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  • Java 多线程断点下载文件_详解

    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

    [java] view plain copy print ?
    1. package com.hoo.entity; 
    2.  
    3. /**
    4. * <b>function:</b> 下载文件信息类
    5. * @author hoojo
    6. * @createDate 2011-9-21 下午05:14:58
    7. * @file DownloadInfo.java
    8. * @package com.hoo.entity
    9. * @project MultiThreadDownLoad
    10. * @blog http://blog.csdn.net/IBM_hoojo
    11. * @email hoojo_@126.com
    12. * @version 1.0
    13. */ 
    14. publicclass DownloadInfo { 
    15.     //下载文件url 
    16.     private String url; 
    17.     //下载文件名称 
    18.     private String fileName; 
    19.     //下载文件路径 
    20.     private String filePath; 
    21.     //分成多少段下载， 每一段用一个线程完成下载 
    22.     privateint splitter; 
    23.      
    24.     //下载文件默认保存路径 
    25.     privatefinalstatic String FILE_PATH = "C:/temp"; 
    26.     //默认分块数、线程数 
    27.     privatefinalstaticint SPLITTER_NUM = 5; 
    28.      
    29.     public DownloadInfo() { 
    30.         super(); 
    31.     } 
    32.      
    33.     /**
    34.      * @param url 下载地址
    35.      */ 
    36.     public DownloadInfo(String url) { 
    37.         this(url, null, null, SPLITTER_NUM); 
    38.     } 
    39.      
    40.     /**
    41.      * @param url 下载地址url
    42.      * @param splitter 分成多少段或是多少个线程下载
    43.      */ 
    44.     public DownloadInfo(String url, int splitter) { 
    45.         this(url, null, null, splitter); 
    46.     } 
    47.      
    48.     /***
    49.      * @param url 下载地址
    50.      * @param fileName 文件名称
    51.      * @param filePath 文件保存路径
    52.      * @param splitter 分成多少段或是多少个线程下载
    53.      */ 
    54.     public DownloadInfo(String url, String fileName, String filePath, int splitter) { 
    55.         super(); 
    56.         if (url == null || "".equals(url)) { 
    57.             throw new RuntimeException("url is not null!"); 
    58.         } 
    59.         this.url =  url; 
    60.         this.fileName = (fileName == null || "".equals(fileName)) ? getFileName(url) : fileName; 
    61.         this.filePath = (filePath == null || "".equals(filePath)) ? FILE_PATH : filePath; 
    62.         this.splitter = (splitter < 1) ? SPLITTER_NUM : splitter; 
    63.     } 
    64.      
    65.     /**
    66.      * <b>function:</b> 通过url获得文件名称
    67.      * @author hoojo
    68.      * @createDate 2011-9-30 下午05:00:00
    69.      * @param url
    70.      * @return
    71.      */ 
    72.     private String getFileName(String url) { 
    73.         return url.substring(url.lastIndexOf("/") + 1, url.length()); 
    74.     } 
    75.      
    76.     public String getUrl() { 
    77.         return url; 
    78.     } 
    79.  
    80.     publicvoid setUrl(String url) { 
    81.         if (url == null || "".equals(url)) { 
    82.             thrownew RuntimeException("url is not null!"); 
    83.         } 
    84.         this.url = url; 
    85.     } 
    86.  
    87.     public String getFileName() { 
    88.         return fileName; 
    89.     } 
    90.  
    91.     publicvoid setFileName(String fileName) { 
    92.         this.fileName = (fileName == null || "".equals(fileName)) ? getFileName(url) : fileName; 
    93.     } 
    94.  
    95.     public String getFilePath() { 
    96.         return filePath; 
    97.     } 
    98.  
    99.     publicvoid setFilePath(String filePath) { 
    100.         this.filePath = (filePath == null || "".equals(filePath)) ? FILE_PATH : filePath; 
    101.     } 
    102.  
    103.     publicint getSplitter() { 
    104.         return splitter; 
    105.     } 
    106.  
    107.     publicvoid setSplitter(int splitter) { 
    108.         this.splitter = (splitter < 1) ? SPLITTER_NUM : splitter; 
    109.     } 
    110.      
    111.     @Override 
    112.     public String toString() { 
    113.         returnthis.url + "#" + this.fileName + "#" + this.filePath + "#" + this.splitter; 
    114.     } 
    115. }  
    package com.hoo.entity;

