org.eclipse.jetty.continuation.Continuation Maven / Gradle / Ivy
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// Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
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// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
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// The Apache License v2.0 is available at
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// You may elect to redistribute this code under either of these licenses.
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package org.eclipse.jetty.continuation;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.Servlet;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.ServletResponseWrapper;
/* ------------------------------------------------------------ */
/**
* Continuation.
*
* A continuation is a mechanism by which a HTTP Request can be suspended and
* restarted after a timeout or an asynchronous event has occurred.
*
* The continuation mechanism is a portable mechanism that will work
* asynchronously without additional configuration of all jetty-7,
* jetty-8 and Servlet 3.0 containers. With the addition of
* the {@link ContinuationFilter}, the mechanism will also work
* asynchronously on jetty-6 and non-asynchronously on any
* servlet 2.5 container.
*
* The Continuation API is a simplification of the richer async API
* provided by the servlet-3.0 and an enhancement of the continuation
* API that was introduced with jetty-6.
*
* Continuation Usage
*
* A continuation object is obtained for a request by calling the
* factory method {@link ContinuationSupport#getContinuation(ServletRequest)}.
* The continuation type returned will depend on the servlet container
* being used.
*
*
* There are two distinct style of operation of the continuation API.
*
* Suspend/Resume Usage
* The suspend/resume style is used when a servlet and/or
* filter is used to generate the response after a asynchronous wait that is
* terminated by an asynchronous handler.
*
*
* Filter/Servlet:
* // if we need to get asynchronous results
* Object results = request.getAttribute("results);
* if (results==null)
* {
* Continuation continuation = ContinuationSupport.getContinuation(request);
* continuation.suspend();
* myAsyncHandler.register(continuation);
* return; // or continuation.undispatch();
* }
*
* async wait ...
*
* Async Handler:
* // when the waited for event happens
* continuation.setAttribute("results",event);
* continuation.resume();
*
* Filter/Servlet:
* // when the request is redispatched
* if (results==null)
* {
* ... // see above
* }
* else
* {
* response.getOutputStream().write(process(results));
* }
*
* Suspend/Complete Usage
*
* The suspend/complete style is used when an asynchronous handler is used to
* generate the response:
*
*
* Filter/Servlet:
* // when we want to enter asynchronous mode
* Continuation continuation = ContinuationSupport.getContinuation(request);
* continuation.suspend(response); // response may be wrapped
* myAsyncHandler.register(continuation);
* return; // or continuation.undispatch();
*
* Wrapping Filter:
* // any filter that had wrapped the response should be implemented like:
* try
* {
* chain.doFilter(request,wrappedResponse);
* }
* finally
* {
* if (!continuation.isResponseWrapped())
* wrappedResponse.finish()
* else
* continuation.addContinuationListener(myCompleteListener)
* }
*
* async wait ...
*
* Async Handler:
* // when the async event happens
* continuation.getServletResponse().getOutputStream().write(process(event));
* continuation.complete()
*
*
* Continuation Timeout
*
* If a continuation is suspended, but neither {@link #complete()} or {@link #resume()} is
* called during the period set by {@link #setTimeout(long)}, then the continuation will
* expire and {@link #isExpired()} will return true.
*
*
* When a continuation expires, the {@link ContinuationListener#onTimeout(Continuation)}
* method is called on any {@link ContinuationListener} that has been registered via the
* {@link #addContinuationListener(ContinuationListener)} method. The onTimeout handlers
* may write a response and call {@link #complete()}. If {@link #complete()} is not called,
* then the container will redispatch the request as if {@link #resume()} had been called,
* except that {@link #isExpired()} will be true and {@link #isResumed()} will be false.
*
*
* @see ContinuationSupport
* @see ContinuationListener
*
*/
public interface Continuation
{
public final static String ATTRIBUTE = "org.eclipse.jetty.continuation";
/* ------------------------------------------------------------ */
/**
* Set the continuation timeout.
*
* @param timeoutMs
* The time in milliseconds to wait before expiring this
* continuation after a call to {@link #suspend()} or {@link #suspend(ServletResponse)}.
* A timeout of <=0 means the continuation will never expire.
