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Thread scope that supports asynchronous threads and bean destruction callbacks
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/*
 * Copyright 2015 devbury LLC
 *
 * 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 devbury.threadscope;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.config.Scope;
import org.springframework.core.NamedThreadLocal;

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;

/**
 * Scope that binds thread scoped beans to a thread local.  This class functions in a similar way to
 * {@link org.springframework.context.support.SimpleThreadScope}.  The difference being ThreadScopeManager
 * supports destruction callbacks such as {@link javax.annotation.PreDestroy}.  If used in conjunction with {@link
 * devbury.threadscope.ThreadScopePropagatingScheduler} as an executor, tasks will be able to access the thread
 * scoped beans of the thread scheduling the task.
 */
public class ThreadScopeManager implements Scope, ServletRequestListener {

    private static final Logger logger = LoggerFactory.getLogger(ThreadScopeManager.class);

    private final ThreadLocal threadLocal =
            new NamedThreadLocal("threadScopeState") {
                @Override
                protected ThreadScopeState initialValue() {
                    return new ThreadScopeState();
                }
            };

    @Override
    public Object get(String name, ObjectFactory objectFactory) {
        ThreadScopeState state = getThreadScopeState();
        Object object = state.getBean(name);
        if (object == null) {
            state.addBean(name, objectFactory);
            object = state.getBean(name);
        }
        return object;
    }

    @Override
    public Object remove(String name) {
        return getThreadScopeState().removeBean(name);
    }

    @Override
    public void registerDestructionCallback(String name, Runnable callback) {
        getThreadScopeState().addDestructionCallback(name, callback);
    }

    @Override
    public Object resolveContextualObject(String key) {
        return null;
    }

    @Override
    public String getConversationId() {
        return Thread.currentThread().getName();
    }

    public ThreadScopeState getThreadScopeState() {
        return threadLocal.get();
    }

    public void bind(ThreadScopeState threadScopeState) {
        logger.debug("Binding {} beans to thread", threadScopeState.size());
        threadLocal.set(threadScopeState);
    }

    public void unbind() {
        logger.debug("Unbinding {} beans from thread", getThreadScopeState().size());
        threadLocal.set(new ThreadScopeState());
    }

    @Override
    public void requestDestroyed(ServletRequestEvent servletRequestEvent) {
        unbind();
    }

    @Override
    public void requestInitialized(ServletRequestEvent servletRequestEvent) {
        // not used
    }
}