Understanding spring-boot-starter-tomcat in Spring Boot

September 30, 2024

Spring Boot simplifies the process of developing stand-alone, production-grade Spring-based applications. One of the key features that make this possible is the use of starters. In this blog post, we’ll dive into the spring-boot-starter-tomcat starter, which provides the necessary dependencies to run an embedded Tomcat server within a Spring Boot application.

What is `spring-boot-starter-tomcat`?

The spring-boot-starter-tomcat is a starter for using Tomcat as the embedded servlet container. By including this starter, you can run your Spring Boot application with an embedded Tomcat server, eliminating the need to deploy your application to an external server.

Adding `spring-boot-starter-tomcat` to Your Project

To use the spring-boot-starter-tomcat, you need to include it in your pom.xml if you’re using Maven:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-tomcat</artifactId>
</dependency>

For Gradle users, add the following to your build.gradle:

implementation 'org.springframework.boot:spring-boot-starter-tomcat'

Basic Configuration

Spring Boot provides a default configuration for the embedded Tomcat server. However, you can customize it through the application.properties file. Here are some common configurations:

Server Port: Change the default port (8080) to another port.
```
server.port=9090
```
Server Address: Bind the server to a specific IP address.
```
server.address=127.0.0.1
```

Error Handling: Customize the error page.

server.error.whitelabel.enabled=false
server.error.path=/custom-error

SSL Configuration: Enable SSL support.

server.ssl.enabled=true
server.ssl.key-store=classpath:keystore.jks
server.ssl.key-store-password=changeit
server.ssl.key-password=changeit

Example Application

Let’s create a simple Spring Boot application that uses the embedded Tomcat server. We’ll create a REST controller to handle HTTP requests.

Create a Spring Boot Application

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

Create a REST Controller

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

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, World!";
    }
}

Run the Application

With the spring-boot-starter-tomcat dependency included, you can run your application using the embedded Tomcat server. Simply run the main method in TomcatExampleApplication class, and your application will be accessible at http://localhost:8080/api/hello.

Advanced Configuration

For more advanced configurations, such as setting the maximum number of threads or customizing the connection timeout, you can refer to the official Spring Boot documentation ¹.

server.tomcat.threads.max=200
server.connection-timeout=5s

Conclusion

The spring-boot-starter-tomcat starter makes it incredibly easy to run a Spring Boot application with an embedded Tomcat server. By including this starter, you can focus on developing your application without worrying about the complexities of deploying to an external server. With the ability to customize the server through the application.properties file, you have full control over the server’s behavior to meet your specific needs.

Spring Developer