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JAVA下实现多线程断点下载

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多线程断点下载：顾名思义是用多线程实现的，断点是当第三方因素（断电、断网等）中断下载时，下次下载可以继续上次下载的地方下载。

 

1、通过getContentLength可以获取要下载文件的大小，这样可以在本机上创建一个相同大小的文件用来下载。

            int fileLength = connection.getContentLength();

2、由于是多线程，所以要给每一个线程均分分配要下载的位置。

            for(int i = 0; i < threadCount; i ++) {
    int startThread = i * blockSize;
    int endThread = (i + 1) * blockSize - 1;
    if( i == blockSize - 1) endThread = fileLength -1;
    new DownloadThread(i, startThread, endThread).start();
                    
}

3、启动每个线程下载时，请求头需要Range参数，值是bytes:xxx-xxx某事。比如"Range:0-10100",代表要下载的位置是从0到10100。

connection.setRequestProperty("Range", "bytes:"+startThred+"-" + endThread);

4、然后每次用RandomAccessFile写入数据到本机文件里。

            while((length = inputStream.read(buffer)) != -1) {
    randomAccessFile.write(buffer, 0, length);
}

 

5、当然每次下载时需要记录本线程下载了多少，以便断点时，下载的时候可以从下次下载的地方下载。

total += length;
int currentThreadPostion = startThred + total;
RandomAccessFile randomAccessFile2 = new RandomAccessFile(file, "rwd");
randomAccessFile2.write(String.valueOf(currentThreadPostion).getBytes());
randomAccessFile2.close();

 

继承Thread类的DownloadThread类代码：

技术分享 技术分享 
                 1
                public
                static
                class DownloadThread extends Thread {
 2privateint threadId;
 3privateint endThread;
 4privateint startThred;
 5public DownloadThread(int threadId, int startThred, int endThread) {
 6this.threadId = threadId;
 7this.startThred = startThred;
 8this.endThread = endThread;
 9        }
10publicvoid run() {
11//分段请求网络连接，分段保存在本地12synchronized (DownloadThread.class) {
13                 currentRunThreadCount += 1;
14            }
15try {
16                 System.err.println("理论线程:"+threadId+",开始位置:"+startThred+",结束位置:"+endThread);
17                 URL url = new URL(path);
18                 HttpURLConnection connection = (HttpURLConnection) url.openConnection();
19                 connection.setRequestMethod("GET");
20                 connection.setConnectTimeout(10 * 1000);
21                 File file = new File(threadId+".txt");
22if(file.exists()) {    //是否断点23                     BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
24                     String lastPostion_str = bufferedReader.readLine();
25                     startThred = Integer.parseInt(lastPostion_str);
26                    bufferedReader.close();
27                }
28//设置分段下载的头信息  Range:做分段29                 connection.setRequestProperty("Range", "bytes:"+startThred+"-" + endThread);
30int code = connection.getResponseCode();
31                System.out.println(code);
32if(code == 206) {    //200:请求全部资源成功  206:代表部分资源请求成功33                     InputStream inputStream = connection.getInputStream();
34                    System.out.println(getFileName(path));
35                     RandomAccessFile randomAccessFile = new RandomAccessFile(new File(getFileName(path)), "rw");
36                    randomAccessFile.seek(startThred);
37byte[] buffer = newbyte[1024*10];
38int length = -1;
39int total = 0;//记录下载的总量40                     System.err.println("实际线程:"+threadId+",开始位置:"+startThred+",结束位置:"+endThread);
41while((length = inputStream.read(buffer)) != -1) {
42                         randomAccessFile.write(buffer, 0, length);
43                         total += length;
44int currentThreadPostion = startThred + total;
45                         RandomAccessFile randomAccessFile2 = new RandomAccessFile(file, "rwd");
46                        randomAccessFile2.write(String.valueOf(currentThreadPostion).getBytes());
47                        randomAccessFile2.close();
48                    }
49                    randomAccessFile.close();
50                    inputStream.close();
51                     System.err.println("线程:"+threadId+"下载完毕");
52synchronized (DownloadThread.class) {
53                         currentRunThreadCount -= 1;
54if(currentRunThreadCount == 0){
55for(int i = 0; i < threadCount; i ++) {
56                                 File file2 = new File(i+".txt");
57                                file2.delete();
58                            }
59                        }
60                    }
61                }
6263             } catch (Exception e) {
64                e.printStackTrace();
65            }
666768super.run();
69        }
70     }
View Code

完整代码：

技术分享 技术分享 
                  1
                package
                 cn.starry.muchThreadDown;

                  2
                  3
                import
                 java.io.BufferedReader;

                  4
                import
                 java.io.File;

                  5
                import
                 java.io.FileInputStream;

                  6
                import
                 java.io.InputStream;

                  7
                import
                 java.io.InputStreamReader;

                  8
                import
                 java.io.RandomAccessFile;

