added method returning slf4j version

Signed-off-by: Ceki Gulcu <ceki@qos.ch>

slf4j-api/src/main/java/org/slf4j/LoggerFactory.java

@@ -198,7 +198,7 @@ private final static void bind() {
                 // SLF4JServiceProvider.initialize() is intended to be called here and nowhere else.
                 PROVIDER.initialize();
                 INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION;
-                reportActualBinding(providersList);
+                reportActualBinding(PROVIDER);
             } else {
                 INITIALIZATION_STATE = NOP_FALLBACK_INITIALIZATION;
                 Reporter.warn("No SLF4J providers were found.");
@@ -405,11 +405,8 @@ private static void reportMultipleBindingAmbiguity(List<SLF4JServiceProvider> pr
         }
     }
 
-    private static void reportActualBinding(List<SLF4JServiceProvider> providerList) {
-        if (!providerList.isEmpty()) {
-            SLF4JServiceProvider provider = providerList.get(0);
-            Reporter.info(CONNECTED_WITH_MSG + provider.getClass().getName() + "]");
-        }
+    private static void reportActualBinding(final SLF4JServiceProvider provider) {
+        Reporter.info(CONNECTED_WITH_MSG + provider.getClass().getName() + "]");
     }
 
     /**

slf4j-api/src/main/java/org/slf4j/helpers/Slf4jEnvUtil.java

@@ -0,0 +1,50 @@
+package org.slf4j.helpers;
+
+import java.lang.module.ModuleDescriptor;
+import java.util.Optional;
+
+public class Slf4jEnvUtil {
+
+
+    /**
+     * <p>Returns the current version of logback, or null if data is not
+     * available.
+     * </p>
+     *
+     * @return current version or null if missing version data
+     * @since 1.3.0
+     */
+    static public String slf4jVersion() {
+        String moduleVersion = slf4jVersionByModule();
+        if(moduleVersion != null)
+            return moduleVersion;
+
+        Package pkg = Slf4jEnvUtil.class.getPackage();
+        if(pkg == null) {
+            return null;
+        }
+        final String pkgVersion = pkg.getImplementationVersion();
+        return pkgVersion;
+    }
+
+    /**
+     * <p>Returns the current version of logback via class.getModule() or null if data is not
+     * available.
+     * </p>
+     *
+     * @since 1.3.0
+     * @return current version or null if missing version data
+     */
+    static private String slf4jVersionByModule() {
+        Module module = Slf4jEnvUtil.class.getModule();
+        if (module == null)
+            return null;
+
+        ModuleDescriptor md = module.getDescriptor();
+        if (md == null)
+            return null;
+        Optional<String> opt = md.rawVersion();
+        return opt.orElse(null);
+    }
+
+}

slf4j-simple/src/test/java/org/slf4j/simple/Slf4jVersionTest.java

@@ -0,0 +1,21 @@
+package org.slf4j.simple;
+
+import org.junit.Test;
+import org.slf4j.helpers.Slf4jEnvUtil;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+public class Slf4jVersionTest {
+
+
+    @Test
+    public void slf4jVersionTest() {
+
+        String version = Slf4jEnvUtil.slf4jVersion();
+        assertNotNull(version);
+        assertTrue(version.startsWith("2"));
+
+    }
+
+}