Android之文件下载

fmms 9年前

在手机上下载一些文件是很常见的,比如下载一本书,下载一首Mp3等等,下面就来通过一个实例来简单介绍一下文件的下载。

文件下载实现的基本步骤:创建一个HttpURLConnection对象,获得一个InputStream对象,设置网络访问权限。

在这个实例中实现歌词和歌曲MP3的下载。

首先我们先看一下布局文件,很简单,只有两个Button控件:

<?xml version="1.0" encoding="utf-8"?>  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"      android:layout_width="fill_parent"      android:layout_height="fill_parent"      android:orientation="vertical" >        <Button           android:id="@+id/downloadText"          android:layout_width="fill_parent"          android:layout_height="wrap_content"          android:text="downloadText"/>      <Button           android:id="@+id/downloadMp3"          android:layout_width="fill_parent"          android:layout_height="wrap_content"          android:text="downloadMp3"/>        </LinearLayout>

下载文件需要用到两个utils工具类,一个工具类(HttpDownloader.java)是用来下载文件用的,另一个(FileUtils.java)是用来将下载的文件写入到SD卡中: /Download/src/cn/android/sword/utils/HttpDownloader.java
package cn.android.sword.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.util.Log;    public class HttpDownloader {   private final static String SWORD="SWORD";   public String download(String urlStr){      URL url = null;    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 (IOException e) {      e.printStackTrace();     }    }    return sb.toString();   }   //返回-1下载文件失败,返回0下载成功,返回1则是文件已存在   public int downFile(String urlStr,String path,String fileName){    InputStream inputStream = null;        FileUtils fileUtils = new FileUtils();    if(fileUtils.isFileExist(fileName)){     return 1;    }else{     try {      inputStream = getInputSteamFromUrl(urlStr);     } catch (IOException e) {      e.printStackTrace();      return -1;     }     File resultFile = fileUtils.write2SDFromInput(path, fileName, inputStream);     if(resultFile == null){      return -1;     }    }    try {     inputStream.close();    } catch (IOException e) {     e.printStackTrace();    }    return 0;   }     private InputStream getInputSteamFromUrl(String urlStr) throws MalformedURLException, IOException {    URL url = null;    url = new URL(urlStr);    HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();    InputStream inputStream = urlConn.getInputStream();    return inputStream;   }  }
/Download/src/cn/android/sword/utils/FileUtils.java
package cn.android.sword.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    */   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 {     //创建目录     createSDDir(path);     //创建文件     file = createSDFile(path+fileName);     //创建输出流     output = new FileOutputStream(file);     //创建缓冲区     byte buffer[] =  new byte[4*1024];     //写入数据     while((input.read(buffer))!=-1){      output.write(buffer);     }     //清空缓存     output.flush();    } catch (IOException e) {     e.printStackTrace();    }finally{     try {      //关闭输出流      output.close();     } catch (IOException e) {      e.printStackTrace();     }    }    return file;   }     }
在Activity中:
/Download/src/cn/android/sword/download/DownloadActivity.java
package cn.android.sword.download;    import cn.android.sword.utils.HttpDownloader;  import android.app.Activity;  import android.os.Bundle;  import android.util.Log;  import android.view.View;  import android.view.View.OnClickListener;  import android.widget.Button;     /*    文件下载的步骤:   1:创建一个Ht't'p'URLConnection对象:HttpURLConnection urlConn = (HttpURLConnection)url.o'penConnection;   2:获得一个InputStream对象:urlConn.getInputStream();   3:设置网络访问权限:android.permissior.INTERNET;      访问SD卡步骤:   得到当前设备SD卡的目录;   Environment.getExternalStorageDirectory();   访问SD卡的权限:   android:permission.WRITE_EXTERNAL_STORAGE    */    public class DownloadActivity extends Activity implements OnClickListener{   private final static String SWORD="SWORD";       //声明两个按钮控件   Button downloadText;      Button downloadMp3;      public void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(R.layout.main);          findViews();      }      //根据Id得到控件   private void findViews() {    downloadText = (Button) this.findViewById(R.id.downloadText);    downloadMp3 = (Button) this.findViewById(R.id.downloadMp3);    //添加监听事件    downloadText.setOnClickListener(this);    downloadMp3.setOnClickListener(this);   }   @Override   public void onClick(View v) {    switch(v.getId()){    case R.id.downloadText:     HttpDownloader httpDownloader = new HttpDownloader();     //所要下载文件的url路径     String lrc = httpDownloader.download("http://192.168.1.101:8080/20111021/a.lrc");     //日志打印输出     Log.i(SWORD,""+lrc);     break;    case R.id.downloadMp3:     HttpDownloader httpDownloader1 = new HttpDownloader();     int result = httpDownloader1.downFile("http://192.168.1.101:8080/20111021/m.mp3","dir/","new.mp3");     Log.i(SWORD,""+result);     break;    default:     Log.i(SWORD,"ERROR");     break;    }   }  }
本例子所下载的歌词文件和MP3文件均为我的pc上的tomcat中项目下的文件,所以需要启动我的tomcat service服务,在虚拟机上运行:

Android之文件下载

点击downloadText,查看控制台日志输出:Android之文件下载

可以看到乱码的文件内容,然后点击downloadMp3,在SD卡的dir目录下我们能看到一个new.mp3的文件,这说明我们的文件下载成功了。

转自:http://blog.csdn.net/jjaze3344/article/details/7251527