MVC框架
一个实现 MVC 模式的应用包含模型、视图、控制器 3 个模块：
模型：封装了应用的数据和业务逻辑，负责管理系统业务数据
视图：负责应用的展示
控制器：负责与用户进行交互，接收用户输入、改变模型、调整视图的显示
基于MVC架构模式的 Java Web 开发
采用了 Servlet + JSP + JavaBean 的技术实现
基于MVC架构模式的 Java Web 开发步骤
1. 定义一系列的 Bean 来表示数据
2. 使用一个 Dispatcher Servlet 和控制类来处理用户请求
3. 在 Servlet 中填充 Bean
4. 在 Servlet 中，将 Bean 存储到 request、session、servletContext中
5. 将请求转发到 JSP 页面
6. 在 JSP 页面中，从 Bean 中提取数据。
其中 Dispatcher servlet 必须完成如下功能：
1. 根据 URI 调用相应的 action
2. 实例化正确的控制器类
3. 根据请求参数值来构造表单 bean
4. 调用控制器对象的相应方法
5. 转发到一个视图（JSP页面）
每个 HTTP 请求都发送给控制器，请求中的 URI 标识出对应的 action。action 代表了应用可以执行的一个操作。一个提供了 Action 的 Java 对象称为 action 对象。
控制器会解析 URI 并调用相应的 action，然后将模型对象放到视图可以访问的区域，以便服务器端数据可以展示在浏览器上。最后控制器利用 RequestDispatcher 跳转到视图（JSP页面），在JSP页面使用 EL 以及定制标签显示数据。
注意：调用 RequestDispatcher.forward 方法并不会停止执行剩余的代码。因此，若 forward 方法不是最后一行代码，则应显示的返回。
使用MVC模式的实例
目录结构如下
代码如下
DispatcherServlet.java
package app16c.servlet;import java.io.IOException;import javax.servlet.RequestDispatcher; 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 app16c.controller.InputProductController; import app16c.controller.SaveProductController;@WebServlet(name = "DispatcherServlet", urlPatterns = {"/product_input.action", "/product_save.action"}) public class DispatcherServlet extends HttpServlet {private static final long serialVersionUID = 1L;public DispatcherServlet() {super();}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {process(request, response);}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}private void process(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String uri = request.getRequestURI();int lastIndex = uri.lastIndexOf("/");String action = uri.substring(lastIndex + 1);String dispatcherUrl = null;if (action.equals("product_input.action")) {InputProductController controller = new InputProductController();dispatcherUrl = controller.handleRequest(request, response);} else if (action.equals("product_save.action")) {SaveProductController controller = new SaveProductController();dispatcherUrl = controller.handleRequest(request, response);}if (dispatcherUrl != null) {RequestDispatcher rd = request.getRequestDispatcher(dispatcherUrl);rd.forward(request, response);}} }
Controller.java
package app16c.controller;import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;public interface Controller {public abstract String handleRequest(HttpServletRequest request, HttpServletResponse response); }
InputProductController.java
package app16c.controller;import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;public class InputProductController implements Controller {@Overridepublic String handleRequest(HttpServletRequest request, HttpServletResponse response) {return "/WEB-INF/jsp/ProductForm.jsp";} }
SaveProductController.java
package app16c.controller;import java.util.List; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import app16c.domain.Product; import app16c.form.ProductForm; import app16c.validator.ProductValidator;public class SaveProductController implements Controller {@Overridepublic String handleRequest(HttpServletRequest request, HttpServletResponse response) {ProductForm productForm = new ProductForm();productForm.setName(request.getParameter("name"));productForm.setDescription(request.getParameter("description"));productForm.setPrice(request.getParameter("price"));ProductValidator productValidator = new ProductValidator();List<String> errors = productValidator.validate(productForm);System.out.println(errors);if (errors.isEmpty()) {Product product = new Product();product.setName(productForm.getName());product.setDescription(productForm.getDescription());product.setPrice(Float.parseFloat(productForm.getPrice()));// insert code to save product to the databaserequest.setAttribute("product", product);return "/WEB-INF/jsp/ProductDetails.jsp";} else {request.setAttribute("errors", errors);request.setAttribute("form", productForm);return "/WEB-INF/jsp/ProductForm.jsp";}} }
ProductValidator.java
package app16c.validator;import java.util.ArrayList; import java.util.List; import app16c.form.ProductForm;public class ProductValidator {public List<String> validate(ProductForm productForm) {List<String> errors = new ArrayList<>();String name = productForm.getName();if (name == null || name.trim().isEmpty()) {errors.add("Product must have a name");}String price = productForm.getPrice();if (price == null || price.trim().isEmpty()) {errors.add("Product must have a price");}else {try {Float.parseFloat(price);} catch (NumberFormatException e) {errors.add("Invalid price value.");}}return errors;} }
Product.java
package app16c.domain;import java.io.Serializable;public class Product implements Serializable { // 一个JavaBean 实现该接口，其实例可以安全的将数据保存到 HttpSession 中。private static final long serialVersionUID = 1L;private String name;private String description;private float price;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getDescription() {return description;}public void setDescription(String description) {this.description = description;}public float getPrice() {return price;}public void setPrice(float price) {this.price = price;} }
ProductForm.java
package app16c.form;// 表单类与 HTML表单相映射，是HTML表单在服务端的代表 public class ProductForm { // 表单类不需要实现 Serializable 接口，因为表单对象很少保存在 HttpSession 中。private String name;private String description;private String price;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getDescription() {return description;}public void setDescription(String description) {this.description = description;}public String getPrice() {return price;}public void setPrice(String price) {this.price = price;} }
ProductForm.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> <!-- taglib指令用来引用标签库并设置标签库的前缀 --><!DOCTYPE html> <html> <head><meta charset="UTF-8"><title>Add Product Form</title><link rel="stylesheet" type="text/css" href="css/main.css" /> <!-- 外部样式表 --> </head> <body><div id="global"><c:if test="${requestScope.errors != null }"> <!-- EL表达式 --><p id="errors">Error(s)!<ul><c:forEach var="error" items="${requestScope.errors }"> <!-- jstl 遍历 --><li>${error }</li></c:forEach></ul></p></c:if><form action="product_save.action" method="post"><fieldset><legend>Add a product</legend><p><label for="name">Product Name: </label><input type="text" id="name" name="name" tabindex="1" /></p><p><label for="description">Description: </label><input type="text" id="description" name="description" tabindex="2" /></p><p><label for="price">Price: </label><input type="text" id="price" name="price" tabindex="3" /></p><p id="buttons"><input id="reset" type="reset" tabindex="4" /><input id="submit" type="submit" tabindex="5" value="Add Product" /></p></fieldset></form></div> </body> </html>
ProductDetails.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <!DOCTYPE html> <html> <head><meta charset="UTF-8"><title>Save Product</title><link rel="stylesheet" type="text/scc" href="css/main.css" /> </head> <body><div id="global"><h4>The product has been saved.</h4><p><h5>Details</h5>Product Name: ${product.name } <br />Description: ${product.description } <br />Price: $${product.price }</p></div> </body> </html>
测试结果
![[UWP]使用Picker实现一个简单的ColorPicker弹窗](https://img2018.cnblogs.com/blog/1239018/201811/1239018-20181115001706426-847255787.png)
