Android中级篇之多线程下载

Android中级篇之多线程下载

2011-06-05 15:50:49

要是先多线程下载，则必须对同一个文件可任意位置的写入 ，java中提供这样一个类可任意写入RandomAccessFile 。通过多线程，可将文件分割成多个子断，每一个线程只需下载一段文件即可。实现效果如图：

下面看代码部分：

1.布局文件 main.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="下载路径" /> <EditText android:id="@+id/mEditText" android:layout_width="fill_parent" android:layout_height="wrap_content" android:singleLine="true" android:text="http://android.yesky.com/uploads/attachments/2010-04/27/a5964152.jpg"/> <ProgressBar android:id="@+id/mBar" android:layout_width="fill_parent" android:layout_height="wrap_content" android:visibility="invisible" style="?android:attr/progressBarStyleHorizontal"/> <Button android:id="@+id/mButton" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="下载"/> </LinearLayout>

2.下载工具类 Download.java

package com.yin.downloader.utils; 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 android.content.Context; import android.util.Log; public class Download { private String SDPath = null; private static final String TAG = "com.yin.download"; private RandomAccessFile randomFile = null; private URL url; private Context context; private String urlStr; private String fileName; private int fileSize; private int totalReadSize; public Download(String urlStr,String fileName,String SDPath,Context context){ this.context = context; this.fileName = fileName; this.urlStr = urlStr; this.SDPath = SDPath; } public void downloadFile(){ try { File file = new File(SDPath+fileName); url = new URL(urlStr); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); //获得下载文件的大小 fileSize = conn.getContentLength(); //设置线程的大小，考虑手机的性能，并不是越大越好 int threadSize = 3; //每个线程下载文件+的部分大小 +1 避免文件下载不完全 int block = fileSize / threadSize +1; for(int i=0;i<3;i++){ int startPosition = i * block; //创建可任意位置读取的文件 randomFile = new RandomAccessFile(file, "rw"); randomFile.seek(startPosition); new DownloadThread(i+1, startPosition, block, randomFile).start(); } } catch (MalformedURLException e) { Log.e(TAG, "MalformedURLException"); e.printStackTrace(); } catch (IOException e) { Log.e(TAG, "IOException"); e.printStackTrace(); } } //下载文件的线程 private class DownloadThread extends Thread{ private int threadID; private int startPosition; private int block; private RandomAccessFile randomFile; public DownloadThread(int threadID, int startPosition, int block, RandomAccessFile randomFile) { super(); this.threadID = threadID; this.startPosition = startPosition; this.block = block; this.randomFile = randomFile; } public void run() { try { HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); //文件下载位置 规定的格式 “byte=xxxx-” String start = "bytes="+startPosition + "-"; //设置文件开始的下载位置 conn.setRequestProperty("Range", start); InputStream is = conn.getInputStream(); byte[] buffer = new byte[4*1024]; int len = -1; int readFileSize = 0; while((readFileSize < block) && ((len = is.read(buffer)) != -1)){ randomFile.write(buffer,0,len); readFileSize += len ; totalReadSize += readFileSize; } System.out.println("线程 ："+threadID+" 下载完成"); is.close(); randomFile.close(); conn.disconnect(); } catch (IOException e) { Log.e(TAG+":child", "IOException"); e.printStackTrace(); } } } public int getFileSize() { return fileSize; } public void setFileSize(int fileSize) { this.fileSize = fileSize; } public int getTotalReadSize() { return totalReadSize; } public void setTotalReadSize(int totalReadSize) { this.totalReadSize = totalReadSize; } }

3.DownloadActivity.java

package com.yin.downloader; import java.util.Timer; import java.util.TimerTask; import android.app.Activity; import android.os.Bundle; import android.os.Environment; import android.os.Handler; import android.os.Message; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.ProgressBar; import android.widget.Toast; import com.yin.downloader.utils.Download; public class DownloadActivity extends Activity { public EditText mEditText; public ProgressBar mBar; public Button mButton; public String urlStr; public String fileName; public String SDPath = "/sdcard/"; public int fileSize; public int totalReadSize; Download download; public Handler handler = new Handler(){ @Override public void handleMessage(Message msg) { mBar.setProgress(download.getTotalReadSize()); mBar.invalidate(); } }; public Timer mTimer = new Timer(); public TimerTask mTask = new TimerTask() { @Override public void run() { Message msg = new Message(); handler.sendMessage(msg); } }; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mEditText = (EditText) findViewById(R.id.mEditText); mBar = (ProgressBar) findViewById(R.id.mBar); mButton = (Button) findViewById(R.id.mButton); mButton.setOnClickListener(new ClickEven()); fileName = "my.jpg"; //判断SDcard是否存在。 if(Environment.getExternalStorageState() == Environment.MEDIA_MOUNTED){ SDPath ="/sdcard/"; }else{ Toast.makeText(this, "SDcard不存在", Toast.LENGTH_LONG).show(); } } private class ClickEven implements OnClickListener{ public void onClick(View v) { urlStr = mEditText.getText().toString(); mBar.setVisibility(View.VISIBLE); download = new Download(urlStr,fileName,SDPath,DownloadActivity.this); download.downloadFile(); //将progressbar的大小设置为下载文件大小 mBar.setMax(download.getFileSize()); //定时刷新 mTimer.schedule(mTask, 0, 200); } } }

此例实现比较简单，还可以加入断点续传的功能，把程序停止时当前线程现在的位置存入数据库中，再次下载时从数据库中取出即可；