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(kāi)URL連接獲取到的InputStream 流，這樣一來(lái)無(wú)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(lái)獲取流。
該功能主要應(yīng)用URLConnection和HttpURLConnection來(lái)實(shí)現(xiàn)，具體實(shí)現(xiàn)方案如下：
代碼如下:
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;
}
代碼如下:
（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(lái)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：
代碼如下:
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;
}
代碼如下:
獲取并下載文本內(nèi)容方法：
代碼如下:
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;
}
代碼如下:
（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(kāi)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(lái)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)：
代碼如下:
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();
}
}
代碼如下:
異步下載文本文件內(nèi)容任務(wù)：
代碼如下:
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]);
}
}
代碼如下:
這樣一來(lái)，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(lái)，望讀者見(jiàn)諒。
代碼如下:
//圖片下載URLs
private String[] mUrl =
{
"http://images.cnitblog.com/i/322919/201405/181111308592436.png",
"http://images.cnitblog.com/i/322919/201405/181111385003770.png",
"http://images.cnitblog.com/i/322919/201405/181111493901865.png",
"http://images.cnitblog.com/i/322919/201405/181111550463327.png",
"http://images.cnitblog.com/i/322919/201405/181117587961455.png",
"http://images.cnitblog.com/i/322919/201405/181118041251414.png",
"http://images.cnitblog.com/i/322919/201405/181119313754936.png",
"http://images.cnitblog.com/i/322919/201405/181119357816682.png",
"http://images.cnitblog.com/i/322919/201405/181119458753432.png",
"http://images.cnitblog.com/i/322919/201405/181119499372608.png",
"http://images.cnitblog.com/i/322919/201405/181120173901329.png",
"http://images.cnitblog.com/i/322919/201405/181120244849561.png",
"http://images.cnitblog.com/i/322919/201405/181120357812013.png",
"http://images.cnitblog.com/i/322919/201405/181120398596959.png"
};
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 = "http://www.sogou.com/docs/about.htm";
//異步下載文本文件內(nèi)容任務(wù)
new DownloadTextTask().execute(strUrl);