Android多线程断点续传下载

学习了多线程下载，而且可以断点续传的逻辑，线程数量可以自己选择，但是线程数量过多手机就承受不起，导致闪退，好在有断点续传。

步骤写在了代码的注释里。大概就是获取服务器文件的大小，在本地新建一个相同大小的文件用来申请空间，然后将服务器的文件读下来写到申请的文件中去。若开多线程，将文件分块，计算每个线程下载的开始位置和结束位置。若断点传输，则保存断开后下载的位置，下次将此位置赋给开始下载的位置即可。细节见代码。

下面是效果图：

布局文件activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <EditText
            android:id="@+id/et_path"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="请输入下载路径"
            android:text="http://10.173.29.234/test.exe" />

        <EditText
            android:id="@+id/et_threadCount"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="请输入线程数量" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="click"
            android:text="下载" />

        <LinearLayout
            android:id="@+id/ll_pb"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#455eee"
            android:orientation="vertical">

        </LinearLayout>
    </LinearLayout>

</android.support.constraint.ConstraintLayout>

创建布局文件，用来动态显示每个线程的进度条

layout.xml:

<?xml version="1.0" encoding="utf-8"?>
<ProgressBar xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/progressBar"
    style="?android:attr/progressBarStyleHorizontal"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />

MainActivity.java:

import...;

public class MainActivity extends AppCompatActivity {

    private EditText et_path;
    private EditText et_threadCount;
    private LinearLayout ll_pb;
    private String path;

    private static int runningThread;// 代表正在运行的线程
    private int threadCount;
    private List<ProgressBar> pbList;//集合存储进度条的引用

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        et_path = findViewById(R.id.et_path);
        et_threadCount = findViewById(R.id.et_threadCount);
        ll_pb = findViewById(R.id.ll_pb);
        //添加一个进度条的引用
        pbList = new ArrayList<ProgressBar>();
    }

    //点击按钮实现下载逻辑
    public void click(View view) {
        //获取下载路径
        path = et_path.getText().toString().trim();
        //获取线程数量
        String threadCounts = et_threadCount.getText().toString().trim();
        //移除以前的进度条添加新的进度条
        ll_pb.removeAllViews();
        threadCount = Integer.parseInt(threadCounts);
        pbList.clear();
        for (int i = 0; i < threadCount; i++) {
            ProgressBar v = (ProgressBar) View.inflate(getApplicationContext(), R.layout.layout, null);

            //把v添加到几何中
            pbList.add(v);

            //动态获取进度条
            ll_pb.addView(v);
        }

        //java逻辑移植
        new Thread() {
            @Override
            public void run() {
                /*************/
                System.out.println("你好");
                try {
                    URL url = new URL(path);
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.setRequestMethod("GET");
                    conn.setConnectTimeout(5000);
                    int code = conn.getResponseCode();
                    if (code == 200) {
                        int length = conn.getContentLength();
                        // 把运行线程的数量赋值给runningThread
                        runningThread = threadCount;

                        System.out.println("length=" + length);
                        // 创建一个和服务器的文件一样大小的文件，提前申请空间
                        RandomAccessFile randomAccessFile = new RandomAccessFile(getFileName(path), "rw");
                        randomAccessFile.setLength(length);
                        // 算出每个线程下载的大小
                        int blockSize = length / threadCount;
                        // 计算每个线程下载的开始位置和结束位置
                        for (int i = 0; i < length; i++) {
                            int startIndex = i * blockSize;// 开始位置
                            int endIndex = (i + 1) * blockSize;// 结束位置
                            // 特殊情况就是最后一个线程
                            if (i == threadCount - 1) {
                                // 说明是最后一个线程
                                endIndex = length - 1;
                            }
                            // 开启线程去服务器下载
                            DownLoadThread downLoadThread = new DownLoadThread(startIndex, endIndex, i);
                            downLoadThread.start();

                        }

                    }
                } catch (MalformedURLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                /*************/
            }
        }.start();

    }

    private class DownLoadThread extends Thread {
        // 通过构造方法吧每个线程的开始位置和结束位置传进来
        private int startIndex;
        private int endIndex;
        private int threadID;
        private int PbMaxSize;//代表当前下载（进度条）的最大值
        private int pblastPosition;//如果中断过，这是进度条上次的位置

        public DownLoadThread(int startIndex, int endIndex, int threadID) {
            this.startIndex = startIndex;
            this.endIndex = endIndex;
            this.threadID = threadID;

        }

        @Override
        public void run() {
            // 实现去服务器下载文件
            try {
                //计算进度条最大值
                PbMaxSize = endIndex - startIndex;
                URL url = new URL(path);
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5000);
                // 如果中间断过，接着上次的位置继续下载，聪慧文件中读取上次下载的位置
                File file = new File(getFileName(path) + threadID + ".txt");
                if (file.exists() && file.length() > 0) {
                    FileInputStream fis = new FileInputStream(file);
                    BufferedReader bufr = new BufferedReader(new InputStreamReader(fis));
                    String lastPosition = bufr.readLine();
                    int lastPosition1 = Integer.parseInt(lastPosition);

                    //赋值给进度条位置
                    pblastPosition = lastPosition1 - startIndex;
                    // 改变一下startIndex的值
                    startIndex = lastPosition1 + 1;
                    System.out.println("线程id：" + threadID + "真实下载的位置：" + lastPosition + "-------" + endIndex);

                    bufr.close();
                    fis.close();

                }

                conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);
                int code = conn.getResponseCode();
                if (code == 206) {
                    // 随机读写文件对象
                    RandomAccessFile raf = new RandomAccessFile(getFileName(path), "rw");
                    // 每个线程从自己的位置开始写

                    raf.seek(startIndex);
                    InputStream in = conn.getInputStream();
                    // 把数据写到文件中
                    int len = -1;
                    byte[] buffer = new byte[1024];
                    int totle = 0;// 代表当前线程下载的大小
                    while ((len = in.read(buffer)) != -1) {
                        raf.write(buffer, 0, len);
                        totle += len;

                        // 实现断点续传就是把当前线程下载的位置保存起来，下次再下载的时候按照上次下载的位置继续下载
                        int currentThreadPosition = startIndex + totle;// 存到一个txt文本中
                        // 用来存储当前线程当前下载的位置
                        RandomAccessFile raff = new RandomAccessFile(getFileName(path) + threadID + ".txt", "rwd");
                        raff.write(String.valueOf(currentThreadPosition).getBytes());
                        raff.close();

                        //设置进度条当前的进度
                        pbList.get(threadID).setMax(PbMaxSize);
                        pbList.get(threadID).setProgress(pblastPosition + totle);
                    }
                    raf.close();
                    System.out.println("线程ID:" + threadID + "下载完成");
                    // 将产生的txt文件删除，每个线程下载完成的具体时间不知道
                    synchronized (DownLoadThread.class) {
                        runningThread--;
                        if (runningThread == 0) {
                            //说明线程执行完毕
                            for (int i = 0; i < threadCount; i++) {

                                File filedel = new File(getFileName(path) + i + ".txt");
                                filedel.delete();
                            }

                        }

                    }

                }
            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }
    }

    public String getFileName(String path) {
        int start = path.lastIndexOf("/") + 1;
        String subString = path.substring(start);
        String fileName = "/data/data/com.lgqrlchinese.heima76android_11_mutildownload/" + subString;
        return fileName;

    }
}

在清单文件中添加以下权限

    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

笔记结束

bug非常多，而且谁又愿意写这么繁琐的逻辑，所以找到别人写开源框架，下一篇将会作下笔记