1.导入依赖
compile 'com.loopj.android:android-async-http:1.4.9'
2.导入权限
<uses-permission android:name="android.permission.INTERNET"></uses-permission><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />3.布局文件
<?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="下载" android:id="@+id/bt_download" /> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="暂停" android:id="@+id/bt_pause" /></LinearLayout>4.主要代码
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"; //下载线程的数量 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; //显示进度和更新进度 private Handler mHandler = new Handler(){ public void handleMessage(android.os.Message msg) { switch (msg.what) { case SET_MAX://设置进度条的最大值 int filelength = msg.arg1; pb.setMax(filelength); break; case UPDATE_VIEW://更新进度条 和 下载的比率 int len = msg.arg1;//新下载的长度 pb.setProgress(pb.getProgress()+len);//设置进度条的刻度 int max = pb.getMax();//获取进度的最大值 int progress = pb.getProgress();//获取已经下载的数据量 // 下载：30 总：100 int result = (progress*100)/max; tv_info.setText("下载:"+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); //数据的回显 //确定下载的文件 String name = getFileName(uri); File file = new File(Environment.getExternalStorageDirectory(), name); if (file.exists()){//文件存在回显 //获取文件的大小 int filelength = (int) file.length(); pb.setMax(filelength); try { //统计原来所有的下载量 int count = 0; //读取下载记录文件 for (int threadid = 0; threadid < threadsize; threadid++) { //获取原来指定线程的下载记录 int existDownloadLength = readDownloadInfo(threadid); count = count + existDownloadLength; } //设置进度条的刻度 pb.setProgress(count); //计算比率 int result = (count * 100) / filelength; tv_info.setText("下载:" + 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); } }); } //暂停 private boolean flag = false;//是否在下载 public void pause(View v){ flag = false; bt_download.setEnabled(true); bt_pause.setEnabled(false); } //下载 public void download(View v){ flag = true; //是在下载 bt_download.setEnabled(false);//一点击变成不可点击 bt_pause.setEnabled(true);//一点击变成可点击 new Thread(){//子线程 public void run() { try { //获取服务器上文件的大小 HttpClient client = new DefaultHttpClient(); HttpHead request = new HttpHead(uri); HttpResponse response = client.execute(request); //response 只有响应头 没有响应体 if(response.getStatusLine().getStatusCode() == 200){ Header[] headers = response.getHeaders("Content-Length"); String value = headers[0].getValue(); //文件大小 int filelength = Integer.parseInt(value); Log.i(TAG, "filelength:"+filelength); //设置进度条的最大值 Message msg_setmax = Message.obtain(mHandler, SET_MAX, filelength, 0); msg_setmax.sendToTarget(); //处理下载记录文件 for(int threadid=0;threadid<threadsize;threadid++){ //对应的下载记录文件 File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt"); //判断文件是否存在 if(!file.exists()){ //创建文件 file.createNewFile(); } } //在sdcard创建和服务器大小一样的文件 String name = getFileName(uri); File file = new File(Environment.getExternalStorageDirectory(),name); //随机访问文件 RandomAccessFile raf = new RandomAccessFile(file, "rwd"); //设置文件的大小 raf.setLength(filelength); //关闭 raf.close(); //计算每条线程的下载量 int block = (filelength%threadsize == 0)?(filelength/threadsize):(filelength/threadsize+1); //开启三条线程执行下载 for(int threadid=0;threadid<threadsize;threadid++){ new DownloadThread(threadid, uri, file, block).start(); } } } catch (Exception e) { e.printStackTrace(); } }; }.start(); } //线程下载类 private class DownloadThread extends Thread{ private int threadid;//线程的id private String uri;//下载的地址 private File file;//下载文件 private int block;//下载的块 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; //计算下载的开始位置和结束位置 start = threadid * block; end = (threadid + 1)*block -1; try { //读取该条线程原来的下载记录 int existDownloadLength = readDownloadInfo(threadid); //修改下载的开始位置 从新下载 start = start + existDownloadLength; } catch (Exception e) { e.printStackTrace(); } } //下载 状态码：200是普通的下载 206是分段下载 Range:范围 @Override public void run() { super.run(); try { RandomAccessFile raf = new RandomAccessFile(file, "rwd"); //跳转到起始位置 raf.seek(start); //分段下载 HttpClient client = new DefaultHttpClient(); HttpGet request = new HttpGet(uri); request.addHeader("Range", "bytes:"+start+"-"+end);//添加请求头 HttpResponse response = client.execute(request); if(response.getStatusLine().getStatusCode() == 200){ InputStream inputStream = response.getEntity().getContent(); //把流写入到文件 byte[] buffer = new byte[1024]; int len = 0; while((len = inputStream.read(buffer)) != -1){ //如果暂停下载 点击暂停 false 就直接return 点击下载true接着下载 if(!flag){ return;//标准线程结束 } //写数据 raf.write(buffer, 0, len); //读取原来下载的数据量 这里读取是为了更新下载记录 int existDownloadLength = readDownloadInfo(threadid);//原来下载的数据量 //计算最新的下载 int newDownloadLength = existDownloadLength + len; //更新下载记录 从新记录最新下载位置 updateDownloadInfo(threadid, newDownloadLength); //更新进度条的显示 下载的百分比 Message update_msg = Message.obtain(mHandler, UPDATE_VIEW, len, 0); update_msg.sendToTarget(); //模拟 看到进度条动的效果 SystemClock.sleep(50); } inputStream.close(); raf.close(); Log.i(TAG, "第"+threadid+"条线程下载完成"); } } catch (Exception e) { e.printStackTrace(); } } } /** * 读取指定线程的下载数据量 * @param threadid 线程的id * @return * @throws Exception */ public int readDownloadInfo(int threadid) throws Exception{ //下载记录文件 File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt"); BufferedReader br = new BufferedReader(new FileReader(file)); //读取一行数据 String content = br.readLine(); int downlength = 0; //如果该文件第一次创建去执行读取操作 文件里面的内容是 null if(!TextUtils.isEmpty(content)){ downlength = Integer.parseInt(content); } //关闭流 br.close(); return downlength; } /** * 更新下载记录 * @param threadid * @param newDownloadLength */ public void updateDownloadInfo(int threadid,int newDownloadLength) throws Exception{ //下载记录文件 File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt"); FileWriter fw = new FileWriter(file); fw.write(newDownloadLength+""); fw.close(); } /** * 获取文件的名称 * @param uri * @return */ private String getFileName(String uri){ return uri.substring(uri.lastIndexOf("/")+1); }}