eclipse - Maven Project Builder is invoked every time I change a source file (GWT)

Question

Recently I converted my GWT web-app (GWT 2.4.0) to a maven project.
I am using maven 2.2.1, gwt-maven plugin (2.4.0), Eclipse Indigo (3.7) and the m2eclipse plugin.

The dependencies and general configuration seem to be fine as the web-app compiles without any problems and also works in production mode.
The same applies to hosted mode.

However I have a strange behavior: When I change a single line in a Java/GWT source file, the Maven Project Builder is invoked and this steps takes painfully long (around 10 secs) and eclipse sometimes becomes unusable during this time.

Is this a normal behavior of m2eclipse?

And if it is, is there any way to speed it up?

Note: I had to configure the life cycle plugin for m2eclipse. Here is the important section of the pom file:

<build>
        <!-- Generate compiled stuff in the folder used for developing mode -->
        <outputDirectory>${webappDirectory}/WEB-INF/classes</outputDirectory>

        <plugins>

            <!-- GWT Maven Plugin -->
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>gwt-maven-plugin</artifactId>
                <version>2.4.0</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                            <goal>test</goal>
                        </goals>
                    </execution>
                </executions>
                <!-- Plugin configuration. There are many available options, see gwt-maven-plugin 
                    documentation at codehaus.org -->
                <configuration>
                    <runTarget>index.html</runTarget>
                    <hostedWebapp>${webappDirectory}</hostedWebapp>
                    <i18nMessagesBundle>com.gmi.nordborglab.testapp.client.Messages</i18nMessagesBundle>
                </configuration>
            </plugin>

            <!-- Copy static web files before executing gwt:run -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.1.1</version>
                <executions>
                    <execution>
                        <phase>compile</phase>
                        <goals>
                            <goal>exploded</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <webappDirectory>${webappDirectory}</webappDirectory>
                </configuration>
            </plugin>
        </plugins>

        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.eclipse.m2e</groupId>
                    <artifactId>lifecycle-mapping</artifactId>
                    <version>1.0.0</version>
                    <configuration>
                        <lifecycleMappingMetadata>
                            <pluginExecutions>
                                <pluginExecution>
                                    <pluginExecutionFilter>
                                        <groupId>org.codehaus.mojo</groupId>
                                        <artifactId>gwt-maven-plugin</artifactId>
                                        <versionRange>[2.4.0,)</versionRange>
                                        <goals>
                                            <goal>resources</goal>
                                            <goal>compile</goal>
                                        </goals>
                                    </pluginExecutionFilter>
                                    <action>
                                        <execute />
                                    </action>
                                </pluginExecution>
                                <pluginExecution>
                                    <pluginExecutionFilter>
                                        <groupId>org.apache.maven.plugins</groupId>
                                        <artifactId>maven-war-plugin</artifactId>
                                        <versionRange>[2.1.1,)</versionRange>
                                        <goals>
                                            <goal>exploded</goal>
                                        </goals>
                                    </pluginExecutionFilter>
                                    <action>
                                        <execute />
                                    </action>
                                </pluginExecution>

                            </pluginExecutions>
                        </lifecycleMappingMetadata>
                    </configuration>
                </plugin>
            </plugins>
        </pluginManagement>

    </build>

Answer 1

This perfectly illustrates why m2e doesn't let any "unknown" plugins to run on incremental build by default ( http://wiki.eclipse.org/M2E_plugin_execution_not_covered#Background ). Most maven plugins aren't fit for incremental building and do a complete build whenever they're invoked (and as a bonus, you might get classloader leakages).

In your plugin management section, you specified that gwt:resources, gwt:compile and war:exploded should be executed. By default, they're executed on incremental builds, that means on EVERY resource change. Since these goals/plugins aren't optimized for an incremental build, they take a while to complete.

If you want to speed things up, you can tell m2e to execute them only on Full builds (i.e. after a project clean) by using

<execute>
  <runOnIncremental>false</runOnIncremental>
</execute>

Then, manually doing an eclipse clean build will automatically trigger their execution. Be aware that JDT sometimes decides to promote incremental builds to full ones.

I believe (but may be wrong) that, if you were using the Google Eclipse Plugin, you could ignore gwt:resources and gwt:compile altogether (by replacing <execute> with <ignore>).