SpringMVC 资源状态转移RESTful

1、RESTful简介

REST：Representational State Transfer，表现层资源状态转移。

a>资源

资源是一种看待服务器的方式，即，将服务器看作是由很多离散的资源组成。每个资源是服务器上一个可命名的抽象概念。因为资源是一个抽象的概念，所以它不仅仅能代表服务器文件系统中的一个文件、数据库中的一张表等等具体的东西，可以将资源设计的要多抽象有多抽象，只要想象力允许而且客户端应用开发者能够理解。与面向对象设计类似，资源是以名词为核心来组织的，首先关注的是名词。一个资源可以由一个或多个URI来标识。URI既是资源的名称，也是资源在Web上的地址。对某个资源感兴趣的客户端应用，可以通过资源的URI与其进行交互。

b>资源的表述

资源的表述是一段对于资源在某个特定时刻的状态的描述。可以在客户端-服务器端之间转移（交换）。资源的表述可以有多种格式，例如HTML/XML/JSON/纯文本/图片/视频/音频等等。资源的表述格式可以通过协商机制来确定。请求-响应方向的表述通常使用不同的格式。

c>状态转移

状态转移说的是：在客户端和服务器端之间转移（transfer）代表资源状态的表述。通过转移和操作资源的表述，来间接实现操作资源的目的。

2、RESTful的实现

具体说，就是 HTTP 协议里面，四个表示操作方式的动词：GET、POST、PUT、DELETE。

它们分别对应四种基本操作：GET 用来获取资源，POST 用来新建资源，PUT 用来更新资源，DELETE 用来删除资源。

REST 风格提倡 URL 地址使用统一的风格设计，从前到后各个单词使用斜杠分开，不使用问号键值对方式携带请求参数，而是将要发送给服务器的数据作为 URL 地址的一部分，以保证整体风格的一致性。

操作	传统方式	REST风格
查询操作	getUserById?id=1	user/1–>get请求方式
保存操作	saveUser	user–>post请求方式
删除操作	deleteUser?id=1	user/1–>delete请求方式
更新操作	updateUser	user–>put请求方式

HiddenHttpMethodFilter

由于浏览器只支持发送get和post方式的请求，那么该如何发送put和delete请求呢？

SpringMVC 提供了 HiddenHttpMethodFilter 帮助我们将 POST 请求转换为 DELETE 或 PUT 请求

HiddenHttpMethodFilter 处理put和delete请求的条件：

a>当前请求的请求方式必须为post

b>当前请求必须传输请求参数_method

满足以上条件，HiddenHttpMethodFilter 过滤器就会将当前请求的请求方式转换为请求参数_method的值，因此请求参数_method的值才是最终的请求方式

在web.xml中注册HiddenHttpMethodFilter

<filter><filter-name>HiddenHttpMethodFilter</filter-name><filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
</filter>
<filter-mapping><filter-name>HiddenHttpMethodFilter</filter-name><url-pattern>/*</url-pattern>
</filter-mapping>

注：

目前为止，SpringMVC中提供了两个过滤器：CharacterEncodingFilter和HiddenHttpMethodFilter

在web.xml中注册时，必须先注册CharacterEncodingFilter，再注册HiddenHttpMethodFilter

原因：

• 在 CharacterEncodingFilter 中通过 request.setCharacterEncoding(encoding) 方法设置字符集的

• request.setCharacterEncoding(encoding) 方法要求前面不能有任何获取请求参数的操作

• 而 HiddenHttpMethodFilter 恰恰有一个获取请求方式的操作：

• String paramValue = request.getParameter(this.methodParam);
  

