05:51:54

* @file BatchDownloadFile.java

* @package com.hoo.download

* @project MultiThreadDownLoad

* @blog http://blog.csdn.net/IBM_hoojo

* @email hoojo_@126.com

* @version 1.0

*/

public class BatchDownloadFile implements Runnable {

//下载文件信息

private DownloadInfo downloadInfo;

//一组开始下载位置

private long [] startPos;

//一组结束下载位置

private long [] endPos;

//休眠时间

private static final int SLEEP_SECONDS = 500;

//子线程下载

private DownloadFile[] fileItem;

//文件长度

private int length;

//是否第一个文件

private boolean first = true;

//是否停止下载

private boolean stop = false;

//临时文件信息

private File tempFile;

public BatchDownloadFile(DownloadInfo downloadInfo) {

this .downloadInfo = downloadInfo;

String tempPath = this .downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName() + ".position" ;

tempFile = new File(tempPath);

//如果存在读入点位置的文件

if (tempFile.exists()) {

first = false;

//就直接读取内容

try {

readPosInfo();

} catch (IOException e) {

e.printStackTrace();

}

} else {

//数组的长度就要分成多少段的数量

startPos = new long [downloadInfo.getSplitter()];

endPos = new long [downloadInfo.getSplitter()];

}

}

@Override

public void run() {

//首次下载，获取下载文件长度

if (first) {

length = this .getFileSize(); //获取文件长度

if (length == -1) {

LogUtils.log( "file length is know!" );

stop = true;

} else if (length == -2) {

LogUtils.log( "read file length is error!" );

stop = true;

} else if (length > 0) {

/**

* eg

* start: 1, 3, 5, 7, 9

* end: 3, 5, 7, 9, length

*/

for ( int i = 0, len = startPos.length; i < len; i++) {

int size = i * (length / len);

startPos[i] = size;

//设置最后一个结束点的位置

if (i == len - 1) {

endPos[i] = length;

} else {

size = (i + 1) * (length / len);

endPos[i] = size;

}

LogUtils.log( "start-end Position[" + i + "]: " + startPos[i] + "-" + endPos[i]);

}

} else {

LogUtils.log( "get file length is error, download is stop!" );

stop = true;

}

}

//子线程开始下载

if (!stop) {

//创建单线程下载对象数组

fileItem = new DownloadFile[startPos.length]; //startPos.length = downloadInfo.getSplitter()

for ( int i = 0; i < startPos.length; i++) {

try {

//创建指定个数单线程下载对象，每个线程独立完成指定块内容的下载

fileItem[i] = new DownloadFile(

downloadInfo.getUrl(),

this .downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName(),

startPos[i], endPos[i], i

);

fileItem[i].start(); //启动线程，开始下载

LogUtils.log( "Thread: " + i + ", startPos: " + startPos[i] + ", endPos: " + endPos[i]);

} catch (IOException e) {

e.printStackTrace();

}

}

//循环写入下载文件长度信息

while (!stop) {

try {

writePosInfo();

LogUtils.log( "downloading……" );

Thread.sleep(SLEEP_SECONDS);

stop = true;

} catch (IOException e) {

e.printStackTrace();

} catch (InterruptedException e) {

e.printStackTrace();

}

for ( int i = 0; i < startPos.length; i++) {

if (!fileItem[i].isDownloadOver()) {

stop = false;

break ;

}

}

}

LogUtils.info( "Download task is finished!" );

}

}

/**

* 将写入点数据保存在临时文件中

* @author hoojo

* @createDate 2011-9-23 下午05:25:37

* @throws IOException

*/

private void writePosInfo() throws IOException {

DataOutputStream dos = new DataOutputStream( new FileOutputStream(tempFile));

dos.writeInt(startPos.length);

for ( int i = 0; i < startPos.length; i++) {

dos.writeLong(fileItem[i].getStartPos());

dos.writeLong(fileItem[i].getEndPos());

//LogUtils.info("[" + fileItem[i].getStartPos() + "#" + fileItem[i].getEndPos() + "]");

}

dos.close();

}

/**

* function:读取写入点的位置信息

* @author hoojo

* @createDate 2011-9-23 下午05:30:29

* @throws IOException

*/

private void readPosInfo() throws IOException {

DataInputStream dis = new DataInputStream( new FileInputStream(tempFile));

int startPosLength = dis.readInt();

startPos = new long [startPosLength];

endPos = new long [startPosLength];

for ( int i = 0; i < startPosLength; i++) {

startPos[i] = dis.readLong();

endPos[i] = dis.readLong();

}

dis.close();

}

/**

* function: 获取下载文件的长度

* @author hoojo

* @createDate 2011-9-26 下午12:15:08

* @return

*/

private int getFileSize() {

int fileLength = -1;

try {

URL url = new URL( this .downloadInfo.getUrl());

