M04 Q14 What is the difference between an embedded container and a WAR?

WAR (Web Application Archive) is a file that represents web module. WAR cannot be executed in standalone mode, it needs to be deployed to Application Server like Tomcat or WildFly.

Embedded container is used to execute executables jars. Embedded container is packed as dependency in executable jar and will be responsible for executing only single application. WAR approach on the other hand uses Application Server which might be used to execute multiple applications at the same time.

To create WAR file with Spring Boot, you need to:

Specify WAR packaging method:

<packaging>war</packaging>

Specify required dependencies. You need to exclude embedded tomcat container dependency by changing the scope to provided. You need to do this cause normally Spring Boot packs the embedded version of the tomcat container. So if you don't mark it as provided you will have a conflict with the classes.

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

Use WAR plugin (explicit specification of this plugin is optional):

 <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.2.3</version>
            </plugin>
        </plugins>
    </build>

To create Executable JAR file with embedded container in Spring Boot, you need to:

Specify required dependencies:

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

Use Spring Boot Maven plugin:

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>