PicoContainer example source code file (AbstractPicoVisitor.java)

This example PicoContainer source code file (AbstractPicoVisitor.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - PicoContainer tags/keywords

error, invocationtargetexception, method, nosuchmethodexception, nosuchmethodexception, object, object, picovisitor, picovisitor, picovisitortraversalexception, picovisitortraversalexception, reflection, runtimeexception, security, throwable, traversal

The PicoContainer AbstractPicoVisitor.java source code

/*****************************************************************************
 * Copyright (C) PicoContainer Organization. All rights reserved.            *
 * ------------------------------------------------------------------------- *
 * The software in this package is published under the terms of the BSD      *
 * style license a copy of which has been included with this distribution in *
 * the LICENSE.txt file.                                                     *
 *****************************************************************************/
package org.picocontainer.visitors;

import org.picocontainer.PicoVisitor;
import org.picocontainer.PicoException;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * Abstract PicoVisitor implementation. A generic traverse method is implemented, that 
 * accepts any object with a method named "accept", that takes a 
 * {@link PicoVisitor}  as argument and and invokes it. Additionally it provides the 
 * {@link #checkTraversal()} method, that throws a {@link PicoVisitorTraversalException},
 * if currently no traversal is running.
 * 
 * @author Jörg Schaible
 */
public abstract class AbstractPicoVisitor implements PicoVisitor {
    private boolean traversal;

    public Object traverse(final Object node) {
        traversal = true;
        Object retval =
                AccessController.doPrivileged(new PrivilegedAction() {
                    public Object run() {
                        try {
                            return node.getClass().getMethod("accept", PicoVisitor.class);
                        } catch (NoSuchMethodException e) {
                            return e;
                        }
                    }
                });
        try {
            if (retval instanceof NoSuchMethodException) {
                throw (NoSuchMethodException) retval;
            }
            Method accept = (Method) retval;
            accept.invoke(node, this);
            return Void.TYPE;
        } catch (NoSuchMethodException e) {
        } catch (IllegalAccessException e) {
        } catch (InvocationTargetException e) {
            Throwable cause = e.getTargetException();
            if (cause instanceof RuntimeException) {
                throw (RuntimeException)cause;
            } else if (cause instanceof Error) {
                throw (Error)cause;
            }
        } finally {
            traversal = false;
        }
        throw new IllegalArgumentException(node.getClass().getName() + " is not a valid type for traversal");
    }

    /**
     * Checks the traversal flag, indicating a currently running traversal of the visitor.
     * @throws PicoVisitorTraversalException if no traversal is active.
     */
    protected void checkTraversal() {
        if (!traversal) {
            throw new PicoVisitorTraversalException(this);
        }
    }

    /**
     * Exception for a PicoVisitor, that is dependent on a defined starting point of the traversal.
     * If the traversal is not initiated with a call of {@link PicoVisitor#traverse}
     *
     * @author joehni
     */
    public static class PicoVisitorTraversalException
            extends PicoException {

        /**
         * Construct the PicoVisitorTraversalException.
         *
         * @param visitor The visitor casing the exception.
         */
        public PicoVisitorTraversalException(PicoVisitor visitor) {
            super("Traversal for PicoVisitor of type " + visitor.getClass().getName() + " must start with the visitor's traverse method");
        }
    }

}