DispatcherServlet in Spring Boot
In Spring Boot, the DispatcherServlet
retains its central role as the front controller for handling all HTTP requests and responses within a web application. However, Spring Boot simplifies the configuration and management of the DispatcherServlet
compared to traditional Spring MVC applications.
Key Features and Functions
- Centralized Request Handling: The
DispatcherServlet
intercepts all incoming requests and delegates them to the appropriate controllers based on URL patterns and request mappings. - Pre-processing and Post-processing: The
DispatcherServlet
allows for pre-processing and post-processing of requests via interceptors, enabling tasks like logging, authentication, and data manipulation. - View Resolution: It resolves logical view names returned by controllers to actual views, such as JSP, Thymeleaf, or other templating engines.
- Exception Handling: The
DispatcherServlet
handles exceptions that occur during request processing, providing a consistent error-handling mechanism through configured exception resolvers.
Configuration in Spring Boot
Spring Boot automatically configures the DispatcherServlet
without requiring explicit definitions in XML or Java classes. This auto-configuration is part of Spring Boot's ability to reduce boilerplate code and simplify setup.
Default Configuration: By default, Spring Boot registers the DispatcherServlet
and maps it to the root URL pattern (/
). This means it will handle all incoming requests.
Customizing the DispatcherServlet
While Spring Boot provides sensible defaults, you can customize the DispatcherServlet
if needed.
- Changing the DispatcherServlet URL Pattern:
- You can customize the URL pattern by configuring the
spring.mvc.servlet.path
property in theapplication.properties
file:
spring.mvc.servlet.path=/api
This configuration changes the default URL pattern from /
to /api
, so the DispatcherServlet
will handle requests starting with /api
.
2. Customizing the DispatcherServlet Bean:
If you need to customize the DispatcherServlet
bean directly, you can define a DispatcherServlet
bean in a configuration class:
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.DispatcherServlet;
@Configuration
public class WebConfig {
@Bean
public DispatcherServlet dispatcherServlet() {
DispatcherServlet dispatcherServlet = new DispatcherServlet();
dispatcherServlet.setThrowExceptionIfNoHandlerFound(true);
return dispatcherServlet;
}
}
Here, we customize the DispatcherServlet
to throw an exception if no handler is found for a request.
3. Customizing the DispatcherServlet Registration:
You can also customize how the DispatcherServlet
is registered in the ServletContext
:
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.DispatcherServlet;
@Configuration
public class WebConfig {
@Bean
public ServletRegistrationBean<DispatcherServlet> dispatcherServletRegistration() {
DispatcherServlet dispatcherServlet = new DispatcherServlet();
ServletRegistrationBean<DispatcherServlet> registrationBean = new ServletRegistrationBean<>(dispatcherServlet, "/custom/*");
registrationBean.setName("customDispatcher");
return registrationBean;
}
}
This example registers the DispatcherServlet
with a custom URL pattern /custom/*
and a custom name customDispatcher
.
Using Interceptors with DispatcherServlet in Spring Boot
Interceptors can be used in Spring Boot in a manner similar to traditional Spring MVC applications. Define the interceptor and register it using WebMvcConfigurer
.
Step 1: Define the Interceptor
import org.springframework.web.servlet.HandlerInterceptor;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class CustomInterceptor 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 ex) throws Exception {
System.out.println("Request and Response is completed");
}
}
Step 2: Register the Interceptor
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 CustomInterceptor())
.addPathPatterns("/api/**")
.excludePathPatterns("/api/login", "/api/register");
}
}
Conclusion
The DispatcherServlet
in Spring Boot simplifies the process of building web applications by providing automatic configuration and reducing the need for boilerplate code. It remains a crucial component, serving as the front controller that manages all HTTP requests and responses. With the ability to customize its behavior and integrate with other Spring features seamlessly, the DispatcherServlet
helps developers build robust and maintainable web applications.