DispatcherServlet in Spring

1. Introduction

DispatcherServlet is the main component of Spring MVC.

It acts as a front controller, meaning:

It receives all HTTP requests
Sends requests to the correct controller
Returns the response to the client

2. What DispatcherServlet Does

Handles incoming requests
Finds the correct controller
Executes business logic
Selects the correct view
Sends response back

3. Working Flow

Step 1: Request

Client sends HTTP request
DispatcherServlet receives it

Step 2: Handler Mapping

Finds which controller will handle the request

Step 3: Controller

Controller processes request
Returns data and view name

Step 4: Model and View

Model = data
View = page name

Step 5: View Resolver

Converts logical view name into actual file

Step 6: Response

Final output sent to client

4. Setup in Spring MVC (XML Based)

Step 1: Configure DispatcherServlet

plaintext

<servlet>
    <servlet-name>frontcontroller-dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>frontcontroller-dispatcher</servlet-name>
    <url-pattern>/app/*</url-pattern>
</servlet-mapping>

Step 2: Create Configuration File

Create file inside WEB-INF
Example: frontcontroller-dispatcher-servlet.xml

Step 3: Run Application

Deploy on Tomcat
DispatcherServlet starts automatically

5. DispatcherServlet in Spring Boot

In Spring Boot, DispatcherServlet is auto-configured.

You do not need to define it manually.

Step 1: Create Spring Boot Project

Use Spring Initializr
Add dependency: Spring Web

Step 2: Model Class

plaintext

package com.example.demo.model;

public class Details {

    private int id;
    private String name;

    public Details(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Step 3: Controller Class

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package com.example.demo.controller;

import com.example.demo.model.Details;
import org.springframework.web.bind.annotation.*;

import java.util.ArrayList;
import java.util.List;

@RestController
@RequestMapping("/api")
public class DetailsController {

    private List<Details> detailsList = new ArrayList<>();

    @GetMapping("/details")
    public List<Details> getAllDetails() {
        return detailsList;
    }

    @PostMapping("/details")
    public String addDetails(@RequestBody Details details) {
        detailsList.add(details);
        return "Data Inserted Successfully";
    }

    @PutMapping("/details/{id}")
    public String updateDetails(@PathVariable int id, @RequestBody Details updatedDetails) {
        for (Details details : detailsList) {
            if (details.getId() == id) {
                details.setName(updatedDetails.getName());
                return "Data Updated Successfully";
            }
        }
        return "Detail not found";
    }

    @DeleteMapping("/details/{id}")
    public String deleteDetails(@PathVariable int id) {
        detailsList.removeIf(details -> details.getId() == id);
        return "Data Deleted Successfully";
    }
}

Step 4: Main Class

plaintext

package com.example.demo;

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

@SpringBootApplication
public class DemoApplication {

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

Step 5: Optional Custom Configuration

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package com.example.demo.config;

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> dispatcherServlet() {

        DispatcherServlet dispatcherServlet = new DispatcherServlet();

        ServletRegistrationBean<DispatcherServlet> registrationBean =
                new ServletRegistrationBean<>(dispatcherServlet);

        registrationBean.addUrlMappings("/api/*");

        return registrationBean;
    }
}

6. Key Points

DispatcherServlet is the core of Spring MVC
Acts as front controller
Handles request flow from start to end
In Spring Boot, it is auto-configured

7. Conclusion

DispatcherServlet simplifies request handling
Centralizes control in web applications
Essential for building Spring MVC and Spring Boot apps