it.bz.opendatahub.alpinebits.middleware.Context Maven / Gradle / Ivy
/*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
package it.bz.opendatahub.alpinebits.middleware;
import java.util.Optional;
/**
* Each {@link Middleware#handleContext(Context, MiddlewareChain)} method is
* provided with a {@link Context} object that is shared by the middlewares.
*
* The context provides methods to store and retrieve data and can
* thus be used for data exchange between the middlewares.
*
* The context implements the {@link ExceptionHandler} interface.
* Context implementations should handle context exceptions that occur while
* the middlewares are executed. This way, the exception handling
* is part of the context and can be specialized if needed.
*/
public interface Context extends ExceptionHandler {
/**
* Returns the value wrapped inside an {@link Optional} to which the specified
* {@link Key} is mapped, or an empty Optional if this {@link Context}
* contains no mapping for the key.
*
* @param key the key whose associated value is to be returned
* @return {@link Optional} containing the value for the given {@link Key},
* or an empty Optional if no value was found
*/
Optional get(Key key);
/**
* Returns the value to which the specified {@link Key} is mapped, or
* throws a {@link RequiredContextKeyMissingException} if this {@link Context}
* contains no mapping for the key.
*
* @param key the key whose associated value is to be returned
* @return the value for the given {@link Key}
* @throws RequiredContextKeyMissingException if no value was found for the
* given {@link Key}
*/
T getOrThrow(Key key);
/**
* Associates the specified value with the specified {@link Key}
* in this {@link Context}. If the context previously contained a mapping
* for the key, the old value is replaced by the specified value.
*
* @param key {@link Key} with which the specified value
* is to be associated
* @return the previous value associated with {@link Key}, or
* null if there was no mapping for key
*/
T put(Key key, T value);
/**
* Removes the mapping for a {@link Key} from this {@link Context}
* if it is present.
*
* Returns the value to which this context previously associated the key,
* or null if the context contained no mapping for the key.
*
*
The context will not contain a mapping for the specified key once the
* call returns.
*
* @param key {@link Key} whose mapping is to be removed
* from the {@link Context}
* @return the previous value associated with {@link Key}, or
* null if there was no mapping for key
*/
T remove(Key key);
/**
* Returns true if this {@link Context} contains a mapping
* for the specified key and false otherwise.
*
* @param key {@link Key} whose presence in this
* {@link Context} is to be tested
* @return true if this map contains a mapping for the
* specified key
*/
boolean contains(Key key);
}