斷點續傳

1.匯入依賴

compile 'com.loopj.android:android-async-http:1.4.9'

2.匯入許可權

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

3.佈局檔案

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.five.fashion.duandianxuchuan.MainActivity">
<ProgressBar
    style="@style/Widget.AppCompat.ProgressBar.Horizontal"
    android:layout_width="match_parent"
    android:layout_height="100dp"
    android:id="@+id/pb"
    />
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/tv_info"
    />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="下載"
        android:id="@+id/bt_download"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="暫停"
        android:id="@+id/bt_pause"
        />
</LinearLayout>
4.主要程式碼

package com.five.fashion.duandianxuchuan;

import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.os.SystemClock;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;

import com.loopj.android.http.HttpGet;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.RandomAccessFile;

import cz.msebera.android.httpclient.Header;
import cz.msebera.android.httpclient.HttpResponse;
import cz.msebera.android.httpclient.client.HttpClient;
import cz.msebera.android.httpclient.client.methods.HttpHead;
import cz.msebera.android.httpclient.impl.client.DefaultHttpClient;


public class MainActivity extends AppCompatActivity {
    protected static final String TAG = "OtherActivity";
    //下載執行緒的數量
    private final static int threadsize = 3;
    protected static final int SET_MAX = 0;
    public static final int UPDATE_VIEW = 1;
    private ProgressBar pb;
    private Button bt_download;
    private Button bt_pause;
    private TextView tv_info;
    //顯示進度和更新進度
    private Handler mHandler = new Handler(){
        public void handleMessage(android.os.Message msg) {
            switch (msg.what) {
                case SET_MAX://設定進度條的最大值
                    int filelength = msg.arg1;
                    pb.setMax(filelength);
                    break;
                case UPDATE_VIEW://更新進度條  和 下載的比率
                    int len = msg.arg1;//新下載的長度
                    pb.setProgress(pb.getProgress()+len);//設定進度條的刻度

                    int max = pb.getMax();//獲取進度的最大值
                    int progress = pb.getProgress();//獲取已經下載的資料量
                    //  下載：30    總：100
                    int result = (progress*100)/max;

                    tv_info.setText("下載:"+result+"%");

                    break;

                default:
                    break;
            }
        };
    };
    String uri = "http://c.hiphotos.baidu.com/image/pic/item/b90e7bec54e736d1e51217c292504fc2d46269f3.jpg";
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
       //找到控制元件
        pb = (ProgressBar) findViewById(R.id.pb);
        tv_info = (TextView) findViewById(R.id.tv_info);
        bt_download = (Button) findViewById(R.id.bt_download);
        bt_pause = (Button) findViewById(R.id.bt_pause);
        //資料的回顯
        //確定下載的檔案
        String name = getFileName(uri);
        File file = new File(Environment.getExternalStorageDirectory(), name);
        if (file.exists()){//檔案存在回顯
            //獲取檔案的大小
            int filelength = (int) file.length();
            pb.setMax(filelength);
            try {
                //統計原來所有的下載量
                int count = 0;
                //讀取下載記錄檔案
                for (int threadid = 0; threadid < threadsize; threadid++) {
                    //獲取原來指定執行緒的下載記錄
                    int existDownloadLength = readDownloadInfo(threadid);
                    count = count + existDownloadLength;
                }
                //設定進度條的刻度
                pb.setProgress(count);

                //計算比率
                int result = (count * 100) / filelength;
                tv_info.setText("下載:" + result + "%");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        bt_download.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                download(v);
            }
        });
        bt_pause.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                pause(v);
            }
        });
    }
    //暫停
    private boolean flag = false;//是否在下載

    public void pause(View v){
        flag = false;
        bt_download.setEnabled(true);
        bt_pause.setEnabled(false);
    }

    //下載
    public void download(View v){
        flag = true; //是在下載
        bt_download.setEnabled(false);//一點選變成不可點選
        bt_pause.setEnabled(true);//一點選變成可點選
        new Thread(){//子執行緒
            public void run() {
                try {
                    //獲取伺服器上檔案的大小
                    HttpClient client = new DefaultHttpClient();
                    HttpHead request = new HttpHead(uri);
                    HttpResponse response = client.execute(request);
                    //response  只有響應頭  沒有響應體
                    if(response.getStatusLine().getStatusCode() == 200){
                        Header[] headers = response.getHeaders("Content-Length");
                        String value = headers[0].getValue();
                        //檔案大小
                        int filelength = Integer.parseInt(value);
                        Log.i(TAG, "filelength:"+filelength);

