android中使用Http下载文件并保存到本地SD卡

1.AndroidMainfest.xml中设置权限

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

2.在FileUtils中封装将数据保存到SD卡的方法

package com.vino.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() {  
        //得到当前外部存储设备的目录  
        // /SDCARD  
        SDPATH = Environment.getExternalStorageDirectory() + "/";  
    }  
    /** 
     * 在SD卡上创建文件 
     *  
     * @throws IOException 
     */  
    public File creatSDFile(String fileName) throws IOException {  
        File file = new File(SDPATH + fileName);  
        file.createNewFile();  
        return file;  
    }  
      
    /** 
     * 在SD卡上创建目录 
     *  
     * @param dirName 
     */  
    public File creatSDDir(String dirName) {  
        File dir = new File(SDPATH + dirName);  
        dir.mkdir();  
        return dir;  
    }  
  
    /** 
     * 判断SD卡上的文件夹是否存在 
     */  
    public boolean isFileExist(String fileName){  
        File file = new File(SDPATH + fileName);  
        return file.exists();  
    }  
      
    /** 
     * 将一个InputStream里面的数据写入到SD卡中 
     */  
    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(Exception e){  
            e.printStackTrace();  
        }  
        finally{  
            try{  
                output.close();  
            }  
            catch(Exception e){  
                e.printStackTrace();  
            }  
        }  
        return file;  
    }
}

3.新建HttpDownloader,用于在MainActivity中调用FileUtils内的方法

package com.vino.utils;

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

public class HttpDownloader {

    private URL url=null;  
    FileUtils fileUtils=new FileUtils();  
    public int downfile(String urlStr,String path,String fileName)  
    {  
        if(fileUtils.isFileExist(path+fileName))  
            {return 1;}  
        else{  
          
        try {  
            InputStream input=null;  
            input = getInputStream(urlStr);  
            File resultFile=fileUtils.write2SDFromInput(path, fileName, input);  
            if(resultFile==null)  
            {  
                return -1;  
            }  
        } catch (IOException e) {  
            // TODO Auto-generated catch block  
            e.printStackTrace();  
        }  
          
        }  
        return 0;  
    }  
  //由于得到一个InputStream对象是所有文件处理前必须的操作，所以将这个操作封装成了一个方法  
       public InputStream getInputStream(String urlStr) throws IOException  
       {       
           InputStream is=null;  
            try {  
                url=new URL(urlStr);  
                HttpURLConnection urlConn=(HttpURLConnection)url.openConnection();  
                is=urlConn.getInputStream();  
                  
            } catch (MalformedURLException e) {  
                // TODO Auto-generated catch block  
                e.printStackTrace();  
            }  
              
            return is;  
       } 
}

4.在MainActivity中运行实例

package com.vino.download;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

import com.vino.utils.HttpDownloader;

public class MainActivity extends Activity {

    private Button button;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button)findViewById(R.id.button);
        button.setOnClickListener(new DownloadListener());
    }

    class DownloadListener implements OnClickListener{

        @Override
        public void onClick(View arg0) {
             
             Thread thread = new Thread(){
                 @Override
                 public void run(){
                     HttpDownloader httpDownLoader=new HttpDownloader();
                     httpDownLoader.downfile("http://192.168.0.102:8080/data/data.txt", "data/", "data.txt");  
//使用Toast时相当于修改了UI,程序报错
//                     if(result==0)  
//                     {  
//                         Toast.makeText(MainActivity.this, "下载成功！", Toast.LENGTH_SHORT).show();  
//                     }  
//                     else if(result==1) {  
//                         Toast.makeText(MainActivity.this, "已有文件！", Toast.LENGTH_SHORT).show();  
//                   }  
//                     else if(result==-1){  
//                         Toast.makeText(MainActivity.this, "下载失败！", Toast.LENGTH_SHORT).show();  
//                     }
                 }
             };
             thread.start();
               
        }
        
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

5.在adb中查看结果,data.txt即为下载的文件

 注意:不能在主线程中通过Http下载文件