基本原理：利用URLConnection獲取要下載文件的長度、頭部等相關信息，並設置響應的頭部信息。並且通過URLConnection獲取輸入流，將文件分成指定的塊，每一塊單獨開辟一個線程完成數據的讀取、寫入。通過輸入流讀取下載文件的信息，然後將讀取的信息用RandomAccessFile隨機寫入到本地文件中。同時，每個線程寫入的數據都文件指針也就是寫入數據的長度，需要保存在一個臨時文件中。這樣當本次下載沒有完成的時候，下次下載的時候就從這個文件中讀取上一次下載的文件長度，然後繼續接著上一次的位置開始下載。並且將本次下載的長度寫入到這個文件中。
一、下載文件信息類、實體
封裝即將下載資源的信息
代碼如下：
package com.hoo.entity;
/**
* <b>function:</b> 下載文件信息類
* @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 [email protected]
* @version 1.0
*/
public class DownloadInfo {
//下載文件url
private String url;
//下載文件名稱
private String fileName;
//下載文件路徑
private String filePath;
//分成多少段下載， 每一段用一個線程完成下載
private int splitter;
//下載文件默認保存路徑
private final static String FILE_PATH = "C:/temp";
//默認分塊數、線程數
private final static int SPLITTER_NUM = 5;
public DownloadInfo() {
super();
}
/**
* @param url 下載地址
*/
public DownloadInfo(String url) {
this(url, null, null, SPLITTER_NUM);
}
/**
* @param url 下載地址url
* @param splitter 分成多少段或是多少個線程下載
*/
public DownloadInfo(String url, int splitter) {
this(url, null, null, splitter);
}
/***
* @param url 下載地址
* @param fileName 文件名稱
* @param filePath 文件保存路徑
* @param splitter 分成多少段或是多少個線程下載
*/
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> 通過url獲得文件名稱
* @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、隨機寫入一段文件
代碼如下：
package com.hoo.download;
import java.io.IOException;
import java.io.RandomAccessFile;
/**
* <b>function:</b> 寫入文件、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 [email protected]
* @version 1.0
*/
public class SaveItemFile {
//存儲文件
private RandomAccessFile itemFile;
public SaveItemFile() throws IOException {
this("", 0);
}
/**
* @param name 文件路徑、名稱
* @param pos 寫入點位置 position
* @throws IOException
*/
public SaveItemFile(String name, long pos) throws IOException {
itemFile = new RandomAccessFile(name, "rw");
//在指定的pos位置開始寫入數據
itemFile.seek(pos);
}
/**
* <b>function:</b> 同步方法寫入文件
* @author hoojo
* @createDate 2011-9-26 下午12:21:22
* @param buff 緩沖數組
* @param start 起始位置
* @param length 長度
* @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();
}
}
}
這個類主要是完成向本地的指定文件指針出開始寫入文件，並返回當前寫入文件的長度（文件指針）。這個類將被線程調用，文件被分成對應的塊後，將被線程調用。每個線程都將會調用這個類完成文件的隨機寫入。
三、單個線程下載文件
代碼如下：
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> 單線程下載文件
* @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 [email protected]
* @version 1.0
*/
public class DownloadFile extends Thread {
//下載文件url
private String url;
//下載文件起始位置
private long startPos;
//下載文件結束位置
private long endPos;
//線程id
private int threadId;
//下載是否完成
private boolean isDownloadOver = false;
private SaveItemFile itemFile;
private static final int BUFF_LENGTH = 1024 * 8;
/**
* @param url 下載文件url
* @param name 文件名稱
* @param startPos 下載文件起點
* @param endPos 下載文件結束點
* @param threadId 線程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;
//分塊下載寫入文件內容
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();
// 設置連接超時時間為10000ms
conn.setConnectTimeout(10000);
// 設置讀取數據超時時間為10000ms
conn.setReadTimeout(10000);
setHeader(conn);
String property = "bytes=" + startPos + "-";
conn.setRequestProperty("RANGE", property);
//輸出log信息
LogUtils.log("開始 " + threadId + "：" + property + endPos);
//printHeader(conn);
//獲取文件輸入流，讀取文件內容
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) {
//寫入文件內容，返回最後寫入的長度
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> 打印下載文件頭部信息
* @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> 設置URLConnection的頭部信息，偽裝請求信息
