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Java 多线程断点下载文件_详解

 
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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

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


二、随机写入一段文件

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

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

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

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

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

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

下载工具类

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

下载测试类

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