Java 多线程断点下载文件

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

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();
        }
    }
}