多线程下载

group24/315863321/src/main/java/com/johnChnia/coderising2017/download/DownloadThread.java

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+package com.johnChnia.coderising2017.download;
+
+import com.johnChnia.coderising2017.download.api.Connection;
+
+import java.io.RandomAccessFile;
+import java.util.concurrent.CyclicBarrier;
+
+public class DownloadThread extends Thread {
+    Connection conn;
+    int startPos;
+    int endPos;
+    CyclicBarrier barrier;
+    String localFile;
+
+    public DownloadThread(Connection conn, int startPos, int endPos, String localFile, CyclicBarrier barrier) {
+        this.conn = conn;
+        this.startPos = startPos;
+        this.endPos = endPos;
+        this.localFile = localFile;
+        this.barrier = barrier;
+    }
+
+    public void run() {
+        try {
+            System.out.println("Begin to read [" + startPos + "-" + endPos + "]");
+            byte[] data = conn.read(startPos, endPos);
+            System.out.println("创建一个随机读取文件的对象");
+            RandomAccessFile file = new RandomAccessFile(localFile, "rw");
+            file.seek(startPos);
+            System.out.println("要写数据了");
+            file.write(data);
+            file.close();
+            conn.close();
+            System.out.println(this.currentThread().getName() + "once over");
+            barrier.await();
+        } catch (Exception e) {
+            // TODO: handle exception
+        }
+    }
+}

group24/315863321/src/main/java/com/johnChnia/coderising2017/download/FileDownloader.java