/**
 * <b>function:</b> 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;
	}
	
	/**
	 * <b>function:</b> 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

    [java] view plain copy print ?
    1. package com.hoo.download; 
    2.  
    3. import java.io.IOException; 
    4. import java.io.RandomAccessFile; 
    5.  
    6. /**
    7. * <b>function:</b> 写入文件、保存文件
    8. * @author hoojo
    9. * @createDate 2011-9-21 下午05:44:02
    10. * @file SaveItemFile.java
    11. * @package com.hoo.download
    12. * @project MultiThreadDownLoad
    13. * @blog http://blog.csdn.net/IBM_hoojo
    14. * @email hoojo_@126.com
    15. * @version 1.0
    16. */ 
    17. publicclass SaveItemFile { 
    18.     //存储文件 
    19.     private RandomAccessFile itemFile; 
    20.      
    21.     public SaveItemFile() throws IOException { 
    22.         this("", 0); 
    23.     } 
    24.      
    25.     /**
    26.      * @param name 文件路径、名称
    27.      * @param pos 写入点位置 position
    28.      * @throws IOException
    29.      */ 
    30.     public SaveItemFile(String name, long pos) throws IOException { 
    31.         itemFile = new RandomAccessFile(name, "rw"); 
    32.         //在指定的pos位置开始写入数据 
    33.         itemFile.seek(pos); 
    34.     } 
    35.      
    36.     /**
    37.      * <b>function:</b> 同步方法写入文件
    38.      * @author hoojo
    39.      * @createDate 2011-9-26 下午12:21:22
    40.      * @param buff 缓冲数组
    41.      * @param start 起始位置
    42.      * @param length 长度
    43.      * @return
    44.      */ 
    45.     publicsynchronizedint write(byte[] buff, int start, int length) { 
    46.         int i = -1; 
    47.         try { 
    48.             itemFile.write(buff, start, length); 
    49.             i = length; 
    50.         } catch (IOException e) { 
    51.             e.printStackTrace(); 
    52.         } 
    53.         return i; 
    54.     } 
    55.      
    56.     publicvoid close() throws IOException { 
    57.         if (itemFile != null) { 
    58.             itemFile.close(); 
    59.         } 
    60.     } 
    61. }  
    package com.hoo.download;

import java.io.IOException;
import java.io.RandomAccessFile;

/**
 * <b>function:</b> 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);
	}
	
