MVC

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Web容器几大常用组件之间的关系，Servlet、JSP、JavaBean、DB

这几个组件之间的关系是MVC模式的基础。

经典MVC使用方法

请求到达Servlet，Servlet将它写到Bean里面（如果需要的话）

Servlet跳转到JSP

JSP来得到Bean里面的数据

下面就以MVC的方法完成一个模糊查询的界面，输入员工的模糊资料，能够查询出他的详细资料（编号、开始姓名、结束姓名、邮箱）。

首先建立一个模糊查询的页面queryForm.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <title>查询页面</title> </head> <body> 查找表单<br/> <form action="/MyMVC/servlet/QueryServlet" method="post">请输入员工姓名 <input name="ename"> <input type="submit" value="模糊查询"> </form> </body></html> 编写Servlet，QueryServlet.java

package wang.servlet;import java.io.IOException;import java.util.List;import javax.servlet.RequestDispatcher;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import wang.dao.EmployeeDao;import wang.po.Employee;public class QueryServlet extends HttpServlet {public QueryServlet() {super();}public void destroy() {super.destroy(); }public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String name = request.getParameter("ename");name = new String(name.getBytes("ISO-8859-1"));EmployeeDao employeeDao = new EmployeeDao();List<Employee> employees = employeeDao.queryEmployeeByName(name);request.setAttribute("employees", employees);ServletContext application = this.getServletContext();RequestDispatcher rd = application.getRequestDispatcher("/queryResult.jsp");rd.forward(request,response);}public void init() throws ServletException {}} 在该Servlet中首先接受界面输入的姓名参数，然后调用Dao（Data access object），到数据库里面查找。

编写Dao，EmployeeDao.java，实现访问数据库以及业务逻辑

package wang.dao;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;import wang.po.Employee;public class EmployeeDao {private Connection conn = null;public void initialConnection() {try {Class.forName("oracle.jdbc.driver.OracleDriver").newInstance(); String url="jdbc:oracle:thin:@localhost:1521:xe"; conn = DriverManager.getConnection(url, "hr", "hr"); } catch (Exception e) {e.printStackTrace();} }public List<Employee> queryEmployeeByName(String name) {List<Employee> employees = new ArrayList<Employee>();String sql = "select * from employees where FIRST_NAME like '%" + name + "%'";try {this.initialConnection();ResultSet rs = conn.createStatement().executeQuery(sql);while(rs.next()) {Employee employee = new Employee();employee.setEmployeeId(rs.getString("EMPLOYEE_ID"));employee.setFirstName(rs.getString("FIRST_NAME"));employee.setLastName(rs.getString("LAST_NAME"));employee.setEmail(rs.getString("EMAIL"));employees.add(employee);}} catch (SQLException e) {e.printStackTrace();} finally {this.closeConnection();}return employees;}public void closeConnection() {try {if(conn!=null) {conn.close();conn = null;}} catch (SQLException e) {e.printStackTrace();}}} 在Dao中使用了POJO类，在一定程度上起到映射数据表的作用

package wang.po;public class Employee {private String employeeId;private String firstName;private String lastName;private String email;public String getEmployeeId() {return employeeId;}public void setEmployeeId(String employeeId) {this.employeeId = employeeId;}public String getFirstName() {return firstName;}public void setFirstName(String firstName) {this.firstName = firstName;}public String getLastName() {return lastName;}public void setLastName(String lastName) {this.lastName = lastName;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}} 在Servlet中得到查找的数据后，下面这几句代码

ServletContext application = this.getServletContext();RequestDispatcher rd = application.getRequestDispatcher("/queryResult.jsp");rd.forward(request,response); 表示跳转到queryResult.jsp页面中去。

注意：由于上面是把数据保存在request中（减少消耗），所以必须使用上面方法的跳转，如果是放在session里面，可以使用下面方法response.sendRedirect(location); 编写queryResult.jsp页面

<%@ page language="java" import="java.util.*,wang.po.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <title>查询结果页面</title> </head> <body> 查询结果<br/> <table> <tr> <td>编号</td> <td>开始姓名</td> <td>结束姓名</td> <td>邮箱</td> </tr> <% List employees = (ArrayList)request.getAttribute("employees"); for (int i=0; i<employees.size(); i++) { Employee employee = (Employee)employees.get(i); %> <tr> <td><%=employee.getEmployeeId() %></td> <td><%=employee.getFirstName() %></td> <td><%=employee.getLastName() %></td> <td><%=employee.getEmail() %></td> </tr> <% } %> </table> </body></html> 启动Tomcat，访问查询页面，输入查询条件

得到查询结果