Add plugins/extension infrastructure

Plugins are stored in `${baseFolder}/plugins` and are loaded
during startup by the PluginManager.

A plugin defines it's metadata in META-INF/MANIFEST.MF:

    Plugin-Class: com.gitblit.plugins.cookbook.CookbookPlugin
    Plugin-Dependencies: foo, bar
    Plugin-Id: gitblit-plugin
    Plugin-Provider: John Doe
    Plugin-Version: 1.0

Plugins can define extension points that can be implemented
by other plugins and they can depend on other plugins:

    Plugin-Dependencies: foo, bar

During the load phase, a directed acyclic graph is built and the loading
order of the dependency chain is reversed using a topological sort;
parent followed by children. The parent plugin classloader is the
combined classloader of all parent plugins.

Change-Id: I738821fa2bff02a5dbe339a944cc7e3c4dd8e299

1 files changed, 56 insertions, 0 deletions

diff --git a/src/main/java/com/gitblit/manager/PluginManager.java b/src/main/java/com/gitblit/manager/PluginManager.java
new file mode 100644
index 00000000..5eb00e92
--- /dev/null
+++ b/src/main/java/com/gitblit/manager/PluginManager.java
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2014 gitblit.com.
+ *
+ * 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 com.gitblit.manager;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import ro.fortsoft.pf4j.DefaultPluginManager;
+
+import com.gitblit.Keys;
+
+/**
+ * The plugin manager maintains the lifecycle of plugins. It is exposed as
+ * Dagger bean. The extension consumers supposed to retrieve plugin  manager
+ * from the Dagger DI and retrieve extensions provided by active plugins.
+ * 
+ * @author David Ostrovsky
+ * 
+ */
+public class PluginManager extends DefaultPluginManager implements
+		IPluginManager {
+
+	private final Logger logger = LoggerFactory.getLogger(getClass());
+
+	public PluginManager(IRuntimeManager runtimeManager) {
+		super(runtimeManager.getFileOrFolder(Keys.plugins.folder,
+				"${baseFolder}/plugins"));
+	}
+
+	@Override
+	public PluginManager start() {
+		logger.info("Plugin manager started");
+		loadPlugins();
+		startPlugins();
+		return this;
+	}
+
+	@Override
+	public PluginManager stop() {
+		stopPlugins();
+		return null;
+	}
+}