                  9
                import
                 java.net.HttpURLConnection;

                 10
                import
                 java.net.MalformedURLException;

                 11
                import
                 java.net.URL;

                 12
                import
                 java.net.URLConnection;

                 13
                 14
                import
                 javax.swing.text.StyledEditorKit.BoldAction;

                 15
                 16
                public
                class
                 MuchThreadDown {

                 17
                 18
                /**
                 19
                     * 
                @param
                 args

                 20
                */
                 21
                private
                static
                int threadCount = 3;
 22privatestaticint blockSize;
 23privatestatic String path = "http://192.168.0.112:8080/itheima74/feiq.exe";
 24privatestaticint currentRunThreadCount = 0;
 25publicstaticvoid main(String[] args) {
 26 27try {
 28             URL url = new URL(path);
 29             HttpURLConnection connection = (HttpURLConnection) url.openConnection();
 30             connection.setRequestMethod("GET");
 31             connection.setConnectTimeout(10 * 1000);
 32int code = connection.getResponseCode();
 33if(code == 200) {
 34int fileLength = connection.getContentLength();
 35                 RandomAccessFile randomAccessFile = new RandomAccessFile(new File(getFileName(path)), "rw");
 36                randomAccessFile.setLength(fileLength);
 37                 blockSize = fileLength / threadCount;
 38for(int i = 0; i < threadCount; i ++) {
 39int startThread = i * blockSize;
 40int endThread = (i + 1) * blockSize - 1;
 41if( i == blockSize - 1) endThread = fileLength -1;
 42new DownloadThread(i, startThread, endThread).start();
 43 44                }
 45            }
 46         } catch (Exception e) {
 47            e.printStackTrace();
 48        }
 49 50    }
 51 52 53publicstaticclass DownloadThread extends Thread {
 54privateint threadId;
 55privateint endThread;
 56privateint startThred;
 57public DownloadThread(int threadId, int startThred, int endThread) {
 58this.threadId = threadId;
 59this.startThred = startThred;
 60this.endThread = endThread;
 61        }
 62publicvoid run() {    
 63synchronized (DownloadThread.class) {
 64                 currentRunThreadCount += 1;
 65            }
 66//分段请求网络连接，分段保存在本地 67try {
 68                 System.err.println("理论线程:"+threadId+",开始位置:"+startThred+",结束位置:"+endThread);
 69                 URL url = new URL(path);
 70                 HttpURLConnection connection = (HttpURLConnection) url.openConnection();
 71                 connection.setRequestMethod("GET");
 72                 connection.setConnectTimeout(10 * 1000);
 73                 File file = new File(threadId+".txt");
 74if(file.exists()) {    //是否断点 75                     BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
 76                     String lastPostion_str = bufferedReader.readLine();
 77                     startThred = Integer.parseInt(lastPostion_str);
 78                    bufferedReader.close();
 79                }
 80//设置分段下载的头信息  Range:做分段 81                 connection.setRequestProperty("Range", "bytes:"+startThred+"-" + endThread);
 82int code = connection.getResponseCode();
 83                System.out.println(code);
 84if(code == 206) {    //200:请求全部资源成功  206:代表部分资源请求成功 85                     InputStream inputStream = connection.getInputStream();
 86                    System.out.println(getFileName(path));
 87                     RandomAccessFile randomAccessFile = new RandomAccessFile(new File(getFileName(path)), "rw");
 88                    randomAccessFile.seek(startThred);
 89byte[] buffer = newbyte[1024*10];
 90int length = -1;
 91int total = 0;//记录下载的总量 92                     System.err.println("实际线程:"+threadId+",开始位置:"+startThred+",结束位置:"+endThread);
 93while((length = inputStream.read(buffer)) != -1) {
 94                         randomAccessFile.write(buffer, 0, length);
 95                         total += length;
 96int currentThreadPostion = startThred + total;
 97                         RandomAccessFile randomAccessFile2 = new RandomAccessFile(file, "rwd");
 98                        randomAccessFile2.write(String.valueOf(currentThreadPostion).getBytes());
 99                        randomAccessFile2.close();
100                    }
101                    randomAccessFile.close();
102                    inputStream.close();
103                     System.err.println("线程:"+threadId+"下载完毕");
104synchronized (DownloadThread.class) {
105                         currentRunThreadCount -= 1;
106if(currentRunThreadCount == 0){
107for(int i = 0; i < threadCount; i ++) {
108                                 File file2 = new File(i+".txt");
109                                file2.delete();
110                            }
111                        }
112                    }
113                }
114115             } catch (Exception e) {
116                e.printStackTrace();
117            }
118119120super.run();
121        }
122    }
123124publicstatic String getFileName(String path) {
125return path.substring(path.lastIndexOf("/")+1);
126    }
127128 }
View Code

 

原文：http://www.cnblogs.com/xingkongyihao/p/7401771.html

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