How to embed Tomcat and Java web apps in an executable JAR

Historically, we packaged production-ready Java web apps as WAR files. A servlet engine, like an IBM WebSphere or Apache Tomcat server, would host multiple applications at once. But for a variety of reasons -- the widespread adoption of microservices and desire to perform highly isolated unit tests, for instance -- the one-to-many relationship between the Java web app and the servlet container has consolidated into a one-to-one.

Embedded Tomcat example prerequsites

This tutorial has only two prerequisites:

You must have the Java Development Kit (JDK) installed and configured. Version 8 of the JDK or newer is preferred.

You must have Maven 3.5 or newer installed.

That's it. You don't even need to download the Apache Tomcat server because Maven's Tomcat plug-in will acquire the Tomcat binaries for you.

Create a new Java web app

mvn archetype:generate -DarchetypeArtifactId=maven-archetype-webapp

When the Maven build completes, we will edit a sample index.jsp file, which you'll find in the following directory:

C:\ROOT\java-web-app\src\main\webapp

Develop Java web apps

Edit the index.jsp file so, when the Java web app runs, we can uniquely identify it as our own. I have updated the provided index.jsp file to read as follows:

Use Maven to embed Tomcat

With the pom.xml file edited and updated with a reference to the Tomcat plug-in for Maven, the final step is to build the project and call on the appropriate goal -- tomcat7:exec-war-only -- to create the executable JAR file. When this Maven goal is invoked, the Tomcat plug-in for Maven will automatically place the embedded Tomcat server inside the executable JAR.

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">   <modelVersion>4.0.0</modelVersion>   <groupId>kr.co.keytech.test</groupId>   <artifactId>java-web-app</artifactId>   <packaging>war</packaging>   <version>1.0-SNAPSHOT</version>   <name>java-web-app Maven Webapp</name>   <url>http://maven.apache.org</url>   <dependencies>     <dependency>       <groupId>junit</groupId>       <artifactId>junit</artifactId>       <version>4.11</version>       <scope>test</scope>     </dependency>   </dependencies> <build>    <!-- plugin to embed Tomcat in a Java JAR file -->     <finalName>tutorial</finalName>     <pluginManagement>       <plugins>           <plugin>              <groupId>org.apache.tomcat.maven</groupId>              <artifactId>tomcat7-maven-plugin</artifactId>              <version>2.1</version>              <configuration>                <!-- context root for Java web apps --> <path>/tutorial</path>  <port>8080</port> <ajpPort>8009</ajpPort> <httpsPort>8443</httpsPort> <contextReloadable>true</contextReloadable>                <!-- name of executable jar file -->                <finalName>executable.jar</finalName>              </configuration> <!-- <configuration> <path>/</path>  <port>18080</port> <ajpPort>18009</ajpPort> <httpsPort>18443</httpsPort> <contextReloadable>true</contextReloadable> <keystoreFile>${user.home}/.keystore</keystoreFile> <keystorePass>changeit</keystorePass> </configuration> -->           </plugin>        </plugins>     </pluginManagement>  </build> </project>

$ mvn clean install tomcat7:exec-war-only

How to run an executable JAR file

To run the executable JAR file, issue the following command:

java -jar executable.jar

http://localhost:8080/tutorial/