001    // Copyright 2006, 2007, 2009 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    //     http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.ioc.def;
016    
017    import org.apache.tapestry5.ioc.ModuleBuilderSource;
018    import org.apache.tapestry5.ioc.ServiceDecorator;
019    import org.apache.tapestry5.ioc.ServiceResources;
020    
021    /**
022     * Definition of a service decorator, which (by default) is derived from a service decorator method.
023     * <p/>
024     * A note on decorator scheduling. The scheduling is based on the desired order of <em>behavior</em>. Thus, if logging
025     * should occur before security checks, and security checks should occur before transaction management, then the desired
026     * decorator order is Logging, Security, Transactions. This might be specified as having Security occur after Logging,
027     * and Transactions occur after Security. It might also be specified by having Logging ordered "before:*", and
028     * Transactions ordered "after:*" with no specified scheduling for Security.
029     * <p/>
030     * Once this order is established, decorators are <em>applied</em> in reverse order. Each decorator's job is to create
031     * an <em>interceptor</em> for the service, that delegates to the next implementation. This implies that the decorators
032     * are executed last to first. In the above example, the core service implementation would be passed to the Transaction
033     * decorator, resulting in the Transaction interceptor. The Transaction interceptor would be passed to the Security
034     * decorator, resulting in the Security interceptor. The Security interceptor would be passed to the Logging decorator,
035     * resulting in the Logging interceptor. Thus at runtime, the Logging interceptor will execute first, then delegate to
036     * the Security interceptor, which would delegate to the Transaction interceptor, which would finally delegate to the
037     * core service implementation.
038     * <p/>
039     * Service decorators are part of the initial version of Tapestry IoC.  Starting in release 5.1, their use has been
040     * deprecated, in favor of {@link org.apache.tapestry5.ioc.AdvisorDef}, which is based on {@link
041     * org.apache.tapestry5.ioc.services.AspectInterceptorBuilder}.
042     * <p/>
043     * Note: service decorators are applied <em>around</em> the interceptor generated via any {@link
044     * org.apache.tapestry5.ioc.AdvisorDef}s (for compatibility with Tapestry 5.0). In general, you should use service
045     * decoration or service advice, not both.
046     */
047    public interface DecoratorDef
048    {
049        /**
050         * Returns the id of the decorator, which is derived from the decorator method name.
051         */
052        String getDecoratorId();
053    
054        /**
055         * Returns zero or more ordering constraint strings, used to order the decorated relative to the other decorators.
056         */
057    
058        String[] getConstraints();
059    
060        /**
061         * Creates an object that can perform the decoration (in the default case, by invoking the decorator method on the
062         * module class or instance.
063         *
064         * @param moduleSource access to the the module  instance associated with the module containing the decorator (not
065         *                     necessarily the module containing the service being decorated)
066         * @param resources    the resources visible <em>to the decorator</em> (which may be in a different module than the
067         *                     service being decorated). Other resource properties (serviceId, serviceInterface, log, etc.)
068         *                     are for the service being decorated.
069         */
070        ServiceDecorator createDecorator(ModuleBuilderSource moduleSource,
071                                         ServiceResources resources);
072    
073        /**
074         * Used to determine which services may be decorated by this decorator. When decorating a service, first the
075         * decorators that target the service are identified, then ordering occurs, then the {@link ServiceDecorator}s are
076         * invoked.
077         *
078         * @param serviceDef
079         * @return true if the decorator applies to the service
080         */
081        boolean matches(ServiceDef serviceDef);
082    }