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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