tapestry-ioc/src/main/java/org/apache/tapestry5/ioc/internal/RecursiveServiceCreationCheckWrapper.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.tapestry5.ioc.internal;

import org.apache.tapestry5.ioc.ObjectCreator;
import org.apache.tapestry5.ioc.def.ServiceDef;
import org.slf4j.Logger;

/**
 * Decorator for {@link org.apache.tapestry5.ioc.ObjectCreator} that ensures the service is only created once. This
 * detects a situation where the service builder for a service directly or indirectly invokes methods on the service
 * itself. This would show up as a second call up the ServiceCreator stack injected into the proxy, potentially leading
 * to endless recursion. We try to identify that recursion and produce a useable exception report.
 */
public class RecursiveServiceCreationCheckWrapper implements ObjectCreator
{
    private final ServiceDef serviceDef;

    private final ObjectCreator delegate;

    private final Logger logger;

    private boolean locked;

    public RecursiveServiceCreationCheckWrapper(ServiceDef serviceDef, ObjectCreator delegate,
                                                Logger logger)
    {
        this.serviceDef = serviceDef;
        this.delegate = delegate;
        this.logger = logger;
    }

    /**
     * We could make this method synchronized, but in the context of creating a service for a proxy, it will already be
     * synchronized (inside the proxy).
     */
    public Object createObject()
    {
        if (locked)
            throw new IllegalStateException(IOCMessages.recursiveServiceBuild(serviceDef));

        // Set the lock, to ensure that recursive service construction fails.

        locked = true;

        try
        {
            return delegate.createObject();
        }
        catch (RuntimeException ex)
        {
            logger.error(IOCMessages.serviceConstructionFailed(serviceDef, ex), ex);

            // Release the lock on failure; the service is now in an unknown state, but we may
            // be able to continue from here.

            locked = false;

            throw ex;
        }

    }
}