add debug messages for PropertiesPluginDescriptorFinder

demo/app/src/main/resources/log4j.properties

@@ -2,5 +2,5 @@ log4j.rootLogger=DEBUG,Console
 
 log4j.appender.Console=org.apache.log4j.ConsoleAppender
 log4j.appender.Console.layout=org.apache.log4j.PatternLayout
-log4j.appender.Console.layout.conversionPattern=%-5p - %-30.30c{1} - %m\n
+log4j.appender.Console.layout.conversionPattern=%-5p - %-32.32c{1} - %m\n
 

pf4j/src/main/java/ro/fortsoft/pf4j/PropertiesPluginDescriptorFinder.java

@@ -19,6 +19,9 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.util.Properties;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import ro.fortsoft.pf4j.util.StringUtils;
 
 /**
@@ -28,10 +31,14 @@ import ro.fortsoft.pf4j.util.StringUtils;
  */
 public class PropertiesPluginDescriptorFinder implements PluginDescriptorFinder {
 
+	private static final Logger log = LoggerFactory.getLogger(PropertiesPluginDescriptorFinder.class);
+	
+	private static final String DEFAULT_PROPERTIES_FILE_NAME = "plugin.properties";
+	
 	private String propertiesFileName;
 
 	public PropertiesPluginDescriptorFinder() {
-		this("plugin.properties");
+		this(DEFAULT_PROPERTIES_FILE_NAME);
 	}
 
 	public PropertiesPluginDescriptorFinder(String propertiesFileName) {
@@ -41,6 +48,7 @@ public class PropertiesPluginDescriptorFinder implements PluginDescriptorFinder
 	@Override
 	public PluginDescriptor find(File pluginRepository) throws PluginException {
         File propertiesFile = new File(pluginRepository, propertiesFileName);
+        log.debug("Lookup plugin descriptor in '{}'", propertiesFile);
         if (!propertiesFile.exists()) {
             throw new PluginException("Cannot find '" + propertiesFile + "' file");
         }