War in jar with Maven

Intro

The following is one way you could go about packaging a war file in a jar file with [Maven](https://maven.apache.org/ "Maven). You might want to do this if you're loading a war file from the classpath programmatically.

For instance, assuming you had myjar.jar on the classpath and myjar.jar contained mywar.war, then you could refer to this war like so: classpath://mywar.war. Simply adding the directory containing your war file on the classpath (as you would to pick up *.class files) would not be enough to get a similar result.

By example

To get something to work with, we can make use of the maven-archetype-webapp archetype:

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$ mvn archetype:create  \
  -DgroupId=com.tmp \
  -DartifactId=warinjar \
  -DarchetypeArtifactId=maven-archetype-webapp
$ cd warinjar

Open up pom.xml in the generated project and change the packaging to jar:

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<packaging>jar</packaging>

The final ingredient is to get the maven-war-plugin in on the action:

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...
<build>
    <finalName>warinjar</finalName>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-war-plugin</artifactId>
            <version>2.6</version>
            <configuration>
                <outputDirectory>${project.build.directory}/classes</outputDirectory>
            </configuration>
            <executions>
                <execution>
                    <id>build-war-in-classes</id>
                    <phase>prepare-package</phase>
                    <goals>
                        <goal>war</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>
...

By setting the output directory to ${project.build.directory}/classes, this plugin will generate warinjar.war in our target/classes directory, the contents of which are picked up when packaging our project (since we set the packaging to jar above).

Running mvn clean package will clean out previous build (by deleting the target directory). It will also execute maven-war-plugin's war goal since we're executing it in the prepare-package lifecycle phase (which happens right before the package phase in Maven's default lifecycle).

This gives us target/classes/warinjar.war which then gets picked up when producing target/warinjar.jar (have a look at the jar's contents).

Of course, you could add another execution to also generate a war outside the jar:

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...
<execution>
    <id>build-war</id>
    <phase>package</phase>
    <configuration>
        <outputDirectory>${project.build.directory}</outputDirectory>
        <warName>waroutjar</warName>
    </configuration>
    <goals>
        <goal>war</goal>
    </goals>
</execution>
...

Note that we need to overwrite the plugin's configuration for this execution. Have a look at the documentation page for default values.

Basically, we're overwriting the default outputDirectory in our plugin's configuration, and so, the execution with id build-war-in-classes will output ${project.build.finalName}.war (i.e. warinjar.war) to ${project.build.directory}/classes.

Had we not overwritten the configuration in the plugin's execution with id build-war, we would have basically overwritten target/classes/warinjar.war with itself.

The final pom file looks like this:

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<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>com.tmp</groupId>
    <artifactId>warinjar</artifactId>
    <packaging>jar</packaging>
    <version>1.0-SNAPSHOT</version>
    <build>
        <finalName>warinjar</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.6</version>
                <configuration>
                    <outputDirectory>${project.build.directory}/classes</outputDirectory>
                </configuration>
                <executions>
                    <execution>
                        <id>build-war-in-classes</id>
                        <phase>prepare-package</phase>
                        <goals>
                            <goal>war</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>build-war</id>
                        <phase>package</phase>
                        <configuration>
                            <outputDirectory>${project.build.directory}</outputDirectory>
                            <warName>waroutjar</warName>
                        </configuration>
                        <goals>
                            <goal>war</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>