added log4j2 configuration support

maven-embedder/src/main/java/org/apache/maven/cli/logging/impl/Log4j2Configuration.java

@@ -0,0 +1,60 @@
+package org.apache.maven.cli.logging.impl;
+
+/*
+ * 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.
+ */
+
+import java.io.File;
+
+import org.apache.maven.cli.logging.BaseSlf4jConfiguration;
+
+/**
+ * Configuration for slf4j-log4j2.
+ * 
+ * @author Hervé Boutemy
+ */
+public class Log4j2Configuration
+    extends BaseSlf4jConfiguration
+{
+    @Override
+    public void setRootLoggerLevel( Level level )
+    {
+        String value = "info";
+        switch ( level )
+        {
+            case DEBUG:
+                value = "debug";
+                break;
+            
+            case INFO:
+                value = "info";
+                break;
+
+            case ERROR:
+                value = "error";
+                break;
+        }
+        System.setProperty( "maven.logging.root.level", value );
+    }
+
+    @Override
+    public void setLoggerFile( File output )
+    {
+        // no op
+    }
+}

maven-embedder/src/main/resources/META-INF/maven/slf4j-configuration.properties

@@ -1,3 +1,4 @@
 # key = Slf4j effective logger factory implementation
 # value = corresponding o.a.m.cli.logging.Slf4jConfiguration class
 org.slf4j.impl.SimpleLoggerFactory org.apache.maven.cli.logging.impl.Slf4jSimpleConfiguration
+org.slf4j.helpers.Log4JLoggerFactory org.apache.maven.cli.logging.impl.Log4j2Configuration