Interceptors in Spring MVC

Interceptors in Spring MVC allow you to intercept HTTP requests and responses. They are useful for cross-cutting concerns like logging, authentication, and handling custom logic before or after the execution of a controller. This guide covers the key concepts and usage of interceptors in Spring MVC, including creating, registering, and configuring interceptors.

Key Concepts of Interceptors

• HandlerInterceptor: An interface that provides three methods to intercept requests: preHandle, postHandle, and afterCompletion.
• preHandle: Called before the handler method is invoked.
• postHandle: Called after the handler method has been invoked but before the view is rendered.
• afterCompletion: Called after the complete request has finished.

Creating an Interceptor

To create an interceptor, implement the HandlerInterceptor interface and override its methods:

LoggingInterceptor.java

// LoggingInterceptor.java
package com.example.springmvc.interceptors;

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

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

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");
    }
}

Registering the Interceptor

To register an interceptor, configure it in your Spring configuration file using WebMvcConfigurerAdapter or a Java-based configuration class:

WebConfig.java

// WebConfig.java
package com.example.springmvc.config;

import com.example.springmvc.interceptors.LoggingInterceptor;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoggingInterceptor());
    }
}

Excluding URL Patterns

You can exclude specific URL patterns from being intercepted:

WebConfig.java (with Exclusions)

// WebConfig.java
package com.example.springmvc.config;

import com.example.springmvc.interceptors.LoggingInterceptor;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoggingInterceptor()).excludePathPatterns("/exclude/*");
    }
}

Using Multiple Interceptors

You can configure multiple interceptors, and they will be executed in the order they are registered:

AnotherInterceptor.java

// AnotherInterceptor.java
package com.example.springmvc.interceptors;

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

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

public class AnotherInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("Another Pre Handle method is Calling");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("Another Post Handle method is Calling");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception exception) throws Exception {
        System.out.println("Another Request and Response is completed");
    }
}

WebConfig.java (with Multiple Interceptors)

// WebConfig.java
package com.example.springmvc.config;

import com.example.springmvc.interceptors.LoggingInterceptor;
import com.example.springmvc.interceptors.AnotherInterceptor;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoggingInterceptor());
        registry.addInterceptor(new AnotherInterceptor());
    }
}

Key Points

Conclusion

Interceptors in Spring MVC provide a powerful mechanism to intercept and manipulate HTTP requests and responses. By implementing and configuring interceptors, developers can address cross-cutting concerns such as logging, authentication, and custom logic execution in a modular and reusable manner. Happy coding!