Prevent accidental printing to System.err in the codebase

This also revises the Checkstyle rule so that invocations such as
System.out.printf() are also forbidden.

Author: sbrannen

Diff for: src/checkstyle/checkstyle-suppressions.xml

@@ -14,7 +14,7 @@
 	<suppress files="[\\/]src[\\/](test|testFixtures)[\\/](java|java21)[\\/]" checks="AnnotationLocation|AnnotationUseStyle|AtclauseOrder|AvoidNestedBlocks|FinalClass|HideUtilityClassConstructor|InnerTypeLast|JavadocStyle|JavadocType|JavadocVariable|LeftCurly|MultipleVariableDeclarations|NeedBraces|OneTopLevelClass|OuterTypeFilename|RequireThis|SpringCatch|SpringJavadoc|SpringNoThis"/>
 	<suppress files="[\\/]src[\\/](test|testFixtures)[\\/](java|java21)[\\/]" checks="RegexpSinglelineJava" id="toLowerCaseWithoutLocale"/>
 	<suppress files="[\\/]src[\\/](test|testFixtures)[\\/](java|java21)[\\/]" checks="RegexpSinglelineJava" id="toUpperCaseWithoutLocale"/>
-	<suppress files="[\\/]src[\\/](test|testFixtures)[\\/](java|java21)[\\/]" checks="RegexpSinglelineJava" id="systemOutPrintln"/>
+	<suppress files="[\\/]src[\\/](test|testFixtures)[\\/](java|java21)[\\/]" checks="RegexpSinglelineJava" id="systemOutErrPrint"/>
 	<suppress files="[\\/]src[\\/](test|testFixtures)[\\/](java|java21)[\\/]org[\\/]springframework[\\/].+(Tests|Suite)" checks="IllegalImport" id="bannedJUnitJupiterImports"/>
 	<suppress files="[\\/]src[\\/](test|testFixtures)[\\/](java|java21)[\\/]" checks="SpringJUnit5" message="should not be public"/>
 
@@ -43,7 +43,8 @@
 
 	<!-- spring-core -->
 	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]springframework[\\/](asm|cglib|objenesis|javapoet)[\\/]" checks=".*"/>
-	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]springframework[\\/]aot[\\/]nativex[\\/]feature[\\/]" checks="RegexpSinglelineJava" id="systemOutPrintln"/>
+	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]springframework[\\/]aot[\\/]nativex[\\/]feature[\\/]" checks="RegexpSinglelineJava" id="systemOutErrPrint"/>
+	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]springframework[\\/](core|util)[\\/](SpringProperties|SystemPropertyUtils)" checks="RegexpSinglelineJava" id="systemOutErrPrint"/>
 	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]springframework[\\/]lang[\\/]" checks="IllegalImport" id="bannedImports" message="javax"/>
 	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]springframework[\\/]lang[\\/]" checks="RegexpSinglelineJava" id="packageLevelNonNullApiAnnotation" />
 	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]springframework[\\/]lang[\\/]" checks="RegexpSinglelineJava" id="packageLevelNonNullFieldsAnnotation" />
@@ -66,7 +67,7 @@
 
 	<!-- spring-jcl -->
 	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]apache[\\/]commons[\\/]logging[\\/]" checks="Header|SpringNoThis|IllegalImport"/>
-	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]apache[\\/]commons[\\/]logging[\\/]" checks="RegexpSinglelineJava" id="systemOutPrintln"/>
+	<suppress files="[\\/]src[\\/]main[\\/]java[\\/]org[\\/]apache[\\/]commons[\\/]logging[\\/]" checks="RegexpSinglelineJava" id="systemOutErrPrint"/>
 
 	<!-- spring-jdbc -->
 	<suppress files="ResultSetWrappingSqlRowSet" checks="JavadocStyle"/>
@@ -123,6 +124,7 @@
 	<suppress files="org[\\/]springframework[\\/]web[\\/]bind[\\/]annotation[\\/]CrossOrigin" checks="JavadocStyle"/>
 	<suppress files="org[\\/]springframework[\\/]web[\\/]bind[\\/]annotation[\\/]RequestMethod" checks="JavadocVariable"/>
 	<suppress files="org[\\/]springframework[\\/]web[\\/]bind[\\/]annotation[\\/]ValueConstants" checks="InterfaceIsType"/>
+	<suppress files="org[\\/]springframework[\\/]web[\\/]util[\\/]ServletContextPropertyUtils" checks="RegexpSinglelineJava" id="systemOutErrPrint"/>
 	<suppress files="PatternParseException" checks="JavadocVariable"/>
 	<suppress files="web[\\/]reactive[\\/]socket[\\/]CloseStatus" checks="JavadocStyle"/>
 	<suppress files="RestClientResponseException" checks="MutableException"/>

Diff for: src/checkstyle/checkstyle.xml

@@ -238,11 +238,11 @@
 			<property name="ignoreComments" value="true"/>
 		</module>
 		<module name="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineJavaCheck">
-			<property name="id" value="systemOutPrintln"/>
-			<property name="format" value="System\.out\.println"/>
+			<property name="id" value="systemOutErrPrint"/>
+			<property name="format" value="System\.(out|err)\.print"/>
 			<property name="maximum" value="0"/>
 			<property name="message"
-					  value="System.out.println calls are forbidden in the main codebase"/>
+					  value="Printing to System.out and System.err is forbidden in the main codebase"/>
 			<property name="ignoreComments" value="true"/>
 		</module>
 		<module