RESTful案例

和传统 CRUD 一样，实现对员工信息的增删改查。
1.搭建环境

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"version="4.0"><!--配置编码过滤器--><filter><filter-name>CharacterEncodingFilter</filter-name><filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class><init-param><param-name>encoding</param-name><param-value>UTF-8</param-value></init-param><init-param><param-name>forceResponseEncoding</param-name><param-value>true</param-value></init-param></filter><filter-mapping><filter-name>CharacterEncodingFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping><!--配置处理请求方式put和delete的HiddenHttpMethodFilter--><filter><filter-name>HiddenHttpMethodFilter</filter-name><filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class></filter><filter-mapping><filter-name>HiddenHttpMethodFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping><!--配置SpringMVC的前端控制器DispatcherServlet--><servlet><servlet-name>DispatcherServlet</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>classpath:springMVC.xml</param-value></init-param><load-on-startup>1</load-on-startup></servlet><servlet-mapping><servlet-name>DispatcherServlet</servlet-name><url-pattern>/</url-pattern></servlet-mapping></web-app>

delete put 方法需要过滤器org.springframework.web.filter.HiddenHttpMethodFilter
记得添加

springMVC.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:context="http://www.springframework.org/schema/context"xmlns:mvc="http://www.springframework.org/schema/mvc"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc https://www.springframework.org/schema/mvc/spring-mvc.xsd"><!--扫描组件--><context:component-scan base-package="com.restful.demo_restful"></context:component-scan><!--配置Thymeleaf视图解析器--><bean id="viewResolver" class="org.thymeleaf.spring5.view.ThymeleafViewResolver"><property name="order" value="1"/><property name="characterEncoding" value="UTF-8"/><property name="templateEngine"><bean class="org.thymeleaf.spring5.SpringTemplateEngine"><property name="templateResolver"><bean class="org.thymeleaf.spring5.templateresolver.SpringResourceTemplateResolver"><!-- 视图前缀 --><property name="prefix" value="/WEB-INF/templates/"/><!-- 视图后缀 --><property name="suffix" value=".html"/><property name="templateMode" value="HTML5"/><property name="characterEncoding" value="UTF-8" /></bean></property></bean></property></bean><!--配置视图控制器--><mvc:view-controller path="/" view-name="index"></mvc:view-controller><mvc:view-controller path="/toAdd" view-name="employee_add"></mvc:view-controller><!--开放对静态资源的访问--><mvc:default-servlet-handler /><!--开启mvc注解驱动--><mvc:annotation-driven /></beans>

Mycontroller.java

package com.restful.demo_restful.controller;import com.restful.demo_restful.dao.EmployeeDao;
import com.restful.demo_restful.pro.Employee;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;import java.util.Collection;/*** ClassName: MyController* Package: com.restful.demo_restful.controller* Description:** @Author Thmiao* @Create 2023/10/24 17:21* @Version 1.0*/@Controller
public class MyController {@AutowiredEmployeeDao employeeDao;// 获取所有的员工@RequestMapping(value = "/employee", method = RequestMethod.GET)public String getEmployeeList(Model model){Collection<Employee> employeeList = employeeDao.getAll();model.addAttribute("employeeList", employeeList);return "employee_list";}// 删除员工@RequestMapping(value = "/employee/{id}", method = RequestMethod.DELETE)public String deleteEmployee(@PathVariable("id") Integer id){employeeDao.delete(id);return "redirect:/employee";}// 添加员工信息@RequestMapping(value = "/employee", method = RequestMethod.POST)public String addEmployee(Employee employee){employeeDao.save(employee);return "redirect:/employee";}// 修改页面@RequestMapping(value = "/employee/{id}", method = RequestMethod.GET)public String getEmployeeById(@PathVariable("id") Integer id, Model model){Employee employee = employeeDao.get(id);model.addAttribute("employee", employee);return "employee_update";}// 修改员工信息@RequestMapping(value = "/employee", method = RequestMethod.PUT)public String updateEmployee(Employee employee){employeeDao.save(employee);return "redirect:/employee";}
}

EmpolyeeDao.java

package com.restful.demo_restful.dao;import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import com.restful.demo_restful.pro.Employee;
import org.springframework.stereotype.Repository;@Repository
public class EmployeeDao {private static Map<Integer, Employee> employees = null;static{employees = new HashMap<Integer, Employee>();employees.put(1001, new Employee(1001, "E-AA", "[e-mail]", 1));employees.put(1002, new Employee(1002, "E-BB", "[e-mail]", 1));employees.put(1003, new Employee(1003, "E-CC", "[e-mail]", 0));employees.put(1004, new Employee(1004, "E-DD", "[e-mail]", 0));employees.put(1005, new Employee(1005, "E-EE", "[e-mail]", 1));}private static Integer initId = 1006;public void save(Employee employee){if(employee.getId() == null){employee.setId(initId++);}employees.put(employee.getId(), employee);}public  Collection<Employee> getAll(){return employees.values();}public Employee get(Integer id){return employees.get(id);}public void delete(Integer id){employees.remove(id);}
}