	/**
	 * <b>function:</b> 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

    [java] view plain copy print ?
    1. package com.hoo.download; 
    2.  
    3. import java.io.IOException; 
    4. import java.io.InputStream; 
    5. import java.net.HttpURLConnection; 
    6. import java.net.MalformedURLException; 
    7. import java.net.URL; 
    8. import java.net.URLConnection; 
    9. import com.hoo.util.LogUtils; 
    10.  
    11. /**
    12. * <b>function:</b> 单线程下载文件
    13. * @author hoojo
    14. * @createDate 2011-9-22 下午02:55:10
    15. * @file DownloadFile.java
    16. * @package com.hoo.download
    17. * @project MultiThreadDownLoad
    18. * @blog http://blog.csdn.net/IBM_hoojo
    19. * @email hoojo_@126.com
    20. * @version 1.0
    21. */ 
    22. publicclass DownloadFile extends Thread { 
    23.      
    24.     //下载文件url 
    25.     private String url; 
    26.     //下载文件起始位置   
    27.     privatelong startPos; 
    28.     //下载文件结束位置 
    29.     privatelong endPos; 
    30.     //线程id 
    31.     privateint threadId; 
    32.      
    33.     //下载是否完成 
    34.     privateboolean isDownloadOver = false; 
    35.  
    36.     private SaveItemFile itemFile; 
    37.      
    38.     privatestaticfinalint BUFF_LENGTH = 1024 * 8; 
    39.      
    40.     /**
    41.      * @param url 下载文件url
    42.      * @param name 文件名称
    43.      * @param startPos 下载文件起点
    44.      * @param endPos 下载文件结束点
    45.      * @param threadId 线程id
    46.      * @throws IOException
    47.      */ 
    48.     public DownloadFile(String url, String name, long startPos, long endPos, int threadId) throws IOException { 
    49.         super(); 
    50.         this.url = url; 
    51.         this.startPos = startPos; 
    52.         this.endPos = endPos; 
    53.         this.threadId = threadId; 
    54.         //分块下载写入文件内容 
    55.         this.itemFile = new SaveItemFile(name, startPos); 
    56.     } 
    57.  
    58.      
    59.     @Override 
    60.     publicvoid run() { 
    61.         while (endPos > startPos && !isDownloadOver) { 
    62.             try { 
    63.                 URL url = new URL(this.url); 
    64.                 HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
    65.                  
    66.                 // 设置连接超时时间为10000ms 
    67.                 conn.setConnectTimeout(10000); 
    68.                 // 设置读取数据超时时间为10000ms 
    69.                 conn.setReadTimeout(10000); 
    70.                  
    71.                 setHeader(conn); 
    72.                  
    73.                 String property = "bytes=" + startPos + "-"; 
    74.                 conn.setRequestProperty("RANGE", property); 
    75.                  
    76.                 //输出log信息 
    77.                 LogUtils.log("开始 " + threadId + "：" + property + endPos); 
    78.                 //printHeader(conn); 
    79.                  
    80.                 //获取文件输入流，读取文件内容 
    81.                 InputStream is = conn.getInputStream(); 
    82.                  
    83.                 byte[] buff = newbyte[BUFF_LENGTH]; 
    84.                 int length = -1; 
    85.                 LogUtils.log("#start#Thread: " + threadId + ", startPos: " + startPos + ", endPos: " + endPos); 
    86.                 while ((length = is.read(buff)) > 0 && startPos < endPos && !isDownloadOver) { 
    87.                     //写入文件内容，返回最后写入的长度 
    88.                     startPos += itemFile.write(buff, 0, length); 
    89.                 } 
    90.                 LogUtils.log("#over#Thread: " + threadId + ", startPos: " + startPos + ", endPos: " + endPos); 
    91.                 LogUtils.log("Thread " + threadId + " is execute over!"); 
    92.                 this.isDownloadOver = true; 
    93.             } catch (MalformedURLException e) { 
    94.                 e.printStackTrace(); 
    95.             } catch (IOException e) { 
    96.                 e.printStackTrace(); 
    97.             } finally { 
    98.                 try { 
    99.                     if (itemFile != null) { 
    100.                         itemFile.close(); 
    101.                     } 
    102.                 } catch (IOException e) { 
    103.                     e.printStackTrace(); 
    104.                 } 
    105.             } 
    106.         } 
    107.         if (endPos < startPos && !isDownloadOver) { 
    108.             LogUtils.log("Thread " + threadId  + " startPos > endPos, not need download file !"); 
    109.             this.isDownloadOver = true; 
    110.         } 
    111.         if (endPos == startPos && !isDownloadOver) { 
    112.             LogUtils.log("Thread " + threadId  + " startPos = endPos, not need download file !"); 
    113.             this.isDownloadOver = true; 
    114.         } 
    115.     } 
    116.      
    117.     /**
    118.      * <b>function:</b> 打印下载文件头部信息
    119.      * @author hoojo
    120.      * @createDate 2011-9-22 下午05:44:35
    121.      * @param conn HttpURLConnection
    122.      */ 
    123.     publicstaticvoid printHeader(URLConnection conn) { 
    124.         int i = 1; 
    125.         while (true) { 
    126.             String header = conn.getHeaderFieldKey(i); 
    127.             i++; 
    128.             if (header != null) { 
    129.                 LogUtils.info(header + ":" + conn.getHeaderField(i)); 
    130.             } else { 
    131.                 break; 
    132.             } 
    133.         } 
    134.     } 
    135.      
    136.     /**
    137.      * <b>function:</b> 设置URLConnection的头部信息，伪装请求信息
    138.      * @author hoojo
    139.      * @createDate 2011-9-28 下午05:29:43
    140.      * @param con
    141.      */ 
    142.     publicstaticvoid setHeader(URLConnection conn) { 
    143.         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"); 
    144.         conn.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3"); 
    145.         conn.setRequestProperty("Accept-Encoding", "utf-8"); 
    146.         conn.setRequestProperty("Accept-Charset", "ISO-8859-1,utf-8;q=0.7,*;q=0.7"); 
    147.         conn.setRequestProperty("Keep-Alive", "300"); 
    148.         conn.setRequestProperty("connnection", "keep-alive"); 
    149.         conn.setRequestProperty("If-Modified-Since", "Fri, 02 Jan 2009 17:00:05 GMT"); 
    150.         conn.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\""); 
    151.         conn.setRequestProperty("Cache-conntrol", "max-age=0"); 
    152.         conn.setRequestProperty("Referer", "http://www.baidu.com"); 
    153.     } 
    154.      
    155.     publicboolean isDownloadOver() { 
    156.         return isDownloadOver; 
    157.     } 
    158.      
    159.     publiclong getStartPos() { 
    160.         return startPos; 
    161.     } 
    162.  
    163.     publiclong getEndPos() { 
    164.         return endPos; 
    165.     } 
    166. }  
    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;

