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>

AndroidMainfest.xml

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;
     }
 }

FileUtils.java

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;
        }
 }

HttpDownloader.java

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);
     }
 }

MainActivity.java

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