Improve example of custom rule (#890)

* Improve example of custom rule

- use constructor for components injection
- use a sisu version from the project

* add maven.compiler.release to example

Author: slawekjaranowski

enforcer-api/src/custom-rule-sample/pom.xml

@@ -34,9 +34,9 @@
   <properties>
     <api.version>${project.version}</api.version>
     <mavenVersion>${mavenVersion}</mavenVersion>
-    <!-- use JDK 1.8 or 11 -->
-    <maven.compiler.source>1.8</maven.compiler.source>
-    <maven.compiler.target>1.8</maven.compiler.target>
+    <maven.compiler.source>8</maven.compiler.source>
+    <maven.compiler.target>8</maven.compiler.target>
+    <maven.compiler.release>8</maven.compiler.release>
   </properties>
 
   <dependencies>
@@ -66,7 +66,7 @@
         <!-- generate index of project components -->
         <groupId>org.eclipse.sisu</groupId>
         <artifactId>sisu-maven-plugin</artifactId>
-        <version>0.9.0.M1</version>
+        <version>${version.sisu-maven-plugin}</version>
         <executions>
           <execution>
             <goals>

enforcer-api/src/custom-rule-sample/src/main/java/org/example/custom/rule/MyCustomRule.java

@@ -24,6 +24,7 @@
 import javax.inject.Named;
 
 import java.util.List;
+import java.util.Objects;
 
 import org.apache.maven.enforcer.rule.api.AbstractEnforcerRule;
 import org.apache.maven.enforcer.rule.api.EnforcerRuleException;
@@ -49,14 +50,18 @@ public class MyCustomRule extends AbstractEnforcerRule {
 
     // Inject needed Maven components
 
-    @Inject
-    private MavenProject project;
+    private final MavenProject project;
 
-    @Inject
-    private MavenSession session;
+    private final MavenSession session;
+
+    private final RuntimeInformation runtimeInformation;
 
     @Inject
-    private RuntimeInformation runtimeInformation;
+    public MyCustomRule(MavenProject project, MavenSession session, RuntimeInformation runtimeInformation) {
+        this.project = Objects.requireNonNull(project);
+        this.session = Objects.requireNonNull(session);
+        this.runtimeInformation = Objects.requireNonNull(runtimeInformation);
+    }
 
     public void execute() throws EnforcerRuleException {