HttpGet請求

在我們平時做的一些項目中，經常會用到連接網絡的功能。這裏以HttpGet爲例子做一個簡單的訪問百度頁面得到其中的代碼的例子。
1 首先，需要得到自己要訪問的服務器地址 

String uriAPI = "http://www.baidu.com";

2 然後創建我們的請求

   HttpGet httpRequest = new HttpGet(uriAPI);

3 執行我們的請求之後得到返回的對象

HttpResponse httpResponse = new DefaultHttpClient().execute(httpRequest);
                            if (httpResponse.getStatusLine().getStatusCode() == 200) {
                           //執行連接成功後的代碼
                            }

/*
完整的代碼
*/

package com.hdu.httppost;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;

import java.io.IOException;


public class MainActivity extends ActionBarActivity {

    private EditText et_load;
    private Button visit;
    private String uriAPI = "http://www.baidu.com";
    private String result;
    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if (msg.what == 1) {
                et_load.setText(result);
            } else if (msg.what == 2) {
                et_load.setText("連接錯誤");
            }
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        et_load = (EditText) findViewById(R.id.et_load);
        visit = (Button) this.findViewById(R.id.visit);

        visit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                new Thread() {
                    public void run() {
                        HttpGet httpRequest = new HttpGet(uriAPI);
                        try {
                            HttpResponse httpResponse = new DefaultHttpClient().execute(httpRequest);
                            if (httpResponse.getStatusLine().getStatusCode() == 200) {
                                result = EntityUtils.toString(httpResponse.getEntity());
                                handler.sendEmptyMessage(1);
                            }
                        } catch (IOException e) {
                            e.printStackTrace();
                        }

                    }
                }.start();
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }


}

這裏有人可能會問爲什麼要新建線程來執行呢？這裏就涉及到android中的UI線程子線程的關係了，android中，UI的更新只能在主線程中， 然而當執行一些比較花費時間的操作的時候，卻不能直接在主線程中進行,因爲會阻塞線程，這樣就需要新建線程了。所以當我們要更新線程的時候，需要從子線程中發送信息給主線程，通知主線程進行操作，因爲要有Handler對象。