日报2015/11/26(第一行代码读书笔记)

使用HttpURLConnection访问百度首页

package com.jackie.networktest;import android.os.Handler;import android.os.Message;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;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;public class MainActivity extends AppCompatActivity {    private Button btnSend;    private TextView tvResponse;    //用于收发消息进行UI更新    private Handler handler = new Handler() {        /**         * 在主线程更新TextView中的内容         * @param msg         */        @Override        public void handleMessage(Message msg) {            if (msg.what == 1) {                String response = ((StringBuilder) msg.obj).toString();                tvResponse.setText(response);            }        }    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        btnSend = (Button) findViewById(R.id.btnSend);        tvResponse = (TextView) findViewById(R.id.tvResponse);        btnSend.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                //访问网络是耗时操作，开辟子线程                new Thread(new Runnable() {                    @Override                    public void run() {                        HttpURLConnection httpURLConnection = null;                        try {                            URL url = new URL("http://www.baidu.com");                            //向百度服务器发起Http请求                            httpURLConnection = (HttpURLConnection) url.openConnection();                            httpURLConnection.setRequestMethod("GET");                            httpURLConnection.setConnectTimeout(8000);                            httpURLConnection.setReadTimeout(8000);                            //获得服务器返回的字节流                            InputStream is = httpURLConnection.getInputStream();                            //包装成输入流                            InputStreamReader isr = new InputStreamReader(is);                            //包装成缓冲流                            BufferedReader br = new BufferedReader(isr);                            //使用StringBuilder来保存字符                            StringBuilder sb = new StringBuilder();                            String line;                            while ((line = br.readLine()) != null) {                                sb.append(line);                            }                            Message message = new Message();                            message.what = 1;                            message.obj = sb;                            //通知handler，封装返回的数据                            handler.sendMessage(message);                        } catch (MalformedURLException e) {                            e.printStackTrace();                        } catch (IOException e) {                            e.printStackTrace();                        } finally {                            //关闭连接                            if (httpURLConnection != null) {                                httpURLConnection.disconnect();                            }                        }                    }                }).start();            }        });    }}

这里返回的是最原始的HTML代码片。

---

使用HttpClient访问百度首页

这个方法现在实际上已经过时了，因为这个类是Apache提供的，
sdk6.0以后取消了HttpClient，设置android SDK的编译版本为23时，且使用了httpClient相关类的库项目，会出现有一些类找不到的错误。

解决方法有两种：

1.在相应的module下的build.gradle
useLibrary 'org.apache.http.legacy'
这句一定要加在 android{ } 当中。

如：

android {    useLibrary 'org.apache.http.legacy'}

2.将在相应的module下的build.gradle中修改compileSdkVersion的值，设置为更小的sdk版本

将上面的代码改为

                        HttpClient httpClient = new DefaultHttpClient();                        HttpGet httpGet = new HttpGet("http://www.baidu.com");                        try {                            HttpResponse httpResponse = httpClient.execute(httpGet);                            HttpEntity httpEntity = httpResponse.getEntity();                            String entity = EntityUtils.toString(httpEntity, "utf-8");                            Message message = new Message();                            message.what = 1;                            message.obj = entity;                            handler.sendMessage(message);

返回的是同样的页面