/*
* 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.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: 480477 $ $Date: 2006-11-29 08:34:52 +0000 (Wed, 29 Nov 2006) $
*/
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
/**
* See the {@link Chain} JavaDoc.
*
* @param command The {@link Command} to be added
*
* @exception IllegalArgumentException if <code>command</code>
* is <code>null</code>
* @exception IllegalStateException if no further configuration is allowed
*/
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;
}
/**
* See the {@link Chain} JavaDoc.
*
* @param context The {@link Context} to be processed by this
* {@link Chain}
*
* @throws Exception if thrown by one of the {@link Command}s
* in this {@link Chain} but not handled by a <code>postprocess()</code>
* method of a {@link Filter}
* @throws IllegalArgumentException if <code>context</code>
* is <code>null</code>
*
* @return <code>true</code> if the processing of this {@link Context}
* has been completed, or <code>false</code> if the processing
* of this {@link Context} should be delegated to a subsequent
* {@link Command} in an enclosing {@link Chain}
*/
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);
}
}