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  • Android 多线程断点下载

    package com.itheima.mutiledownloader;
    
    import java.io.BufferedReader;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.io.RandomAccessFile;
    import java.net.HttpURLConnection;
    import java.net.MalformedURLException;
    import java.net.ProtocolException;
    import java.net.URL;
    import java.util.ArrayList;
    import java.util.List;
    
    import android.os.Bundle;
    import android.os.Environment;
    import android.os.Handler;
    import android.os.Message;
    import android.renderscript.Program.TextureType;
    import android.text.TextUtils;
    import android.app.Activity;
    import android.view.Menu;
    import android.view.View;
    import android.view.ViewGroup.LayoutParams;
    import android.widget.EditText;
    import android.widget.LinearLayout;
    import android.widget.ProgressBar;
    import android.widget.Toast;
    
    public class MainActivity extends Activity {
            protected static final int DOWNLOAD_ERROR = 1;
            private static final int THREAD_DOWNLOAD_ERROR = 2;
            public static final int DONWLOAD_FINISH = 3;
            private EditText et_path;
            private EditText et_number;
            private LinearLayout ll_pb;
            private String path;
            private static int threadCount = 4;
            private static int blockSize = 0;
            private static int livingThread = 0;
            
            private List<ProgressBar> pbs;
    
            private Handler handler = new Handler() {
                    public void handleMessage(android.os.Message msg) {
                            switch (msg.what) {
                            case DOWNLOAD_ERROR:
                                    Toast.makeText(getApplicationContext(), "初始化下载失败", 1).show();
                                    break;
                            case THREAD_DOWNLOAD_ERROR:
                                    String str = (String) msg.obj;
                                    Toast.makeText(getApplicationContext(), str, 1).show();
                                    break;
                            case DONWLOAD_FINISH:
                                    Toast.makeText(getApplicationContext(), "下载完毕", 1).show();
                                    findViewById(R.id.bt).setEnabled(true);
                                    break;
                            }
                    };
            };
    
            @Override
            protected void onCreate(Bundle savedInstanceState) {
                    super.onCreate(savedInstanceState);
                    setContentView(R.layout.activity_main);
                    et_path = (EditText) findViewById(R.id.et_path);
                    et_number = (EditText) findViewById(R.id.et_number);
                    ll_pb = (LinearLayout) findViewById(R.id.ll_pb);
    
            }
    
            public void click(View view) {
                    path = et_path.getText().toString().trim();
                    String strNumber = et_number.getText().toString().trim();
                    if (TextUtils.isEmpty(path) || TextUtils.isEmpty(strNumber)) {
                            Toast.makeText(this, "请输入参数", 0).show();
                            return;
                    } else {
                            // 下载的线程的个数
                            threadCount = Integer.parseInt(strNumber);
                            pbs = new ArrayList<ProgressBar>();
                            ll_pb.removeAllViews();
                            for (int i = 0; i < threadCount; i++) {
                                    ProgressBar pb = (ProgressBar) View.inflate(
                                                    getApplicationContext(), R.layout.pb_item, null);
                                    pb.setPadding(5, 5, 5, 5);
                                    ll_pb.addView(pb, LayoutParams.MATCH_PARENT, 12);
                                    //在集合里面添加进度条的引用.
                                    pbs.add(pb);
                            }
                            findViewById(R.id.bt).setEnabled(false);
                            new Thread() {
                                    public void run() {
                                            try {
                                                    URL url = new URL(path);
                                                    HttpURLConnection conn = (HttpURLConnection) url
                                                                    .openConnection();
                                                    conn.setRequestMethod("GET");
                                                    conn.setConnectTimeout(5000);
                                                    // 服务器文件的长度
                                                    int length = conn.getContentLength();
                                                    // 本地创建一个大小跟服务器一样的文件
                                                    RandomAccessFile raf = new RandomAccessFile(Environment
                                                                    .getExternalStorageDirectory()
                                                                    .getAbsolutePath()
                                                                    + "/" + getFileName(path), "rw");
                                                    raf.setLength(length);
                                                    System.out.println("文件的总长度:" + length);
                                                    // 计算每个线程下载的位置.
                                                    blockSize = length / threadCount;
                                                    System.out.println("每一个块的平均长度:" + blockSize);
                                                    livingThread = threadCount;
                                                    for (int i = 1; i <= threadCount; i++) {
                                                            int startIndex = (i - 1) * blockSize;
                                                            int endIndex = i * blockSize - 1;
                                                            if (i == threadCount) {
                                                                    endIndex = length;
                                                            }
                                                            //设置进度条的总进度
                                                            pbs.get(i-1).setMax(endIndex-startIndex);
                                                            new Thread(
                                                                            new DownLoadTask(i, startIndex, endIndex))
                                                                            .start();
                                                    }
                                            } catch (Exception e) {
                                                    e.printStackTrace();
                                                    Message msg = Message.obtain();
                                                    msg.what = DOWNLOAD_ERROR;
                                                    handler.sendMessage(msg);
                                            }
                                    };
                            }.start();
    
