IBuild — Servlet Notes

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Key Topics to Know

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Web App Architecture — How Servlet works inside a Container

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The Container — What it provides & why we use it instead of plain Java

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Request Handling Lifecycle — How Request/Response objects are created & managed

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Deployment Descriptor (DD) — Using web.xml to map URLs to Servlets

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MVC Pattern — Separating Business Logic from Presentation

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Core Definitions

Container

A Java app (e.g. Tomcat) that controls the Servlet. Loads classes, creates objects, calls doGet() / doPost(), and manages resources.

Servlet

A Java class with NO main() method. Runs under Container control to generate dynamic content in response to client requests.

DD — web.xml

An XML config file. Maps URLs to Servlets & handles security. No recompilation needed when changed!

MVC Pattern

Model (data & logic) + View (JSP) + Controller (Servlet routing). Keeps code clean & reusable.

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What the Container Provides — 5 Benefits

1

Communications Support

No Socket code needed. Container handles all web server communication automatically.

2

Lifecycle Management

Controls Servlet birth & death: loading → instantiation → destruction → GC.

3

Multithreading Support

New Thread created automatically per request. You don't manage threads!

4

JSP Support

Container translates JSP → real Java. 100% the Container's responsibility.

5

Declarative Security

Manage security via XML config. No complex security code inside the Servlet.

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Tomcat Note

Web Container only — NOT a full J2EE server. No EJB Container!

Quick Facts — Memorize!

Servlet has NO main() method

Container creates HttpServletRequest & HttpServletResponse

Container calls service() → decides doGet() or doPost() based on HTTP method

When request ends → Thread dies + Request/Response objects are destroyed

// Request flow

Client → HTTP Request → Container → creates Thread → creates Request/Response → calls service() → doGet() or doPost() → Response sent → Thread killed

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A Servlet Has 3 Names

#	Name Type	Example
1	Real file path	`classes/registration/SignUpServlet.class`
2	Internal deploy name (DD)	`EnrollServlet`
3	Public URL name	`/registerMe`

// Why mapping?

Mapping in the DD gives you flexibility to rename files or restructure without breaking client URLs. It also hides the real file structure from the public for added security.

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MVC Design Pattern

Controller

Servlet

Receives client request. Talks to Model. Decides which View to show.

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Model

Plain Java Class

Business Logic & Data. Knows NOTHING about the web or presentation.

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View

JSP Page

Presentation only. Takes data from Model and displays it to user.

// Why use MVC? Putting Business Logic inside the Servlet = hard to maintain & can't reuse in mobile or Swing apps. MVC keeps things clean, separated, and reusable.