Use logger instead of System.out.println for demo

demo/app/src/main/java/org/pf4j/demo/Boot.java

@@ -22,6 +22,8 @@ import org.pf4j.ExtensionFinder;
 import org.pf4j.PluginManager;
 import org.pf4j.PluginWrapper;
 import org.pf4j.demo.api.Greeting;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.util.List;
 import java.util.Set;
@@ -33,21 +35,14 @@ import java.util.Set;
  */
 public class Boot {
 
+    private static final Logger log = LoggerFactory.getLogger(Boot.class);
+
     public static void main(String[] args) {
         // print logo
         printLogo();
 
         // create the plugin manager
-        final PluginManager pluginManager = new DefaultPluginManager() {
-
-            protected ExtensionFinder createExtensionFinder() {
-                DefaultExtensionFinder extensionFinder = (DefaultExtensionFinder) super.createExtensionFinder();
-                extensionFinder.addServiceProviderExtensionFinder(); // to activate "HowdyGreeting" extension
-
-                return extensionFinder;
-            }
-
-        };
+        PluginManager pluginManager = createPluginManager();
 
         // load the plugins
         pluginManager.loadPlugins();
@@ -60,59 +55,59 @@ public class Boot {
 
         // retrieves the extensions for Greeting extension point
         List<Greeting> greetings = pluginManager.getExtensions(Greeting.class);
-        System.out.println(String.format("Found %d extensions for extension point '%s'", greetings.size(), Greeting.class.getName()));
+        log.info("Found {} extensions for extension point '{}'", greetings.size(), Greeting.class.getName());
         for (Greeting greeting : greetings) {
-            System.out.println(">>> " + greeting.getGreeting());
+            log.info(">>> {}", greeting.getGreeting());
         }
 
         // print extensions from classpath (non plugin)
-        System.out.println("Extensions added by classpath:");
+        log.info("Extensions added by classpath:");
         Set<String> extensionClassNames = pluginManager.getExtensionClassNames(null);
         for (String extension : extensionClassNames) {
-            System.out.println("   " + extension);
+            log.info("   {}", extension);
         }
 
-        System.out.println("Extension classes by classpath:");
+        log.info("Extension classes by classpath:");
         List<Class<? extends Greeting>> greetingsClasses = pluginManager.getExtensionClasses(Greeting.class);
         for (Class<? extends Greeting> greeting : greetingsClasses) {
-            System.out.println("   Class: " + greeting.getCanonicalName());
+            log.info("   Class: {}", greeting.getCanonicalName());
         }
 
         // print extensions ids for each started plugin
         List<PluginWrapper> startedPlugins = pluginManager.getStartedPlugins();
         for (PluginWrapper plugin : startedPlugins) {
             String pluginId = plugin.getDescriptor().getPluginId();
-            System.out.println(String.format("Extensions added by plugin '%s':", pluginId));
+            log.info("Extensions added by plugin '{}}':", pluginId);
             extensionClassNames = pluginManager.getExtensionClassNames(pluginId);
             for (String extension : extensionClassNames) {
-                System.out.println("   " + extension);
+                log.info("   {}", extension);
             }
         }
 
         // print the extensions instances for Greeting extension point for each started plugin
         for (PluginWrapper plugin : startedPlugins) {
             String pluginId = plugin.getDescriptor().getPluginId();
-            System.out.println(String.format("Extensions instances added by plugin '%s' for extension point '%s':", pluginId, Greeting.class.getName()));
+            log.info("Extensions instances added by plugin '{}' for extension point '{}':", pluginId, Greeting.class.getName());
             List<Greeting> extensions = pluginManager.getExtensions(Greeting.class, pluginId);
             for (Object extension : extensions) {
-                System.out.println("   " + extension);
+                log.info("   {}", extension);
             }
         }
 
         // print extensions instances from classpath (non plugin)
-        System.out.println("Extensions instances added by classpath:");
+        log.info("Extensions instances added by classpath:");
         List extensions = pluginManager.getExtensions((String) null);
         for (Object extension : extensions) {
-            System.out.println("   " + extension);
+            log.info("   {}", extension);
         }
 
         // print extensions instances for each started plugin
         for (PluginWrapper plugin : startedPlugins) {
             String pluginId = plugin.getDescriptor().getPluginId();
-            System.out.println(String.format("Extensions instances added by plugin '%s':", pluginId));
+            log.info("Extensions instances added by plugin '{}':", pluginId);
             extensions = pluginManager.getExtensions(pluginId);
             for (Object extension : extensions) {
-                System.out.println("   " + extension);
+                log.info("   {}", extension);
             }
         }
 
@@ -131,9 +126,22 @@ public class Boot {
     }
 
     private static void printLogo() {
-        System.out.println(StringUtils.repeat("#", 40));
-        System.out.println(StringUtils.center("PF4J-DEMO", 40));
-        System.out.println(StringUtils.repeat("#", 40));
+        log.info(StringUtils.repeat("#", 40));
+        log.info(StringUtils.center("PF4J-DEMO", 40));
+        log.info(StringUtils.repeat("#", 40));
+    }
+
+    private static PluginManager createPluginManager() {
+        return new DefaultPluginManager() {
+
+            protected ExtensionFinder createExtensionFinder() {
+                DefaultExtensionFinder extensionFinder = (DefaultExtensionFinder) super.createExtensionFinder();
+                extensionFinder.addServiceProviderExtensionFinder(); // to activate "HowdyGreeting" extension
+
+                return extensionFinder;
+            }
+
+        };
     }
 
 }

demo/plugins/plugin1/src/main/java/org/pf4j/demo/welcome/WelcomePlugin.java

@@ -34,16 +34,16 @@ public class WelcomePlugin extends Plugin {
 
     @Override
     public void start() {
-        System.out.println("WelcomePlugin.start()");
+        log.info("WelcomePlugin.start()");
         // for testing the development mode
         if (RuntimeMode.DEVELOPMENT.equals(wrapper.getRuntimeMode())) {
-            System.out.println(StringUtils.upperCase("WelcomePlugin"));
+            log.info(StringUtils.upperCase("WelcomePlugin"));
         }
     }
 
     @Override
     public void stop() {
-        System.out.println("WelcomePlugin.stop()");
+        log.info("WelcomePlugin.stop()");
     }
 
     @Extension

demo/plugins/plugin2/src/main/java/org/pf4j/demo/hello/HelloPlugin.java

@@ -33,12 +33,12 @@ public class HelloPlugin extends Plugin {
 
     @Override
     public void start() {
-        System.out.println("HelloPlugin.start()");
+        log.info("HelloPlugin.start()");
     }
 
     @Override
     public void stop() {
-        System.out.println("HelloPlugin.stop()");
+        log.info("HelloPlugin.stop()");
     }
 
     @Extension(ordinal=1)