/**
 * <b>function:</b> 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;
		}
	}
	
	/**
	 * <b>function:</b> 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;
			}
		}
	}
	
	/**
	 * <b>function:</b> 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

    [java] view plain copy print ?
    1. package com.hoo.download; 
    2.  
    3. import java.io.DataInputStream; 
    4. import java.io.DataOutputStream; 
    5. import java.io.File; 
    6. import java.io.FileInputStream; 
    7. import java.io.FileOutputStream; 
    8. import java.io.IOException; 
    9. import java.net.HttpURLConnection; 
    10. import java.net.MalformedURLException; 
    11. import java.net.URL; 
    12. import com.hoo.entity.DownloadInfo; 
    13. import com.hoo.util.LogUtils; 
    14.  
    15. /**
    16. * <b>function:</b> 分批量下载文件
    17. * @author hoojo
    18. * @createDate 2011-9-22 下午05:51:54
    19. * @file BatchDownloadFile.java
    20. * @package com.hoo.download
    21. * @project MultiThreadDownLoad
    22. * @blog http://blog.csdn.net/IBM_hoojo
    23. * @email hoojo_@126.com
    24. * @version 1.0
    25. */ 
    26. publicclass BatchDownloadFile implements Runnable { 
    27.     //下载文件信息  
    28.     private DownloadInfo downloadInfo; 
    29.     //一组开始下载位置 
    30.     privatelong[] startPos; 
    31.     //一组结束下载位置 
    32.     privatelong[] endPos; 
    33.     //休眠时间 
    34.     privatestaticfinalint SLEEP_SECONDS = 500; 
    35.     //子线程下载 
    36.     private DownloadFile[] fileItem; 
    37.     //文件长度 
    38.     privateint length; 
    39.     //是否第一个文件 
    40.     privateboolean first = true; 
    41.     //是否停止下载 
    42.     privateboolean stop = false; 
    43.     //临时文件信息 
    44.     private File tempFile; 
    45.      
    46.     public BatchDownloadFile(DownloadInfo downloadInfo) { 
    47.         this.downloadInfo = downloadInfo; 
    48.         String tempPath = this.downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName() + ".position"; 
    49.         tempFile = new File(tempPath); 
    50.         //如果存在读入点位置的文件 
    51.         if (tempFile.exists()) { 
    52.             first = false; 
    53.             //就直接读取内容 
    54.             try { 
    55.                 readPosInfo(); 
    56.             } catch (IOException e) { 
    57.                 e.printStackTrace(); 
    58.             } 
    59.         } else { 
    60.             //数组的长度就要分成多少段的数量 
    61.             startPos = newlong[downloadInfo.getSplitter()]; 
    62.             endPos = newlong[downloadInfo.getSplitter()]; 
    63.         } 
    64.     } 
    65.      
    66.     @Override 
    67.     publicvoid run() { 
    68.         //首次下载，获取下载文件长度 
    69.         if (first) { 
    70.             length = this.getFileSize();//获取文件长度 
    71.             if (length == -1) { 
    72.                 LogUtils.log("file length is know!"); 
    73.                 stop = true; 
    74.             } elseif (length == -2) { 
    75.                 LogUtils.log("read file length is error!"); 
    76.                 stop = true; 
    77.             } else if (length > 0) { 
    78.                 /**
    79.                  * eg
    80.                  * start: 1, 3, 5, 7, 9
    81.                  * end: 3, 5, 7, 9, length
    82.                  */ 
    83.                 for (int i = 0, len = startPos.length; i < len; i++) { 
    84.                     int size = i * (length / len); 
    85.                     startPos[i] = size; 
    86.                      
    87.                     //设置最后一个结束点的位置 
    88.                     if (i == len - 1) { 
    89.                         endPos[i] = length; 
    90.                     } else { 
    91.                         size = (i + 1) * (length / len); 
    92.                         endPos[i] = size; 
    93.                     } 
    94.                     LogUtils.log("start-end Position[" + i + "]: " + startPos[i] + "-" + endPos[i]); 
    95.                 } 
    96.             } else { 
    97.                 LogUtils.log("get file length is error, download is stop!"); 
    98.                 stop = true; 
    99.             } 
    100.         } 
    101.          
    102.         //子线程开始下载 
    103.         if (!stop) { 
    104.             //创建单线程下载对象数组 
    105.             fileItem = new DownloadFile[startPos.length];//startPos.length = downloadInfo.getSplitter() 
    106.             for (int i = 0; i < startPos.length; i++) { 
    107.                 try { 
    108.                     //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 
    109.                     fileItem[i] = new DownloadFile( 
    110.                         downloadInfo.getUrl(),  
    111.                         this.downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName(),  
    112.                         startPos[i], endPos[i], i 
    113.                     ); 
    114.                     fileItem[i].start();//启动线程，开始下载 