                        //設定進度條的最大值
                        Message msg_setmax = Message.obtain(mHandler, SET_MAX, filelength, 0);
                        msg_setmax.sendToTarget();


                        //處理下載記錄檔案
                        for(int threadid=0;threadid<threadsize;threadid++){
                            //對應的下載記錄檔案
                            File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
                            //判斷檔案是否存在
                            if(!file.exists()){
                                //建立檔案
                                file.createNewFile();
                            }
                        }

                        //在sdcard建立和伺服器大小一樣的檔案
                        String name = getFileName(uri);
                        File file = new File(Environment.getExternalStorageDirectory(),name);
                        //隨機訪問檔案
                        RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                        //設定檔案的大小
                        raf.setLength(filelength);
                        //關閉
                        raf.close();

                        //計算每條執行緒的下載量
                        int block = (filelength%threadsize == 0)?(filelength/threadsize):(filelength/threadsize+1);
                        //開啟三條執行緒執行下載
                        for(int threadid=0;threadid<threadsize;threadid++){
                            new DownloadThread(threadid, uri, file, block).start();
                        }
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            };
        }.start();
    }


    //執行緒下載類
    private class DownloadThread extends Thread{
        private int threadid;//執行緒的id
        private String uri;//下載的地址
        private File file;//下載檔案
        private int block;//下載的塊
        private int start;
        private int end;

        public DownloadThread(int threadid, String uri, File file, int block) {
            super();
            this.threadid = threadid;
            this.uri = uri;
            this.file = file;
            this.block = block;
            //計算下載的開始位置和結束位置
            start = threadid * block;
            end = (threadid + 1)*block -1;

            try {
                //讀取該條執行緒原來的下載記錄
                int existDownloadLength = readDownloadInfo(threadid);

                //修改下載的開始位置   從新下載
                start = start + existDownloadLength;
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        //下載   狀態碼：200是普通的下載      206是分段下載        Range:範圍
        @Override
        public void run() {
            super.run();
            try {
                RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                //跳轉到起始位置
                raf.seek(start);

                //分段下載
                HttpClient client = new DefaultHttpClient();
                HttpGet request = new HttpGet(uri);
                request.addHeader("Range", "bytes:"+start+"-"+end);//新增請求頭
                HttpResponse response = client.execute(request);
                if(response.getStatusLine().getStatusCode() == 200){
                    InputStream inputStream = response.getEntity().getContent();
                    //把流寫入到檔案
                    byte[] buffer = new byte[1024];
                    int len = 0;
                    while((len = inputStream.read(buffer)) != -1){
                        //如果暫停下載  點選暫停 false 就直接return 點選下載true接著下載
                        if(!flag){
                            return;//標準執行緒結束
                        }
                        //寫資料
                        raf.write(buffer, 0, len);

                        //讀取原來下載的資料量 這裡讀取是為了更新下載記錄
                        int existDownloadLength = readDownloadInfo(threadid);//原來下載的資料量

                        //計算最新的下載
                        int newDownloadLength = existDownloadLength + len;

                        //更新下載記錄 從新記錄最新下載位置
                        updateDownloadInfo(threadid, newDownloadLength);
                        //更新進度條的顯示   下載的百分比
                        Message update_msg = Message.obtain(mHandler, UPDATE_VIEW, len, 0);
                        update_msg.sendToTarget();
                        //模擬  看到進度條動的效果
                        SystemClock.sleep(50);
                    }
                    inputStream.close();
                    raf.close();
                    Log.i(TAG, "第"+threadid+"條執行緒下載完成");
                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }


    /**
     * 讀取指定執行緒的下載資料量
     * @param threadid  執行緒的id
     * @return
     * @throws Exception
     */
    public int readDownloadInfo(int threadid) throws Exception{
        //下載記錄檔案
        File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
        BufferedReader br = new BufferedReader(new FileReader(file));
        //讀取一行資料
        String content = br.readLine();

        int downlength = 0;
        //如果該檔案第一次建立去執行讀取操作  檔案裡面的內容是 null
        if(!TextUtils.isEmpty(content)){
            downlength = Integer.parseInt(content);
        }
        //關閉流
        br.close();
        return downlength;
    }


    /**
     * 更新下載記錄
     * @param threadid
     * @param newDownloadLength
     */
    public void updateDownloadInfo(int threadid,int newDownloadLength) throws Exception{
        //下載記錄檔案
        File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
        FileWriter fw = new FileWriter(file);
        fw.write(newDownloadLength+"");
        fw.close();
    }

    /**
     * 獲取檔案的名稱
     * @param uri
     * @return
     */
    private String getFileName(String uri){
        return uri.substring(uri.lastIndexOf("/")+1);
    }

}