What is eclipse-ecj.jar and how to get it?

ecj is the Eclipse Java compiler and Ant plug-in
if you installed eclipse with java support you should already have it. Inside eclipse that file is referenced as "ecj.jar" you can try searching ecj.jar in www.eclipse.org, but by its own I don't think it'll be of any use.
Do you need it for some particular reason? maybe an error message, or something?

OK, I'll resurrect this thread. Same issue... I need ecj.jar, don't know what it is or why.

[root@desc tmp]# rpm -ivh tomcat6-6.0.18-8.1.fc11.noarch.rpm tomcat6-lib-6.0.18-8.1.fc11.noarch.rpm tomcat6-jsp-2.1-api-6.0.18-8.1.fc11.noarch.rpm tomcat6-servlet-2.5-api-6.0.18-8.1.fc11.noarch.rpm
error: Failed dependencies:
/usr/share/java/ecj.jar is needed by tomcat6-lib-6.0.18-8.1.fc11.noarch

Googling tells me it has something to do with "Eclipse". I see:

ls -l /usr/share/java/eclipse-ecj.jar
lrwxrwxrwx 1 root root 68 Dec 8 17:12 /usr/share/java/eclipse-ecj.jar -> /usr/share/eclipse/plugins/org.eclipse.jdt.core_3.2.1.v_677_R32x.jar

For giggles, I symlinked /usr/share/java/ecj.jar to /usr/share/eclipse/plugins/org.eclipse.jdt.core_3.2.1.v_677_R32x.jar but that didn't work, or at least it didn't satisfy the dependency.

My OS is RHEL5.2 What is the "correct" way for me to get this file? I do have eclipse-ecj-3.2.1-19.el5 installed.

To avoid previous message, check priorities between jpackage and base repos, or just exclude eclipse-ecj from base repo if You have installed ecj from jpackage repo.