Android_文件下载

 1 import mars.utils.HttpDownloader;
 2 import android.app.Activity;
 3 import android.os.Bundle;
 4 import android.view.View;
 5 import android.view.View.OnClickListener;
 6 import android.widget.Button;
 7 
 8 public class Download extends Activity {
 9     /** Called when the activity is first created. */
10     //定义两个按键
11     private Button downloadTxtButton;
12     private Button downloadMp3Button;
13     @Override
14     //创建主窗口
15     public void onCreate(Bundle savedInstanceState) {
16         super.onCreate(savedInstanceState);
17         setContentView(R.layout.main);
18         downloadTxtButton = (Button)findViewById(R.id.downloadTxt);
19         downloadTxtButton.setOnClickListener(new DownloadTxtListener());
20         downloadMp3Button = (Button)findViewById(R.id.downloadMp3);
21         downloadMp3Button.setOnClickListener(new DownloadMp3Listener());
22     }
23     
24     //实现OnClickListener接口
25     class DownloadTxtListener implements OnClickListener{
26 
27         @Override
28         public void onClick(View v) {
29             //新建自己定义的HttpDownloader对象
30             HttpDownloader httpDownloader = new HttpDownloader();
31             //得到下载的文本文件的字符串                        http://image.baidu.com/channel/listdownload?word=download&ie=utf8&countop=0&fr=detail&url=http://g.hiphotos.baidu.com/album/w%3D2048/sign=4106f3c3d000baa1ba2c40bb7328b812/0e2442a7d933c8950f78a654d01373f08202009e.jpg&col=%E7%BE%8E%E5%A5%B3&image_id=4815797214&tag=%E5%B0%8F%E6%B8%85%E6%96%B0
32             String lrc = httpDownloader.download("http://image.baidu.com/channel/listdownload?word=download&ie=utf8&countop=0&fr=detail&url=http://g.hiphotos.baidu.com/album/w%3D2048/sign=4106f3c3d000baa1ba2c40bb7328b812/0e2442a7d933c8950f78a654d01373f08202009e.jpg&col=%E7%BE%8E%E5%A5%B3&image_id=4815797214&tag=%E5%B0%8F%E6%B8%85%E6%96%B0");
33             System.out.println(lrc);
34         }
35         
36     }
37     class DownloadMp3Listener implements OnClickListener{
38 
39         @Override
40         public void onClick(View v) {
41             // TODO Auto-generated method stub
42             HttpDownloader httpDownloader = new HttpDownloader();
43             int result = httpDownloader.downFile("http://image.baidu.com/channel/listdownload?word=download&ie=utf8&countop=0&fr=detail&url=http://g.hiphotos.baidu.com/album/w%3D2048/sign=4106f3c3d000baa1ba2c40bb7328b812/0e2442a7d933c8950f78a654d01373f08202009e.jpg&col=%E7%BE%8E%E5%A5%B3&image_id=4815797214&tag=%E5%B0%8F%E6%B8%85%E6%96%B0", "voa/", "a1.jpg");
44             System.out.println(result);
45         }
46         
47     }
48     
49 }


