为什么Maven Eclipse插件会破坏Maven码头插件？

Question

I would like to have the maven eclipse plugin regenerate my .classpath whenever a build is run, and I did so by using the following configuration:

    <!--
        Generate a new .classpath each time the build is run, but don't try
        to download sources or javadocs
    -->
    <profile>
        <id>elipse-update</id>
        <activation>
            <file>
                <exists>.classpath</exists>
            </file>
        </activation>
        <build>
            <plugins>
                <plugin>
                    <artifactId>maven-eclipse-plugin</artifactId>
                    <executions>
                        <execution>
                            <phase>generate-sources</phase>
                            <goals>
                                <goal>eclipse</goal>
                            </goals>
                            <configuration>
                                <downloadSources>false</downloadSources>
                                <downloadJavadocs>false</downloadJavadocs>
                            </configuration>
                        </execution>
                    </executions>
                </plugin>
            </plugins>
        </build>
    </profile>

For some reason, this causes the maven jetty plugin to fail with ClassNotFoundException errors (it complains about all sorts of Spring classes not being there). Of course, it worked without a hit when I didn't have the maven eclipse plugin installed. Here's an example of what I'm talking about:

$ mvn jetty:run
[INFO] Scanning for projects...
...
[INFO] Starting jetty 6.1.22 ...
2010-02-11 20:53:08.984:INFO::jetty-6.1.22
2010-02-11 20:53:09.109:WARN::Could not instantiate listener org.springframework.web.context.ContextLoaderListener
java.lang.ClassNotFoundException: org.springframework.web.context.ContextLoaderListener
        at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at org.codehaus.classworlds.RealmClassLoader.loadClassDirect(RealmClassLoader.java:195)
        at org.codehaus.classworlds.DefaultClassRealm.loadClass(DefaultClassRealm.java:255)
        at org.codehaus.classworlds.DefaultClassRealm.loadClass(DefaultClassRealm.java:274)
        at org.codehaus.classworlds.RealmClassLoader.loadClass(RealmClassLoader.java:214)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:251)

Of course, if I delete that eclipse plugin section, I can run jetty as expected:

$ mvn jetty:run
[INFO] Scanning for projects...
...
Feb 11, 2010 8:55:28 PM org.springframework.web.context.ContextLoader initWebApplicationContext
INFO: Root WebApplicationContext: initialization completed in 1672 ms
2010-02-11 20:55:28.687:INFO::Started SelectChannelConnector@0.0.0.0:8080
[INFO] Started Jetty Server
[INFO] Starting scanner at interval of 5 seconds.

Some things I know:

• Yes, I only activate this profile if the .classpath is present. This seems counter-intuitive, but I have a reason: I have another profile that activates when the .classpath is absent which runs the eclipse plugin with the options for downloading source code and javadocs set to true. I don't want this to happen each build, so I created a separate plugin config for when the classpath is already there.
• Yes, I could simply create properties that held the values of the options I wish to change instead of specifying the entire plugin config again. In that case, I would just set a eclipse.downloadSources property to true or false depending on the presence of the classpath and have a single plugin definition in the regular build section.

Any advice? This is a strange problem.

Thanks, LES

Answer 1

I suspect the Maven Eclipse Plugin to mess do some classpath woodo that affects the jetty plugin later.

But to be honest, this is not a very common way to use the Eclipse plugin, at least not to my knowledge. Most people don't include it in their build, they just run it when the POM has changed and this generally doesn't happen every build. Moreover, touching the .classpath confuses Eclipse if I remember well and forces a clean rebuild of the project which is pretty annoying.

So at the end, and I'm sorry for that, this seems to introduce more annoyances than benefits. You can try to open a Jira issue though.

Answer 2

You really don't want to run the maven-eclipse-plugin on every build when there's a .classpath present. I can't tell you exactly what it does to the classpaths, but this is not how it's intended to be used. The assumption is that when you run it you only run eclipse:eclipse (or some other goal).

Why do you want to keep re-running it?