GetNameData2.java【後端】

package ch01;

import java.io.IOException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;

@WebServlet("/GetNameData2")
public class GetNameData2 extends HttpServlet {
    // 這個Servlet負責把「職務代理人姓名資料」傳回前端，並由JavaScript AJAX呼叫。

    private static final long serialVersionUID = 1L;
    private DataSource dataSource = null;

    @Override
    public void init() throws ServletException {
        super.init();
        // initialize method
        try {
            Context context = new InitialContext();
            dataSource = (DataSource) context.lookup("java:comp/env/jdbc/ExamOne");
        } catch (NamingException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }// end of doGet method

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }// end of doPost method

    private void processRequest(HttpServletRequest request, HttpServletResponse response) throws IOException {
        /* Setting the Encoding of Input Data */
        request.setCharacterEncoding("UTF-8");

        /* Setting the encoding of the output data to the web page */
        response.setContentType("text/html; charset=UTF-8");

        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        StringBuilder stringBuilder = new StringBuilder();
        try {
            connection = dataSource.getConnection();
            String queryStatement = "SELECT cname FROM Employee";// 查詢資料指令，把名單查出來。
            statement = connection.createStatement();
            resultSet = statement.executeQuery(queryStatement);
            boolean isSecond = false;
            // flag第一次為false，第二次才被設定為true
            while (resultSet.next()) {
                // 邊查資料，邊動態產生名字陣列，並用逗號隔開。
                if (true == isSecond) {
                    stringBuilder.append(",");
                } else {
                    isSecond = true;
                }
                stringBuilder.append(resultSet.getString("cname"));
            }
            response.getWriter().print(stringBuilder.toString());// 一定要加這行程式碼印出來。才可以讓AJAX把動態產生的下拉式選單製作出來。
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            if (resultSet != null) {
                try {
                    resultSet.close();
                    resultSet = null;
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (statement != null) {
                try {
                    statement.close();
                    statement = null;
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (connection != null) {
                try {
                    connection.close();
                    connection = null;
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        } // end of finally
    }// end of processRequest method
}// end of getNameData2 Servlet