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+package com.johnChnia.coderising2017.download;
+
+import com.johnChnia.coderising2017.download.api.Connection;
+import com.johnChnia.coderising2017.download.api.ConnectionManager;
+import com.johnChnia.coderising2017.download.api.DownloadListener;
+
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.util.concurrent.CyclicBarrier;
+
+
+public class FileDownloader {
+    private String url;
+    private String localFile = "YNote.exe";
+    DownloadListener listener;
+    ConnectionManager cm;
+
+    private static final int DOWNLOAD_THREAD_NUM = 3;
+
+    public FileDownloader(String _url) {
+        this.url = _url;
+//		this.localFile = localFile;
+    }
+
+    public void execute() {
+        // 在这里实现你的代码， 注意： 需要用多线程实现下载
+        // 这个类依赖于其他几个接口，你需要写这几个接口的实现代码
+        // （1） ConnectionManager  可以打开一个连接，通过Connection可以读取其中的一段（用StartPos,endPos来指定）
+        // （2）DownloadListener, 由于是多线程下载，调用这个类的客户端不知道什么时候结束，所以你需要实现当所有线程都执行完以后，调用listener的notifiedFinished方法，这样客户端就能收到通知
+        // 具体的实现思路：
+        // 1. 需要调用ConnectionManager的 open 方法打开连接，然后通过 Connection.getContentLength方法获得文件的长度
+        // 2. 至少启动3个线程下载，注意每个线程需要先调用ConnectionManager的open方法
+        // 	     然后调用 read 方法， read 方法中有读取文件的开始位置和结束位置的参数，返回值是byte[] 数组
+        // 3.把 byte 数组写入到文件中
+        // 4.所有的线程都下载完成以后，需要调用 listener 的 notifiedFinished 方法
+
+        // 下面的代码是实例代码，也就是说只有一个线程，你需要改造成多线程的
+        CyclicBarrier barrier = new CyclicBarrier(DOWNLOAD_THREAD_NUM, new Runnable() {// 当所有的Thread都调用 await方法时，会执行后面的 barrierAction,调用后面这个线程
+            @Override
+            public void run() {
+                listener.notifyFinished();
+            }
+        });
+
+        Connection conn = null;
+        try {
+            conn = cm.open(this.url);
+            int length = conn.getContentLength();// 拿到将要下载文件的长度
+            createPlaceHolderFile(this.localFile, length);//占位
+            System.out.println("占位完毕");
+            int[][] ranges = allocateDownloadRange(DOWNLOAD_THREAD_NUM, length);// 给每个线程分配开始位置和结束位置
+            // 开始下载文件
+            System.out.println("开始下载文件");
+            for (int i = 0; i < DOWNLOAD_THREAD_NUM; i++) {
+                DownloadThread thread = new DownloadThread(
+                        cm.open(url),
+                        ranges[i][0],
+                        ranges[i][1],
+                        localFile,
+                        barrier);
+                thread.start();
+                System.out.println("第" + (i + 1) + "个线程已经启动");
+            }
+
+        } catch (Exception e) {
+            e.printStackTrace();
+        } finally {
+            System.out.println("即将关闭连接");
+            if (conn != null) {
+                conn.close();
+                System.out.println("关闭连接成功");
+            }
+        }
+    }
+
+    public void setListener(DownloadListener listener) {
+        this.listener = listener;
+    }
+
+    public void setConnectionManager(ConnectionManager ucm) {
+        this.cm = ucm;
+    }
+
+    public DownloadListener getListener() {
+        return this.listener;
+    }
+
+    private void createPlaceHolderFile(String fileName, int contentLen) throws IOException {
+        RandomAccessFile file = new RandomAccessFile(fileName, "rw");
+        file.setLength(contentLen);
+//        for (int i = 0; i < contentLen; i++) {
+//            file.write(0);
+//        }
+        file.close();
+    }
+
+    /**
+     * 给出线程数和文件长度，返回一个二维数组，里面存的是每个线程下载的开始位置和结束位置
+     *
+     * @param threadNum
+     * @param contentLen
+     * @return
+     */
+    private int[][] allocateDownloadRange(int threadNum, int contentLen) {
+        int[][] ranges = new int[threadNum][2];// 用二维数组存下每个线程的开始位置和结束位置
+
+        int eachThreadSize = contentLen / threadNum;// 每个线程需要下载的文件大小
+        int left = contentLen % threadNum;// 剩下的归最后一个线程来处理
+
+        for (int i = 0; i < threadNum; i++) {
+            int startPos = i * eachThreadSize;
+            int endPos = (i + 1) * eachThreadSize - 1;
+            if ((i == (threadNum - 1))) {
+                endPos += left;
+            }
+            ranges[i][0] = startPos;
+            ranges[i][1] = endPos;
+        }
+
+        return ranges;
+    }
+
+}

group24/315863321/src/main/java/com/johnChnia/coderising2017/download/FileDownloaderTest.java

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+package com.johnChnia.coderising2017.download;
+
+import com.johnChnia.coderising2017.download.api.ConnectionManager;
+import com.johnChnia.coderising2017.download.api.DownloadListener;
+import com.johnChnia.coderising2017.download.impl.ConnectionManagerImpl;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.FileNotFoundException;
+
+public class FileDownloaderTest {
+    boolean downloadFinished = false;
+    @Before
+    public void setUp() throws Exception {
+    }
+
+    @After
+    public void tearDown() throws Exception {
+    }
+
+    @Test
+    public void testDownload() throws FileNotFoundException {
+
+        String url = "http://download.ydstatic.com/notewebsite/downloads/YNote.exe";
+
+
+        FileDownloader downloader = new FileDownloader(url);
+
+
+        ConnectionManager cm = new ConnectionManagerImpl();
+        downloader.setConnectionManager(cm);
+
+        downloader.setListener(new DownloadListener() {
+            @Override
+            public void notifyFinished() {
+                downloadFinished = true;
+            }
+
+        });
+
+
+        downloader.execute();
+
+        // 等待多线程下载程序执行完毕
+        while (!downloadFinished) {
+            try {
+                System.out.println("还没有下载完成，休眠五秒");
+                //休眠5秒
+                Thread.sleep(5000);
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+        }
+        System.out.println("下载完成！");
+
+
+
+    }
+
+}

group24/315863321/src/main/java/com/johnChnia/coderising2017/download/api/Connection.java

