用 Java 实现断点续传-实现 (HTTP)

断点续传内核的实现
主要用了 6 个类，包括一个测试类。
SiteFileFetch.java 负责整个文件的抓取，控制内部线程 (FileSplitterFetch 类 )。
FileSplitterFetch.java 负责部分文件的抓取。
FileAccess.java 负责文件的存储。
SiteInfoBean.java 要抓取的文件的信息，如文件保存的目录，名字，抓取文件的 URL 等。
Utility.java 工具类，放一些简单的方法。
TestMethod.java 测试类。
下面是源程序：

package cn.hiservice.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.URL;

/**
 * 
 * @author Administrator
 * 
 */
public class SiteFileFetch extends Thread {
	SiteInfoBean siteInfoBean = null; // 文件信息 Bean
	long[] nStartPos; // 开始位置
	long[] nEndPos; // 结束位置
	FileSplitterFetch[] fileSplitterFetch; // 子线程对象
	long nFileLength; // 文件长度
	boolean bFirst = true; // 是否第一次取文件
	boolean bStop = false; // 停止标志
	File tmpFile; // 文件下载的临时信息
	DataOutputStream output; // 输出到文件的输出流

	public SiteFileFetch(SiteInfoBean bean) throws IOException {
		siteInfoBean = bean;
		tmpFile = new File(bean.getSFilePath() + File.separator
				+ bean.getSFileName() + ".info");
		System.out.println(tmpFile);
		if (tmpFile.exists()) {
			bFirst = false;
			read_nPos();
		} else {
			nStartPos = new long[bean.getNSplitter()];
			nEndPos = new long[bean.getNSplitter()];
		}
	}

	public void run() {
		// 获得文件长度
		// 分割文件
		// 实例 FileSplitterFetch
		// 启动 FileSplitterFetch 线程
		// 等待子线程返回
		try {
			if (bFirst) {
				nFileLength = getFileSize();

				if (nFileLength == -1) {
					System.err.println("File Length is not known!");
				} else if (nFileLength == -2) {
					System.err.println("File is not access!");
				} else {
					for (int i = 0; i < nStartPos.length; i++) {
						nStartPos[i] = (long) (i * (nFileLength / nStartPos.length));
					}
					for (int i = 0; i < nEndPos.length - 1; i++) {
						nEndPos[i] = nStartPos[i + 1];
					}
					nEndPos[nEndPos.length - 1] = nFileLength;
				}
			}
			// 启动子线程
			fileSplitterFetch = new FileSplitterFetch[nStartPos.length];
			for (int i = 0; i < nStartPos.length; i++) {
				fileSplitterFetch[i] = new FileSplitterFetch(siteInfoBean
						.getSSiteURL(), siteInfoBean.getSFilePath()
						+ File.separator + siteInfoBean.getSFileName(),
						nStartPos[i], nEndPos[i], i);
				Utility.log("Thread " + i + " , nStartPos = " + nStartPos[i]
						+ ", nEndPos = " + nEndPos[i]);
				fileSplitterFetch[i].start();
			}
			/*
			 * fileSplitterFetch[nPos.length-1] = new
			 * FileSplitterFetch(siteInfoBean.getSSiteURL(),
			 * siteInfoBean.getSFilePath() + File.separator +
			 * siteInfoBean.getSFileName
			 * (),nPos[nPos.length-1],nFileLength,nPos.length-1);
			 */
			// Utility.log("Thread " +(nPos.length-1) +
			// ",nStartPos = "+nPos[nPos.length-1]+",
			// nEndPos = " + nFileLength);
			// fileSplitterFetch[nPos.length-1].start();
			// 等待子线程结束
			// int count = 0;
			// 是否结束 while 循环
			boolean breakWhile = false;
			while (!bStop) {
				write_nPos();
				Utility.sleep(500);
				breakWhile = true;
				for (int i = 0; i < nStartPos.length; i++) {
					if (!fileSplitterFetch[i].bDownOver) {
						breakWhile = false;
						break;
					}
				}
				if (breakWhile)
					break;
				// count++;
				// if(count>4)
				// siteStop();
			}
			System.err.println("文件下载结束！");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	// 获得文件长度
	public long getFileSize() {
		int nFileLength = -1;
		try {
			URL url = new URL(siteInfoBean.getSSiteURL());
			HttpURLConnection httpConnection = (HttpURLConnection) url
					.openConnection();
			httpConnection.setRequestProperty("User-Agent", "NetFox");
			int responseCode = httpConnection.getResponseCode();
			if (responseCode >= 400) {
				processErrorCode(responseCode);
				return -2; // -2 represent access is error
			}
			String sHeader;
			for (int i = 1;; i++) {
				// DataInputStream in = new
				// DataInputStream(httpConnection.getInputStream ());
				// Utility.log(in.readLine());
				sHeader = httpConnection.getHeaderFieldKey(i);
				if (sHeader != null) {
					if (sHeader.equals("Content-Length")) {
						nFileLength = Integer.parseInt(httpConnection
								.getHeaderField(sHeader));
						break;
					}
				} else
					break;
			}
		} catch (IOException e) {
			e.printStackTrace();
		} catch (Exception e) {
			e.printStackTrace();
		}
		Utility.log(nFileLength);
		return nFileLength;
	}