                    }
            }
    
            /**
             * 获取下载的文件的名称
             * 
             * @param path
             * @return
             */
            private static String getFileName(String path) {
                    int start = path.lastIndexOf("/") + 1;
                    return path.substring(start);
            }
    
            private class DownLoadTask implements Runnable {
    
                    private int id;
                    private int startIndex;
                    private int endIndex;
    
                    public DownLoadTask(int id, int startIndex, int endIndex) {
                            this.id = id;
                            this.startIndex = startIndex;
                            this.endIndex = endIndex;
                    }
    
                    @Override
                    public void run() {
                            try {
                                    int downloadCount =  0 ;
                                    URL url = new URL(path);
                                    HttpURLConnection conn = (HttpURLConnection) url
                                                    .openConnection();
                                    conn.setRequestMethod("GET");
                                    conn.setConnectTimeout(5000);
                                    // 在每次下载之前,检查是否存在已经下载大小的记录文件.
                                    File f = new File(Environment.getExternalStorageDirectory()
                                                    .getAbsolutePath()
                                                    + "/"
                                                    + getFileName(path)
                                                    + id
                                                    + ".txt");
                                    if (f.exists() && f.length() > 0) {
                                            FileInputStream fis = new FileInputStream(f);
                                            BufferedReader br = new BufferedReader(
                                                            new InputStreamReader(fis));
                                            // 已经下载的大小.
                                            downloadCount = Integer.parseInt(br.readLine());
                                            startIndex += downloadCount;
                                            br.close();
                                            fis.close();
                                    }
                                    conn.setRequestProperty("Range", "bytes=" + startIndex + "-"
                                                    + endIndex);
                                    System.out.println("线程id:" + id + " 下载的位置:" + startIndex
                                                    + "~~~" + endIndex);
                                    RandomAccessFile raf = new RandomAccessFile(Environment
                                                    .getExternalStorageDirectory().getAbsolutePath()
                                                    + "/"
                                                    + getFileName(path), "rwd");
                                    InputStream is = conn.getInputStream();
                                    // 指定线程下载存放文件的开始位置.
                                    raf.seek(startIndex);
                                    int len = 0;
                                    byte[] buffer = new byte[4096];
                                    int total = 0;// 记录当前线程下载的大小.
                                    while ((len = is.read(buffer)) != -1) {
                                            File file = new File(Environment
                                                            .getExternalStorageDirectory().getAbsolutePath()
                                                            + "/" + getFileName(path) + id + ".txt");
                                            RandomAccessFile positionRaf = new RandomAccessFile(file,
                                                            "rwd");
                                            raf.write(buffer, 0, len);
                                            total += len;
                                            positionRaf.write(String.valueOf(total).getBytes());
                                            positionRaf.close();
                                            pbs.get(id-1).setProgress(total+downloadCount);
                                    }
                                    raf.close();
                                    is.close();
                                    System.out.println("线程:" + id + "下载完毕...");
                            } catch (Exception e) {
                                    e.printStackTrace();
                                    Message msg = Message.obtain();
                                    msg.what = THREAD_DOWNLOAD_ERROR;
                                    msg.obj = "线程:" + id + "下载失败.";
                                    handler.sendMessage(msg);
                            } finally {
                                    synchronized (MainActivity.this) {
                                            livingThread--;
                                            if (livingThread <= 0) {
                                                    System.out.println("全部下载完毕...");
                                                    Message msg = Message.obtain();
                                                    msg.what = DONWLOAD_FINISH;
                                                    handler.sendMessage(msg);
                                                    for (int i = 1; i <= threadCount; i++) {
                                                            File f = new File(Environment
                                                                            .getExternalStorageDirectory()
                                                                            .getAbsolutePath()
                                                                            + "/" + getFileName(path) + i + ".txt");
                                                            System.out.println(f.delete());
                                                    }
                                            }
                                    }
    
                            }
                    }
            }
    }
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  • 原文地址:https://www.cnblogs.com/zhujiabin/p/4227657.html
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