Having Maven create a nice zip File and separate Configuration

A co-worker and I are preparing a presentation about Amazon EC2 for other developers in my company. To show some stuff in action, we decided to write two JMS powered applications. One is sending messages, the other is receiving messages and persisting them into a database. During the presentation we will roll this out onto 3 EC2 nodes. Each application is build using Maven. To have it as convenient as possible, I changed the Maven package build phase to produce a single zip-file. The zip-file can be copied over to the EC2 node, where it is extracted. The zip-file contains one big "uber-jar" (with all the third party dependencies included) and a single properties-file to be able to set host and port for the JMS communication. We use ActiveMQ as JMS vendor in our projects.

Once the big zip-file has been extracted on the EC2 nodes and the properties have been set, you can start the producer and the consumer from the Main class. (Note the little dot infront of .:consumer... - this is needed so that the properties-file is found)

java -cp .:consumer-1.0-SNAPSHOT-final.jar package.MessageReceiver

For the packaging of the big zip-files, I use the Maven Assembly plugin during the package phase. The configuration looks like this:

<assembly xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.0 http://maven.apache.org/xsd/assembly-1.1.0.xsd">
    <id>final</id>
    <formats>
        <format>jar</format>
    </formats>
    <includeBaseDirectory>false</includeBaseDirectory>
    <dependencySets>
        <dependencySet>
            <unpack>true</unpack>
            <scope>runtime</scope>
            <useProjectArtifact>false</useProjectArtifact>
        </dependencySet>
    </dependencySets>
    <fileSets>
        <fileSet>
            <directory>${project.build.outputDirectory}</directory>
            <outputDirectory>/</outputDirectory>
            <excludes>
                <exclude>consumer.properties</exclude>
            </excludes>
        </fileSet>
    </fileSets>
</assembly>

src/main/assembly/jar.xml

This explodes all third party dependency jar files and merges them into one big uber-jar file. The properties-file is excluded from the uber-jar (this name sounds hilarious if you are from Germany by the way).

<assembly xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.0 http://maven.apache.org/xsd/assembly-1.1.0.xsd">
    <id>bin</id>
    <formats>
        <format>zip</format>
    </formats>
    <includeBaseDirectory>false</includeBaseDirectory>
    <fileSets>
        <fileSet>
            <directory>${project.basedir}/src/main/resources</directory>
            <outputDirectory/>
            <includes>
                <include>consumer.properties</include>
            </includes>
        </fileSet>
        <fileSet>
            <directory>${project.build.directory}</directory>
            <outputDirectory/>
            <includes>
                <include>*-final.jar</include>
            </includes>
        </fileSet>
    </fileSets>
</assembly>

src/main/assembly/zip.xml

This creates a zip-archive containing the "uber-jar" and the properties-file. Notice that the "uber-jar" has the suffix of "-final" equal to the id-attribute in the jar.xml file.

<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<configuration>
    <archive>
        <manifest>
            <mainClass>package.MessageReceiver</mainClass>
        </manifest>
    </archive>
    <descriptorRefs>
        <descriptorRef>jar-with-dependencies</descriptorRef>
    </descriptorRefs>
    <descriptors>
        <descriptor>src/main/assembly/jar.xml</descriptor>
        <descriptor>src/main/assembly/zip.xml</descriptor>
    </descriptors>
</configuration>
<executions>
    <execution>
        <id>make-assembly</id>
        <phase>package</phase>
        <goals>
            <goal>single</goal>
        </goals>
    </execution>
</executions>
</plugin>

pom.xml

This code snippet runs the maven-assembly-plugin during the package phase.

Everything went well when we finished the producer application last week. Today I ran into some weird errors when I worked on the consumer end. Trying to start the MessageReceiver main class gave me the following error:

Caused by: org.xml.sax.SAXParseException: cvc-complex-type.2.4.c: The matching wildcard is strict, but no declaration can be found for element 'amq:broker'.

I was able to resolve this error with the help of the ActiveMQ XML reference page, only to stumble into the next problem:

Caused by: org.springframework.beans.factory.parsing.BeanDefinitionParsingException: Configuration problem: Unable to locate Spring NamespaceHandler for XML schema namespace http://www.springframework.org/schema/context

It did not really jump me at first why this was happening. There a unit tests which load the Spring Context, they run fine. Maven runs the test in the package phase, they passed fine. So this was odd. After doing some research, I found out that the maven-assembly-plugin is responsible for this. Apparently Spring needs the spring.handlers and spring.schemas files to be present in the META-INF directory of the "uber-jar". A lot of other people had already hit the same problem before me. Some of them recommend the use of the maven-shade-plugin with the following setup:

<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>1.3.1</version>

<executions>
    <execution>
        <phase>package</phase>
        <goals>
            <goal>shade</goal>
        </goals>
        <configuration>
            <finalName>${artifactId}-${version}-final</finalName>
            <transformers>
                <transformer implementation="
org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                    <mainClass>
com.sabre.newgermanrail.dbitool.DbiTool
</mainClass>
                </transformer>
                <transformer implementation="
org.apache.maven.plugins.shade.resource.AppendingTransformer">
                    <resource>META-INF/spring.handlers</resource>
                </transformer>
                <transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
                    <resource>META-INF/spring.schemas</resource>
                </transformer>
  <transformer implementation="
org.apache.maven.plugins.shade.resource.DontIncludeResourceTransformer">
                    <resource>consumer.properties</resource>
                </transformer>
            </transformers>
        </configuration>
    </execution>
</executions>
</plugin>

pom.xml

With the help of Transformers, the spring.handlers and spring.schemas files are added. If you are using Spring 3.x, there are many small spring-xyz.jar files and each of these comes with a spring.handlers and spring.schemas file. The maven-shade-plugin will append the content of each of these files using the AppendingTransformer. As you can see in the example above, I am again excluding my properties-file using the DontIncludeResourceTransformer. I decided to keep the zip-archiving part from the maven-assembly-plugin. Maybe this is something the maven-shade-plugin could do for me as well, not sure.