多线程加载

来源：互联网发布：python 读取文件名编辑：程序博客网时间：2024/06/15 05:24

========================导依赖加权限======================

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

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

============================布局=========================

<LinearLayout    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"    android:orientation="vertical"   ><TextView    android:id="@+id/tv_path"    android:text="多线程下载地址"    android:layout_width="match_parent"    android:layout_marginTop="50dp"    android:layout_height="wrap_content"/>    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:onClick="download"        android:text="下载" /></LinearLayout>

==========================逻辑代码========================

public class MainActivity extends AppCompatActivity {    protected static final String TAG = "MainActivity";    //下载线程的数量    private final static int threadsize = 3;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);    }    public void download(View v){        new Thread(){            public void run() {                try {                     //创建HttpClient对象                    HttpClient client = new DefaultHttpClient();                    //http://c.hiphotos.baidu.com/image/pic/item/b90e7bec54e736d1e51217c292504fc2d46269f3.jpg                    //https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1495040157701&di=e75c9d745a6af178d07e3e3b78e3cb3b&imgtype=0&src=http%3A%2F%2Fimg.pconline.com.cn%2Fimages%2Fupload%2Fupc%2Ftx%2Fwallpaper%2F1502%2F03%2Fc0%2F2703334_1422958313278_800x600.jpg                    //String uri = "http://c.hiphotos.baidu.com/image/pic/item/b90e7bec54e736d1e51217c292504fc2d46269f3.jpg";                     String uri="http://wx1.sinaimg.cn/mw690/005RzqMsly1fia3omupu1j31900y27wh.jpg";                   //从头信息里获取文件大小 不获取内容                    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){                        //从响应头里获取长度                        Header[] headers = response.getHeaders("Content-Length");                        String value = headers[0].getValue();                        //一 获取服务器上文件的大小                        int filelength = Integer.parseInt(value);                        Log.i(TAG, "filelength:"+filelength);                        //二 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;        }        //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);                //分段下载真实内容                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){                        //写数据                        raf.write(buffer, 0, len);                    }                    inputStream.close();                    raf.close();                    Log.i(TAG, "第"+threadid+"条线程下载完成");                }            } catch (Exception e) {                e.printStackTrace();            }        }    }    private String getFileName(String uri){        return uri.substring(uri.lastIndexOf("/")+1);    }}

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