    115.                     LogUtils.log("Thread: " + i + ", startPos: " + startPos[i] + ", endPos: " + endPos[i]); 
    116.                 } catch (IOException e) { 
    117.                     e.printStackTrace(); 
    118.                 } 
    119.             } 
    120.              
    121.             //循环写入下载文件长度信息 
    122.             while (!stop) { 
    123.                 try { 
    124.                     writePosInfo(); 
    125.                     LogUtils.log("downloading……"); 
    126.                     Thread.sleep(SLEEP_SECONDS); 
    127.                     stop = true; 
    128.                 } catch (IOException e) { 
    129.                     e.printStackTrace(); 
    130.                 } catch (InterruptedException e) { 
    131.                     e.printStackTrace(); 
    132.                 } 
    133.                 for (int i = 0; i < startPos.length; i++) { 
    134.                     if (!fileItem[i].isDownloadOver()) { 
    135.                         stop = false; 
    136.                         break; 
    137.                     } 
    138.                 } 
    139.             } 
    140.             LogUtils.info("Download task is finished!"); 
    141.         } 
    142.     } 
    143.      
    144.     /**
    145.      * 将写入点数据保存在临时文件中
    146.      * @author hoojo
    147.      * @createDate 2011-9-23 下午05:25:37
    148.      * @throws IOException
    149.      */ 
    150.     privatevoid writePosInfo() throws IOException { 
    151.         DataOutputStream dos = new DataOutputStream(new FileOutputStream(tempFile)); 
    152.         dos.writeInt(startPos.length); 
    153.         for (int i = 0; i < startPos.length; i++) { 
    154.             dos.writeLong(fileItem[i].getStartPos()); 
    155.             dos.writeLong(fileItem[i].getEndPos()); 
    156.             //LogUtils.info("[" + fileItem[i].getStartPos() + "#" + fileItem[i].getEndPos() + "]"); 
    157.         } 
    158.         dos.close(); 
    159.     } 
    160.      
    161.     /**
    162.      * <b>function:</b>读取写入点的位置信息
    163.      * @author hoojo
    164.      * @createDate 2011-9-23 下午05:30:29
    165.      * @throws IOException
    166.      */ 
    167.     privatevoid readPosInfo() throws IOException { 
    168.         DataInputStream dis = new DataInputStream(new FileInputStream(tempFile)); 
    169.         int startPosLength = dis.readInt(); 
    170.         startPos = newlong[startPosLength]; 
    171.         endPos = new long[startPosLength]; 
    172.         for (int i = 0; i < startPosLength; i++) { 
    173.             startPos[i] = dis.readLong(); 
    174.             endPos[i] = dis.readLong(); 
    175.         } 
    176.         dis.close(); 
    177.     } 
    178.      
    179.     /**
    180.      * <b>function:</b> 获取下载文件的长度
    181.      * @author hoojo
    182.      * @createDate 2011-9-26 下午12:15:08
    183.      * @return
    184.      */ 
    185.     privateint getFileSize() { 
    186.         int fileLength = -1; 
    187.         try { 
    188.             URL url = new URL(this.downloadInfo.getUrl()); 
    189.             HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
    190.              
    191.             DownloadFile.setHeader(conn); 
    192.  
    193.             int stateCode = conn.getResponseCode(); 
    194.             //判断http status是否为HTTP/1.1 206 Partial Content或者200 OK 
    195.             if (stateCode != HttpURLConnection.HTTP_OK && stateCode != HttpURLConnection.HTTP_PARTIAL) { 
    196.                 LogUtils.log("Error Code: " + stateCode); 
    197.                 return -2; 
    198.             } elseif (stateCode >= 400) { 
    199.                 LogUtils.log("Error Code: " + stateCode); 
    200.                 return -2; 
    201.             } else { 
    202.                 //获取长度 
    203.                 fileLength = conn.getContentLength(); 
    204.                 LogUtils.log("FileLength: " + fileLength); 
    205.             } 
    206.              
    207.             //读取文件长度 
    208.             /*for (int i = 1; ; i++) {
    209.                 String header = conn.getHeaderFieldKey(i);
    210.                 if (header != null) {
    211.                     if ("Content-Length".equals(header)) {
    212.                         fileLength = Integer.parseInt(conn.getHeaderField(i));
    213.                         break;
    214.                     }
    215.                 } else {
    216.                     break;
    217.                 }
    218.             }
    219.             */ 
    220.              
    221.             DownloadFile.printHeader(conn); 
    222.         } catch (MalformedURLException e) { 
    223.             e.printStackTrace(); 
    224.         } catch (IOException e) { 
    225.             e.printStackTrace(); 
    226.         } 
    227.         return fileLength; 
    228.     } 
    229. }  
    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;

