Spring Boot Interceptor example

In Spring Boot web application, you can register interceptors for the handlers to implement common checking or logic. For example, a handler interceptor can check the time taken by request, check authorization, perform auditing etc.

An Interceptor is similar to a Servlet Filter, but an Interceptor allows custom pre-processing and you can also stop the execution of the handler and custom post-processing.

Implementing Interceptor

To create an interceptor in Spring Boot, you need to implement the HandlerInterceptor interface. You need to implement following three methods defined in HandlerInterceptor interface:

• preHandle() method - this is called after handler object is chosen, but before HandlerAdapter invokes the handler.
• postHandle() method - this is called after HandlerAdapter invokes the handler, but before the DispatcherServlet renders the view.
• afterCompletion() method - this is called after request is processed and view is rendered.

 <?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	
    <modelVersion>4.0.0</modelVersion>
	
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
        <relativePath/>
    </parent>
	
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Spring Boot Interceptor</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

    </dependencies>
    <!-- To create an executable jar -->
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>    

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringBootInterceptorApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBootInterceptorApplication.class, args);
    }
}       

package com.example.demo;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class SpringBootInterceptorController {

    @GetMapping("/")
    public String hello() {
        System.out.println("Returning respone");
        return "Hello World";
    }
}        

package com.example.demo;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

@Component
public class LoggingInterceptor implements HandlerInterceptor {
	
    @Override
    public boolean preHandle(HttpServletRequest request,
            HttpServletResponse response, Object handler) throws Exception {

        System.out.println("Pre Handle method is Calling");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request,
            HttpServletResponse response, Object handler,
            ModelAndView modelAndView) throws Exception {

        System.out.println("Post Handle method is Calling");
    }

    @Override
    public void afterCompletion(HttpServletRequest request,
            HttpServletResponse response, Object handler, Exception exception)
            throws Exception {

        System.out.println("Request and Response is completed");
    }
}       

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.config.annotation
.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation
.WebMvcConfigurer;

@Component
public class InterceptorConfig implements WebMvcConfigurer    {
   @Autowired
   LoggingInterceptor loggingInterceptor;

   @Override
   public void addInterceptors(InterceptorRegistry registry) {
      registry.addInterceptor(loggingInterceptor).addPathPatterns("/**");
   }
}   

Pre Handle method is Calling
Returning respone
Post Handle method is Calling
Request and Response is completed