自定义的类HttpDownloader

  1 import java.io.BufferedReader;
  2 import java.io.File;
  3 import java.io.IOException;
  4 import java.io.InputStream;
  5 import java.io.InputStreamReader;
  6 import java.net.HttpURLConnection;
  7 import java.net.MalformedURLException;
  8 import java.net.URL;
  9 
 10 
 11 public class HttpDownloader {
 12     private URL url = null;
 13 
 14     /**
 15      * 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
 16      * 1.创建一个URL对象
 17      * 2.通过URL对象，创建一个HttpURLConnection对象
 18      * 3.得到InputStram
 19      * 4.从InputStream当中读取数据
 20      * @param urlStr
 21      * @return
 22      */
 23     public String download(String urlStr) {
 24         //字符缓冲区
 25         StringBuffer sb = new StringBuffer();
 26         String line = null;
 27         //io里的字符缓冲流对象
 28         BufferedReader buffer = null;
 29         try {
 30             // 创建一个URL对象
 31             url = new URL(urlStr);
 32             // 创建一个Http连接
 33             HttpURLConnection urlConn = (HttpURLConnection) url
 34                     .openConnection();
 35             // 使用IO流读取数据，调用HttpURLConnection对象的getInputStream方法得到下载对象的InputStream，再套上其他IO管
 36             buffer = new BufferedReader(new InputStreamReader(urlConn
 37                     .getInputStream()));
 38             //读取一行
 39             while ((line = buffer.readLine()) != null) {
 40                 //加到字符缓冲区的字符后面
 41                 sb.append(line);
 42             }
 43         } catch (Exception e) {
 44             e.printStackTrace();
 45         } finally {
 46             try {
 47                 buffer.close();
 48             } catch (Exception e) {
 49                 e.printStackTrace();
 50             }
 51         }
 52         return sb.toString();
 53     }
 54 
 55     /**
 56      * 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。（文件URL地址，文件要存储的路径，文件名字）
 57      */
 58     public int downFile(String urlStr, String path, String fileName) {
 59         InputStream inputStream = null;
 60         try {
 61             //新建文件工具对象
 62             FileUtils fileUtils = new FileUtils();
 63             //先判断文件是否存在
 64             if (fileUtils.isFileExist(path + fileName)) {
 65                 return 1;
 66             } else {
 67                 //从URL中得到输出管道inputstream即输入流
 68                 inputStream = getInputStreamFromUrl(urlStr);
 69                 //调用文件工具的写数据到SD卡方法返回一个文件对象（完整文件）
 70                 File resultFile = fileUtils.write2SDFromInput(path,fileName, inputStream);
 71                 if (resultFile == null) {
 72                     return -1;
 73                 }
 74             }
 75         } catch (Exception e) {
 76             e.printStackTrace();
 77             return -1;
 78         } finally {
 79             try {
 80                 inputStream.close();
 81             } catch (Exception e) {
 82                 e.printStackTrace();
 83             }
 84         }
 85         return 0;
 86     }
 87 
 88     /**
 89      * 根据URL得到输入流
 90      * 
 91      * @param urlStr
 92      * @return
 93      * @throws MalformedURLException
 94      * @throws IOException
 95      */
 96     public InputStream getInputStreamFromUrl(String urlStr)
 97             throws MalformedURLException, IOException {
 98         //根据string新建URL
 99         url = new URL(urlStr);
100         //调用URL的openConnection方法并下行转换成HttpURLConnection对象
101         HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
102         //再调用HttpURLConnection对象的getInputStream方法取得URL的输入流即输出管道
103         InputStream inputStream = urlConn.getInputStream();
104         //返回管道
105         return inputStream;
106     }
107 }


自定义文件工具类

 1 import java.io.File;
 2 import java.io.FileOutputStream;
 3 import java.io.IOException;
 4 import java.io.InputStream;
 5 import java.io.OutputStream;
 6 
 7 import android.os.Environment;
 8 
 9 public class FileUtils {
10     private String SDPATH;
11 
12     //得到SD卡文件所在的目录即SD卡路径
13     public String getSDPATH() {
14         return SDPATH;
15     }
16     public FileUtils() {
17         //得到当前外部存储设备的目录
18         // /SDCARD
19         SDPATH = Environment.getExternalStorageDirectory() + "/";
20     }
21     /**
22      * 在SD卡上创建文件
23      * 
24      * @throws IOException
25      */
26     public File creatSDFile(String fileName) throws IOException {
27         //首先先创建File文件对象
28         File file = new File(SDPATH + fileName);
29         //调用File的createNewFile方法创建一个空的文件
30         file.createNewFile();
31         //返回文件对象
32         return file;
33     }
34     
35     /**
36      * 在SD卡上创建目录
37      * 
38      * @param dirName
39      */
40     public File creatSDDir(String dirName) {
41         File dir = new File(SDPATH + dirName);
42         dir.mkdirs();
43         return dir;
44     }
45 
46     /**
47      * 判断SD卡上的文件夹是否存在
48      */
49     public boolean isFileExist(String fileName){
50         File file = new File(SDPATH + fileName);
51         return file.exists();
52     }
53     
54     /**
55      * 将一个InputStream里面的数据写入到SD卡中，即从InputStream管道读取数据写到SD卡中
56      */
57     public File write2SDFromInput(String path,String fileName,InputStream input){
58         File file = null;
59         OutputStream output = null;
60         try{
61             //建立文件目录
62             creatSDDir(path);
63             //创建空文件
64             file = creatSDFile(path + fileName);
65             //把新建的输入管道插到新建的空文件上
66             output = new FileOutputStream(file);
67             //定义缓冲区大小为4K
68             byte buffer [] = new byte[4 * 1024];
69             //从输出管道读取数据到缓冲区中，然后通过输入管道从缓冲区写入数据到文件中
70             while((input.read(buffer)) != -1){
71                 output.write(buffer);
72             }
73             //管道清空
74             output.flush();
75         }
76         catch(Exception e){
77             e.printStackTrace();
78         }
79         finally{
80             try{
81                 output.close();
82             }
83             catch(Exception e){
84                 e.printStackTrace();
85             }
86         }
87         return file;
88     }
89 
90 }

最后不要忘了manifest加SDcard权限：

1     <uses-sdk android:minSdkVersion="4" />
2 
3     <uses-permission android:name="android.permission.INTERNET"/>
4     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
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原文地址：https://www.cnblogs.com/humanchan/p/3219321.html