DispatcherServlet

The Front Controller

💡 DispatcherServlet ek OFFICE RECEPTIONIST hai — HAR visitor (request) pehle RECEPTIONIST (DispatcherServlet) se milta hai, jo phir DECIDE karta hai KIS DEPARTMENT (controller) ko bhejna hai — visitor khud DIRECTLY department mein nahi ghus sakta.

DispatcherServlet Spring MVC ka CENTRAL component hai — HAR incoming HTTP request YAHI SE hoke guzarта hai. Ye "Front Controller" design pattern hai — EK SINGLE entry point, jo request ko ANALYZE karके, SAHI controller method ko ROUTE karta hai.

DispatcherServlet ke process mein KAI steps hain: HandlerMapping se PUCHNA (kaun sa controller method?), HandlerAdapter se method INVOKE karvaна, aur agar view-based response hai to ViewResolver se ACTUAL view (HTML) resolve karvaна. REST APIs mein, view resolution SKIP ho jaati hai (@ResponseBody ki wajah se).

// Application flow (conceptually):
// 1. HTTP request aata hai → DispatcherServlet
// 2. DispatcherServlet → HandlerMapping ("kaun sa method?")
// 3. HandlerMapping → UserController.getUser() milta hai
// 4. Method execute hota hai, result return karta hai
// 5. @RestController mein: result JSON mein convert hoke response ban jaata hai

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DispatcherServlet ek OFFICE RECEPTIONIST hai — HAR visitor (request) pehle RECEPTIONIST (DispatcherServlet) se milta hai, jo phir DECIDE karta hai KIS DEPARTMENT (controller) ko bhejna hai — visitor khud DIRECTLY department mein nahi ghus sakta.

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⚡ झट से Recap

Front Controller pattern — EK entry point saari requests ke liye
HandlerMapping URL ko controller method se JODता hai
Spring Boot mein AUTOMATICALLY configured

इस page में (2 subtopics)

DispatcherServlet "FRONT CONTROLLER" design pattern IMPLEMENT karta hai — EK SINGLE entry point SAARI requests ke liye, jo phir unhe APPROPRIATE handler ko route karta hai. Isse cross-cutting concerns (logging, security checks) EK JAGAH handle ho sakte hain, HAR controller mein duplicate karne ke bajaye.

💡Tip: DispatcherServlet KHUD ek Servlet hai (Java EE ka standard concept) — Spring ise WRAP karके, apni SMART routing logic add karta hai.

Request aane par, DispatcherServlet HandlerMapping se PUCHTA hai "is URL ke liye KAUN SA controller method chalाना hai?" — @RequestMapping/@GetMapping annotations SCAN karके, ye mapping PEHLE SE build kar li jaati hai application startup par, taaki HAR request par lookup FAST ho.

DispatcherServlet = single entry point, saari requests ke liye
HandlerMapping = URL → controller method ka mapping
HandlerAdapter = actual method ko invoke karta hai

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Code10x

DispatcherServlet

The Front Controller Pattern

Handler Mapping — Finding the Right Controller