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

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());   }    //下载歌词文件按钮监听器   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文件按钮监听器   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;   } }

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