001    // Copyright 2010 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.services;
016    
017    /**
018     * A wrapper around {@link PerthreadManager#get(Object)} and {@link PerthreadManager#put(Object, Object)}.
019     * 
020     * @since 5.2.0
021     */
022    public interface PerThreadValue<T>
023    {
024        /** Is a value stored (even null)? */
025        boolean exists();
026    
027        /** Reads the current per-thread value, or returns null if no value has been stored. */
028        T get();
029    
030        /**
031         * Gets the current per-thread value if it exists (even if null), or the defaultValue
032         * if no value has been stored.
033         */
034        T get(T defaultValue);
035    
036        /** Sets the current per-thread value, then returns that value. */
037        T set(T newValue);
038    }