使用HTTP协议 下载文件

 

文件下载步骤：

  1. 创建一个HttpURLConnection对象 HttpURLConnection urlConn = （HttpURLConnection）url.openConnection();

  2. 获得一个InputStream对象  urlConn.getInputStream();

 

下载的文件当中的内容是文本，函数的返回值就是文件当中的内容：

答：步骤1.创建一个URL对象，        2.通过URL对象,创建一个HttpURLConnection对象

            3.得到InputStream，            4.从InputStream当中读取数据

 

将下载的文件写入SDCARD：

         得到当前设备SD卡的目录：Environment.getExternalStorageDirectory();

         访问SD卡的权限，见注意。

   HttpDownloader 类

package com.examples.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;

import android.app.backup.FileBackupHelper;

public class HttpDownloader {
    URL url = null;
 //下载文档文件
 public String download(String urlstr)
 {
  StringBuffer sb = new StringBuffer(); 
  String line = null;
  BufferedReader buffer = null;
  try {
   url = new URL(urlstr);
   HttpURLConnection httpConn = (HttpURLConnection)url.openConnection();
   buffer= new BufferedReader(new InputStreamReader(httpConn.getInputStream()));//IO包的封装
   while((line=buffer.readLine())!=null)
   {
    sb.append(line);
   }
  } catch (Exception e) {

   e.printStackTrace();
  }
  finally
  {
   try {
    buffer.close();
   } catch (Exception e) {
    e.printStackTrace();
   }
  }
  return sb.toString();
 }
 
 //返回-1：表示下载文件出错；返回0：表示下载成功；返回1：表示文件已经存在
 public int downfile(String urlstr,String path,String filename)
 {
  InputStream input = null;
  try {
   FileUtils fileUtils = new FileUtils();
   if(fileUtils.isFileExist(path + filename))
   {
    return 1;
   }
   else
   {
    input = getInputStreamFromUrl(urlstr);
    File resultFile = fileUtils.write2SDFromInput(path, filename, input);
    if(resultFile == null)
    {
     return -1;
    }
   }
  } catch (IOException e) {
   e.printStackTrace();
   return -1;
  }
  return 0;
 }
 
 public InputStream getInputStreamFromUrl(String urlstr) throws IOException
 {
  url = new URL(urlstr);
  HttpURLConnection httpConn = (HttpURLConnection)url.openConnection();
  InputStream input = httpConn.getInputStream();
  return input;
 }
}

 

        FileUtils 类

package com.examples.utils;

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

import android.os.Environment;

public class FileUtils {
    private String SDPATH;
    //构造函数
 public  FileUtils()
 {
  //得到当前外部存储设备的目录
  SDPATH = Environment.getExternalStorageDirectory()+ "/";   //getPath方法看可以不要不
 }
 //返回SD卡目录
 public String getSDPATH()
 {
  return SDPATH;
 }
 //在SD卡上创建文件
 public File createSDFile(String filename) throws IOException
 {
  File file = new File(SDPATH +filename);
  file.createNewFile();
  return file;
 }
 //在SD卡上创建目录
 public File createSDDir(String dirName)
 {
  File dir = new File(SDPATH + dirName);
  dir.mkdir();
  return dir;
 }
 //判断SD卡上文件是否存在
 public boolean isFileExist(String filename)
 {
  File file = new File(SDPATH + filename);
  return file.exists();
 }
 //将一个InputStream里的数据写入SD卡中
 public File write2SDFromInput(String path,String filename,InputStream input)
 {
  OutputStream output = null;
  File file =null;
  try
  {
   createSDDir(path);
   file = createSDFile(path + filename);
   output = new  FileOutputStream(file);//构造FileOutputStream用于给文件中写入内容
   byte buffer[] = new byte[4*1024];
    while(input.read(buffer) !=-1)
    {
     output.write(buffer);
    }
    output.flush();
  }catch(Exception ex)
  {
   ex.printStackTrace();
  }
  finally
  {
   try
   {
    output.close();
   }catch(Exception e)
   {
    e.printStackTrace();
   } 
  }
  return file;
 }
}

 

       download 类

package com.examples.download;

import com.examples.utils.HttpDownloader;

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

public class download extends Activity {
    /** Called when the activity is first created. */
 private Button downTxt;
 private Button downFile;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
       
        downTxt = (Button)findViewById(R.id.downtxt);
        downFile = (Button)findViewById(R.id.downfile);
        downTxt.setOnClickListener(new downTxtListener());
        downFile.setOnClickListener(new downFileListener());
    }
   
    class  downTxtListener implements OnClickListener
    {
     @Override
     public void onClick(View v) {
      HttpDownloader httpdownloader = new HttpDownloader();
      String srt=httpdownloader.download("http://202.193.82.14:8080/vao1500/1.srt");
      System.out.println(srt);
     }
    }
   
    class  downFileListener implements OnClickListener
    {
     @Override
     public void onClick(View v) {
      HttpDownloader httpdownloader = new HttpDownloader(); 
      int result=httpdownloader.downfile("http://202.193.80.14:8080/vao1500/a1.mp3", "voa/", "a1.mp3");
      System.out.println(result);
     }
    }
}

 

 

注意：访问网络的权限（在AndroidManifest.xml中设置） <uses-permission android:name="android.permission.INTERNET" />

          具有写的权利  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

          InputStream是读取数据，OutputStream是写入数据。