C[omp]ute

From: "andrew cooke" <andrew@...>

Date: Fri, 17 Mar 2006 12:33:33 -0400 (CLT)

[This from an email I just sent at work]

This is probably going to be a fairly common problem, and is something
that could affect deployment.

Java famously has a problem when different (and incompatible) versions of
jars exist on the classpath (google "Java Jar Hell").  This is
particularly true for XML libraries, which have to track rapidly evolving
standards.

For example, Java 1.5 includes Xerces 2.6.2 (same classes, renamed to
com.sun), but Apache Commmons Pool (which several 3rd party packages
depend on) depends on Xerces 2.0.2.  Having both Xerces jars in the same
classpath causes problems.

To work around this:
- we need to exclude certain dependncies in Maven
- we need to be aware fo possible problems during deployment

I have solved (I believe) my immediate problems by blocking Xerces
dependencies in Maven.  In the POM I define dependencies like:

    <dependency>
      <groupId>some.group</groupId>
      <artifactId>some.artifact</artifactId>
      <version>version</version>
      <exclusions>
        <exclusion>
          <groupId>xerces</groupId>
          <artifactId>xerces</artifactId>
        </exclusion>
      </exclusions>
    </dependency>

For deployment this may be insufficient.  Xerces may already be present in
JBoss, for example.

Andrew