Java – How to manage the ClassPath in WebSphere

javawebsphere

I have a problem with my web module classpath in Websphere v6.1.

In my WEB-INF/lib I have a largish number of jar files which include xercesImpl.jar and xmlparserv2.jar. I need both jars to be present, but they appear to confict with each other. Specifically, each jar contains a META-INF/services directory so, when we try to get an instance of a DocumentBuilderFactory via JAXP, which instance we get depends upon the order in which these two jars appear in the classpath.

I always want to use the xerces instance of the DocumentBuildFactory, so I want to push xercesImpl.jar to the front of the classpath. I've tried to do this by specifying a Class-Path section in the Manifest file for the war file, but the class path that I actually get in my WAS Module Compound CLass Loader in is very strange. I seem to get some standard stuff that WAS puts on, followed by the contents of WEB-INF lib in alphabetical order, followed by the classpath specified by the Manifest file.

If I don't put a manifest file into the war at all, I get the standard stuff followed by the contents of WEB-INF/lib but in an arbitrary order.

What am I missing? Is there a way in which I can set the class path up to be exactly what I want?

Dave

Best Solution

I assume by WebSphere, you mean the regular J2EE Application Server (and not something like Community Edition; WebSphere is a brand name applied to a number of IBM products).

I think your options are limited. Since the dependencies look quite explicit, I would prefer a programmatic approach rather than relying on the vagaries of the classpath (like creating factory instances explicitly rather than relying on the SPI).

If that isn't an option, you might want to look at making one of your dependencies an EAR project utility JAR and configure MODULE classloading with a PARENT_LAST classloading policy on the WAR. This can be configured via the browser admin console (or via the RAD tooling if you use it).

Another thing I'd look at is the WAS Shared Libraries feature (under Environment in the browser admin console). These can be associated with servers or applications. The downside is that this requires more configuration.

Related Solutions

Java – What are the differences between a HashMap and a Hashtable in Java

There are several differences between HashMap and Hashtable in Java:

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.

Since synchronization is not an issue for you, I'd recommend HashMap. If synchronization becomes an issue, you may also look at ConcurrentHashMap.

Java – How to efficiently iterate over each entry in a Java Map

Map<String, String> map = ...
for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

On Java 10+:

for (var entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

Best Solution

Related Solutions

Java – What are the differences between a HashMap and a Hashtable in Java

Java – How to efficiently iterate over each entry in a Java Map

Related Question