*/
void setTimeout(long timeoutMs);
/* ------------------------------------------------------------ */
/**
* Suspend the processing of the request and associated
* {@link ServletResponse}.
*
*
* After this method has been called, the lifecycle of the request will be
* extended beyond the return to the container from the
* {@link Servlet#service(ServletRequest, ServletResponse)} method and
* {@link Filter#doFilter(ServletRequest, ServletResponse, FilterChain)}
* calls. When a suspended request is returned to the container after
* a dispatch, then the container will not commit the associated response
* (unless an exception other than {@link ContinuationThrowable} is thrown).
*
*
*
* When the thread calling the filter chain and/or servlet has returned to
* the container with a suspended request, the thread is freed for other
* tasks and the request is held until either:
*
* - a call to {@link #resume()}.
* - a call to {@link #complete()}.
* - the timeout expires.
*
*
* Typically suspend with no arguments is uses when a call to {@link #resume()}
* is expected. If a call to {@link #complete()} is expected, then the
* {@link #suspend(ServletResponse)} method should be used instead of this method.
*
*
* @exception IllegalStateException
* If the request cannot be suspended
*/
void suspend();
/* ------------------------------------------------------------ */
/**
* Suspend the processing of the request and associated
* {@link ServletResponse}.
*
*
* After this method has been called, the lifecycle of the request will be
* extended beyond the return to the container from the
* {@link Servlet#service(ServletRequest, ServletResponse)} method and
* {@link Filter#doFilter(ServletRequest, ServletResponse, FilterChain)}
* calls. When a suspended request is returned to the container after
* a dispatch, then the container will not commit the associated response
* (unless an exception other than {@link ContinuationThrowable} is thrown).
*
*
* When the thread calling the filter chain and/or servlet has returned to
* the container with a suspended request, the thread is freed for other
* tasks and the request is held until either:
*
* - a call to {@link #resume()}.
* - a call to {@link #complete()}.
* - the timeout expires.
*
*
* Typically suspend with a response argument is uses when a call to {@link #complete()}
* is expected. If a call to {@link #resume()} is expected, then the
* {@link #suspend()} method should be used instead of this method.
*
*
* Filters that may wrap the response object should check {@link #isResponseWrapped()}
* to decide if they should destroy/finish the wrapper. If {@link #isResponseWrapped()}
* returns true, then the wrapped request has been passed to the asynchronous
* handler and the wrapper should not be destroyed/finished until after a call to
* {@link #complete()} (potentially using a {@link ContinuationListener#onComplete(Continuation)}
* listener).
*
* @param response The response to return via a call to {@link #getServletResponse()}
* @exception IllegalStateException
* If the request cannot be suspended
*/
void suspend(ServletResponse response);
/* ------------------------------------------------------------ */
/**
* Resume a suspended request.
*
*
* This method can be called by any thread that has been passed a reference
* to a continuation. When called the request is redispatched to the
* normal filter chain and servlet processing with {@link #isInitial()} false.
*
*
* If resume is called before a suspended request is returned to the
* container (ie the thread that called {@link #suspend()} is still
* within the filter chain and/or servlet service method), then the resume
* does not take effect until the call to the filter chain and/or servlet
* returns to the container. In this case both {@link #isSuspended()} and
* {@link #isResumed()} return true. Multiple calls to resume are ignored.
*
*
* Typically resume() is used after a call to {@link #suspend()} with
* no arguments. The dispatch after a resume call will use the original
* request and response objects, even if {@link #suspend(ServletResponse)}
* had been passed a wrapped response.
*
*
* @see #suspend()
* @exception IllegalStateException if the request is not suspended.
*
*/
void resume();
/* ------------------------------------------------------------ */
/**
* Complete a suspended request.
*
*
* This method can be called by any thread that has been passed a reference
* to a suspended request. When a request is completed, the associated
* response object committed and flushed. The request is not redispatched.
*
*
*
* If complete is called before a suspended request is returned to the
* container (ie the thread that called {@link #suspend()} is still
* within the filter chain and/or servlet service method), then the complete
* does not take effect until the call to the filter chain and/or servlet
* returns to the container. In this case both {@link #isSuspended()} and
* {@link #isResumed()} return true.
