Android多线程断点续传

Android

多线程下载，

就是将服务器上的文件分为几段，然后去分段下载，然后用RandomAccessFile这个类将文件组合到一起。

断点续传

就是把已经下载的文件进度保存起来，再次下载的时候就继续下载。

具体代码：

package demand.example.tyhj.download;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.Toast;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
public class MainActivity extends AppCompatActivity {
    EditText editText;
    Button button;
    ProgressBar progressBar;
    //文件长度
    private int leanth;
    //下载进度
    private int total = 0;
    //下载地址
    private URL url;
    //下载的文件
    private File file;
    //开始或者暂停下载
    private boolean downLoading;
    //用于保存下载线程（每段为一个线程）
    private List<HashMap<String, Integer>> threadList;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        threadList = new ArrayList<>();
        editText = (EditText) findViewById(R.id.fileUrl);
        button = (Button) findViewById(R.id.btn_download);
        progressBar = (ProgressBar) findViewById(R.id.progressBar);
        //editText.setText("http://192.168.31.215:8080/Download/downLoadFile/move.mp4");
        progressBar.setProgress(0);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (downLoading) {
                    downLoading = false;
                    button.setText("开始");
                    return;
                }
                downLoading = true;
                button.setText("暂停");
                if (threadList.size() == 0) {
                    //之前没有开始下载文件
                    new Thread(new Runnable() {
                        @Override
                        public void run() {
                            try {
                                url = new URL(editText.getText().toString());
                                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                                connection.setRequestMethod("GET");
                                connection.setConnectTimeout(500);
                                //获取文件的大小
                                leanth = connection.getContentLength();
                                Log.e("开始长度：",leanth+"");
                                //设置进度条的长度
                                progressBar.setMax(leanth/1024);
                                //文件不存在
                                if (leanth < 0) {
                                    handler.obtainMessage(1, 0, 0).sendToTarget();
                                    return;
                                }
                                //保存文件地址
                                file = new File(Environment.getExternalStorageDirectory(), getName(editText.getText().toString()));
                                //设置分割下载的文件
                                RandomAccessFile random = new RandomAccessFile(file, "rw");
                                random.setLength(leanth);
                                //分为三段下载
                                int blockSize = leanth / 3;
                                for (int i = 0; i < 3; i++) {
                                    int begin = i * blockSize;
                                    int end = (i + 1) * blockSize;
                                    if (i == 2)
                                        end = leanth;
                                    //设置每段下载的长度
                                    HashMap<String, Integer> map = new HashMap<String, Integer>();
                                    map.put("begin", begin);
                                    map.put("end", end);
                                    map.put("finished", 0);
                                    threadList.add(map);
                                    //创建线程下载文件
                                    Thread t = new Thread(new Download(begin, end, file, url, i));
                                    t.start();
                                }
                            } catch (MalformedURLException e) {
                                Toast.makeText(MainActivity.this, "Url错误", Toast.LENGTH_SHORT).show();
                                e.printStackTrace();
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                        }
                    }).start();
                } else {
                    //恢复下载
                    for (int i = 0; i < threadList.size(); i++) {
                        HashMap<String, Integer> map = threadList.get(i);
                        int begin = map.get("begin");
                        int end = map.get("end");
                        int finished = map.get("finished");
                        Thread t = new Thread(new Download(begin + finished, end, file, url, i));
                        t.start();
                    }
                }
            }
        });
    }
    //获取现在文件的名字
    private String getName(String url) {
        return url.substring(url.lastIndexOf("/") + 1, url.length());
    }
    //下载类
    class Download implements Runnable {
        private int begin;
        private int end;
        private File file;
        private URL url;
        private int id;
        public Download(int begin, int end, File file, URL url, int id) {
            this.begin = begin;
            this.end = end;
            this.file = file;
            this.url = url;
            this.id = id;
        }
        @Override
        public void run() {
            try {
                //判断是否下载完成
                if (begin > end)
                    return;
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.setRequestMethod("GET");
                connection.setConnectTimeout(500);
                //设置需要下载的位置
                connection.setRequestProperty("Range", "bytes=" + begin + "-" + end);
                InputStream is = connection.getInputStream();
                byte[] buff = new byte[1024 * 1024];
                RandomAccessFile accessFile = new RandomAccessFile(file, "rw");
                //设置写入文件的位置
                accessFile.seek(begin);
                int len = 0;
                HashMap<String, Integer> map = threadList.get(id);
                //开始下载
                while ((len = is.read(buff)) != -1&&downLoading) {
                    accessFile.write(buff, 0, len);
                    //更新总下载进度
                    updateProgress(len);
                    //更新每段的下载进度
                    map.put("finished", map.get("finished") + len);
                }
                is.close();
                accessFile.close();
            } catch (IOException e) {
                handler.sendEmptyMessage(1);
                e.printStackTrace();
            }
        }
    }
    //更新总下载进度
    synchronized private void updateProgress(int add) {
        total += add;
        handler.obtainMessage(0, total, 0).sendToTarget();
    }
    Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if (msg.what == 0) {
                //更新UI
                progressBar.setProgress(msg.arg1/1024);
                Log.e("长度：",msg.arg1+"");
                if (msg.arg1 >= leanth)
                    Toast.makeText(MainActivity.this, "下载完成", Toast.LENGTH_SHORT).show();
            } else if (msg.what == 1) {
                Toast.makeText(MainActivity.this, "文件不存在", Toast.LENGTH_SHORT).show();
                downLoading = false;
                button.setText("开始");
            }
        }
    };
}