android 4.4 下载文件

来源：互联网发布：返利软件有哪些编辑：程序博客网时间：2024/04/30 18:32

在android4.0以后，下载程序如果在主线程中出现的话，会报android.os.NetworkOnMainThreadException 错误。这可能是因为，在android的4.0以后使编码更加规范。在主线程中下载可能会导致线程的假死状态。造成用户的体验度不高。这里我用android4.4编写了一个下载的demo。

下载文件的步骤：
1.创建一个HttpURLConnection对象
HttpURLConnection urlConn = （HttpURLConnection ）url.openConnection（）；
2.获得一个InputStream对象
urlConn.getInputStream（）
3.访问网络权限
android.permission.INTERNET

访问sd卡步骤
1.得到当前设备SD卡的目录
Environment.getExternalStorageDIrectory()
2.访问SD卡的权限
android.permission.WRITE_EXTERNAL_STORAGE

下面贴出代码，方便大家浏览。

首先是AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.yx.download"
    android:versionCode="1"
    android:versionName="1.0" >

   <uses-permission android:name="android.permission.INTERNET"/>
   <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> 
    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />
    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.yx.download.DownLoadActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>
其次是DownLoadActivity文件

package com.yx.download;

import com.yx.utils.HttpDownLoad;

import android.os.Bundle;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Message;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class DownLoadActivity extends Activity {

   private Button downLoadMP3;
   private Button downLoadTXT;
   private HandlerThread thread;
   Handler handler = new Handler();
   @Override
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_main);
       downLoadMP3 = (Button) findViewById(R.id.downLoadMP3);
       downLoadTXT = (Button) findViewById(R.id.downLoadTXT);
       downLoadMP3.setOnClickListener(new downLoadMP3Listener());
       downLoadTXT.setOnClickListener(new downLoadTXTListener());

       //生成一个HandlerThread对象，实现使用looper来处理消息队列的功能,其实就是启用另一个线程，使下载不在主线程之中
       thread = new HandlerThread("handler_thread");
       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;
   }

   class downLoadMP3Listener implements OnClickListener{
       @Override
       public void onClick(View arg0) {
           handler=new Handler(thread.getLooper());
           handler.post(runMP3);//将执行下载MP3的线程压入栈内
       }

   }

   class downLoadTXTListener implements OnClickListener{
       @Override
       public void onClick(View arg0) {
           handler=new Handler(thread.getLooper());
           handler.post(runTXT);
       }

   }

   //下载MP3线程
   Runnable runMP3 = new Runnable() {
       @Override
       public void run() {
           HttpDownLoad httpDownLoad = new HttpDownLoad();
           int result = httpDownLoad.downFile("http://192.168.0.103:8080/testAndroidDownLoad/aa.mp3", "voa/", "ass.mp3");
           System.out.println(result);
       }
   };
   //下载文本线程
   Runnable runTXT = new Runnable() {
   @Override
   public void run() {
       HttpDownLoad httpDownLoad = new HttpDownLoad();
       String str=httpDownLoad.downLoad("http://192.168.0.103:8080/testAndroidDownLoad/aa.lrc");
       System.out.println(str);
   }
   };
}

为了方便使用，有如下两个帮助类，分别为HttpDownLoad和FileUtils

======HttpDownLoad.java========

package com.yx.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 HttpDownLoad {

   private URL url=null;
   /**
   * 只可以下载文本文件，下载到内存中
   * @param urlStr 文件网络路径
   * @return
   */
   public String downLoad(String urlStr){
       StringBuffer sb = new StringBuffer();
       String line=null;
       BufferedReader buffer = null;
       try {
           //创建URL对象
           url = new URL(urlStr);
           //创建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 (IOException e) {
               e.printStackTrace();
           }
       }
       return sb.toString();
   }

   /**
   * 下载到sd卡中
   * @param urlStr 下载的地址
   * @param path 存放路径
   * @param fileName 存放的文件名
   * @return -1:下载文件出错；0：文件下载成功；1：文件已经存在
   */
   public int downFile(String urlStr,String path,String fileName){
       InputStream inputStream = null;
       FileUtils fileUtils = new FileUtils();
       if(fileUtils.isFileExist(path+fileName)){
           System.out.println("已经有文件了");
           return 1;
       }else{
           try {
               System.out.println("还没文件");
               inputStream = getInputStreamByUrl(urlStr);
               File file = fileUtils.write2SDFromInput(path, fileName, inputStream);
               if(null==file){
                   return -1;
               }
           } catch (Exception e) {
               e.printStackTrace();
               return -1;
           }finally{
               try {
                   inputStream.close();
               } catch (IOException e) {
                   e.printStackTrace();
               }
           }
       }
       return 0;

   }

   /**
   * 根据url获得InputStream
   * @param urlStr
   * @return
   * @throws IOException
   */
   public InputStream getInputStreamByUrl(String urlStr) throws IOException{
       url = new URL(urlStr);
       HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
       InputStream inputStream = urlConn.getInputStream();
       return inputStream;
   }
}
=========FileUtils.java=======
package com.yx.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SD卡的路径
       SDPATH = Environment.getExternalStorageDirectory()+"/";
   }
   /**
   * 在SD卡上创建文件
   * @param fileName 文件名
   * @return
   * @throws IOException
   */
   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
   * @param dirName
   * @return
   */
   public File createSDDir(String dirName){
       File dir = new File(SDPATH+dirName);
       dir.mkdir();
       return dir;
   }
   /**
   * 判断文件是否存在
   * @param fileName
   * @return
   */
   public boolean isFileExist(String fileName){
       File file = new File(SDPATH+fileName);
       return file.exists();
   }

   /**
   * 向sd卡中写入数据
   * @param path 路径
   * @param fileName 文件名
   * @param input InputStream数据流
   * @return
   */
   public File write2SDFromInput(String path,String fileName,InputStream input){
       File file = null;
       OutputStream out = null;
       try {
           createSDDir(path);
           file = createSDFile(path+fileName);
           out = new FileOutputStream(file);
           byte buffer[] = new byte[4*1024];
           while(input.read(buffer)!=-1){
               out.write(buffer);
           }
           out.flush();
       } catch (IOException e) {
           e.printStackTrace();
       }finally{
           try {
               out.close();
           } catch (IOException e) {
               e.printStackTrace();
           }
       }
       return file;
   }
}

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