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1）從指定的URL獲取對(duì)應(yīng)的流

既然要獲取網(wǎng)絡(luò)資源，那么首先得有個(gè)URL，那么這里我首先封裝一個(gè)打開URL連接獲取到的InputStream 流，這樣一來無論是圖片資源還是文本文件資源都可以使用該接口方法來獲取流。

該功能主要應(yīng)用URLConnection和HttpURLConnection來實(shí)現(xiàn)，具體實(shí)現(xiàn)方案如下：

private InputStream openHttpConnection(String urlString) throws IOException{

InputStream in = null;

int response = -1;

URL url = new URL(urlString);

URLConnection conn = url.openConnection();

if(!(conn instanceof HttpURLConnection)){

throw new IOException("It is not an HTTP connection");

}

try {

HttpURLConnection httpConn = (HttpURLConnection) conn;

httpConn.setAllowUserInteraction(false);

httpConn.setInstanceFollowRedirects(true);

httpConn.setRequestMethod("GET");

httpConn.connect();

response = httpConn.getResponseCode();

if (response == HttpURLConnection.HTTP_OK) {

in = httpConn.getInputStream();

}

} catch (Exception ex) {

Log.v("Networking",ex.getLocalizedMessage());

throw new IOException("Error connecting");

}

return in;

}

（2）封裝了上面的獲取流方法接口后，我們就可以利用上面封裝的方法來獲取并下載相應(yīng)圖片和文本文件內(nèi)容了

獲取并下載圖片資源方法：

private Bitmap downloadImage(String url){

Bitmap bitmap = null;

InputStream in = null;

try {

in = openHttpConnection(url);

bitmap = BitmapFactory.decodeStream(in);

in.close();

} catch (IOException e) {

// TODO Auto-generated catch block

Log.v("NetworkingActivity", e.getLocalizedMessage());

}

return bitmap;

}

獲取并下載文本內(nèi)容方法：

private String downloadText(String url){

int BUFFER_SIZE = 2000;

InputStream is = null;

try {

is = openHttpConnection(url);

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

return "";

}

InputStreamReader isr = new InputStreamReader(is);

int charRead;

String str="";

char[] inputBuffer = new char[BUFFER_SIZE];

try {

while((charRead=isr.read(inputBuffer))>0){

String readString = String.copyValueOf(inputBuffer, 0, charRead);

str += readString;

inputBuffer = new char[BUFFER_SIZE];

}

is.close();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

return "";

}

return str;

}

（3）在獲取下載圖片資源和文本內(nèi)容資源方法都完成后，現(xiàn)在就可以開始下載任務(wù)了，為了防止等待效應(yīng)，一般采用異步任務(wù)來下載網(wǎng)絡(luò)資源。

對(duì)對(duì)應(yīng)的下載資源任務(wù)封裝各自的異步下載任務(wù)即可。下面就是實(shí)現(xiàn)異步下載任務(wù)的方案：

異步下載圖片任務(wù)：

private class DownloadImageTask extends AsyncTask<String, Bitmap, Long>{

long imagesCount = 0;

ProgressBar progressBar;

public DownloadImageTask(ProgressBar pBar){

this.progressBar = pBar;

}

@Override

protected Long doInBackground(String... urls) {

// TODO Auto-generated method stub

for(int i = 0; i < urls.length;i++){

Bitmap imageDownloaded = downloadImage(urls[i]);

if(imageDownloaded!=null){

imagesCount ++;

publishProgress(imageDownloaded);

try {

Thread.sleep(300);

} catch (InterruptedException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

}

return imagesCount;

}

//display the image downloaded

@Override

protected void onProgressUpdate(Bitmap... bitmaps) {

// TODO Auto-generated method stub

ivImg.setImageBitmap(bitmaps[0]);

progressBar.setProgress((int) imagesCount*10);

}

//when all the images have been downloaded

@Override

protected void onPostExecute(Long imageDownloaded) {

// TODO Auto-generated method stub

String str = "下載完成！一共下載了"+imagesCount +"張圖片";

Toast.makeText(getBaseContext(), str, Toast.LENGTH_SHORT).show();

}

}

異步下載文本文件內(nèi)容任務(wù)：

private class DownloadTextTask extends AsyncTask<String, Void, String>{

@Override

protected void onPostExecute(String result) {

// TODO Auto-generated method stub

Toast.makeText(getBaseContext(), result, Toast.LENGTH_LONG).show();

}

@Override

protected String doInBackground(String... urls) {

// TODO Auto-generated method stub

return downloadText(urls[0]);

}

}

這樣一來，異步下載網(wǎng)絡(luò)資源就完成了。

下面為了讀者方便測(cè)試，下面提供本文實(shí)例代碼中的相關(guān)網(wǎng)絡(luò)資源URL，以方便大家自己測(cè)試使用。其余非核心代碼就不在貼出來，望讀者見諒。

//圖片下載URLs

private String[] mUrl =

{

"",

""

};

progressBar = (ProgressBar) findViewById(R.id.progressBar);

progressBar.setMax(mUrl.length*10);

progressBar.setVisibility(View.VISIBLE);

//異步下載圖片任務(wù)

DownloadImageTask task = new DownloadImageTask(progressBar);

task.execute(mUrl);

//文本文件URL

String strUrl = "";

//異步下載文本文件內(nèi)容任務(wù)

new DownloadTextTask().execute(strUrl);

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