Android 使用HttpURLConnection 下载

需要的权限 访问互联网和读写SD卡

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


使用HttpURLConnection 其他函数方法访问网络步骤:


1. 得到URL 对象
2. 调用URL对象的openConnection方法, 并将返回值向下转型为HttpURLConnection 对象
    URLConnection    openConnection(Proxy proxy)
    Returns a new connection to the resource referred to by this URL.

3. 调用HttpURLConnection对象的getInputStream()方法, 获取到字节流的网络数据

HttpURLConnection 其他常用函数

            urlConnection.setRequestMethod("GET");
            urlConnection.setConnectTimeout(8000);
            urlConnection.setReadTimeout(8000);

处理文本文件:

构建BufferedReader对象的好处是因为它有readLine()方法可以读取一行数据

inputStream 字节流  , inputStreamReader 把字节流转换成字符流,读出来的是一个个的字符, 处理起来还是很麻烦,

于是在字符流的基础上类似再套上一层管道BufferedReader,就可以一行一行的读取数据了

BufferedReader buffer = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()))

BufferedReader 按行读取返回的String对象,可以存储到StringBuffer中

String line = null;
StringBuffer sb = new StringBuffer();

while(line = buffer.readLine() != null ){
    sb.append(line);
}

从输入流读取二进制文件后写入

OutputStream outputStream = new FileOutputStream(outputFile);
byte[] buffer = new byte[1024 * 4] ;
int readLen ;
while( (readLen = input.read(buffer,0,buffer.length)) != -1 ) {
                outputStream.write(buffer,0,readLen);
}

======================================================

访问SDCARD

判断是SD卡是否正常挂载
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))

得到当前设备SD卡目录, Enviroment静态类的一个方法
Environment.getExternalStorageDirectory()


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HttpDownloader 的部分代码, 下载文件

public class HttpDownloader {
    
    // 开线程下载, 并保存到SD卡下指定的目录, 回调函数返回结果到主线程
    public void downFile (final String urlStr, final String path,final String fileName, final HttpCallbackListener listener) {
        // 如果没有SD卡的话 , 直接退出函数
        
        if(! Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
            Log.d("SDCARD ERROR","无法访问SD卡");
            return;
        }
        
        // 正常下载的话调用listener.onFinish("SUCCESS") 返回字符串SUCCESS,
        // 文件存在则直接调用 onFinish("EXISTED")和onFinish("SUCCESS")返回EXISTED和SUCCESS,并不重新下载
        // 异常和其他错误调用onError
        new Thread(new Runnable(){

            @Override
            public void run() {

                FileUtils fileUtil = new FileUtils();
                //int result = -1;
                if (fileUtil.isFileExist(path + fileName)){
                    if(listener != null) {
                        listener.onFinish("EXISTED");
                    }
                }else {
                    InputStream input = null;
                    try {
                        input = getInputStreamFromUrl(urlStr);
                        //Log.d("SD 卡路径",fileUtil.getSDPATH());
                        File resultFile = fileUtil.write2SDFromInput(path, fileName, input);
                        
                        //调用下载方法后, 一般如果出错的话异常会抛出的,如果返回的文件为null则下载失败,
                        if (resultFile == null) {
                            if(null != listener) {
                                listener.onError(new Exception("文件下载出错"));
                            }
                        }
                    } catch (Exception e) {
                        //创建URL对象异常, 下载异常, 对SD卡的IO异常 , 都可能在这里看LogCat调试
                        e.printStackTrace();
                        if(null != listener) {
                            listener.onError(e);
                        }
                        
                    }finally {
                        try {
                            if (null != input ) input.close();
                        } catch (IOException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }    
                }
                
                //result = 0;
                if(listener != null) {
                    listener.onFinish("SUCCESS");
                }
                
            }}).start();

    }
    
    
    public InputStream getInputStreamFromUrl(String urlStr) throws MalformedURLException, IOException {
        URL url = new URL (urlStr);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        return connection.getInputStream();
    }
}

=============================================================================================

回调接口类

public interface HttpCallbackListener {

    void onFinish(String response);

    void onError(Exception e);
    

}

=============================================================================================



Activity 里面使用下载类

         

  String UrlTxt = new String("http://192.168.1.111/test.mp3");
            HttpDownloader downloader = new HttpDownloader();
            HttpCallbackListener httpcallback = new HttpCallbackListener() {

                @Override
                public void onFinish(String response) {
                    Log.d("下载二进制文件完成,结果=>" , response);
                    
                }

                @Override
                public void onError(Exception e) {
                    // TODO Auto-generated method stub
                    Log.d("下载二进制文件错误" , e.getMessage());
                }
                
            };
    downloader.downFile(UrlTxt, "test/", "newname.mp3", httpcallback);