	// 保存下载信息（文件指针位置）
	private void write_nPos() {
		try {
			output = new DataOutputStream(new FileOutputStream(tmpFile));
			output.writeInt(nStartPos.length);
			for (int i = 0; i < nStartPos.length; i++) {
				// output.writeLong(nPos[i]);
				output.writeLong(fileSplitterFetch[i].nStartPos);
				output.writeLong(fileSplitterFetch[i].nEndPos);
			}
			output.close();
		} catch (IOException e) {
			e.printStackTrace();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	// 读取保存的下载信息（文件指针位置）
	private void read_nPos() {
		try {
			DataInputStream input = new DataInputStream(new FileInputStream(
					tmpFile));
			int nCount = input.readInt();
			nStartPos = new long[nCount];
			nEndPos = new long[nCount];
			for (int i = 0; i < nStartPos.length; i++) {
				nStartPos[i] = input.readLong();
				nEndPos[i] = input.readLong();
			}
			input.close();
		} catch (IOException e) {
			e.printStackTrace();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	private void processErrorCode(int nErrorCode) {
		System.err.println("Error Code : " + nErrorCode);
	}

	// 停止文件下载
	public void siteStop() {
		bStop = true;
		for (int i = 0; i < nStartPos.length; i++)
			fileSplitterFetch[i].splitterStop();
	}

	public static void main(String[] args) {
		new TestMethod();
	}
}

package cn.hiservice.download;

/* 
 **FileSplitterFetch.java 
 */

import java.io.*;
import java.net.*;

public class FileSplitterFetch extends Thread {
	String sURL; // File URL
	long nStartPos; // File Snippet Start Position
	long nEndPos; // File Snippet End Position
	int nThreadID; // Thread's ID
	boolean bDownOver = false; // Downing is over
	boolean bStop = false; // Stop identical
	FileAccessI fileAccessI = null; // File Access interface

	public FileSplitterFetch(String sURL, String sName, long nStart, long nEnd,
			int id) throws IOException {
		this.sURL = sURL;
		this.nStartPos = nStart;
		this.nEndPos = nEnd;
		nThreadID = id;
		fileAccessI = new FileAccessI(sName, nStartPos);
	}

