java 多线程下载

 1   import java.io.ByteArrayOutputStream;
 2 import java.io.InputStream;
 3 
 4 public class StreamTool {
 5     /**
 6      * 把一个inputstream里面的内容转化成一个byte[]
 7      */
 8     public static byte[] getBytes(InputStream is) throws Exception {
 9         ByteArrayOutputStream bos = new ByteArrayOutputStream();
10         byte[] buffer = new byte[1024];
11         int len = 0;
12         while ((len = is.read(buffer)) != -1) {
13             bos.write(buffer, 0, len);
14         }
15         is.close();
16         bos.flush();
17         byte[] result = bos.toByteArray();
18         System.out.println(new String(result));
19         return result;
20     }
21 }

  1 import java.io.File;
  2 import java.io.FileInputStream;
  3 import java.io.FileOutputStream;
  4 import java.io.InputStream;
  5 import java.io.RandomAccessFile;
  6 import java.net.HttpURLConnection;
  7 import java.net.URL;
  8 
  9 public class TestDownload {
 10     public static final String path = "http://192.168.1.100:8080/aaa.exe";
 11 
 12     public static void main(String[] args) throws Exception {
 13         URL url = new URL(path);
 14         HttpURLConnection conn = (HttpURLConnection) url.openConnection();
 15         conn.setRequestMethod("GET");
 16         conn.setConnectTimeout(5000);
 17         conn.setRequestProperty("User-Agent",
 18            "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
 19         int code = conn.getResponseCode();
 20         if (code == 200) {
 21             int len = conn.getContentLength();
 22             RandomAccessFile file = new RandomAccessFile(
 23                "C:/Users/DELL/Desktop/" + getFilenName(path), "rwd");
 24             // 1.设置本地文件大小跟服务器的文件大小一致
 25             file.setLength(len);
 26 
 27             // 2 .假设开启3 个线程
 28             int threadnumber = 3;
 29             int blocksize = len / threadnumber;
 30             /**
 31              * 线程1 0~ blocksize 线程2 1*bolocksize ~ 2*blocksize 线程3 2                   *blocksize ~
 32              * 文件末尾
 33              */
 34             for (int i = 0; i < threadnumber; i++) {
 35                 int startposition = i * blocksize;
 36                 int endpositon = (i + 1) * blocksize;
 37                 if (i == (threadnumber - 1)) {
 38                     // 最后一个线程
 39                     endpositon = len;
 40                 }
 41                 DownLoadTask task = new DownLoadTask(
                       i, path, startposition,endpositon);
 43                 task.start();
 44             }
 45         }
 46     }
 47 
 48     public static String getFilenName(String path) {
 49         int start = path.lastIndexOf("/") + 1;
 50         return path.substring(start, path.length());
 51     }
 52 
 53 }
 54 
 55 class DownLoadTask extends Thread {
 56     public static final String path = "http://192.168.1.100:8080/aaa.exe";
 57     int threadid;
 58     String filepath;
 59     int startposition;
 60     int endpositon;
 61 
 62     public DownLoadTask(int threadid, String filepath, 
                int startposition, int endpositon) {
 64         this.threadid = threadid;
 65         this.filepath = filepath;
 66         this.startposition = startposition;
 67         this.endpositon = endpositon;
 69     }
 70 
 71     @Override
 72     public void run() {
 73         try {
 74             File postionfile = new File(threadid + ".txt");
 75             URL url = new URL(filepath);
 76             HttpURLConnection conn = (HttpURLConnection) url.openConnection();
 77             System.out.println("线程" + threadid + "正在下载 " + "开始位置 : "
 78                     + startposition + "结束位置 " + endpositon);
 79 
 80             // 断点操作
 81             if (postionfile.exists()) { 
 82                 FileInputStream fis = new FileInputStream(postionfile);
 83                 byte[] result = StreamTool.getBytes(fis);
 84                 int newstartposition = Integer.parseInt(new String(result));
 85                 if (newstartposition > startposition) { // 如果新的位置 > 开始位置。
 86                     startposition = newstartposition;
 87                 }
 88             }
 89 
 90             // "Range", "bytes=2097152-4194303")
 91             conn.setRequestProperty("Range", "bytes=" + startposition + "-"
 92                     + endpositon);
 93             conn.setRequestMethod("GET");
 94             conn.setConnectTimeout(5000);
 95             conn.setRequestProperty("User-Agent",
 96                     "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
 97             InputStream is = conn.getInputStream();
 98             RandomAccessFile file = new RandomAccessFile(
 99                     "C:/Users/DELL/Desktop/" + getFilenName(path), "rwd");
100             // 设置 数据从文件哪个位置开始写
101             file.seek(startposition);
102             byte[] buffer = new byte[1024];
103             int len = 0;
104             
105             // 代表当前读到的服务器数据的位置 ,同时这个值已经存储的文件的位置
106             int currentPostion = startposition;
107             
108             // 创建一个文件对象 ,记录当前某个文件的下载位置
109             while ((len = is.read(buffer)) != -1) {
110                 file.write(buffer, 0, len);
111 
112                 currentPostion += len;
113                 // 需要把currentPostion 信息给持久化到存储设备
114                 String position = currentPostion + "";
115                 System.out.println("线程 .." + threadid + "....开始位置..."
116                         + startposition + "..当前位置..." + currentPostion
117                         + "...结束位置...." + endpositon);
118                 FileOutputStream fos = new FileOutputStream(postionfile);
119                 fos.write(position.getBytes());
120                 fos.flush();
121                 fos.close();
122             }
123             file.close();
124             System.out.println("线程" + threadid + "下载完毕");
125             // 当线程下载完毕后 把文件删除掉
126             if (postionfile.exists()) {
127                 postionfile.delete();
128             }
129         } catch (Exception e) {
130             e.printStackTrace();
131         }
132         super.run();
133     }
134 
135     public static String getFilenName(String path) {
136         int start = path.lastIndexOf("/") + 1;
137         return path.substring(start, path.length());
138     }
139 
140 }

1 public class test1 {
2     public static void main(String[] args) throws Exception {
3         RandomAccessFile file = new RandomAccessFile("haha.txt", "rwd");
4         file.setLength(1024 * 1024);
5     }
6 }