From d93033003aa3ccd77ff5405815f9d8c133769346 Mon Sep 17 00:00:00 2001
From: Arthit Suriyawongkul <arthit@gmail.com>
Date: Fri, 18 Sep 2026 11:23:18 +0100
Subject: [PATCH 1/3] Add Maven Checkstyle

Signed-off-by: Arthit Suriyawongkul <arthit@gmail.com>
---
 .github/workflows/build.yml |  2 ++
 checkstyle.xml              | 31 +++++++++++++++++++++++++++++++
 pom.xml                     | 10 ++++++++++
 3 files changed, 43 insertions(+)
 create mode 100644 checkstyle.xml

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 657d139..375e1f8 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -45,3 +45,5 @@ jobs:
         else
            mvn --batch-mode --update-snapshots verify
         fi
+    - name: Checkstyle analysis
+      run: mvn --batch-mode checkstyle:check
diff --git a/checkstyle.xml b/checkstyle.xml
new file mode 100644
index 0000000..a218ddb
--- /dev/null
+++ b/checkstyle.xml
@@ -0,0 +1,31 @@
+<?xml version="1.0"?>
+<!DOCTYPE module PUBLIC
+    "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+    "https://checkstyle.org/dtds/configuration_1_3.dtd">
+
+<!--
+  Lean ruleset: correctness/maintainability checks only, not code style.
+-->
+<module name="Checker">
+    <module name="TreeWalker">
+        <module name="EqualsHashCode"/>
+        <module name="EqualsAvoidNull"/>
+        <module name="EmptyCatchBlock"/>
+        <module name="EmptyStatement"/>
+        <module name="EmptyBlock">
+            <property name="option" value="text"/>
+            <property name="tokens" value="LITERAL_TRY, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE"/>
+        </module>
+        <module name="UnusedImports"/>
+        <module name="RedundantImport"/>
+        <module name="SimplifyBooleanExpression"/>
+        <module name="SimplifyBooleanReturn"/>
+        <module name="StringLiteralEquality"/>
+        <module name="ModifiedControlVariable"/>
+        <module name="MissingSwitchDefault"/>
+        <module name="FallThrough"/>
+        <module name="OneStatementPerLine"/>
+        <module name="CovariantEquals"/>
+        <module name="NoFinalizer"/>
+    </module>
+</module>
diff --git a/pom.xml b/pom.xml
index 06e74e6..581a309 100644
--- a/pom.xml
+++ b/pom.xml
@@ -371,6 +371,16 @@
 				<artifactId>sonar-maven-plugin</artifactId>
 				<version>5.8.0.7211</version>
 			  </plugin>
+			  <plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-checkstyle-plugin</artifactId>
+				<version>3.6.0</version>
+				<configuration>
+					<configLocation>checkstyle.xml</configLocation>
+					<failOnViolation>false</failOnViolation>
+					<violationSeverity>warning</violationSeverity>
+				</configuration>
+			  </plugin>
 		</plugins>
   	</build>
 </project>

From d5024c71710b399d8db2addc1033f96adb928cb6 Mon Sep 17 00:00:00 2001
From: Arthit Suriyawongkul <arthit@gmail.com>
Date: Sun, 20 Sep 2026 23:21:28 +0100
Subject: [PATCH 2/3] Fix control variable style

Signed-off-by: Arthit Suriyawongkul <arthit@gmail.com>
---
 pom.xml                                                    | 3 +++
 src/main/java/org/spdx/tools/Verify.java                   | 7 +++----
 .../org/spdx/tools/schema/AbstractOwlRdfConverter.java     | 2 +-
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/pom.xml b/pom.xml
index d0a0e87..0694e14 100644
--- a/pom.xml
+++ b/pom.xml
@@ -411,6 +411,9 @@
 					<configLocation>checkstyle.xml</configLocation>
 					<failOnViolation>false</failOnViolation>
 					<violationSeverity>warning</violationSeverity>
+				</configuration>
+			  </plugin>
+			  <plugin>
 				<groupId>com.github.spotbugs</groupId>
 				<artifactId>spotbugs-maven-plugin</artifactId>
 				<version>4.9.3.2</version>
diff --git a/src/main/java/org/spdx/tools/Verify.java b/src/main/java/org/spdx/tools/Verify.java
index 64056b7..1736ceb 100644
--- a/src/main/java/org/spdx/tools/Verify.java
+++ b/src/main/java/org/spdx/tools/Verify.java
@@ -228,10 +228,9 @@ public static List<String> verify(String filePath, SerFileType fileType) throws
 			for (String verifyMsg:verify) {
 				if (!retval.contains(verifyMsg)) {
 					// Check for deprecated licenses - should be warnings, not errors
-					if (verifyMsg.contains(" is deprecated.")) {
-						verifyMsg = verifyMsg.replaceAll("error:", "warning:");
-					}
-					retval.add(verifyMsg);
+					String msg = verifyMsg.contains(" is deprecated.")
+							? verifyMsg.replaceAll("error:", "warning:") : verifyMsg;
+					retval.add(msg);
 				}
 			}
 		}
diff --git a/src/main/java/org/spdx/tools/schema/AbstractOwlRdfConverter.java b/src/main/java/org/spdx/tools/schema/AbstractOwlRdfConverter.java
index 778b815..287f438 100644
--- a/src/main/java/org/spdx/tools/schema/AbstractOwlRdfConverter.java
+++ b/src/main/java/org/spdx/tools/schema/AbstractOwlRdfConverter.java
@@ -221,7 +221,7 @@ private void interpretRestrictions(List<OntClass.Restriction> restrictions) {
 				// get the type from the range of the property
 				property.ranges().forEach(range -> {
 					if (range.isURIResource()) {
-						if (Objects.isNull(typeUri) || typeUri.equals("http://www.w3.org/2000/01/rdf-schema#Literal")) {
+						if (Objects.isNull(typeUri) || "http://www.w3.org/2000/01/rdf-schema#Literal".equals(typeUri)) {
 							typeUri = range.asResource().getURI();
 						}
 					}

From fdb5b92bac89a15963ee0180f8c063fd3622924f Mon Sep 17 00:00:00 2001
From: Arthit Suriyawongkul <arthit@gmail.com>
Date: Sun, 20 Sep 2026 23:23:09 +0100
Subject: [PATCH 3/3] checkstyle: Set failOnViolation = true

Signed-off-by: Arthit Suriyawongkul <arthit@gmail.com>
---
 pom.xml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pom.xml b/pom.xml
index 0694e14..e23cbbc 100644
--- a/pom.xml
+++ b/pom.xml
@@ -409,7 +409,7 @@
 				<version>3.6.0</version>
 				<configuration>
 					<configLocation>checkstyle.xml</configLocation>
-					<failOnViolation>false</failOnViolation>
+					<failOnViolation>true</failOnViolation>
 					<violationSeverity>warning</violationSeverity>
 				</configuration>
 			  </plugin>