Improve DevelopmentPluginClasspath according #195 (#219)

pf4j/src/main/java/org/pf4j/DevelopmentPluginClasspath.java

@@ -16,17 +16,39 @@
 package org.pf4j;
 
 /**
- * Overwrite classes directories to {@code target/classes} and lib directories to {@code target/lib}.
+ * It's a compound {@link PluginClasspath} ({@link #MAVEN} + {@link #GRADLE} + {@link #KOTLIN})
+ * used in development mode ({@link RuntimeMode#DEVELOPMENT}).
  *
  * @author Decebal Suiu
  */
 public class DevelopmentPluginClasspath extends PluginClasspath {
 
-	public DevelopmentPluginClasspath() {
-		super();
+    /**
+     * The development plugin classpath for <a href="https://maven.apache.org">Maven</a>.
+     * The classes directory is {@code target/classes} and the lib directory is {@code target/lib}.
+     */
+    public static final PluginClasspath MAVEN = new PluginClasspath().addClassesDirectories("target/classes").addLibDirectories("target/lib");
 
-        addClassesDirectories("target/classes");
-        addLibDirectories("target/lib");
+    /**
+     * The development plugin classpath for <a href="https://gradle.org">Gradle</a>.
+     * The classes directories are {@code build/classes/java/main, build/resources/main}.
+     */
+    public static final PluginClasspath GRADLE = new PluginClasspath().addClassesDirectories("build/classes/java/main", "build/resources/main");
+
+    /**
+     * The development plugin classpath for <a href="https://kotlinlang.org">Kotlin</a>.
+     * The classes directories are {@code build/classes/kotlin/main", build/resources/main, build/tmp/kapt3/classes/main}.
+     */
+    public static final PluginClasspath KOTLIN = new PluginClasspath().addClassesDirectories("build/classes/kotlin/main", "build/resources/main", "build/tmp/kapt3/classes/main");
+
+    public DevelopmentPluginClasspath() {
+        addClassesDirectories(MAVEN.getClassesDirectories());
+        addClassesDirectories(GRADLE.getClassesDirectories());
+        addClassesDirectories(KOTLIN.getClassesDirectories());
+
+        addLibDirectories(MAVEN.getLibDirectories());
+        addLibDirectories(GRADLE.getLibDirectories());
+        addLibDirectories(KOTLIN.getLibDirectories());
     }
 
 }

pf4j/src/main/java/org/pf4j/PluginClasspath.java

@@ -15,9 +15,10 @@
  */
 package org.pf4j;
 
-import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.List;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
 
 /**
  * The classpath of the plugin.
@@ -27,28 +28,35 @@ import java.util.List;
  */
 public class PluginClasspath {
 
-	private List<String> classesDirectories;
-	private List<String> libDirectories;
+    private Set<String> classesDirectories = new HashSet<>();
+    private Set<String> libDirectories = new HashSet<>();
 
-	public PluginClasspath() {
-		classesDirectories = new ArrayList<>();
-		libDirectories = new ArrayList<>();
-	}
+    public Set<String> getClassesDirectories() {
+        return classesDirectories;
+    }
 
-	public List<String> getClassesDirectories() {
-		return classesDirectories;
-	}
+    public PluginClasspath addClassesDirectories(String... classesDirectories) {
+        return addClassesDirectories(Arrays.asList(classesDirectories));
+    }
 
-	public void addClassesDirectories(String... classesDirectories) {
-		this.classesDirectories.addAll(Arrays.asList(classesDirectories));
-	}
+    public PluginClasspath addClassesDirectories(Collection<String> classesDirectories) {
+        this.classesDirectories.addAll(classesDirectories);
 
-	public List<String> getLibDirectories() {
-		return libDirectories;
-	}
+        return this;
+    }
 
-	public void addLibDirectories(String... libDirectories) {
-		this.libDirectories.addAll(Arrays.asList(libDirectories));
-	}
+    public Set<String> getLibDirectories() {
+        return libDirectories;
+    }
+
+    public PluginClasspath addLibDirectories(String... libDirectories) {
+        return addLibDirectories(Arrays.asList(libDirectories));
+    }
+
+    public PluginClasspath addLibDirectories(Collection<String> libDirectories) {
+        this.libDirectories.addAll(libDirectories);
+
+        return this;
+    }
 
 }