/**
 * <b>function:</b> 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();
	}
	
	/**
	 * <b>function:</b>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();
	}
	
	/**
	 * <b>function:</b> 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

    [java] view plain copy print ?
    1. package com.hoo.util; 
    2.  
    3. /**
    4. * <b>function:</b> 日志工具类
    5. * @author hoojo
    6. * @createDate 2011-9-21 下午05:21:27
    7. * @file LogUtils.java
    8. * @package com.hoo.util
    9. * @project MultiThreadDownLoad
    10. * @blog http://blog.csdn.net/IBM_hoojo
    11. * @email hoojo_@126.com
    12. * @version 1.0
    13. */ 
    14. publicabstractclass LogUtils { 
    15.      
    16.     publicstaticvoid log(Object message) { 
    17.         System.err.println(message); 
    18.     } 
    19.      
    20.     publicstaticvoid log(String message) { 
    21.         System.err.println(message); 
    22.     } 
    23.      
    24.     publicstaticvoid log(int message) { 
    25.         System.err.println(message); 
    26.     } 
    27.      
    28.     publicstaticvoid info(Object message) { 
    29.         System.out.println(message); 
    30.     } 
    31.      
    32.     publicstaticvoid info(String message) { 
    33.         System.out.println(message); 
    34.     } 
    35.      
    36.     publicstaticvoid info(int message) { 
    37.         System.out.println(message); 
    38.     } 
    39. }  
    package com.hoo.util;

