org.apache.commons.chain.impl.ChainBase.java Source code

Introduction

Here is the source code for org.apache.commons.chain.impl.ChainBase.java

Source

/*
 * Copyright 1999-2004 The Apache Software Foundation
 *
 * 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 org.apache.commons.chain.impl;

import java.util.Collection;
import java.util.Iterator;
import org.apache.commons.chain.Chain;
import org.apache.commons.chain.Command;
import org.apache.commons.chain.Context;
import org.apache.commons.chain.Filter;

/**
 * <p>Convenience base class for {@link Chain} implementations.</p>
 *
 * @author Craig R. McClanahan
 * @version $Revision: 1.6 $ $Date: 2004/11/30 05:52:23 $
 */

public class ChainBase implements Chain {

    // ----------------------------------------------------------- Constructors

    /**
     * <p>Construct a {@link Chain} with no configured {@link Command}s.</p>
     */
    public ChainBase() {

    }

    /**
     * <p>Construct a {@link Chain} configured with the specified
     * {@link Command}.</p>
     *
     * @param command The {@link Command} to be configured
     *
     * @exception IllegalArgumentException if <code>command</code>
     *  is <code>null</code>
     */
    public ChainBase(Command command) {

        addCommand(command);

    }

    /**
     * <p>Construct a {@link Chain} configured with the specified
     * {@link Command}s.</p>
     *
     * @param commands The {@link Command}s to be configured
     *
     * @exception IllegalArgumentException if <code>commands</code>,
     *  or one of the individual {@link Command} elements,
     *  is <code>null</code>
     */
    public ChainBase(Command[] commands) {

        if (commands == null) {
            throw new IllegalArgumentException();
        }
        for (int i = 0; i < commands.length; i++) {
            addCommand(commands[i]);
        }

    }

    /**
     * <p>Construct a {@link Chain} configured with the specified
     * {@link Command}s.</p>
     *
     * @param commands The {@link Command}s to be configured
     *
     * @exception IllegalArgumentException if <code>commands</code>,
     *  or one of the individual {@link Command} elements,
     *  is <code>null</code>
     */
    public ChainBase(Collection commands) {

        if (commands == null) {
            throw new IllegalArgumentException();
        }
        Iterator elements = commands.iterator();
        while (elements.hasNext()) {
            addCommand((Command) elements.next());
        }

    }

    // ----------------------------------------------------- Instance Variables

    /**
     * <p>The list of {@link Command}s configured for this {@link Chain}, in
     * the order in which they may delegate processing to the remainder of
     * the {@link Chain}.</p>
     */
    protected Command[] commands = new Command[0];

    /**
     * <p>Flag indicating whether the configuration of our commands list
     * has been frozen by a call to the <code>execute()</code> method.</p>
     */
    protected boolean frozen = false;

    // ---------------------------------------------------------- Chain Methods

    // Documented in Chain interface
    public void addCommand(Command command) {

        if (command == null) {
            throw new IllegalArgumentException();
        }
        if (frozen) {
            throw new IllegalStateException();
        }
        Command[] results = new Command[commands.length + 1];
        System.arraycopy(commands, 0, results, 0, commands.length);
        results[commands.length] = command;
        commands = results;

    }

    // Documented in Chain interface
    public boolean execute(Context context) throws Exception {

        // Verify our parameters
        if (context == null) {
            throw new IllegalArgumentException();
        }

        // Freeze the configuration of the command list
        frozen = true;

        // Execute the commands in this list until one returns true
        // or throws an exception
        boolean saveResult = false;
        Exception saveException = null;
        int i = 0;
        int n = commands.length;
        ;
        for (i = 0; i < n; i++) {
            try {
                saveResult = commands[i].execute(context);
                if (saveResult) {
                    break;
                }
            } catch (Exception e) {
                saveException = e;
                break;
            }
        }

        // Call postprocess methods on Filters in reverse order
        if (i >= n) { // Fell off the end of the chain
            i--;
        }
        boolean handled = false;
        boolean result = false;
        for (int j = i; j >= 0; j--) {
            if (commands[j] instanceof Filter) {
                try {
                    result = ((Filter) commands[j]).postprocess(context, saveException);
                    if (result) {
                        handled = true;
                    }
                } catch (Exception e) {
                    ; // Silently ignore
                }
            }
        }

        // Return the exception or result state from the last execute()
        if ((saveException != null) && !handled) {
            throw saveException;
        } else {
            return (saveResult);
        }

    }

    // -------------------------------------------------------- Package Methods

    /**
     * <p>Return an array of the configured {@link Command}s for this
     * {@link Chain}.  This method is package private, and is used only
     * for the unit tests.</p>
     */
    Command[] getCommands() {

        return (commands);

    }

}