Added Slf4jBindingChecker

NOTICE

@@ -146,6 +146,7 @@ The following software have components provided under the terms of this license:
 - lang-mustache (from https://github.com/elastic/elasticsearch)
 - lettuce (from http://github.com/mp911de/lettuce/wiki)
 - micrometer-core (from https://github.com/micrometer-metrics/micrometer)
+- micrometer-registry-azure-monitor (from https://github.com/micrometer-metrics/micrometer)
 - org.apiguardian:apiguardian-api (from https://github.com/apiguardian-team/apiguardian)
 - org.opentest4j:opentest4j (from https://github.com/ota4j-team/opentest4j)
 - parent-join (from https://github.com/elastic/elasticsearch)

pom.xml

@@ -21,7 +21,7 @@
   <groupId>org.opengroup.osdu</groupId>
   <artifactId>core-lib-azure</artifactId>
   <packaging>jar</packaging>
-  <version>0.0.36</version>
+  <version>0.0.37</version>
   <name>core-lib-azure</name>
 
   <properties>

src/main/java/org/opengroup/osdu/azure/logging/Slf4JBindingChecker.java

+//  Copyright © Microsoft Corporation
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//       http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+
+package org.opengroup.osdu.azure.logging;
+
+import org.slf4j.LoggerFactory;
+import org.slf4j.helpers.Util;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.stereotype.Component;
+
+import javax.annotation.PostConstruct;
+import java.io.IOException;
+import java.net.URL;
+import java.util.Enumeration;
+import java.util.LinkedHashSet;
+import java.util.Set;
+
+/**
+ * Checks if slf4j got bound with log4j2 correctly.
+ */
+@Component
+@ConditionalOnProperty(value = "logging.checkSlf4jBinding.enabled", havingValue = "true", matchIfMissing = false)
+public class Slf4JBindingChecker {
+
+    private final String staticLoggerBinderPath = "org/slf4j/impl/StaticLoggerBinder.class";
+    private Set<URL> staticLoggerBinderPathSet = new LinkedHashSet<URL>();
+
+    /**
+     * Since this methods is annotated with @PostConstruct, it is called only once.
+     * Its job is to fail the application if slf4j is not correctly bound to log4j2.
+     */
+    @PostConstruct
+    public void performCheck() {
+        Set<URL> pathSet = findPossibleStaticLoggerBinderPathSet();
+        if (!checkPathSet(pathSet)) {
+            throw new RuntimeException("\nAPPLICATION FAILED TO START\nslf4j is not correctly bound to log4j2\n");
+        }
+    }
+
+    /**
+     * Find all the resources on classpath with the name "org/slf4j/impl/StaticLoggerBinder.class".
+     * If there are multiple resources, that means there are multiple slf4j bindings present
+     * @return set of resources on classpath with name "org/slf4j/impl/StaticLoggerBinder.class"
+     */
+    private Set<URL> findPossibleStaticLoggerBinderPathSet() {
+        try {
+            ClassLoader loggerFactoryClassLoader = LoggerFactory.class.getClassLoader();
+            Enumeration<URL> paths;
+            if (loggerFactoryClassLoader == null) {
+                paths = ClassLoader.getSystemResources(staticLoggerBinderPath);
+            } else {
+                paths = loggerFactoryClassLoader.getResources(staticLoggerBinderPath);
+            }
+            while (paths.hasMoreElements()) {
+                URL path = paths.nextElement();
+                staticLoggerBinderPathSet.add(path);
+            }
+        } catch (IOException ioe) {
+            Util.report("Error getting resources from path", ioe);
+        }
+        return staticLoggerBinderPathSet;
+    }
+
+    /**
+     * If numbers of paths is greater than 1, then there are multiple bindings on classpath for slf4j
+     * In this case, slf4j will not bind correctly with log4j2.
+     * For binding to happen correctly, we need only one binding to be present, and that should of log4j2
+     * @param binderPathSet set of resources on classpath with name "org/slf4j/impl/StaticLoggerBinder.class"
+     * @return true if only one binding is found of log4j2 type, else return false
+     */
+    private boolean checkPathSet(final Set<URL> binderPathSet) {
+        if (binderPathSet.size() == 1) {
+            URL path = binderPathSet.iterator().next();
+            if (path.toString().contains("log4j-slf4j-impl-")) {
+                return true;
+            }
+        }
+        return false;
+    }
+}