如前文所示的TCP局域网传送东西，除了对传输层的TCP/UDP支持良好外，Android对HTTP(超文本传输协议)也提供了很好的支持，这里包括两种接口:
1、标准Java接口(java.net) —-HttpURLConnection，可以实现简单的基于URL请求、响应功能；
2、Apache接口(org.appache.http)—-HttpClient，使用起来更方面更强大。一般来说，用这种接口。不过本文还是把第一种接口过一下。
任何一种接口，无外乎四个基本功能:访问网页、下载图片或文件、上传文件.本文示范的是访问网页和下载图片。HttpURLConnection继承自URLConnection类，用它可以发送和接口任何类型和长度的数据，且预先不用知道数据流的长度，可以设置请求方式get或post、超时时间。
下面直接贴代码，代码目的有两个，一是访问百度首页，获取其返回的html字符串，二是给定URL下载个图片并显示出来。后续将展开系列博文介绍HTTP相关知识。
activity_main.xml
<RelativeLayout xmlns:android=""xmlns:tools=""android:id="@+id/parent_view"android:layout_width="match_parent"android:layout_height="match_parent"android:paddingBottom="@dimen/activity_vertical_margin"android:paddingLeft="@dimen/activity_horizontal_margin"android:paddingRight="@dimen/activity_horizontal_margin"android:paddingTop="@dimen/activity_vertical_margin"tools:context=".MainActivity" ><FrameLayoutandroid:layout_width="match_parent"android:layout_height="match_parent" ><TextViewandroid:id="@+id/textview_show"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="@string/hello_world" /><ImageViewandroid:id="@+id/imagview_show"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_gravity="center" /></FrameLayout><Buttonandroid:id="@+id/btn_visit_web"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignParentBottom="true"android:layout_alignParentLeft="true"android:text="访问百度" /><Buttonandroid:id="@+id/btn_download_img"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignParentBottom="true"android:layout_toRightOf="@id/btn_visit_web"android:text="下载图片"/></RelativeLayout>MainActivity.javapackage org.yanzi.httpurlconnection;import java.io.BufferedReader;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;import android.app.Activity;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.os.Bundle;import android.view.Menu;import android.view.View;import android.view.ViewGroup;import android.widget.Button;import android.widget.ImageView;import android.widget.ProgressBar;import android.widget.RelativeLayout;import android.widget.TextView;public class MainActivity extends Activity {Button visitWebBtn = null;Button downImgBtn = null;TextView showTextView = null;ImageView showImageView = null;String resultStr = "";ProgressBar progressBar = null;ViewGroup viewGroup = null;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);initUI();visitWebBtn.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubshowImageView.setVisibility(View.GONE);showTextView.setVisibility(View.VISIBLE);Thread visitBaiduThread = new Thread(new VisitWebRunnable());visitBaiduThread.start();try {visitBaiduThread.join();if(!resultStr.equals("")){showTextView.setText(resultStr);}} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}});downImgBtn.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubshowImageView.setVisibility(View.VISIBLE);showTextView.setVisibility(View.GONE);String imgUrl = "";new DownImgAsyncTask().execute(imgUrl);}});}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.main, menu);return true;}public void initUI(){showTextView = (TextView)findViewById(R.id.textview_show);showImageView = (ImageView)findViewById(R.id.imagview_show);downImgBtn = (Button)findViewById(R.id.btn_download_img);visitWebBtn = (Button)findViewById(R.id.btn_visit_web);}/** * 获取指定URL的响应字符串 * @param urlString * @return */private String getURLResponse(String urlString){HttpURLConnection conn = null; //连接对象InputStream is = null;String resultData = "";try {URL url = new URL(urlString); //URL对象conn = (HttpURLConnection)url.openConnection(); //使用URL打开一个链接conn.setDoInput(true); //允许输入流，即允许下载conn.setDoOutput(true); //允许输出流，即允许上传conn.setUseCaches(false); //不使用缓冲conn.setRequestMethod("GET"); //使用get请求is = conn.getInputStream(); //获取输入流，此时才真正建立链接InputStreamReader isr = new InputStreamReader(is);BufferedReader bufferReader = new BufferedReader(isr);String inputLine = "";while((inputLine = bufferReader.readLine()) != null){resultData += inputLine + "\n";}} catch (MalformedURLException e) {// TODO Auto-generated catch blocke.printStackTrace();}catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}finally{if(is != null){try {is.close();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}if(conn != null){conn.disconnect();}}return resultData;}/** * 从指定URL获取图片 * @param url * @return */private Bitmap getImageBitmap(String url){URL imgUrl = null;Bitmap bitmap = null;try {imgUrl = new URL(url);HttpURLConnection conn = (HttpURLConnection)imgUrl.openConnection();conn.setDoInput(true);conn.connect();InputStream is = conn.getInputStream();bitmap = BitmapFactory.decodeStream(is);is.close();} catch (MalformedURLException e) {// TODO Auto-generated catch blocke.printStackTrace();}catch(IOException e){e.printStackTrace();}return bitmap;}class VisitWebRunnable implements Runnable{@Overridepublic void run() {// TODO Auto-generated method stubString data = getURLResponse("");resultStr = data;}}class DownImgAsyncTask extends AsyncTask<String, Void, Bitmap>{@Overrideprotected void onPreExecute() {// TODO Auto-generated method stubsuper.onPreExecute();showImageView.setImageBitmap(null);showProgressBar();//显示进度条提示框}@Overrideprotected Bitmap doInBackground(String… params) {// TODO Auto-generated method stubBitmap b = getImageBitmap(params[0]);return b;}@Overrideprotected void onPostExecute(Bitmap result) {// TODO Auto-generated method stubsuper.onPostExecute(result);if(result!=null){dismissProgressBar();showImageView.setImageBitmap(result);}}}/** * 在母布局中间显示进度条 */private void showProgressBar(){progressBar = new ProgressBar(this, null, android.R.attr.progressBarStyleLarge);RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,ViewGroup.LayoutParams.WRAP_CONTENT);params.addRule(RelativeLayout.CENTER_IN_PARENT, RelativeLayout.TRUE);progressBar.setVisibility(View.VISIBLE);Context context = getApplicationContext();viewGroup = (ViewGroup)findViewById(R.id.parent_view);//MainActivity.this.addContentView(progressBar, params);viewGroup.addView(progressBar, params);}/** * 隐藏进度条 */private void dismissProgressBar(){if(progressBar != null){progressBar.setVisibility(View.GONE);viewGroup.removeView(progressBar);progressBar = null;}}}AndroidManifest.xml里记得加访问网络的权限:
<uses-permission android:name="android.permission.INTERNET"/>
注意事项:
美好的生命应该充满期待惊喜和感激
