android断点下载并显示进度，关于handler，和主线程不能联网采取子线程联网下载，和多线程下载学习

package cn.multidownload;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

import connectservice.ConnectStream;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
import android.os.Build;

public class MainActivity extends ActionBarActivity {
	private EditText ed_address;
	@SuppressWarnings("unused")
	private Button bt_download;
	private ProgressBar probar;
	private TextView tv_v;
	public  int totalsize;
	private int cout=0;
	public Handler handler=new Handler(){

		@Override
		public void handleMessage(Message msg) {
			// TODO Auto-generated method stub
				Object pro=msg.obj;
				if(pro instanceof Integer)
				{
				probar.setProgress((Integer) pro);
				tv_v.setText("已完成："+pro+"%");
				}
				if(pro instanceof String)
				{
					Toast.makeText(MainActivity.this, " 文件已存在", Toast.LENGTH_SHORT).show();
				}
			super.handleMessage(msg);
		}
		
	};
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ed_address=(EditText) findViewById(R.id.ed_address);
        bt_download=(Button) findViewById(R.id.bt_download);
        probar=(ProgressBar) findViewById(R.id.progressBar1);
        tv_v=(TextView) findViewById(R.id.tv_pro);
        probar.setMax(100);
        
        
    }

    public void download(View v) throws FileNotFoundException
    {
    	String st=ed_address.getText().toString();
    	if(st.equals(""))
    	{
    		Toast.makeText(this, "地址不能为空！", Toast.LENGTH_SHORT).show();
    		return;
    	}
    	Thread front=new Thread(new FrontDown());
    	try {
    		front.start();
			front.join();
			
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
    	
    	int numberthread=3;
    	
    	for(int id=1;id<=numberthread;id++)
    	{
    		new Thread(new Down(id,numberthread)).start();
    	}
    	
    	
    }

    
    
    
    class FrontDown implements Runnable
    {

		@Override
		public void run() {
			// TODO Auto-generated method stub
			try{
		    	String st=ed_address.getText().toString();
		     	URL url=new URL(st);
				HttpURLConnection con=(HttpURLConnection) url.openConnection();
				con.setConnectTimeout(5000);
				totalsize=con.getContentLength();
				System.out.println(totalsize);
		    	}catch(Exception e)
		    	{
		    	}
		}
    	
    }
    
    
 class Down implements Runnable
 {
	 private int startposition;
	 private int endposition;
	 private int threadId;
	 private int numberofthread;
	 
	 public Down(int threadId,int numberofthread)
	 {
		 this.threadId=threadId;
		 this.numberofthread=numberofthread;
	 }
	 
	 public void setposition()
	 {
		 int blocksize=totalsize/numberofthread;
		 this.startposition=(threadId-1)*blocksize;
		 if(threadId==numberofthread)
			 this. endposition=totalsize;
		 else
		 this.endposition=this.startposition+blocksize-1;
	 }
	
		public void run() 
		{
			String address=ed_address.getText().toString();
			int d=address.lastIndexOf("/");
	    	String name=address.substring(d, address.length());
	    	File f=new File(Environment.getDataDirectory(), name);
			
			try {
				
					setposition();
					System.out.println(startposition+ "       "+endposition);
				 	URL url=new URL(address);
					HttpURLConnection con=(HttpURLConnection) url.openConnection();
					con.setRequestProperty("Range", "bytes="+(this.startposition)+"-"+this.endposition);
					con.setConnectTimeout(5000);
					con.setRequestMethod("GET");
					InputStream input=con.getInputStream();
					
				RandomAccessFile output=new RandomAccessFile(f,"rwd");
				output.seek(startposition);
				int len=-1;
				byte[] buf=new byte[1024];
						while((len=input.read(buf))!=-1)
						{
							output.write(buf,0,len);
							synchronized(MainActivity.class){
							cout+=len;
							Message  msg=new Message ();
							msg.obj=(cout*100)/totalsize;
							handler.sendMessage(msg);
							}
						}
						output.close();
						input.close();
						System.out.println(threadId+"下载完成");
						
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			
		}
}
    

}

　　xml文件

<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android1="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffff00"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="cn.multidownload.MainActivity$PlaceholderFragment" >
    
 <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:lines="2"
        android:text="http://tomcat.apache.org/images/tomcat.png" 
        android:id="@+id/ed_address"/>
 
 
 
 <Button
     	android:layout_below="@+id/ed_address"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Download：" 
        android:onClick="download"
        android:id="@+id/bt_download"
        />

 <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/progressBar1"
       	android:text="已完成："
       	android:textSize="10dp"
        android:id="@+id/tv_pro"
        
        />
 <ProgressBar
     android1:id="@+id/progressBar1"
     style="?android:attr/progressBarStyleHorizontal"
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"
     android:layout_alignLeft="@+id/bt_download"
     android:layout_below="@+id/bt_download"
     android:layout_marginLeft="20dp"
     android:layout_marginTop="32dp" />
 
</RelativeLayout>

　　其中清单文件一定要配置网络权限。