SpringMVC之RESTful（含实际代码操作）

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前言

RESTful

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一、RESTful简介

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

• 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。
• 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。
• 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。

二、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

三、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：

• 当前请求的请求方式必须为post
• 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>HiddenHttpMethodFilterfilter-name>
<filter-class>org.springframework.web.filter.HiddenHttpMethodFilterfilterclass>
filter>
<filter-mapping>
<filter-name>HiddenHttpMethodFilterfilter-name>
<url-pattern>/*url-pattern>
filter-mapping>

注：
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);

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四、源码实例

实现：和传统 CRUD 一样，实现对员工信息的增删改查。

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

1.工程文件图

红框内是用到的文件，其他不需要管，注意文件夹结构。

2.Employee实体类

package com.dragon.mvc.bean;

public class Employee {
    private Integer id;
    private String lastName;
    private String email;
    //1 male, 0 female
    private 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() {
    }
    public Employee(Integer id, String lastName, String email, Integer gender) {
        this.id = id;
        this.lastName = lastName;
        this.email = email;
        this.gender = gender;
    }
}

2.dao层：EmployeeDao类

package com.dragon.mvc.dao;

import com.dragon.mvc.bean.Employee;
import org.springframework.stereotype.Repository;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

@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", "[email protected]", 1));
        employees.put(1002, new Employee(1002, "E-BB", "[email protected]", 1));
        employees.put(1003, new Employee(1003, "E-CC", "[email protected]", 0));
        employees.put(1004, new Employee(1004, "E-DD", "[email protected]", 0));
        employees.put(1005, new Employee(1005, "E-EE", "[email protected]", 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);
    }

}

3.首页：index.html

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

4.控制层：EmployeeController类

package com.dragon.mvc.controller;

import com.dragon.mvc.bean.Employee;
import com.dragon.mvc.dao.EmployeeDao;
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;

@Controller
public class EmployeeController {
    @Autowired
    private EmployeeDao employeeDao;
    @RequestMapping(value = "/employee",method = RequestMethod.GET)
    public String getAllEmpolyee(Model model){
        Collection<Employee> employeelist=employeeDao.getAll();
        model.addAttribute("employeelist",employeelist);
        return "employee_list";
    }
    @RequestMapping(value = "/employee/{id}", method = RequestMethod.DELETE)
    public String deleteEmployee(@PathVariable("id") Integer id){
        employeeDao.delete(id);
        return "redirect:/employee";
    }
    @RequestMapping(value = "/employee", method = RequestMethod.POST)
    public String addEmployee(Employee employee){
        employeeDao.save(employee);
        return "redirect:/employee";
    }
    @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";
    }
    @RequestMapping(value = "/employee", method = RequestMethod.PUT)
    public String updateEmployee(Employee employee){
        employeeDao.save(employee);
        return "redirect:/employee";
    }


}

5.employee_add.html页面

DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>add employeetitle>
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<br>
    <input type="radio" name="gender" value="0">female<br>
    <input type="submit" value="add">
form>
body>
html>

6.employee_list.html页面

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Employee info</title>
</head>
<body>
<table id="dataTable" border="1" 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>
<form id="deleteForm" method="post">
  <input type="hidden" name="_method" value="delete">
</form>
<script type="text/javascript" th:src="@{/static/js/vue.js}"></script>
<script type="text/javascript">
  var vue=new Vue({
    el:"#dataTable",
    methods:{
      deleteEmployee:function (event) {
        var delete_form = document.getElementById("deleteForm");
        delete_form.action = event.target.href;
        delete_form.submit();
        event.preventDefault();
    }
  }
  });
</script>
</body>
</html>

7.employee_update.html页面

DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Update Employeetitle>
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>
  
  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>

8.web.xml

<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">
    
    <servlet>
        <servlet-name>springMVCservlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServletservlet-class>
        <init-param>
            <param-name>contextConfigLocationparam-name>
            <param-value>classpath:springMVC.xmlparam-value>
        init-param>
        <load-on-startup>1load-on-startup>
    servlet>
    <servlet-mapping>
        <servlet-name>springMVCservlet-name>
        <url-pattern>/url-pattern>
    servlet-mapping>
    <filter>
        <filter-name>CharacterEncodingFilterfilter-name>
        <filter-class>org.springframework.web.filter.CharacterEncodingFilterfilter-class>
        <init-param>
            <param-name>encodingparam-name>
            <param-value>UTF-8param-value>
        init-param>
        <init-param>
            <param-name>forceResponseEncodingparam-name>
            <param-value>trueparam-value>
        init-param>
    filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilterfilter-name>
        <url-pattern>/*url-pattern>
    filter-mapping>
    <filter>
        <filter-name>HiddenHttpMethodFilterfilter-name>
        <filter-class>org.springframework.web.filter.HiddenHttpMethodFilterfilter-class>
    filter>
    <filter-mapping>
        <filter-name>HiddenHttpMethodFilterfilter-name>
        <url-pattern>/*url-pattern>
    filter-mapping>
web-app>

9.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">
    <!--扫描控制层组件-->
    <context:component-scan base-package="com.dragon.mvc"></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>
<!--    开放对静态资源的访问-->
    <mvc:default-servlet-handler/>
    <!--
        path：设置处理的请求地址
        view-name：设置请求地址所对应的视图名称
     -->
    <mvc:view-controller path="/" view-name="index"></mvc:view-controller>
    <mvc:view-controller path="/toAdd" view-name="employee_add"></mvc:view-controller>
    <mvc:annotation-driven />
</beans>

总结

以上就是RESTful的讲解。