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Central module for Tapestry, containing interfaces to the Java
Servlet API and all core services and components.
// Copyright 2006, 2008 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.services;
import java.util.NoSuchElementException;
/**
* Provides access to environment objects, which are almost always provided to enclosed components by enclosing
* components. Environmental services are a form of very late binding.
*
* The Environment acts like a collection of stacks. Each stack contains environmental objects of a given type. Most
* often, a stack has zero or one elements, but on occasion, a particular component will push an override onto the stack
* for the benefit of the components it encloses.
*
* @see org.apache.tapestry5.annotations.Environmental
* @see org.apache.tapestry5.services.EnvironmentalShadowBuilder
*/
public interface Environment
{
/**
* Peeks at the current top of the indicated stack.
*
* @param the type of environmental object
* @param type class used to select the object
* @return the current object of that type, or null if no service of that type has been added
*/
T peek(Class type);
/**
* Peeks at the current top of the indicated stack (which must have a non-null value).
*
* @param the type of environmental object
* @param type class used to select the object
* @return the current object of the specified type
* @throws RuntimeException if no service of that type has been added
*/
T peekRequired(Class type);
/**
* Removes and returns the top environmental object of the selected type.
*
* @param the type of environmental object
* @param type class used to select the object
* @return the object just removed
* @throws NoSuchElementException if the environmental stack (for the specified type) is empty
*/
T pop(Class type);
/**
* Pushes a new service onto the stack. The old service at the top of the stack is returned (it may be null).
*
* @param the type of environmental object
* @param type class used to select the object
* @param instance the service object
* @return the previous top service
*/
T push(Class type, T instance);
/**
* Clears all stacks; used when initializing the Environment before a render.
*/
void clear();
/**
* For some type, returns a temporary access object for the type. The access object is efficient because it ties
* directly to the thread's instance of the Environment service, it also caches the current value. The access
* object must be discarded at the end of the request (it will be unusable at that point anyway).
*
* @param type type of environmental object
* @param
* @return access object that can be used to see the current environmental object of the type
* @since 5.0.19
* @deprecated No longer gives a performance advantage due to pool-less pages
*/
EnvironmentalAccess getAccess(Class type);
}