*
*
*
* Typically resume() is used after a call to {@link #suspend(ServletResponse)} with
* a possibly wrapped response. The async handler should use the response
* provided by {@link #getServletResponse()} to write the response before
* calling {@link #complete()}. If the request was suspended with a
* call to {@link #suspend()} then no response object will be available via
* {@link #getServletResponse()}.
*
*
*
* Once complete has been called and any thread calling the filter chain
* and/or servlet chain has returned to the container, the request lifecycle
* is complete. The container is able to recycle request objects, so it is
* not valid hold a request or continuation reference after the end of the
* life cycle.
*
* @see #suspend()
* @exception IllegalStateException
* if the request is not suspended.
*
*/
void complete();
/* ------------------------------------------------------------ */
/**
* @return true after {@link #suspend()} has been called and before the
* request has been redispatched due to being resumed, completed or
* timed out.
*/
boolean isSuspended();
/* ------------------------------------------------------------ */
/**
* @return true if the request has been redispatched by a call to
* {@link #resume()}. Returns false after any subsequent call to
* suspend
*/
boolean isResumed();
/* ------------------------------------------------------------ */
/**
* @return true after a request has been redispatched as the result of a
* timeout. Returns false after any subsequent call to suspend.
*/
boolean isExpired();
/* ------------------------------------------------------------ */
/**
* @return true while the request is within the initial dispatch to the
* filter chain and/or servlet. Will return false once the calling
* thread has returned to the container after suspend has been
* called and during any subsequent redispatch.
*/
boolean isInitial();
/* ------------------------------------------------------------ */
/**
* Is the suspended response wrapped.
*
* Filters that wrap the response object should check this method to
* determine if they should destroy/finish the wrapped response. If
* the request was suspended with a call to {@link #suspend(ServletResponse)}
* that passed the wrapped response, then the filter should register
* a {@link ContinuationListener} to destroy/finish the wrapped response
* during a call to {@link ContinuationListener#onComplete(Continuation)}.
* @return True if {@link #suspend(ServletResponse)} has been passed a
* {@link ServletResponseWrapper} instance.
*/
boolean isResponseWrapped();
/* ------------------------------------------------------------ */
/**
* Get the suspended response.
* @return the {@link ServletResponse} passed to {@link #suspend(ServletResponse)}.
*/
ServletResponse getServletResponse();
/* ------------------------------------------------------------ */
/**
* Add a ContinuationListener.
*
* @param listener
*/
void addContinuationListener(ContinuationListener listener);
/* ------------------------------------------------------------ */
/** Set a request attribute.
* This method is a convenience method to call the {@link ServletRequest#setAttribute(String, Object)}
* method on the associated request object.
* This is a thread safe call and may be called by any thread.
* @param name the attribute name
* @param attribute the attribute value
*/
public void setAttribute(String name, Object attribute);
/* ------------------------------------------------------------ */
/** Get a request attribute.
* This method is a convenience method to call the {@link ServletRequest#getAttribute(String)}
* method on the associated request object.
* This is a thread safe call and may be called by any thread.
* @param name the attribute name
* @return the attribute value
*/
public Object getAttribute(String name);
/* ------------------------------------------------------------ */
/** Remove a request attribute.
* This method is a convenience method to call the {@link ServletRequest#removeAttribute(String)}
* method on the associated request object.
* This is a thread safe call and may be called by any thread.
* @param name the attribute name
*/
public void removeAttribute(String name);
/* ------------------------------------------------------------ */
/**
* Undispatch the request.
*
* This method can be called on a suspended continuation in order
* to exit the dispatch to the filter/servlet by throwing a {@link ContinuationThrowable}
* which is caught either by the container or the {@link ContinuationFilter}.
* This is an alternative to simply returning from the dispatch in the case
* where filters in the filter chain may not be prepared to handle a suspended
* request.
*
* This method should only be used as a last resort and a normal return is a prefereable
* solution if filters can be updated to handle that case.
*
* @throws ContinuationThrowable thrown if the request is suspended. The instance of the
* exception may be reused on subsequent calls, so the stack frame may not be accurate.
*/
public void undispatch() throws ContinuationThrowable;
}