[java] InvalidJavaBean - update rule doc

pmd-java/src/main/resources/category/java/design.xml

@@ -904,15 +904,30 @@ public class Foo {
     <rule name="InvalidJavaBean"
           language="java"
           since="6.52.0"
-          message="Invalid Java Bean"
+          message="The bean ''{0}'' is missing a getter for property ''{1}''."
           class="net.sourceforge.pmd.lang.java.rule.design.InvalidJavaBeanRule"
           externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_design.html#invalidjavabean">
         <description>
+Identifies beans, that don't follow the [JavaBeans API specification](https://download.oracle.com/otndocs/jcp/7224-javabeans-1.01-fr-spec-oth-JSpec/).
 
+Each non-static field should have both a getter and a setter method. If the field is just used internally and is not
+a bean property, then the field should be marked as `transient`.
+
+The rule verifies that the type of the field is the same as the result type of the getter. And that this type matches
+the type used in the setter.
+
+The rule also checks, that there is a no-arg or default constructor available.
+
+Optionally the rule also verifies, that the bean implements `java.io.Serializable`. While this is a requirement for the
+original JavaBeans specification, frameworks nowadays don't strictly require this anymore.
+
+In order to avoid many false positives in classes that are not beans, the rule needs to be explicitly
+enabled by configuring the property `packages`.
         </description>
         <priority>3</priority>
         <example>
 <![CDATA[
+package org.example.beans;
 public class MyBean {        // <-- bean is not serializable, missing "implements Serializable"
     private String label;    // <-- missing setter for property "label"
 

pmd-java/src/main/resources/rulesets/java/quickstart.xml

@@ -141,6 +141,11 @@
     <rule ref="category/java/design.xml/FinalFieldCouldBeStatic"/>
     <!-- <rule ref="category/java/design.xml/GodClass" /> -->
     <!-- <rule ref="category/java/design.xml/ImmutableField" /> -->
+    <!-- <rule ref="category/java/design.xml/InvalidJavaBean">-->
+    <!--     <properties>-->
+    <!--         <property name="packages" value="org.example.beans" />-->
+    <!--     </properties>-->
+    <!-- </rule>-->
     <!-- <rule ref="category/java/design.xml/LawOfDemeter" /> -->
     <rule ref="category/java/design.xml/LogicInversion"/>
     <!-- <rule ref="category/java/design.xml/LoosePackageCoupling"> -->

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/design/xml/InvalidJavaBean.xml

@@ -7,14 +7,14 @@
     <test-code>
         <description>Example code</description>
         <rule-property name="ensureSerialization">true</rule-property>
-        <rule-property name="packages"></rule-property>
         <expected-problems>2</expected-problems>
-        <expected-linenumbers>1,2</expected-linenumbers>
+        <expected-linenumbers>2,3</expected-linenumbers>
         <expected-messages>
             <message>The bean 'MyBean' does not implement java.io.Serializable.</message>
             <message>The bean 'MyBean' is missing a setter for property 'Label'.</message>
         </expected-messages>
         <code><![CDATA[
+package org.example.beans;
 public class MyBean {        // <-- bean is not serializable, missing "implements Serializable"
     private String label;    // <-- missing setter for property "label"