How to Escape the \'Xerces Hell\' in Java with Maven?

Navigating the Perils of Xerces Hell in Java with Maven

As Java developers, dealing with the notorious "Xerces hell" can often lead to frustration and countless hours of debugging. This problem arises due to the complex history of Xerces, a widely used XML parser in the Java ecosystem, coupled with the fragmented nature of its Maven dependencies.

Understanding the Roots of the Problem

In its early days, Xerces did not adhere to Maven's release process and did not assign clear versions to its artifacts. Furthermore, the division of Xerces into two jars, xml-apis and xercesImpl, along with variations in uploaded versions, has caused conflicts in Maven dependency resolution.

Complicating matters, servlet containers often bundle Xerces in their own libraries, potentially introducing classpath clashes. Additionally, the JRE includes a version of Xerces through the Java API for XML Processing (JAXP), further heightening the potential for conflicts.

Consequences of Xerces Hell

The lack of consistent versions and dependencies can result in:

• Conflict Resolution Issues: Maven may include multiple versions of Xerces dependencies due to different groupIds, leading to runtime conflicts.
• Classloader Hell: Applications may experience classpath confusion due to overlapping Xerces implementations from multiple sources, such as Maven dependencies, servlet containers, and the JRE.

Addressing the Problem

Enforcing strict control over all Xerces dependencies through exclusions or providing can be difficult, especially in a large software project. Additionally, third-party libraries might not be compatible with the Xerces version provided by the JAXP in a specific JRE.

Solution: Leveraging Maven Central Xerces Jars

Recent developments have provided a solution to the Xerces hell problem. As of February 20th, 2013, versions of Xerces, including xercesImpl and xmlApis, have been made available on Maven Central.

For example, including the following dependency in your Maven POM will resolve all conflicts and ensure the use of the official Xerces implementation:

<dependency>
    <groupId>xerces</groupId>
    <artifactId>xercesImpl</artifactId>
    <version>2.11.0</version>
</dependency>

By leveraging the centrally managed Xerces artifacts, developers can avoid the complexities of maintaining multiple versions and resolving conflicts. The uniformity of versions provided ensures compatibility across platforms and frameworks.

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