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, 39 insertions, 0 deletions

diff --git a/src/main/java/com/gitblit/manager/IPluginManager.java b/src/main/java/com/gitblit/manager/IPluginManager.java
new file mode 100644
index 00000000..670e9769
--- /dev/null
+++ b/src/main/java/com/gitblit/manager/IPluginManager.java
@@ -0,0 +1,39 @@
+/*
+ * 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 java.util.List;
+
+import ro.fortsoft.pf4j.PluginWrapper;
+
+public interface IPluginManager extends IManager {
+
+	/**
+	 * Retrieves the extension for given class 'clazz'.
+	 *
+	 * @param clazz extension point class to retrieve extension for
+	 * @return list of extensions
+	 */
+	public <T> List<T> getExtensions(Class<T> clazz);
+
+	/**
+     * Retrieves the {@link PluginWrapper} that loaded the given class 'clazz'.
+     *
+     * @param clazz extension point class to retrieve extension for
+     * @return PluginWrapper that loaded the given class
+     */
+    public PluginWrapper whichPlugin(Class<?> clazz);
+}