android实现文件下载功能

android在网络上下载文件，供大家参考，具体内容如下

步骤:

1.使用HTTP协议下载文件

- 创建一个HttpURLConnection对象 : HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
- 获取一个InputStream对象 : urlConn.getInputStream()
- 访问网络的权限 : android.permission.INTERNET

2.将下载的文件写入SDCARD
- 得到当前设备SD卡的目录 : Environment.getExternalStrageDirectory()
- 访问SD卡的权限 : android.permission.WRITE_EXTERNAL_STORAGE

代码: 

activity_main.xml

<RelativeLayout 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=".MainActivity" >

<Button
   android:id="@+id/btn_txt"
   android:layout_width="match_parent"
   android:layout_height="wrap_content"
   android:text="download lrc" />

<Button
   android:id="@+id/btn_mp3"
   android:layout_width="match_parent"
   android:layout_height="wrap_content"
   android:layout_below="@id/btn_txt"
   android:text="download mp3" />

</RelativeLayout>

MainActivity.java

package com.chay.download;

import com.chay.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 MainActivity extends Activity {

String urlStr_txt = "http://192.168.56.1:8080/mp3/wan.lrc";
 String urlStr_mp3 = "http://192.168.56.1:8080/mp3/wan.mp3";
 String path = "mp3/";
 String fileName = "wan.mp3";
 private Button downloadTxtButton;
 private Button downloadMp3Button;

@Override
 protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   downloadTxtButton = (Button) findViewById(R.id.btn_txt);
   downloadTxtButton.setOnClickListener(new DownloadTxtListener());
   downloadMp3Button = (Button) findViewById(R.id.btn_mp3);
   downloadMp3Button.setOnClickListener(new DownloadMp3Listener());
 }

//下载歌词文件按钮 *
 class DownloadTxtListener implements OnClickListener {
   @Override
   public void onClick(View v) {
     Thread t = new DownloadTxtThread();  
     t.start();
     System.out.println("txt--->");
   }
 }
 //下载歌词文件线程
 class DownloadTxtThread extends Thread{
   @Override
   public void run() {
     HttpDownloader httpDownloader = new HttpDownloader();
     String lrc = httpDownloader.download(urlStr_txt);
     System.out.println(lrc);
   }
 }
 //下载MP3文件按钮 *
 class DownloadMp3Listener implements OnClickListener {
   @Override
   public void onClick(View v) {
     Thread h = new DownMp3Thread();
     h.start();
     System.out.println("mp3--->");
   }
 }
 //下载MP3文件线程
 class DownMp3Thread extends Thread{
   @Override
   public void run() {
     HttpDownloader httpDownloader = new HttpDownloader();
     int result = httpDownloader.downFile(urlStr_mp3, path, fileName);
     System.out.println(result);
   }
 }  
}

工具类:

HttpDownloader.java

package com.chay.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;

/**
  * 根据URL下载文件，前提是这个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
  * 1.创建一个URL对象
  * 2.通过URL对象，创建一个HttpURLConnection对象
  * 3.得到InputStram
  * 4.从InputStream当中读取数据
  * @param urlStr
  * @return
  */
 public String download(String urlStr) {
   StringBuffer sb = new StringBuffer();
   String line = null;
   BufferedReader buffer = null;
   try {
     // 创建一个URL对象
     url = new URL(urlStr);
     // 创建一个Http连接
     HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
     // 使用IO流读取数据
     buffer = new BufferedReader(new InputStreamReader(urlConn.getInputStream()));
     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();
 }

/**
  * 该函数返回整形 -1：代表下载文件出错   0：代表下载文件成功   1：代表文件已经存在
  */
 public int downFile(String urlStr, String path, String fileName) {
   InputStream inputStream = null;
   try {
     FileUtils fileUtils = new FileUtils();

if (fileUtils.isFileExist(path + fileName)) {
       return 1;
     } else {
       inputStream = getInputStreamFromUrl(urlStr);
       File resultFile = fileUtils.write2SDFromInput(path,fileName, inputStream);
       if (resultFile == null) {
         return -1;
       }
     }
   } catch (Exception e) {
     e.printStackTrace();
     return -1;
   } finally {
     try {
       inputStream.close();
     } catch (Exception e) {
       e.printStackTrace();
     }
   }
   return 0;
 }

/**
  * 根据URL得到输入流
  *
  * @param urlStr
  * @return
  * @throws MalformedURLException
  * @throws IOException
  */
 public InputStream getInputStreamFromUrl(String urlStr)
     throws MalformedURLException, IOException {
   url = new URL(urlStr);
   HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
   InputStream inputStream = urlConn.getInputStream();
   return inputStream;
 }
}

FileUtils.java

package com.chay.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.mkdirs();
   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;
 }
}

 如果不能下载，请先将windows防火墙关闭。

来源：http://blog.csdn.net/ycwol/article/details/44546337