/*
 * Copyright (c) 2006, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.tools.jconsole;

import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JPanel;
import javax.swing.SwingWorker;

A JConsole plugin class. JConsole uses the service provider mechanism to search the JConsole plugins. Users can provide their JConsole plugins in a jar file containing a file named 
META-INF/services/com.sun.tools.jconsole.JConsolePlugin
 This file contains one line for each plugin, for example,
com.sun.example.JTop
 which is the fully qualified class name of the class implementing JConsolePlugin. 
 To load the JConsole plugins in JConsole, run:
jconsole -pluginpath <plugin-path> 
 where <plugin-path> specifies the paths of JConsole plugins to look up which can be a directory or a jar file. Multiple paths are separated by the path separator character of the platform. 
 When a new JConsole window is created for a connection, an instance of each JConsolePlugin will be created. The JConsoleContext object is not available at its construction time. JConsole will set the JConsoleContext object for a plugin after the plugin object is created. It will then call its getTabs method and add the returned tabs to the JConsole window. 
See Also:
ServiceLoader
Since:
1.6/**
 * A JConsole plugin class.  JConsole uses the
 * {@link java.util.ServiceLoader service provider}
 * mechanism to search the JConsole plugins.
 * Users can provide their JConsole plugins in a jar file
 * containing a file named
 *
 * <blockquote><pre>
 * META-INF/services/com.sun.tools.jconsole.JConsolePlugin</pre></blockquote>
 *
 * <p> This file contains one line for each plugin, for example,
 *
 * <blockquote><pre>
 * com.sun.example.JTop</pre></blockquote>
 * <p> which is the fully qualified class name of the class implementing
 * {@code JConsolePlugin}.
 *
 * <p> To load the JConsole plugins in JConsole, run:
 *
 * <blockquote><pre>
 * jconsole -pluginpath &lt;plugin-path&gt; </pre></blockquote>
 *
 * <p> where {@code <plugin-path>} specifies the paths of JConsole
 * plugins to look up which can be a directory or a jar file. Multiple
 * paths are separated by the path separator character of the platform.
 *
 * <p> When a new JConsole window is created for a connection,
 * an instance of each {@code JConsolePlugin} will be created.
 * The {@code JConsoleContext} object is not available at its
 * construction time.
 * JConsole will set the {@link JConsoleContext} object for
 * a plugin after the plugin object is created.  It will then
 * call its {@link #getTabs getTabs} method and add the returned
 * tabs to the JConsole window.
 *
 * @see java.util.ServiceLoader
 *
 * @since 1.6
 */
public abstract class JConsolePlugin {
    private volatile JConsoleContext context = null;
    private List<PropertyChangeListener> listeners = null;

    
Constructor.
/**
     * Constructor.
     */
    protected JConsolePlugin() {
    }

    
Sets the JConsoleContext object representing the connection to an application. This method will be called only once after the plugin is created and before the getTabs is called. The given context can be in any connection state when this method is called. 
Params:
context – a JConsoleContext object/**
     * Sets the {@link JConsoleContext JConsoleContext} object representing
     * the connection to an application.  This method will be called
     * only once after the plugin is created and before the {@link #getTabs}
     * is called. The given {@code context} can be in any
     * {@link JConsoleContext#getConnectionState connection state} when
     * this method is called.
     *
     * @param context a {@code JConsoleContext} object
     */
    public final synchronized void setContext(JConsoleContext context) {
        this.context = context;
        if (listeners != null) {
            for (PropertyChangeListener l : listeners) {
                context.addPropertyChangeListener(l);
            }
            // throw away the listener list
            listeners = null;
        }
    }

    
Returns the JConsoleContext object representing the connection to an application. This method may return null if it is called before the context is initialized. 
Returns:
the JConsoleContext object representing the connection to an application./**
     * Returns the {@link JConsoleContext JConsoleContext} object representing
     * the connection to an application.  This method may return {@code null}
     * if it is called before the {@link #setContext context} is initialized.
     *
     * @return the {@link JConsoleContext JConsoleContext} object representing
     *         the connection to an application.
     */
    public final JConsoleContext getContext() {
        return context;
    }

    
Returns the tabs to be added in JConsole window.
 The returned map contains one entry for each tab to be added in the tabbed pane in a JConsole window with the tab name as the key and the JPanel object as the value. This method returns an empty map if no tab is added by this plugin. This method will be called from the Event Dispatch Thread
once at the new connection time.
Returns:
a map of a tab name and a JPanel object representing the tabs to be added in the JConsole window; or an empty map./**
     * Returns the tabs to be added in JConsole window.
     * <p>
     * The returned map contains one entry for each tab
     * to be added in the tabbed pane in a JConsole window with
     * the tab name as the key
     * and the {@link JPanel} object as the value.
     * This method returns an empty map if no tab is added by this plugin.
     * This method will be called from the <i>Event Dispatch Thread</i>
     * once at the new connection time.
     *
     * @return a map of a tab name and a {@link JPanel} object
     *         representing the tabs to be added in the JConsole window;
     *         or an empty map.
     */
    public abstract java.util.Map<String, JPanel> getTabs();

    
Returns a SwingWorker to perform the GUI update for this plugin at the same interval as JConsole updates the GUI. 
 JConsole schedules the GUI update at an interval specified for a connection. This method will be called at every update to obtain a SwingWorker for each plugin. 
 JConsole will invoke the execute() method to schedule the returned SwingWorker for execution if: 

  
 the SwingWorker object has not been executed (i.e. the SwingWorker.getState method returns PENDING state); and
  
 the SwingWorker object returned in the previous update has completed the task if it was not null (i.e. the SwingWorker.isDone method returns true).