	public void run() {
		while (nStartPos < nEndPos && !bStop) {
			try {
				URL url = new URL(sURL);
				HttpURLConnection httpConnection = (HttpURLConnection) url
						.openConnection();
				httpConnection.setRequestProperty("User-Agent", "NetFox");
				String sProperty = "bytes=" + nStartPos + "-";
				httpConnection.setRequestProperty("RANGE", sProperty);
				Utility.log(sProperty);
				InputStream input = httpConnection.getInputStream();
				// logResponseHead(httpConnection);
				byte[] b = new byte[1024];
				int nRead;
				while ((nRead = input.read(b, 0, 1024)) > 0
						&& nStartPos < nEndPos && !bStop) {
					nStartPos += fileAccessI.write(b, 0, nRead);
					// if(nThreadID == 1)
					// Utility.log("nStartPos = " + nStartPos + ", nEndPos = " +
					// nEndPos);
				}
				Utility.log("Thread " + nThreadID + " is over!");
				bDownOver = true;
				// nPos = fileAccessI.write (b,0,nRead);
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}

	// 打印回应的头信息
	public void logResponseHead(HttpURLConnection con) {
		for (int i = 1;; i++) {
			String header = con.getHeaderFieldKey(i);
			if (header != null)
				// responseHeaders.put(header,httpConnection.getHeaderField(header));
				Utility.log(header + " : " + con.getHeaderField(header));
			else
				break;
		}
	}

	public void splitterStop() {
		bStop = true;
	}
}

package cn.hiservice.download;

public class SiteInfoBean {
	private String sSiteURL; // Site's URL
	private String sFilePath; // Saved File's Path
	private String sFileName; // Saved File's Name
	private int nSplitter; // Count of Splited Downloading File

	public SiteInfoBean() {
		// default value of nSplitter is 5
		this("", "", "", 5);
	}

	public SiteInfoBean(String sURL, String sPath, String sName, int nSpiltter) {
		sSiteURL = sURL;
		sFilePath = sPath;
		sFileName = sName;
		this.nSplitter = nSpiltter;
	}

	public String getSSiteURL() {
		return sSiteURL;
	}

	public void setSSiteURL(String value) {
		sSiteURL = value;
	}

	public String getSFilePath() {
		return sFilePath;
	}

	public void setSFilePath(String value) {
		sFilePath = value;
	}

	public String getSFileName() {
		return sFileName;
	}

	public void setSFileName(String value) {
		sFileName = value;
	}

	public int getNSplitter() {
		return nSplitter;
	}

	public void setNSplitter(int nCount) {
		nSplitter = nCount;
	}
}

package cn.hiservice.download;

/* 
 **FileAccess.java 
 */

import java.io.*;

public class FileAccessI implements Serializable {

	private static final long serialVersionUID = 1L;
	RandomAccessFile oSavedFile;
	long nPos;

	public FileAccessI() throws IOException {
		this("", 0);
	}

	public FileAccessI(String sName, long nPos) throws IOException {
		oSavedFile = new RandomAccessFile(sName, "rw");
		this.nPos = nPos;
		oSavedFile.seek(nPos);
	}

	public synchronized int write(byte[] b, int nStart, int nLen) {
		int n = -1;
		try {
			oSavedFile.write(b, nStart, nLen);
			n = nLen;
		} catch (IOException e) {
			e.printStackTrace();
		}
		return n;
	}
}

package cn.hiservice.download;

/* 
 **Utility.java 
 */

public class Utility {
	public Utility() {
	}

	public static void sleep(int nSecond) {
		try {
			Thread.sleep(nSecond);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public static void log(String sMsg) {
//		System.err.println(sMsg);
	}

	public static void log(int sMsg) {
		System.err.println(sMsg);
	}
}

package cn.hiservice.download;

import org.junit.Test;

/* 
 **TestMethod.java 
 */

public class TestMethod {
	
	public  TestMethod() { 
		try {
			SiteInfoBean bean = new SiteInfoBean(
					"http://localhost:8088/FileDownLoad/Ducati_Windows7.themepack", "D:\\temp",
					"Ducati_Windows7.themepack", 3);
			SiteFileFetch fileFetch = new SiteFileFetch(bean);
			fileFetch.start();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}