hlship-20080520/tapestry-core/src/main/java/org/apache/tapestry/internal/services/EnvironmentImpl.java

// Copyright 2006, 2007 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.tapestry.internal.services;

import static org.apache.tapestry.ioc.IOCConstants.PERTHREAD_SCOPE;
import org.apache.tapestry.ioc.annotation.Scope;
import org.apache.tapestry.ioc.internal.util.CollectionFactory;
import static org.apache.tapestry.ioc.internal.util.CollectionFactory.newLinkedList;
import org.apache.tapestry.services.Environment;

import java.util.LinkedList;
import java.util.List;
import java.util.Map;

/**
 * A non-threadsafe implementation (expects to use the "perthread" service lifecyle).
 */
@Scope(PERTHREAD_SCOPE)
public class EnvironmentImpl implements Environment
{
    // My generics mojo breaks down when we talk about the key and the value being related
    // types.

    private final Map<Class, LinkedList> stacks = CollectionFactory.newMap();

    @SuppressWarnings("unchecked")
    private <T> LinkedList<T> stackFor(Class<T> type)
    {
        LinkedList<T> result = stacks.get(type);

        if (result == null)
        {
            result = newLinkedList();
            stacks.put(type, result);
        }

        return result;
    }

    public <T> T peek(Class<T> type)
    {
        LinkedList<T> stack = stackFor(type);

        return stack.isEmpty() ? null : stack.getFirst();
    }

    public <T> T peekRequired(Class<T> type)
    {
        T result = peek(type);

        if (result == null)
        {
            List<Class> types = CollectionFactory.newList();
            for (Map.Entry<Class, LinkedList> e : stacks.entrySet())
            {
                LinkedList list = e.getValue();

                if (list != null && !list.isEmpty()) types.add(e.getKey());
            }

            throw new RuntimeException(ServicesMessages.missingFromEnvironment(type, types));
        }

        return result;
    }

    public <T> T pop(Class<T> type)
    {
        LinkedList<T> stack = stackFor(type);

        return stack.removeFirst();
    }

    public <T> T push(Class<T> type, T instance)
    {
        LinkedList<T> stack = stackFor(type);

        T result = stack.isEmpty() ? null : stack.getFirst();

        stack.addFirst(instance);

        return result;
    }

    public void clear()
    {
        stacks.clear();
    }
}