Deploy a Spring Boot REST App as a WAR to Tomcat 10

In this tutorial, the reader will learn how to deploy a Spring Boot REST app to Tomcat 10.

According to Apache, the Jakarta EE platform is the evolution of the Java EE platform. Tomcat 10 and later implement specifications developed as part of Jakarta EE. Tomcat 9 and earlier implement specifications developed as part of Java EE. Due to this reason applications developed for Tomcat 9 and earlier will not run on Tomcat 10. However, there is still a way to do it.

Java EE-based applications designed for Tomcat 9 and earlier may be placed in the $CATALINA_BASE/webapps-javaee directory and Tomcat will automatically convert them to Jakarta EE and copy them to the webapps directory. This conversion is performed using the Apache Tomcat migration tool for the Jakarta EE tool which is also available as a separate download for off-line use.

To demonstrate how to deploy a Spring Boot REST application to a standalone Tomcat 10 server, in this tutorial, we will do the following:

  1. Download and install Apache Tomcat 10,
  2. Create and build a very simple Spring Boot REST application,
  3. Deploy WAR file to a standalone Tomcat 10.

Tomcat 10 Installation

Use the following link to download Tomcat 10.

For windows users, add the following to environment variables with the name CATALINA_HOME.

  • C:\Program Files\Apache Software Foundation\Tomcat 10.0

To start Tomcat issue the following command on windows command prompt.

C:\Program Files\Apache Software Foundation\Tomcat 10.0\bin>startup

If the configurations are correct the following will be the output after starting Tomcat.

C:\Program Files\Apache Software Foundation\Tomcat 10.0\bin>startup
Using CATALINA_BASE:   "C:\Program Files\Apache Software Foundation\Tomcat 10.0"
Using CATALINA_HOME:   "C:\Program Files\Apache Software Foundation\Tomcat 10.0"
Using CATALINA_TMPDIR: "C:\Program Files\Apache Software Foundation\Tomcat 10.0\temp"
Using JRE_HOME:        "C:\Program Files\Java\jdk-11.0.10"
Using CLASSPATH:       "C:\Program Files\Apache Software Foundation\Tomcat 10.0\bin\bootstrap.jar;C:\Program Files\Apache Software Foundation\Tomcat 10.0\bin\tomcat-juli.jar"
Using CATALINA_OPTS:   ""
C:\Program Files\Apache Software Foundation\Tomcat 10.0\bin>

Creating a Spring Boot Application

Navigate to Spring Initializr and create a new project with the dependencies shown below. Extract the generated zip folder and import the project to Intellij or your preferred IDE.

Set the packaging type to WAR.

<packaging>war</packaging>

Since we are going to use an external Tomcat, add provided tag to tomcat dependency in pom.xml.

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

In the main application extend SpringBootServletInitializer and @Override configure method to enable us to run the application from Tomcat the classical way.

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;

@SpringBootApplication
public class Tomcat10Application extends SpringBootServletInitializer {

    public static void main(String[] args) {
        SpringApplication.run(Tomcat10Application.class, args);
    }

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return builder.sources(Tomcat10Application.class);
    }
}

Create a User model

Create a class named User in a package called model with the following fields.

  • firstName
  • lastName
  • email
public class User {
    private String firstName;
    private String lastName;
    private String email;

    public User(String firstName, String lastName, String email) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }
    // Generate toString method
}

Create a User Controller

Create a class named UserController in a package called the controller and create a user object which will be returned when a user issues the following request.

  • /user/read/one
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/user")
public class UserController {

    @GetMapping("/read/one")
    public String readUser(){
        User user = new User("John","doe","[email protected]");

        return user.toString();
    }
}

Deploying the application on Tomcat 10

Navigate to the Tomcat installation directory mostly found under program files and create a folder named webapps-javaee.

On a command prompt, navigate to your project source, and generate a WAR file using the following command.

mvnw verify

Add the generated WAR file to webapps-javaee folder where it will be automatically migrated by Tomcat and added to webapps folder where it can then be deployed to the client.

Restart Tomcat and note the following logs on server startup.

Using jakartaee-migration Tool

Alternatively, the application can be migrated using the following command.

java  -jar jakartaee-migration-*-shaded.jar <source> <destination>

Once the command has executed successfully, restart Tomcat.

Once you restart the server, Tomcat will migrate the application automatically and add it to webapps folder under Tomcat installation.

On your preferred browser issue the following link which will return a user object that was created in the controller.

  • HTTP://localhost:8080/tomcat10-0.0.1-SNAPSHOT/user/read/one

Conclusion

In this tutorial, you have learned how to deploy a Spring Boot REST application to Tomcat 10 by leveraging the default functionality provided by Tomcat 10 to migrate Java EE applications. You have observed how Tomcat 10 migrates the application behind the scene and generates an application that can be run on Tomcat 10.

Happy coding!

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