* @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;
}
}
這個類主要是完成單個線程的文件下載，將通過URLConnection讀取指定url的資源信息。然後用InputStream讀取文件內容，然後調用調用SaveItemFile類，向本地寫入當前要讀取的塊的內容。
四、分段多線程寫入文件內容
代碼如下：
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> 分批量下載文件
* @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 [email protected]
* @version 1.0
*/
public class BatchDownloadFile implements Runnable {
//下載文件信息
private DownloadInfo downloadInfo;
//一組開始下載位置
private long[] startPos;
//一組結束下載位置
private long[] endPos;
//休眠時間
private static final int SLEEP_SECONDS = 500;
//子線程下載
private DownloadFile[] fileItem;
//文件長度
private int length;
//是否第一個文件
private boolean first = true;
//是否停止下載
private boolean stop = false;
//臨時文件信息
private File tempFile;
public BatchDownloadFile(DownloadInfo downloadInfo) {
this.downloadInfo = downloadInfo;
String tempPath = this.downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName() + ".position";
tempFile = new File(tempPath);
//如果存在讀入點位置的文件
if (tempFile.exists()) {
first = false;
//就直接讀取內容
try {
readPosInfo();
} catch (IOException e) {
e.printStackTrace();
}
} else {
//數組的長度就要分成多少段的數量
startPos = new long[downloadInfo.getSplitter()];
endPos = new long[downloadInfo.getSplitter()];
}
}
@Override
public void run() {
//首次下載，獲取下載文件長度
if (first) {
length = this.getFileSize();//獲取文件長度
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;
//設置最後一個結束點的位置
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;
}
}
//子線程開始下載
if (!stop) {
//創建單線程下載對象數組
fileItem = new DownloadFile[startPos.length];//startPos.length = downloadInfo.getSplitter()
for (int i = 0; i < startPos.length; i++) {
try {
//創建指定個數單線程下載對象，每個線程獨立完成指定塊內容的下載
fileItem[i] = new DownloadFile(
downloadInfo.getUrl(),
this.downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName(),
startPos[i], endPos[i], i
);
fileItem[i].start();//啟動線程，開始下載
LogUtils.log("Thread: " + i + ", startPos: " + startPos[i] + ", endPos: " + endPos[i]);
} catch (IOException e) {
e.printStackTrace();
}
}
//循環寫入下載文件長度信息
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!");
}
}
/**
* 將寫入點數據保存在臨時文件中
* @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>讀取寫入點的位置信息
* @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> 獲取下載文件的長度
* @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();
//判斷http status是否為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 {
//獲取長度
fileLength = conn.getContentLength();
LogUtils.log("FileLength: " + fileLength);
}
//讀取文件長度
/*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;
}
}
這個類主要是完成讀取指定url資源的內容，獲取該資源的長度。然後將該資源分成指定的塊數，將每塊的起始下載位置、結束下載位置，分別保存在一個數組中。每塊都單獨開辟一個獨立線程開始下載。在開始下載之前，需要創建一個臨時文件，寫入當前下載線程的開始下載指針位置和結束下載指針位置。
五、工具類、測試類
日志工具類
代碼如下：
package com.hoo.util;
/**
* <b>function:</b> 日志工具類
* @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 [email protected]
* @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);
}
}
下載工具類
代碼如下：
package com.hoo.util;
import com.hoo.download.BatchDownloadFile;
import com.hoo.entity.DownloadInfo;
/**
* <b>function:</b> 分塊多線程下載工具類
* @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 [email protected]
* @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();
}
}
下載測試類
代碼如下：
package com.hoo.test;
import com.hoo.util.DownloadUtils;
/**
* <b>function:</b> 下載測試
* @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 [email protected]
* @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);
}
}
多線程下載主要在第三部和第四部，其他的地方還是很好理解。源碼中提供相應的注釋了，便於理解。
