一、REST風格是啥?
REST(Representational State Transfer)
:表述性狀態傳遞,它是一種針對網絡應用的設計和開發方式,可以降低開發的複雜性,提高系統的可伸縮性。
簡單來說,HTTP協議本身是無狀態的協議,客戶端想要操作服務器,可以通過請求資源的方式,將"狀態"進行傳遞。
- GET請求表示獲取資源。
- POST請求表示新建資源。
- PUT請求表示更新資源。
- DELETE請求表示刪除資源。
首先我們需要有一個基本的共識就是,瀏覽器的form表單中,只能有兩種請求的方式,GET和POST。那麼問題來了,PUT和DELETE如何來表示呢?服務器怎麼確認你發的是這倆請求呢?我們需要做些什麼呢?
- 配置支持REST風格的過濾器:
HiddenHttpMethodFilter
。 - Controller控制器在註解上規定接收方法的方式。
- 前端通過form表單提交,且提交方式爲post,再定義一個名爲_method的參數,值爲請求方式PUT或DELETE。
原理很簡單,我們看看HiddenHttpMethodFilter
的源碼就知道了:
//HiddenHttpMethodFilter
/** Default method parameter: _method */
public static final String DEFAULT_METHOD_PARAM = "_method";
@Override
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
HttpServletRequest requestToUse = request;
//前端必須是post提交的參數
if ("POST".equals(request.getMethod()) && request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) == null) {
//獲取名爲methodParam的值,其實就是_method的值
String paramValue = request.getParameter(this.methodParam);
if (StringUtils.hasLength(paramValue)) {
//裝飾器模式對request進行了增強,重寫了getMethod方法:put--> PUT
requestToUse = new HttpMethodRequestWrapper(request, paramValue);
}
}
//最後放行的是增強後的request
filterChain.doFilter(requestToUse, response);
}
二、配置支持REST風格過濾器
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
version="3.0">
<!--配置中文亂碼過濾器-->
<filter>
<filter-name>characterEncodingFilter</filter-name>
<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
<init-param>
<!--指定編碼方式-->
<param-name>encoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
<init-param>
<!--解決請求和響應亂碼setCharacterEncoding-->
<param-name>forceEncoding</param-name>
<param-value>true</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>characterEncodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter>
<!--Spring對Rest風格的支持: 將普通請求轉化爲規定形式的PUT DELETE-->
<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>
<!--配置前端控制器-->
<servlet>
<servlet-name>dispatcherServlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<!--加載類路徑下的配置文件-->
<param-value>classpath:springmvc.xml</param-value>
</init-param>
<!--服務器啓動時創建對象,值越小,優先級越高,越先創建對象-->
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcherServlet</servlet-name>
<!--注意不是/*,而是,因爲/*還會攔截*.jsp等請求-->
<url-pattern>/</url-pattern>
</servlet-mapping>
</web-app>
三、配置spirngMVC
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<!-- 開啓註解掃描 -->
<context:component-scan base-package="com.smday"/>
<!-- 視圖解析器對象 -->
<bean id="internalResourceViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/pages/"/>
<property name="suffix" value=".jsp"/>
</bean>
<!-- 開啓SpringMVC框架註解的支持 -->
<mvc:annotation-driven/>
<!--放行靜態資源-->
<mvc:default-servlet-handler/>
</beans>
四、定義控制器
@Controller
@RequestMapping("/restful")
public class RestController {
@RequestMapping(value = "/user/{id}",method = RequestMethod.GET)
public String getUser(@PathVariable("id") Integer id){
System.out.printf("==> 查詢%d號用戶",id);
return "success";
}
@RequestMapping(value = "/user/{id}",method = RequestMethod.DELETE)
public String deleteUser(@PathVariable("id") Integer id){
System.out.printf("==> 刪除%d號用戶",id);
return "success";
}
@RequestMapping(value = "/user/{id}",method = RequestMethod.PUT)
public String updateUser(@PathVariable("id") Integer id){
System.out.printf("==> 更新%d號用戶",id);
return "success";
}
@RequestMapping(value = "/user",method = RequestMethod.POST)
public String addUser(){
System.out.print("==> 添加1號用戶");
return "success";
}
}
五、前端定義表單
<%--
Date: 2020/5/2
Time: 19:50
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<%--增刪改查 超鏈接是get請求 --%>
<a href="restful/user/1">GET 查詢1號用戶</a><br>
<form action="restful/user/1" method="post">
<%--傳遞一個參數_method ,值爲請求類型--%>
<input name="_method" value="delete">
<input type="submit" value="DELETE 刪除1號用戶">
</form>
<form action="restful/user/1" method="post">
<input name="_method" value="put">
<input type="submit" value="PUT 更新1號用戶">
</form>
<form action="restful/user" method="post">
<input type="submit" value="POST 添加1號用戶">
</form>
</body>
</html>