GUACAMOLE-2181: Ensure our custom logging factory is used.

guacamole/src/main/java/org/apache/guacamole/GuacamoleServletContainerInitializer.java

@@ -0,0 +1,64 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.apache.guacamole;
+
+import java.util.Set;
+import javax.servlet.ServletContainerInitializer;
+import javax.servlet.ServletContext;
+import javax.servlet.ServletException;
+import org.apache.guacamole.log.GuacamoleLogbackServiceProvider;
+import org.slf4j.LoggerFactory;
+import org.slf4j.helpers.Reporter;
+
+/**
+ * ServletContainerInitializer which forces the SLF4J service provider to be
+ * Guacamole's built-in logging system. This is necessary as Logback also
+ * includes an SLF4J service provider, and there is no guarantee which provider
+ * will be chosen by SLF4J in the case that multiple are present.
+ * <p>
+ * SLF4J uses a "slf4j.provider" system property to allow a specific provider
+ * to be chosen, which this initializer sets automatically.
+ */
+public class GuacamoleServletContainerInitializer implements ServletContainerInitializer {
+
+    @Override
+    public void onStartup(Set<Class<?>> c, ServletContext ctx) throws ServletException {
+
+        // Ideally, we want to use Guacamole's built-in logging facility, but
+        // we shouldn't override the administrator if they have their own SLF4J
+        // provider that needs to be used instead (ie: for some log aggregation
+        // service)
+        if (System.getProperty(LoggerFactory.PROVIDER_PROPERTY_KEY) == null) {
+
+            System.setProperty(LoggerFactory.PROVIDER_PROPERTY_KEY,
+                    GuacamoleLogbackServiceProvider.class.getCanonicalName());
+
+            // Avoid excessive verbosity from SLF4J unless the administrator
+            // has explicitly chosen SLF4J's verbosity level (the SLF4J provider
+            // class will otherwise be logged at startup, which is an internal
+            // detail and not typically needed)
+            if (System.getProperty(Reporter.SLF4J_INTERNAL_VERBOSITY_KEY) == null)
+                System.setProperty(Reporter.SLF4J_INTERNAL_VERBOSITY_KEY, "WARN");
+
+        }
+
+    }
+
+}

guacamole/src/main/resources/META-INF/services/javax.servlet.ServletContainerInitializer

@@ -0,0 +1 @@
+org.apache.guacamole.GuacamoleServletContainerInitializer

guacamole/src/main/webapp/WEB-INF/web.xml

@@ -28,6 +28,14 @@
         <welcome-file>index.html</welcome-file>
     </welcome-file-list>
 
+    <!-- Ensure that our own ServletContainerInitializer is used to initialize
+    logging, and that Logback does not potentially initialize SLF4J first (which
+    would prevent our custom logging from taking effect) -->
+    <context-param>
+        <param-name>logbackDisableServletContainerInitializer</param-name>
+        <param-value>true</param-value>
+    </context-param>
+
     <!-- Request that the browser always revalidate its cached copy of index.html -->
     <filter>
         <filter-name>cacheRevalidationFilter</filter-name>