/**
 * <b>function:</b> 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

    [java] view plain copy print ?
    1. package com.hoo.util; 
    2.  
    3. import com.hoo.download.BatchDownloadFile; 
    4. import com.hoo.entity.DownloadInfo; 
    5.  
    6. /**
    7. * <b>function:</b> 分块多线程下载工具类
    8. * @author hoojo
    9. * @createDate 2011-9-28 下午05:22:18
    10. * @file DownloadUtils.java
    11. * @package com.hoo.util
    12. * @project MultiThreadDownLoad
    13. * @blog http://blog.csdn.net/IBM_hoojo
    14. * @email hoojo_@126.com
    15. * @version 1.0
    16. */ 
    17. publicabstractclass DownloadUtils { 
    18.  
    19.     publicstaticvoid download(String url) { 
    20.         DownloadInfo bean = new DownloadInfo(url); 
    21.         LogUtils.info(bean); 
    22.         BatchDownloadFile down = new BatchDownloadFile(bean); 
    23.         new Thread(down).start(); 
    24.     } 
    25.      
    26.     publicstaticvoid download(String url, int threadNum) { 
    27.         DownloadInfo bean = new DownloadInfo(url, threadNum); 
    28.         LogUtils.info(bean); 
    29.         BatchDownloadFile down = new BatchDownloadFile(bean); 
    30.         new Thread(down).start(); 
    31.     } 
    32.      
    33.     publicstaticvoid download(String url, String fileName, String filePath, int threadNum) { 
    34.         DownloadInfo bean = new DownloadInfo(url, fileName, filePath, threadNum); 
    35.         LogUtils.info(bean); 
    36.         BatchDownloadFile down = new BatchDownloadFile(bean); 
    37.         new Thread(down).start(); 
    38.     } 
    39. }  
    package com.hoo.util;

import com.hoo.download.BatchDownloadFile;
import com.hoo.entity.DownloadInfo;

/**
 * <b>function:</b> 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

    [java] view plain copy print ?
    1. package com.hoo.test; 
    2.  
    3. import com.hoo.util.DownloadUtils; 
    4.  
    5. /**
    6. * <b>function:</b> 下载测试
    7. * @author hoojo
    8. * @createDate 2011-9-23 下午05:49:46
    9. * @file TestDownloadMain.java
    10. * @package com.hoo.download
    11. * @project MultiThreadDownLoad
    12. * @blog http://blog.csdn.net/IBM_hoojo
    13. * @email hoojo_@126.com
    14. * @version 1.0
    15. */ 
    16. publicclass TestDownloadMain { 
    17.  
    18.     publicstaticvoid main(String[] args) { 
    19.         /*DownloadInfo bean = new DownloadInfo("http://i7.meishichina.com/Health/UploadFiles/201109/2011092116224363.jpg");
    20.         System.out.println(bean);
    21.         BatchDownloadFile down = new BatchDownloadFile(bean);
    22.         new Thread(down).start();*/ 
    23.          
    24.         //DownloadUtils.download("http://i7.meishichina.com/Health/UploadFiles/201109/2011092116224363.jpg"); 
    25.         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); 
    26.     } 
    27. }  
    package com.hoo.test;

import com.hoo.util.DownloadUtils;

/**
 * <b>function:</b> 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。

    本文转载于：http://blog.csdn.net/ibm_hoojo/article/details/6838222
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  • 原文地址：https://www.cnblogs.com/xinyuyuanm/p/2999219.html
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