Android 多線程下載

 

package my.Thread; 

 

import java.io.BufferedInputStream; 

import java.io.RandomAccessFile; 

import java.net.HttpURLConnection; 

import java.net.URL; 

import java.net.URLConnection; 

import java.util.concurrent.CountDownLatch; 

 

 

import android.app.Activity; 

import android.os.Bundle; 

import android.os.Environment; 

import android.view.View; 

import android.view.View.OnClickListener; 

import android.widget.Button; 

import android.widget.TextView; 

 

public class ManyThreadActivity extends Activity { 

    /** Called when the activity is first created. */ 

     private Button button; 

     private TextView textView; 

     private static final int THREAD_COUNT = 4; 

     private CountDownLatch latch = new CountDownLatch(THREAD_COUNT); 

     private long completeLength = 0; 

     private long fileLength; 

     public static String SaveFile=Environment.getExternalStorageDirectory()+"/DownFile/"+"test.Mp3";   

     public static final String url="http://210.30.12.33:8080/mp3/Beyond.mp3"; 

    @Override 

    public void onCreate(Bundle savedInstanceState) { 

        super.onCreate(savedInstanceState); 

        setContentView(R.layout.main); 

        button=(Button)findViewById(R.id.button1); 

        textView=(TextView) findViewById(R.id.editText1); 

        textView.setText(url); 

        button.setOnClickListener(new MyListener()); 

    } 

    class MyListener implements OnClickListener{ 

 

        @Override 

        public void onClick(View v) { 

            // TODO Auto-generated method stub 

            try { 

                download(url); 

            } catch (Exception e) { 

                // TODO Auto-generated catch block 

                e.printStackTrace(); 

            } 

        } 

         

    } 

 

    //進行下載的線程 

    class DownloadThread extends Thread { 

        private URL url; 

        private RandomAccessFile file; 

        private long from; 

        private long end; 

 

        /**

         * @param url 下載的URL

         * @param file 下載完成之後儲存的檔案

         * @param from 當前線程對應檔案的起始位置

         * @param end 當前線程對應檔案的結束位置

         */ 

        DownloadThread(URL url, RandomAccessFile file, long from, long end) { 

            this.url = url; 

            this.file = file; 

            this.from = from; 

            this.end = end; 

        } 

 

        public void run() { 

            try { 

                long pos = from; 

                byte[] buf = new byte[1024*8]; 

 

                HttpURLConnection cn = (HttpURLConnection) url.openConnection(); 

                

                //佈建要求的起始和結束位置。 

                cn.setRequestProperty("Range", "bytes=" + from + "-" + end); 

 

                BufferedInputStream bis = new BufferedInputStream(cn.getInputStream()); 

                int len; 

                while ((len = bis.read(buf)) > 0) { 

                    synchronized (file) { 

                        file.seek(pos); 

                        file.write(buf, 0, len); 

                    } 

                    pos += len; 

                    completeLength += len; 

                    System.out.println(completeLength * 100 / fileLength + "%"); 

                } 

                cn.disconnect(); 

            } catch (Exception e) { 

                e.printStackTrace(); 

            } 

            latch.countDown(); 

        } 

    } 

 

    public void download(String address) throws Exception { 

        URL url = new URL(address); 

        URLConnection cn = url.openConnection(); 

        fileLength = cn.getContentLength(); 

        long packageLength = fileLength / THREAD_COUNT;//每個線程要下載的位元組數 

        long leftLength = fileLength % THREAD_COUNT;//剩下的位元組數 

        

        RandomAccessFile file = new RandomAccessFile(SaveFile, "rw"); 

        

        System.out.println(fileLength); 

        //計算每個線程請求的起始位置和結束位置。 

        /*

         * 第一個線程的起始位置是0~0+packageLength(每個線程要下載的位元組數)

         * 第二個線程的起始位置是endPos+1(第一個線程的packageLength+1)~endPos+1+packageLength

         * 第二個線程的起始位置是.........

         */ 

        long pos = 0; 

        for (int i = 0; i < THREAD_COUNT; i++) { 

            long endPos = pos + packageLength; 

            new DownloadThread(url, file, pos, endPos).start(); 

            if(leftLength > 0) { 

                endPos++; 

                leftLength--; 

            } 

            pos = endPos; 

        } 

        latch.await(); 

    } 

 

} 

 

儲存為test.mp3檔案

 

摘自 偉哥~ YZ