Interceptors
are used to intercept the request.
Example 1:
You
may want to preprocess the input before handing it over to actual controller
class.
Example 2:
You
may want to calculate the execution time of the request. You can do that by
using interceptors.
How to create an
interceptor?
There
are two ways.
a.
By
implementing org.springframework.web.servlet.HandlerInterceptor interface
interface
b.
By
extending the class org.springframework.web.servlet.handler.HandlerInterceptorAdapter
HandlerInterceptor
interface
HandlerInterceptor
interface provides below three methods.
default boolean
preHandle(HttpServletRequest request, HttpServletResponse response, Object
handler)throws Exception
default void
postHandle(HttpServletRequest request, HttpServletResponse response, Object
handler, @Nullable ModelAndView modelAndView) throws Exception
default void
afterCompletion(HttpServletRequest request, HttpServletResponse response,
Object handler, @Nullable Exception ex) throws Exception
default boolean
preHandle(HttpServletRequest request, HttpServletResponse response, Object
handler)throws Exception
This
method is called before the request is handed over to the handler method. This
method should return true if the execution chain should proceed with the next
interceptor or the handler itself. Else, DispatcherServlet assumes that this
interceptor has already dealt with the response itself.
default void postHandle(HttpServletRequest request,
HttpServletResponse response, Object handler, @Nullable ModelAndView
modelAndView) throws Exception
Called
after HandlerAdapter actually invoked the handler, but before the
DispatcherServlet renders the view.
default void afterCompletion(HttpServletRequest request,
HttpServletResponse response, Object handler, @Nullable Exception ex) throws
Exception
Callback after
completion of request processing, that is, after rendering the view.
You
need to register the interceptor in dispatcher servlet like below.
<mvc:interceptors>
<bean
class="com.sample.myApp.interceptors.PerformanceReportInterceptor"
/>
</mvc:interceptors>
Find
the below working application.
package com.sample.myApp.controllers; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.servlet.ModelAndView; @Controller public class HelloWorldController { @RequestMapping("/welcome") public ModelAndView getHelloMessage() { ModelAndView modelAndView = new ModelAndView("welcome"); modelAndView.addObject("message", "Dear User, Good Morning"); return modelAndView; } }
I
defined an interceptor that is used to calculate the exection time of the
request.
PerformanceReportInterceptor.java
package com.sample.myApp.interceptors; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.springframework.lang.Nullable; import org.springframework.web.servlet.HandlerInterceptor; import org.springframework.web.servlet.ModelAndView; public class PerformanceReportInterceptor implements HandlerInterceptor { private long startTime; public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { startTime = System.nanoTime(); return true; } public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception { long executionTime = System.nanoTime() - startTime; modelAndView.addObject("executionTime", executionTime); } }
Create
welcome.jsp file under WEB-INF/jsp folder.
welcome.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <title>Hello World Spring Web MVC</title> </head> <body> <h1>${message}</h1> <h3> ${message} <br /> Execution Time : ${executionTime} nanoseconds<br /> </h3> </body> </html>
Create
web.xml, HelloWorld-servlet.xml files under WEB-INF folder.
web.xml
<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> <display-name>Spring MVC Hello WorldApplication</display-name> <servlet> <servlet-name>HelloWorld</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>HelloWorld</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> </web-app>
HelloWorld-servlet.xml
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context" xmlns:mvc="http://www.springframework.org/schema/mvc" 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-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd"> <mvc:annotation-driven /> <context:component-scan base-package="com.sample.myApp" /> <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/" /> <property name="suffix" value=".jsp" /> </bean> <mvc:interceptors> <bean class="com.sample.myApp.interceptors.PerformanceReportInterceptor" /> </mvc:interceptors> </beans>
Create
index.jsp file under webapp folder.
index.jsp
<%@taglib prefix="form" uri="http://www.springframework.org/tags/form"%> <html> <head> <title>Welcome Page</title> </head> <body> <h2>Click on below button to get welcome page</h2> <form method="post" action="/springdemo/welcome" id="f1"> <input type="submit" name="submit" value="submit" style="font-size: 18px;" /> </form> </body> </html>
Project
structure looks like below.
Run
the application on server. You can able to see below screen.
Click
on submit button, you can able to see below screen.
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