Maven, GWT and ECJ

When compiling a GWT webapp with the GWT Maven Plugin, you might encounter an exception such as

java.lang.NoSuchFieldError: warningThreshold

The reason is having ECJ in your classpath with a version different from what GWT includes. Unfortunately, GWT’s version is not repackaged and thus clashes with other versions. The quick fix is setting the gwtSdkFirstInClasspath configuration option for the gwt-maven-plugin (available since 2.1.0-1, see this issue):

<plugin>
  <groupId>org.codehaus.mojo</groupId>
  <artifactId>gwt-maven-plugin</artifactId>
  <version>2.1.0-1</version>
  <configuration>
    ...
    <gwtSdkFirstInClasspath>true</gwtSdkFirstInClasspath>
  </configuration>

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