maven assembly plugin - Idea to avoid that spring.handlers/spring.schemas get overwritten when merging multiple spring dependencies in a single jar

Question

I got the error Unable to locate NamespaceHandler when using context:annotation-config running (java -jar) a jar assembled by the maven-assembly-plugin and containing my project and all its dependencies.

As other people correctly spotted on the forum.springsource.org thread (message #7/8) the problem occurs because the files META-INF/spring.handlers and META-INF/spring.schemas that are present in different jars, get overwritten when the maven-assembly-plugin repackages the jars in a single file.

Looking at the content of two spring-*.jar files you can see the files sits in the same position relatively to the classpath

$ jar tf spring-oxm-3.0.3.RELEASE.jar
META-INF/spring.handlers
META-INF/spring.schemas
org/springframework/oxm/GenericMarshaller.class
...

$ jar tf spring-context-3.0.3.RELEASE.jar
META-INF/spring.handlers
META-INF/spring.schemas
org/springframework/context/ApplicationContext.class

Isn't it is possible to put the META-INF folder in a specific package? If so the idea I'd suggest, (hope it's applicable) is to put the META-INF/spring.shemas and META-INF/spring.handlers files under the package they refer to.

$ jar tf spring-oxm-3.0.3.RELEASE.jar
org/springframework/oxm/META-INF/spring.schemas
org/springframework/oxm/META-INF/spring.handlers
org/springframework/oxm/GenericMarshaller.class
...

$ jar tf spring-context-3.0.3.RELEASE.jar
org/springframework/context/META-INF/spring.handlers
org/springframework/context/META-INF/spring.schemas
org/springframework/context/ApplicationContext.class

This way they won't conflict when merged in a single jar. What do you think about it?

Answer 1

I managed to get rid of the bug using the shader plugin instead of the (buggy) assembler plugin:

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                    <configuration>
                        <transformers>
                            <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                <mainClass>at.seresunit.lecturemanager_connector.App</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>
                        </transformers>
                    </configuration>
                </execution>
            </executions>
        </plugin>

I think I found the solution on the springsource forums.. it has been quite some time since I looked it up.. can't really remember the author. Kudos to him anyways :p

cheers