Apache Tomcat is an open-source Java servlet container that implements the Java Servlet, JavaServer Pages (JSP), Java Expression Language (EL), and WebSocket technologies. It is widely used for deploying Java-based web applications, particularly those developed using the Spring Boot framework.

Why use Tomcat with Spring Boot?

Compatibility:

Spring Boot, by default, comes with an embedded Tomcat server, which allows developers to run Spring Boot applications without requiring external servers. However, in production environments, deploying Spring Boot applications on external Tomcat servers is common for scalability, security, and operational reasons.

War Deployment:

Spring Boot applications can be packaged as .jar (executable jar with an embedded server) or .war (for deployment in external servlet containers like Tomcat). When using .war packaging, Tomcat can be used to host the Spring Boot application.

Steps to Deploy a Spring Boot Application on Tomcat

1. Install Tomcat:

Download Apache Tomcat from the official site: Apache Tomcat.

2. Convert Spring Boot App to a WAR:

Spring Boot applications are packaged as .jar files by default, but to deploy them on an external Tomcat server, you need to package them as a .war.

To do this:

Update pom.xml for a Maven-based project to package it as a WAR by changing the packaging element:

war

Ensure your main application class extends SpringBootServletInitializer to enable deployment as a WAR: import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.boot.web.servlet.support.SpringBootServletInitializer; @SpringBootApplication public class MyApplication extends SpringBootServletInitializer { public static void main(String[] args) { SpringApplication.run(MyApplication.class, args); } }

3. Build the WAR File:

Use Maven (or Gradle if you use Gradle) to package the application: mvn clean package This will generate a .war file in the target directory.

4. Configure Tomcat for Deployment:

Place the .war file in the webapps directory of your Tomcat installation. Alternatively, you can deploy the WAR via the Tomcat Manager (if installed and configured). Access the Tomcat Manager at http://localhost:8080/manager (or your custom port), log in, and use the "Deploy" section to upload the WAR file.

5. Access the Application:

Once deployed, Tomcat automatically extracts and runs the WAR file. You can access the deployed application at http://localhost:8080/{app-name}, where {app-name} is the name of your .war file.

Configuration Tips:

1. Change Default Port:

If you want to run multiple services on the same machine, you might want to change Tomcat’s port number. Open conf/server.xml and locate the <Connector element <Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> Change the port value to the desired number.

2. Enable Tomcat Manager

Tomcat Manager is a useful web-based tool to manage applications deployed on Tomcat. However, it’s often disabled by default. To enable it, modify the tomcat-users.xml file (found in conf/) and add a user with manager role: <role rolename="manager-gui"/> <user username="admin" password="admin_password" roles="manager-gui"/>

3.Logging

Use Tomcat’s logging system for monitoring errors and application behavior. Logs can be found under the logs folder in the Tomcat installation directory.

4. Context Path

To modify the context path (the URL at which the app is accessible), you can either rename the WAR file (e.g., renaming myapp.war to ROOT.war makes it accessible at /) or modify the conf/server.xml file.

Key Points to Remember:

Tomcat is a lightweight servlet container used for running Java web applications. You can deploy Spring Boot applications on Tomcat by packaging them as WAR files. Ensure proper configuration in pom.xml and extend SpringBootServletInitializer to make the app deployable on Tomcat. Manage and monitor the application using Tomcat’s Manager interface or logs.

This setup is commonly used in production for hosting Spring Boot apps that require more robust application management than the embedded Tomcat offers.