 Otherwise, SwingWorker object will not be scheduled to work. 
 A plugin can schedule its own GUI update and this method will return null. 
Returns:
a SwingWorker to perform the GUI update; or null./**
     * Returns a {@link SwingWorker} to perform
     * the GUI update for this plugin at the same interval
     * as JConsole updates the GUI.
     * <p>
     * JConsole schedules the GUI update at an interval specified
     * for a connection.  This method will be called at every
     * update to obtain a {@code SwingWorker} for each plugin.
     * <p>
     * JConsole will invoke the {@link SwingWorker#execute execute()}
     * method to schedule the returned {@code SwingWorker} for execution
     * if:
     * <ul>
     *   <li> the {@code SwingWorker} object has not been executed
     *        (i.e. the {@link SwingWorker#getState} method
     *        returns {@link javax.swing.SwingWorker.StateValue#PENDING PENDING}
     *        state); and</li>
     *   <li> the {@code SwingWorker} object returned in the previous
     *        update has completed the task if it was not {@code null}
     *        (i.e. the {@link SwingWorker#isDone SwingWorker.isDone} method
     *        returns {@code true}).</li>
     * </ul>
     * <br>
     * Otherwise, {@code SwingWorker} object will not be scheduled to work.
     *
     * <p>
     * A plugin can schedule its own GUI update and this method
     * will return {@code null}.
     *
     * @return a {@code SwingWorker} to perform the GUI update; or
     *         {@code null}.
     */
    public abstract SwingWorker<?,?> newSwingWorker();

    
Dispose this plugin. This method is called by JConsole to inform that this plugin will be discarded and that it should free any resources that it has allocated. The JConsoleContext can be in any connection state when this method is called. /**
     * Dispose this plugin. This method is called by JConsole to inform
     * that this plugin will be discarded and that it should free
     * any resources that it has allocated.
     * The {@link #getContext JConsoleContext} can be in any
     * {@link JConsoleContext#getConnectionState connection state} when
     * this method is called.
     */
    public void dispose() {
        // Default nop implementation
    }

    
Adds a PropertyChangeListener to the JConsoleContext object for this plugin. This method is a convenient method for this plugin to register a listener when the JConsoleContext object may or may not be available. 
For example, a plugin constructor can call this method to register a listener to listen to the connectionState property changes and the listener will be added to the JConsoleContext object when it is available. 
Params:
listener –  The PropertyChangeListener to be added
Throws:
NullPointerException – if listener is null./**
     * Adds a {@link PropertyChangeListener PropertyChangeListener}
     * to the {@link #getContext JConsoleContext} object for this plugin.
     * This method is a convenient method for this plugin to register
     * a listener when the {@code JConsoleContext} object may or
     * may not be available.
     *
     * <p>For example, a plugin constructor can
     * call this method to register a listener to listen to the
     * {@link JConsoleContext.ConnectionState connectionState}
     * property changes and the listener will be added to the
     * {@link JConsoleContext#addPropertyChangeListener JConsoleContext}
     * object when it is available.
     *
     * @param listener  The {@code PropertyChangeListener} to be added
     *
     * @throws NullPointerException if {@code listener} is {@code null}.
     */
    public final void addContextPropertyChangeListener(PropertyChangeListener listener) {
        if (listener == null) {
            throw new NullPointerException("listener is null");
        }

        if (context == null) {
            // defer registration of the listener until setContext() is called
            synchronized (this) {
                // check again if context is not set
                if (context == null) {
                    // maintain a listener list to be added later
                    if (listeners == null) {
                        listeners = new ArrayList<PropertyChangeListener>();
                    }
                    listeners.add(listener);
                    return;
                }
            }
        }
        context.addPropertyChangeListener(listener);
    }

    
Removes a PropertyChangeListener from the listener list of the JConsoleContext object for this plugin. If listener was never added, no exception is thrown and no action is taken. 
Params:
listener – the PropertyChangeListener to be removed
Throws:
NullPointerException – if listener is null./**
     * Removes a {@link PropertyChangeListener PropertyChangeListener}
     * from the listener list of the {@link #getContext JConsoleContext}
     * object for this plugin.
     * If {@code listener} was never added, no exception is
     * thrown and no action is taken.
     *
     * @param listener the {@code PropertyChangeListener} to be removed
     *
     * @throws NullPointerException if {@code listener} is {@code null}.
     */
    public final void removeContextPropertyChangeListener(PropertyChangeListener listener) {
        if (listener == null) {
            throw new NullPointerException("listener is null");
        }

        if (context == null) {
            // defer registration of the listener until setContext() is called
            synchronized (this) {
                // check again if context is not set
                if (context == null) {
                    if (listeners != null) {
                        listeners.remove(listener);
                    }
                    return;
                }
            }
        }
        context.removePropertyChangeListener(listener);
    }
}