/*
* 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.karaf.shell.api.action;
/**
* <p>An action is the default implementation of the commands in karaf.
* In OSGi, Actions are discovered using an extender and a new instance
* of the class is created when the command is invoked, so that the
* implementation does not need to be thread safe.</p>
*
* <p>Before the call to the execute method the action is checked for
* fields annotated with @Reference and injected with services coming
* from the SessionFactory's Registry or from the OSGi registry.
* Methods annotated with @Init are then called. The next step is to
* inject command line parameters into fields annotated with @Option
* and @Argument and then call the execute method.</p>
*
* <p>Any class implementing Action must have a no argument constructor. This
* is necessary so the help generator can instantiate the class and get the
* default values.</p>
*
* <p>In order to make commands available from the non-OSGi shell,
* the commands must be listed in a file available at
* META-INF/services/org/apache/karaf/shell/commmands.</p>
*
* @see org.apache.karaf.shell.api.action.Command
* @see org.apache.karaf.shell.api.action.lifecycle.Service
*/
public interface Action {
/**
* Execute the action which has been injected with services from the
* registry, options and arguments from the command line.
*
* @return <code>null</code> or the result of the action execution
* @throws Exception in case of execution failure.
*/
Object execute() throws Exception;
}