org.ripla.web.util.ControllerStack.java Source code

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Here is the source code for org.ripla.web.util.ControllerStack.java

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/*******************************************************************************
 * Copyright (c) 2012-2014 RelationWare, Benno Luthiger
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 * RelationWare, Benno Luthiger
 ******************************************************************************/
package org.ripla.web.util;

import java.util.Stack;

import org.ripla.web.interfaces.IPluggable;

import com.vaadin.server.VaadinSession;

/**
 * A stack of <code>IPluggable</code> instances.
 * 
 * @author Luthiger
 */
public class ControllerStack {
    private static final int DFT_SIZE = 5;

    private final Stack<IPluggable> taskStack;
    private final int stackSize;

    /**
     * Constructor with specified stack size.
     * 
     * @param inStackSize
     *            int the stack size
     */
    public ControllerStack(final int inStackSize) {
        taskStack = new Stack<IPluggable>();
        stackSize = inStackSize;
    }

    /**
     * Constructor with default stack size.
     */
    public ControllerStack() {
        this(DFT_SIZE);
    }

    /**
     * Tests if this stack is empty.
     * 
     * @return boolean <code>true</code> it the stack is empty,
     *         <code>false</code> otherwise
     */
    public boolean empty() {
        return taskStack.empty();
    }

    /**
     * Looks at the controller at the top of this stack without removing it from
     * the stack.
     * 
     * @return {@link IPluggable}
     */
    public IPluggable peek() {
        return taskStack.peek();
    }

    /**
     * Removes the controller at the top of this stack and returns that object
     * as the value of this function. If the stack is empty, an
     * EmptyStackException is thrown.
     * 
     * @return {@link IPluggable}
     */
    public IPluggable pop() {
        return taskStack.pop();
    }

    /**
     * Pushes a controller onto the top of this stack. If the stack exceeds the
     * specified size, the element at the stack bottom is thrown away. The
     * controller is pushed to the stack only if it's not equal to the
     * controller at the stack's top.
     * 
     * @param inController
     *            {@link IPluggable}
     * @return {@link IPluggable}
     */
    public IPluggable push(final IPluggable inController) {
        if (!empty()) {
            if (inController.equals(taskStack.peek()))
                return inController;
        }

        final IPluggable out = taskStack.push(inController);
        if (taskStack.size() > stackSize) {
            taskStack.removeElementAt(0);
        }
        return out;
    }

    /**
     * Removes all of the elements from this stack.
     */
    public void clear() {
        taskStack.clear();
    }

    /**
     * Convenience method to return the user's controller stack.
     * 
     * @return {@link ControllerStack} the user's unique controller stack
     */
    public static ControllerStack getControllerStack() {
        try {
            VaadinSession.getCurrent().getLockInstance().lock();
            ControllerStack out = VaadinSession.getCurrent().getAttribute(ControllerStack.class);
            if (out == null) {
                out = new ControllerStack();
                VaadinSession.getCurrent().setAttribute(ControllerStack.class, out);
            }
            return out;
        } finally {
            VaadinSession.getCurrent().getLockInstance().unlock();
        }
    }

}