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+package com.johnChnia.coderising2017.download.api;
+
+import java.io.IOException;
+
+public interface Connection {
+    /**
+     * 给定开始和结束位置， 读取数据， 返回值是字节数组
+     *
+     * @param startPos 开始位置， 从0开始
+     * @param endPos   结束位置
+     * @return
+     */
+    public byte[] read(int startPos, int endPos) throws IOException;
+
+
+    /**
+     * 得到数据内容的长度
+     *
+     * @return
+     */
+    public int getContentLength();
+
+    /**
+     * 关闭连接
+     */
+    public void close();
+}

group24/315863321/src/main/java/com/johnChnia/coderising2017/download/api/ConnectionException.java

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+package com.johnChnia.coderising2017.download.api;
+
+public class ConnectionException extends Exception {
+
+}

group24/315863321/src/main/java/com/johnChnia/coderising2017/download/api/ConnectionManager.java

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+package com.johnChnia.coderising2017.download.api;
+
+public interface ConnectionManager {
+	/**
+	 * 给定一个url , 打开一个连接
+	 * @param url
+	 * @return
+	 */
+	public Connection open(String url) throws ConnectionException;	
+}

group24/315863321/src/main/java/com/johnChnia/coderising2017/download/api/DownloadListener.java

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+package com.johnChnia.coderising2017.download.api;
+
+public interface DownloadListener {
+	public void notifyFinished();
+}

group24/315863321/src/main/java/com/johnChnia/coderising2017/download/impl/ConnectionImpl.java

@@ -0,0 +1,71 @@
+package com.johnChnia.coderising2017.download.impl;
+
+import com.johnChnia.coderising2017.download.api.Connection;
+import com.johnChnia.coderising2017.download.api.ConnectionException;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.HttpURLConnection;
+import java.net.URL;
+import java.net.URLConnection;
+import java.util.Arrays;
+
+public class ConnectionImpl implements Connection {
+    URL url;
+    static final int BUFFER_SIZE = 1024;
+
+    ConnectionImpl(String _url) throws ConnectionException {
+        try {
+            url = new URL(_url);
+        } catch (Exception e) {
+            throw new ConnectionException();
+        }
+    }
+    @Override
+    public byte[] read(int startPos, int endPos) throws IOException {
+        //开始
+        System.out.println("开始");
+        HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
+        // 设置读取的位置
+        httpConn.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);
+        // 从URL连接获得输入流
+        InputStream is = httpConn.getInputStream();
+
+        //is.skip(startPos);
+        byte[] buff = new byte[BUFFER_SIZE];
+        int totalLen = endPos - startPos + 1;
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+
+        while(baos.size() < totalLen){
+            int len = is.read(buff);
+            if(len<0){
+                break;
+            }
+            baos.write(buff,0,len);
+        }
+
+        if(baos.size() > totalLen){
+            byte[] data = baos.toByteArray();
+            return Arrays.copyOf(data, totalLen);
+        }
+        return baos.toByteArray();
+    }
+
+    @Override
+    public int getContentLength() {
+        URLConnection con;
+        try {
+            con = url.openConnection();
+            return con.getContentLength();
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+        return -1;
+    }
+
+    @Override
+    public void close() {
+
+    }
+}

group24/315863321/src/main/java/com/johnChnia/coderising2017/download/impl/ConnectionManagerImpl.java

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+package com.johnChnia.coderising2017.download.impl;
+
+import com.johnChnia.coderising2017.download.api.Connection;
+import com.johnChnia.coderising2017.download.api.ConnectionException;
+import com.johnChnia.coderising2017.download.api.ConnectionManager;
+
+public class ConnectionManagerImpl implements ConnectionManager {
+
+    @Override
+    public Connection open(String url) throws ConnectionException {
+        return new ConnectionImpl(url);
+    }
+
+}