Android&MyDownload

com.zachary.download:

package com.zachary.download;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.zachary.utils.HttpDownloader;

public class Download extends Activity {
    private Button downloadTxtButton = null;
    private Button downloadMp3Button = null;
    private EditText myEditText = null;
    private TextView myTextView = null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_download);
        downloadTxtButton = (Button)findViewById(R.id.downloadTxtButton);
        downloadMp3Button = (Button)findViewById(R.id.downloadMp3Button);
        myEditText = (EditText)findViewById(R.id.myEditText);
        myTextView = (TextView)findViewById(R.id.myTextView);
        downloadTxtButton.setOnClickListener(new OnClickListener(){

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                String urlStr = myEditText.getText().toString();
                Toast.makeText(Download.this, "Begin to read the file", Toast.LENGTH_LONG).show();
                HttpDownloader myHttpDownloader = new HttpDownloader();
                String txt = myHttpDownloader.download(urlStr);
                Toast.makeText(Download.this, "Download the file", Toast.LENGTH_LONG).show();                
                myTextView.setText(txt);
            }
            
        });
        
        downloadMp3Button.setOnClickListener(new OnClickListener(){

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                String urlStr = myEditText.getText().toString();
                HttpDownloader myHttpDownloader = new HttpDownloader();
                if(myHttpDownloader.downFile(urlStr, "myDownload/","a.mp3") == 0)
                    myTextView.setText("Success!!!");
                else myTextView.setText("Oh,No!");
            }
            
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.download, menu);
        return true;
    }

}

com.zachary.utils:

package com.zachary.utils;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import android.os.Environment;

public class FileUtils {
    private String SDPATH;
    
    public String getSDPATH(){
        return SDPATH;
    }
    public FileUtils(){
        SDPATH = Environment.getExternalStorageDirectory() + "/";
    }
    
    /**
     * Create the file named filename on the SDCard
     * @param filename
     * @return
     * @throws IOException
     */
    public File creatSDFile(String filename)    throws IOException{
        File file = new File(SDPATH + filename);
        file.createNewFile();
        return file;
    }
    
    /**
     * Creat the dir from the dirName
     * @param dirName
     * @return    the File
     */
    public File creatSDDir(String dirName){
        File dir = new File(SDPATH + dirName);
        dir.mkdir();
        return dir;
    }
    
    public boolean isFileExist(String fileName){
        File file = new File(SDPATH + fileName);
        return file.exists();
    }
    
    public File write2SDFromInput(String path, String fileName, InputStream input){
        File file = null;
        OutputStream output = null;
        
        try {
            creatSDDir(path);
            file = creatSDFile(path + fileName);
            output = new FileOutputStream(file);
            byte buffer[] = new byte[4 * 1024];
            while((input.read(buffer)) != -1)
                output.write(buffer);
            output.flush();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        finally{
            try {
                output.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return file;
    }
}

package com.zachary.utils;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;


public class HttpDownloader {
    private URL url = null;
    
    /**
     * Using the URL to download the file of txt, and the return is the content of the file
     * @param urlStr
     * @return    
     */
    public String  download(String urlStr){
        StringBuffer sb = new StringBuffer();
        String line = null;
        BufferedReader buffer = null;
        try {
            url = new URL(urlStr);
            HttpURLConnection urlConn = (HttpURLConnection)url.openConnection();
            
            //在此使用了一种叫做装饰者的设计模式
            //InputStream one Byte one times
            //InputStreamReader one Char one times
            //BufferedReader one line one times
            buffer = new BufferedReader(new InputStreamReader(urlConn.getInputStream()));
            while((line = buffer.readLine())!=null)
                sb.append(line);
        
            
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            try {
                buffer.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return sb.toString();
    }
    
    /**
     * @param urlStr
     * @param path
     * @param fileName
     * @return    -1:the file has an error; 0:the file has downloaded; 1:the file has exited 
     */
    public int downFile(String urlStr, String path, String fileName){
        InputStream inputStream = null;
        FileUtils fileUtils = new FileUtils();
        if(fileUtils.isFileExist(path + fileName))
            return 1;
        else {
            try {
                inputStream = getInputStreamFromUrl(urlStr);
                File resultFile = fileUtils.write2SDFromInput(path ,fileName, inputStream);
                if(resultFile == null)
                    return -1;
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                return -1;
            }finally{
                try {
                    inputStream.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
        return 0; 
    }
    public InputStream getInputStreamFromUrl(String urlStr) throws IOException{
        url =new URL(urlStr);
        HttpURLConnection urlConn = (HttpURLConnection)url.openConnection();
        InputStream inputStream = urlConn.getInputStream();
        return inputStream;
    }
}

<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: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=".Download"
    android:orientation="vertical" >

    <EditText
        android:id="@+id/myEditText"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:hint="Please enter the URL" />
    <Button
        android:id="@+id/downloadTxtButton"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Download Txt"/>
    <Button
        android:id="@+id/downloadMp3Button"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Download Mp3"/>"
    <TextView
        android:id="@+id/myTextView"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Something about download"/>
</LinearLayout>

另外，AndroidManifest.xml：加入以下权限

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

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