    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
    015package 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 */
    024public 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}