Employee.java

package com.restful.demo_restful.pro;public class Employee {private Integer id;private String lastName;private String email;//1 male, 0 femaleprivate Integer gender;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}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;}public Integer getGender() {return gender;}public void setGender(Integer gender) {this.gender = gender;}public Employee(Integer id, String lastName, String email, Integer gender) {super();this.id = id;this.lastName = lastName;this.email = email;this.gender = gender;}public Employee() {}
}

myjs.js

var vue = new Vue({"el":"#dataTable",methods:{//event表示当前事件deleteEmployee:function (event) {//阻止超链接的默认跳转行为event.preventDefault();//通过id获取表单标签var delete_form = document.getElementById("delete_form");//将触发事件的超链接的href属性为表单的action属性赋值delete_form.action = event.target.href;//提交表单delete_form.submit();}
}
});

employee_add.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head><meta charset="UTF-8"><title>Add Employee</title>
</head>
<body><form th:action="@{/employee}" method="post">lastName:<input type="text" name="lastName"><br>email:<input type="text" name="email"><br>gender:<input type="radio" name="gender" value="1">male<input type="radio" name="gender" value="0">female<br><input type="submit" value="add"><br>
</form></body>
</html>

employee_list.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head><meta charset="UTF-8"><title>Employee Info</title><script type="text/javascript" th:src="@{/static/js/vue.js}"></script></head>
<body><table id="dataTable" border="1" cellpadding="0" cellspacing="0" style="text-align: center;" ><tr><th colspan="5">Employee Info</th></tr><tr><th>id</th><th>lastName</th><th>email</th><th>gender</th><th>options(<a th:href="@{/toAdd}">add</a>)</th></tr><tr th:each="employee : ${employeeList}"><td th:text="${employee.id}"></td><td th:text="${employee.lastName}"></td><td th:text="${employee.email}"></td><td th:text="${employee.gender}"></td><td><a class="deleteA" @click="deleteEmployee" th:href="@{'/employee/'+${employee.id}}">delete</a><a th:href="@{'/employee/'+${employee.id}}">update</a></td></tr>
</table><!-- 作用：通过超链接控制表单的提交，将post请求转换为delete请求 -->
<form id="delete_form" method="post"><!-- HiddenHttpMethodFilter要求：必须传输_method请求参数，并且值为最终的请求方式 --><input type="hidden" name="_method" value="DELETE"/>
<!--    <input type="hidden" name="_method" value="delete"/>-->
</form>
</body>
<script type="text/javascript" th:src="@{/static/js/myjs.js}"></script>
</html>

employee_update.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head><meta charset="UTF-8"><title>Update Employee</title>
</head>
<body><form th:action="@{/employee}" method="post"><input type="hidden" name="_method" value="put"><input type="hidden" name="id" th:value="${employee.id}">lastName:<input type="text" name="lastName" th:value="${employee.lastName}"><br>email:<input type="text" name="email" th:value="${employee.email}"><br><!--th:field="${employee.gender}"可用于单选框或复选框的回显若单选框的value和employee.gender的值一致，则添加checked="checked"属性-->gender:<input type="radio" name="gender" value="1" th:field="${employee.gender}">male<input type="radio" name="gender" value="0" th:field="${employee.gender}">female<br><input type="submit" value="update"><br>
</form></body>
</html>

index.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head><meta charset="UTF-8" ><title>Title</title>
</head>
<body>
<h1>首页</h1>
<a th:href="@{/employee}">访问员工信息</a>
</body>
</html>

spring 环境 。还有vue.js记得导入！

功能清单

功能	URL 地址	请求方式
访问首页√	/	GET
查询全部数据√	/employee	GET
删除√	/employee/2	DELETE
跳转到添加数据页面√	/toAdd	GET
执行保存√	/employee	POST
跳转到更新数据页面√	/employee/2	GET
执行更新√	/employee	PUT