Android_文件下载

import mars.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 Download extends Activity {
    /** Called when the activity is first created. */
    //定义两个按键
    private Button downloadTxtButton;
    private Button downloadMp3Button;
    @Override
    //创建主窗口
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        downloadTxtButton = (Button)findViewById(R.id.downloadTxt);
        downloadTxtButton.setOnClickListener(new DownloadTxtListener());
        downloadMp3Button = (Button)findViewById(R.id.downloadMp3);
        downloadMp3Button.setOnClickListener(new DownloadMp3Listener());
    }
    
    //实现OnClickListener接口
    class DownloadTxtListener implements OnClickListener{

        @Override
        public void onClick(View v) {
            //新建自己定义的HttpDownloader对象
            HttpDownloader httpDownloader = new HttpDownloader();
            //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
            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");
            System.out.println(lrc);
        }
        
    }
    class DownloadMp3Listener implements OnClickListener{

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            HttpDownloader httpDownloader = new HttpDownloader();
            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");
            System.out.println(result);
        }
        
    }
    
}

自定义的类HttpDownloader

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) {
        //字符缓冲区
        StringBuffer sb = new StringBuffer();
        String line = null;
        //io里的字符缓冲流对象
        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，调用HttpURLConnection对象的getInputStream方法得到下载对象的InputStream，再套上其他IO管
            buffer = new BufferedReader(new InputStreamReader(urlConn
                    .getInputStream()));
            //读取一行
            while ((line = buffer.readLine()) != null) {
                //加到字符缓冲区的字符后面
                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。（文件URL地址，文件要存储的路径，文件名字）
     */
    public int downFile(String urlStr, String path, String fileName) {
        InputStream inputStream = null;
        try {
            //新建文件工具对象
            FileUtils fileUtils = new FileUtils();
            //先判断文件是否存在
            if (fileUtils.isFileExist(path + fileName)) {
                return 1;
            } else {
                //从URL中得到输出管道inputstream即输入流
                inputStream = getInputStreamFromUrl(urlStr);
                //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）
                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 {
        //根据string新建URL
        url = new URL(urlStr);
        //调用URL的openConnection方法并下行转换成HttpURLConnection对象
        HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
        //再调用HttpURLConnection对象的getInputStream方法取得URL的输入流即输出管道
        InputStream inputStream = urlConn.getInputStream();
        //返回管道
        return inputStream;
    }
}

自定义文件工具类

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;

    //得到SD卡文件所在的目录即SD卡路径
    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 {
        //首先先创建File文件对象
        File file = new File(SDPATH + fileName);
        //调用File的createNewFile方法创建一个空的文件
        file.createNewFile();
        //返回文件对象
        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，即从InputStream管道读取数据写到SD卡中
     */
    public File write2SDFromInput(String path,String fileName,InputStream input){
        File file = null;
        OutputStream output = null;
        try{
            //建立文件目录
            creatSDDir(path);
            //创建空文件
            file = creatSDFile(path + fileName);
            //把新建的输入管道插到新建的空文件上
            output = new FileOutputStream(file);
            //定义缓冲区大小为4K
            byte buffer [] = new byte[4 * 1024];
            //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
            while((input.read(buffer)) != -1){
                output.write(buffer);
            }
            //管道清空
            output.flush();
        }
        catch(Exception e){
            e.printStackTrace();
        }
        finally{
            try{
                output.close();
            }
            catch(Exception e){
                e.printStackTrace();
            }
        }
        return file;
    }

}

最后不要忘了manifest加SDcard权限：

    <uses-sdk android:minSdkVersion="4" />

    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>