HttpURLConnection conn = (HttpURLConnection) url.openConnection();

DownloadFile.setHeader(conn);

int stateCode = conn.getResponseCode();

//判断http status是否为HTTP/1.1 206 Partial Content或者200 OK

if (stateCode != HttpURLConnection.HTTP_OK && stateCode != HttpURLConnection.HTTP_PARTIAL) {

LogUtils.log( "Error Code: " + stateCode);

return -2;

} else if (stateCode >= 400) {

LogUtils.log( "Error Code: " + stateCode);

return -2;

} else {

//获取长度

fileLength = conn.getContentLength();

LogUtils.log( "FileLength: " + fileLength);

}

//读取文件长度

/*for (int i = 1; ; i++) {

String header = conn.getHeaderFieldKey(i);

if (header != null) {

if ("Content-Length".equals(header)) {

fileLength = Integer.parseInt(conn.getHeaderField(i));

break;

}

} else {

break;

}

}

*/

DownloadFile.printHeader(conn);

} catch (MalformedURLException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

return fileLength;

}

}

这个类主要是完成读取指定url资源的内容，获取该资源的长度。然后将该资源分成指定的块数，将每块的起始下载位置、结束下载位置，分别保存在一个数组中。每块都单独开辟一个独立线程开始下载。在开始下载之前，需要创建一个临时文件，写入当前下载线程的开始下载指针位置和结束下载指针位置。

五、工具类、测试类

日志工具类

package com.hoo.util;

/**

* function: 日志工具类

* @author hoojo

* @createDate 2011-9-21 下午05:21:27

* @file LogUtils.java

* @package com.hoo.util

* @project MultiThreadDownLoad

* @blog http://blog.csdn.net/IBM_hoojo

* @email hoojo_@126.com

* @version 1.0

*/

public abstract class LogUtils {

public static void log(Object message) {

System.err.println(message);

}

public static void log(String message) {

System.err.println(message);

}

public static void log( int message) {

System.err.println(message);

}

public static void info(Object message) {

System.out.println(message);

}

public static void info(String message) {

System.out.println(message);

}

public static void info( int message) {

System.out.println(message);

}

}

下载工具类

package com.hoo.util;

import com.hoo.download.BatchDownloadFile;

import com.hoo.entity.DownloadInfo;

/**

* function: 分块多线程下载工具类

* @author hoojo

* @createDate 2011-9-28 下午05:22:18

* @file DownloadUtils.java

* @package com.hoo.util

* @project MultiThreadDownLoad

* @blog http://blog.csdn.net/IBM_hoojo

* @email hoojo_@126.com

* @version 1.0

*/

public abstract class DownloadUtils {

public static void download(String url) {

DownloadInfo bean = new DownloadInfo(url);

LogUtils.info(bean);

BatchDownloadFile down = new BatchDownloadFile(bean);

new Thread(down).start();

}

public static void download(String url, int threadNum) {

DownloadInfo bean = new DownloadInfo(url, threadNum);

LogUtils.info(bean);

BatchDownloadFile down = new BatchDownloadFile(bean);

new Thread(down).start();

}

public static void download(String url, String fileName, String filePath, int threadNum) {

DownloadInfo bean = new DownloadInfo(url, fileName, filePath, threadNum);

LogUtils.info(bean);

BatchDownloadFile down = new BatchDownloadFile(bean);

new Thread(down).start();

}

}

下载测试类

package com.hoo.test;

import com.hoo.util.DownloadUtils;

/**

* function: 下载测试

* @author hoojo

* @createDate 2011-9-23 下午05:49:46

* @file TestDownloadMain.java

* @package com.hoo.download

* @project MultiThreadDownLoad

* @blog http://blog.csdn.net/IBM_hoojo

* @email hoojo_@126.com

* @version 1.0

*/

public class TestDownloadMain {

public static void main(String[] args) {

/*DownloadInfo bean = new DownloadInfo("http://i7.meishichina.com/Health/UploadFiles/201109/2011092116224363.jpg");

System.out.println(bean);

BatchDownloadFile down = new BatchDownloadFile(bean);

new Thread(down).start();*/

//DownloadUtils.download("http://i7.meishichina.com/Health/UploadFiles/201109/2011092116224363.jpg");

DownloadUtils.download( "http://mp3.baidu.com/j?j=2&url=http%3A%2F%2Fzhangmenshiting2.baidu.com%2Fdata%2Fmusic%2F1669425%2F%25E9%2599%25B7%25E5%2585%25A5%25E7%2588%25B1%25E9%2587%258C%25E9%259D%25A2.mp3%3Fxcode%3D2ff36fb70737c816553396c56deab3f1" , "aa.mp3" , "c:/temp" , 5);

}

}

多线程下载主要在第三部和第四部，其他的地方还是很好理解。源码中提供相应的注释了，便于理解。

Java 多线程断点下载文件

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