idea写一个Servlet以实现增删改查 Emp表，连接数据库

好的，以下是一个示例代码，可以实现基本的增删改查功能：

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/EmpServlet")
public class EmpServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private Connection conn;
    private PreparedStatement pstmt;
    private ResultSet rs;

    public void init() {
        String driver = "com.mysql.jdbc.Driver";
        String url = "jdbc:mysql://localhost:3306/test";
        String user = "root";
        String password = "123456";

        try {
            Class.forName(driver);
            conn = DriverManager.getConnection(url, user, password);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        String action = request.getParameter("action");

        if (action.equals("addEmp")) {
            String empno = request.getParameter("empno");
            String ename = request.getParameter("ename");
            String job = request.getParameter("job");
            String mgr = request.getParameter("mgr");
            String hiredate = request.getParameter("hiredate");
            String sal = request.getParameter("sal");
            String comm = request.getParameter("comm");
            String deptno = request.getParameter("deptno");

            String sql = "INSERT INTO emp (empno, ename, job, mgr, hiredate, sal, comm, deptno) VALUES (?, ?, ?, ?, ?, ?, ?, ?)";

            try {
                pstmt = conn.prepareStatement(sql);
                pstmt.setString(1, empno);
                pstmt.setString(2, ename);
                pstmt.setString(3, job);
                pstmt.setString(4, mgr);
                pstmt.setString(5, hiredate);
                pstmt.setString(6, sal);
                pstmt.setString(7, comm);
                pstmt.setString(8, deptno);
                pstmt.executeUpdate();
                out.println("添加成功！");
            } catch (SQLException e) {
                e.printStackTrace();
            }
        } else if (action.equals("deleteEmp")) {
            String empno = request.getParameter("empno");

            String sql = "DELETE FROM emp WHERE empno = ?";

            try {
                pstmt = conn.prepareStatement(sql);
                pstmt.setString(1, empno);
                pstmt.executeUpdate();
                out.println("删除成功！");
            } catch (SQLException e) {
                e.printStackTrace();
            }
        } else if (action.equals("updateEmp")) {
            String empno = request.getParameter("empno");
            String ename = request.getParameter("ename");
            String job = request.getParameter("job");
            String mgr = request.getParameter("mgr");
            String hiredate = request.getParameter("hiredate");
            String sal = request.getParameter("sal");
            String comm = request.getParameter("comm");
            String deptno = request.getParameter("deptno");

            String sql = "UPDATE emp SET ename = ?, job = ?, mgr = ?, hiredate = ?, sal = ?, comm = ?, deptno = ? WHERE empno = ?";

            try {
                pstmt = conn.prepareStatement(sql);
                pstmt.setString(1, ename);
                pstmt.setString(2, job);
                pstmt.setString(3, mgr);
                pstmt.setString(4, hiredate);
                pstmt.setString(5, sal);
                pstmt.setString(6, comm);
                pstmt.setString(7, deptno);
                pstmt.setString(8, empno);
                pstmt.executeUpdate();
                out.println("修改成功！");
            } catch (SQLException e) {
                e.printStackTrace();
            }
        } else if (action.equals("queryEmp")) {
            String empno = request.getParameter("empno");
            String ename = request.getParameter("ename");

            String sql = "SELECT * FROM emp WHERE 1 = 1";

            if (empno != null && !empno.trim().equals("")) {
                sql += " AND empno = '" + empno + "'";
            }

            if (ename != null && !ename.trim().equals("")) {
                sql += " AND ename = '" + ename + "'";
            }

            try {
                pstmt = conn.prepareStatement(sql);
                rs = pstmt.executeQuery();

                while (rs.next()) {
                    out.println("empno: " + rs.getString("empno") + "<br>");
                    out.println("ename: " + rs.getString("ename") + "<br>");
                    out.println("job: " + rs.getString("job") + "<br>");
                    out.println("mgr: " + rs.getString("mgr") + "<br>");
                    out.println("hiredate: " + rs.getString("hiredate") + "<br>");
                    out.println("sal: " + rs.getString("sal") + "<br>");
                    out.println("comm: " + rs.getString("comm") + "<br>");
                    out.println("deptno: " + rs.getString("deptno") + "<br><br>");
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    public void destroy() {
        try {
            if (rs != null) {
                rs.close();
            }

            if (pstmt != null) {
                pstmt.close();
            }

            if (conn != null) {
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

在这个例子中，我们使用了MySQL数据库，数据库名为test，用户名为root，密码为123456。你可以根据自己的实际情况修改这些参数。在init()方法中，我们使用了JDBC驱动来连接数据库。

在doPost()方法中，我们首先获取前端传来的action参数，根据参数的不同执行不同的操作。如果action为addEmp，表示进行插入操作，我们从request中获取表单数据，使用PreparedStatement对数据库进行操作。如果action为deleteEmp，表示进行删除操作，我们从request中获取要删除的empno，对数据库进行操作。如果action为updateEmp，表示进行更新操作，我们从request中获取要更新的empno以及表单数据，对数据库进行操作。如果action为queryEmp，表示进行查询操作，我们从request中获取要查询的empno和ename，根据不同的情况构造不同的SQL语句，使用PreparedStatement查询数据库，并将结果输出到前端。

最后，我们在destroy()方法中关闭ResultSet、PreparedStatement和Connection对象，释放资源。