static-analysis/pmd-rules/src/main/resources/org/apache/geode/pmd/staticimmutable.xml

<?xml version="1.0"?>
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<ruleset name="Custom Rules"
         xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 https://pmd.sourceforge.io/ruleset_2_0_0.xsd">

    <description>
        My custom rules
    </description>
    <rule name="StaticFieldsMustBeImmutable"
          message="All static final fields must be immutable objects. No mutable static state is allowed."
          language="java"
          class="org.apache.geode.pmd.StaticFieldsMustBeImmutable">
        <description>
            Geode does not allow mutable static fields within the product code. All static
            fields must be marked final and be immutable objects.

            If the value of your static field is actually immutable, you can annotate the field
            itself with @Immutable, and it will be ignored by this rule.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
              public class SomeClass {
                //This field could be mutated by some outside code
                private static final Map field = new HashMap();
              }
			]]>
        </example>
    </rule>
</ruleset>