新增網路訪問許可權

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

package com.zdsoft.httpget;

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.EditText;
import android.widget.Toast;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;

public class MainActivity extends AppCompatActivity {
    private EditText et_username, et_password;
    private Button bt_login;
    private String result = "";//伺服器返回結果
    private String URL_BASE = "http://192.168.12.187:8080/test/servlet/LoginServlet";//介面地址


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initView();
        bt_login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                final Handler handler = new Handler() {
                    @Override
                    public void handleMessage(Message msg) {
                        //更新UI
                        if (msg.what == 1) {
                            Toast.makeText(MainActivity.this, result, Toast.LENGTH_SHORT).show();
                            et_username.setText("");
                            et_password.setText("");

                        }
                    }

                };
                new Thread() {
                    @Override
                    public void run() {
                        //網路訪問，登入
                        //get方式
                        //loginGet(et_username.getText().toString(), et_password.getText().toString());
                        //post方式
                        loginPost(et_username.getText().toString(), et_password.getText().toString());
                        Message message = new Message();
                        message.what = 1;
                        handler.sendMessage(message);
                    }
                }.start();
            }
        });
    }

    private void initView() {
        et_username = (EditText) findViewById(R.id.et_username);
        et_password = (EditText) findViewById(R.id.et_password);
        bt_login = (Button) findViewById(R.id.bt_login);
    }

    /**
     * get方式提交
     * 使用者登入
     *
     * @param username
     * @param password
     */
    private void loginGet(String username, String password) {

        try {
            //獲取URL物件
            URL url = new URL(URL_BASE + "?username=" + URLEncoder.encode(username, "UTF-8") + "&password=" + URLEncoder.encode(password, "UTF-8") + "");
            //獲取HttpURLConnection
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            //獲取輸入流
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            //讀取伺服器返回結果
            StringBuffer sb = new StringBuffer();
            String line = "";
            while ((line = bufferedReader.readLine()) != null) {
                sb.append(line);
            }
            result = sb.toString();
            //關閉流，斷開連結
            bufferedReader.close();
            connection.disconnect();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    /**
     * post方式提交
     * 使用者登入
     *
     * @param username
     * @param password
     */
    private void loginPost(String username, String password) {
        try {
            //獲取URL物件
            URL url = new URL(URL_BASE);
            //獲取HttpURLConnection
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("POST");
            //設定允許輸入、輸出
            conn.setDoInput(true);
            conn.setDoOutput(true);
            //設定請求的頭
            conn.setRequestProperty("content-type", "application/x-www-form-urlencoded");
            conn.setRequestProperty("charset", "utf-8");
            //獲取輸出流
            OutputStream os = conn.getOutputStream();
            String date = "username=" + URLEncoder.encode(username, "UTF-8") + "&password=" + URLEncoder.encode(password, "UTF-8") + "";
            os.write(date.getBytes());
            os.flush();
            //獲取BufferedReader，讀取伺服器返回資訊
            BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line = "";
            StringBuffer sb = new StringBuffer();
            while ((line = br.readLine()) != null) {
                sb.append(line);
            }
            result = sb.toString();
            //關閉流，斷開連結
            os.close();
            conn.disconnect();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}