    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     * Provides access to per-thread (and, by extension, per-request) data, managed by the {@link PerthreadManager}.
    019     * A PerThreadValue stores a particular type of information.
    020     *
    021     * @see org.apache.tapestry5.ioc.services.PerthreadManager#createValue()
    022     * @since 5.2.0
    023     */
    024    public interface PerThreadValue<T>
    025    {
    026        /**
    027         * Is a value stored (even null)?
    028         */
    029        boolean exists();
    030
    031        /**
    032         * Reads the current per-thread value, or returns null if no value has been stored.
    033         */
    034        T get();
    035
    036        /**
    037         * Gets the current per-thread value if it exists (even if null), or the defaultValue
    038         * if no value has been stored.
    039         */
    040        T get(T defaultValue);
    041
    042        /**
    043         * Sets the current per-thread value, then returns that value.
    044         */
    045        T set(T newValue);
    046    }