17. Deployment, Tomcat & Spring MVC Progression

WAR Packaging, Provided Scope & Embedded Tomcat

Master WAR deployment models, Maven provided dependency scope to prevent classloader collisions, external Tomcat management, and Spring Boot embedded container mechanics.

WAR Packaging, Provided Scope & Embedded Tomcat

Java web applications can be deployed either using traditional Web Application Archives (WARs) hosted inside an external Tomcat server or via self-contained executable JARs with embedded Tomcat containers in Spring Boot.

1. Web Application Archive (WAR) Packaging

A WAR (.war) is a standardized Java zip archive structured specifically for Servlet Containers:

servlet-crud.war
├── META-INF/
├── WEB-INF/
│   ├── web.xml              ──► Deployment Descriptor (URL-to-Servlet Mappings)
│   ├── classes/             ──► Compiled application .class files
│   └── lib/                 ──► Third-party JAR dependencies
└── index.html, static assets

Deploying to External Tomcat

  1. Build the WAR artifact: mvn clean package ──► generates target/myapp.war
  2. Copy myapp.war into Tomcat's webapps/ folder: cp myapp.war ~/tools/apache-tomcat/webapps/
  3. Tomcat auto-extracts myapp.war into an exploded directory webapps/myapp/
  4. Access via Context Path URL: http://localhost:8080/myapp/hello

2. The Maven <scope>provided</scope> Rule

When developing Servlets for external Tomcat, your code imports classes like jakarta.servlet.http.HttpServlet.

<!-- Maven Dependency in pom.xml -->
<dependency>
    <groupId>jakarta.servlet</groupId>
    <artifactId>jakarta.servlet-api</artifactId>
    <version>6.0.0</version>
    <scope>provided</scope> <!-- CRITICAL -->
</dependency>

Why <scope>provided</scope> Is Mandatory

WITHOUT PROVIDED SCOPE (Default compile scope):
Maven packages servlet-api.jar INSIDE the WAR (WEB-INF/lib/servlet-api.jar).
Runtime Result: External Tomcat already has servlet-api.jar in its /lib folder!
──► Classloader Conflict! (ClassCastException, LinkageError, unpredictable crashes)

WITH PROVIDED SCOPE:
Maven uses servlet-api.jar ONLY for compilation.
Maven EXCLUDES servlet-api.jar from the packaged WAR.
──► Clean Runtime! External Tomcat supplies its own container Servlet API classes.

[!TIP] Dependency Ownership Rule: When a runtime container (Tomcat) provides an infrastructure API, mark the Maven dependency as provided so it compiles successfully without bundling duplicate container classes into your WAR.

3. External Tomcat vs Embedded Tomcat in Spring Boot

TRADITIONAL EXTERNAL TOMCAT:
"Put the application INSIDE the server"
Application (.war) ──► Copy to External Tomcat Server ──► Start Tomcat

SPRING BOOT EMBEDDED TOMCAT:
"Put the server INSIDE the application"
Embedded Tomcat (.jar) ──► Embedded in Spring Boot App ──► java -jar app.jar
DimensionTraditional External TomcatSpring Boot Embedded Tomcat
Server InstallationInstalled separately on OS hostBundled inside application JAR via spring-boot-starter-web
Deployment Artifact.war (Web Application Archive).jar (Executable Java Archive)
Execution Command./catalina.sh run or ./startup.shjava -jar myapp.jar
Lifecycle ControlHost administrator controls Tomcat processSpring Boot main() starts embedded Tomcat on boot

4. External Tomcat Administration & Port Troubleshooting

Starting & Stopping External Tomcat

# Linux / macOS
cd ~/apache-tomcat-10.1.x
chmod +x bin/*.sh
./bin/startup.sh  # Run in background
./bin/shutdown.sh # Graceful shutdown

# Windows
cd C:\apache-tomcat-10.1.x
bin\startup.bat
bin\shutdown.bat

Port 8080 Collision Resolution

If Tomcat fails to start due to Port 8080 already in use:

# Linux / macOS: Find PID on port 8080 and terminate
lsof -i :8080
kill -9 <PID>

# Windows: Find PID on port 8080 and terminate
netstat -ano | findstr :8080
taskkill /PID <PID> /F

❓ Knowledge Check

Knowledge Check

What happens if you omit <scope>provided</scope> for the Servlet API when building a WAR for external Tomcat?

Knowledge Check

What is the key architectural shift introduced by Spring Boot embedded Tomcat?

Servlet Lifecycle, Concurrency & Request Pipeline

Master the Servlet lifecycle pipeline (init, service, destroy), multithreaded single-instance concurrency hazards, and request/response abstractions.

DispatcherServlet, Spring MVC & Production Pitfalls

Master the architectural progression from raw Servlets to Spring MVC DispatcherServlet, complete request sequence flows, production pitfalls, and self-assessments.

On this page

WAR Packaging, Provided Scope & Embedded Tomcat1. Web Application Archive (WAR) PackagingDeploying to External Tomcat2. The Maven <scope>provided</scope> RuleWhy <scope>provided</scope> Is Mandatory3. External Tomcat vs Embedded Tomcat in Spring Boot4. External Tomcat Administration & Port TroubleshootingStarting & Stopping External TomcatPort 8080 Collision Resolution❓ Knowledge Check