android 网络下载文件 和 读写sdcard 方法

原创：kylin_zeng  http://blog.chinaunix.net/uid/23795897.html 在此感谢mars 老师的帮助。
转载请注明原创出处，尊重他人的劳动成果。

1、访问网络和sdcard 权限：



2、创建两个按钮：
 downloadTxtButton = (Button)findViewById(R.id.downloadTxt);
 downloadTxtButton.setOnClickListener(new DownloadTxtListener());
 downloadMp3Button = (Button)findViewById(R.id.downloadMp3);
 downloadMp3Button.setOnClickListener(new DownloadMp3Listener());

3、设置监听器：
class DownloadTxtListener implements OnClickListener{
        @Override
        public void onClick(View v) {
                HttpDownloader httpDownloader = new HttpDownloader();          //这个是下载的类自己封装的类
                String lrc = httpDownloader.download("");
                 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("", "voa/", "a1.mp3");
                    System.out.println(result);
            }
}


4、下载的 HttpDownloader 类：
/**
* 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 class HttpDownloader {
        private URL url = null;


        public String download(String urlStr) {            //download 函数，实现下载后返回字符串。
                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();      //FileUtils 是自己定义的一个读写sdcard的类

                            if (fileUtils.isFileExist(path + fileName)) {
                                         return 1;
                             } else {
                                            inputStream = getInputStreamFromUrl(urlStr);  //自己定义的一个函数，从给的url网址获取数据流，见下面
                                            File resultFile = fileUtils.write2SDFromInput(path,fileName, inputStream);  //FileUtils 类里面的一个函数，讲数据流写到sdcard中。
                                            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;
           }
}




5、读写sdcard的FileUtils类：

public class FileUtils {

    private String SDPATH;

    public String getSDPATH() {
        return SDPATH;
    }
    public FileUtils() {           // 构造函数，new FileUtils 时就执行这个，
        //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){      //最大每次只能输出4K
        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;
    }

}

mars视频教程ppt和代码01_18_src.zip