Android初級開發（九）——網絡交互—HttpURLConnection

一、使用HttpURLConnection的步驟
1、獲取到HttpURLConnection的實例，並傳入目標的網絡地址，然後調用openConnection()方法

URL url = new URL("http://www.baidu.com");
HttpURLConnection connection = (HttpURLConnection)url.openConnection();

2、設置HTTP請求所使用的方法GET和POST
GET:從服務器那裏獲取數據
之後再調用getInputStream()方法獲取到服務器返回的輸入流

connection.setRequestMethod("GET");
InputStream in = connection.getInputStream();

POST:提交數據給服務器
每條數據都要以鍵值對的形式存在，數據與數據之間用“&”符號隔開

connection.setRequestMethod("POST");
DataOutputStream out = new DataOutputStream(connection.getOutputStream());
out.writeBytes("username=admin&password=123456");

3、調用disconnect()方法將HTTP連接關閉掉

connection.disconnect();

二、實例
需求：一個按鈕用於發送HTTP請求，一個文本框用於將服務器返回的數據顯示出來
1、效果圖

2、佈局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
   <Button
       android:id="@+id/send_request"
       android:layout_width="match_parent"
       android:layout_height="80dp"
       android:text="發送請求"
       android:textSize="25dp"/>
    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <TextView
            android:id="@+id/response_text"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </ScrollView>


</LinearLayout>

3、MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    TextView responseText;
    Button sendRequset;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        sendRequset = (Button) findViewById(R.id.send_request);
        responseText = (TextView) findViewById(R.id.response_text);
        sendRequset.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        if (view.getId() == R.id.send_request){
            sendRequsetWithHttpURLConnection();
        }
    }

    private void sendRequsetWithHttpURLConnection() {
        //開啓線程來發起網絡請求
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection connection = null;
                BufferedReader reader = null;
                try {
                    URL url = new URL("http://www.baidu.com");
                    connection = (HttpURLConnection) url.openConnection();

                    //提交數據給服務器的步驟
                   // connection.setRequestMethod("POST");
                   // DataOutputStream out = new DataOutputStream(connection.getOutputStream());
                   // out.writeBytes("username=admin&password=123456");

                    connection.setRequestMethod("GET");
                    //設置鏈接超時的毫秒數
                    connection.setConnectTimeout(8000);
                    //設置讀取超時的毫秒數
                    connection.setReadTimeout(8000);
                    InputStream in = connection.getInputStream();
                    //下面對獲取到的輸入流進行讀取
                    reader = new BufferedReader(new InputStreamReader(in));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = reader.readLine())!=null){
                        response.append(line);
                    }
                    showResponse(response.toString());
                }catch (Exception e){
                    e.printStackTrace();
                }finally {
                    if(reader != null){
                        try {
                            reader.close();
                        }catch (IOException e){
                            e.printStackTrace();
                        }
                    }
                    if (connection != null){
                        connection.disconnect();
                    }
                }
            }
        }).start();
    }

    //結果傳入showResponse方法中
    private void showResponse(final String s) {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                //在這裏進行UI操作，將結果顯示到界面上
                responseText.setText(s);
            }
        });
    }
}

4、聲明網絡權限

<uses-permission android:name="android.permission.INTERNET"/>