javax.servlet.AsyncContext

public interface AsyncContext

Class representing the execution context for an asynchronous operation that was initiated on a ServletRequest.(对每一个ServletRequest的每个异步操作都有一个AsyncContext?还是一个ServletRequest只有一个AsynContext?)（一个ServletRequest只有一个AsyncContext）
An AsyncContext is created and initialized by a call to ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse).
我可没有看到任何的异步操作，难道是ServletRequest本身?
Repeated invocations of these methods will return the same AsyncContext instance, reinitialized as appropriate.
In the event that an asynchronous operation has timed out, the container must run through these steps:

• Invoke, at their onTimeout method, all AsyncListener instances registered with the ServletRequest on which the asynchronous operation was initiated.
• If none of the listeners called complete() or any of the dispatch() methods, perform an error dispatch with a status code equal to HttpServletResponse.SC_INTERNAL_SERVER_ERROR.

• If no matching error page was found, or the error page did not call complete() or any of the dispatch() methods, call complete().

  Since:

  Servlet 3.0

  Field Summary

Modifier and Type Field and Description static String ASYNC_CONTEXT_PATH
The name of the request attribute under which the original context path is made available to the target of a dispatch(String) or dispatch(ServletContext,String) static String ASYNC_PATH_INFO
The name of the request attribute under which the original path info is made available to the target of a dispatch(String) or dispatch(ServletContext,String) static String ASYNC_QUERY_STRING
The name of the request attribute under which the original query string is made available to the target of a dispatch(String) or dispatch(ServletContext,String) static String ASYNC_REQUEST_URI
The name of the request attribute under which the original request URI is made available to the target of a dispatch(String) or dispatch(ServletContext,String) static String ASYNC_SERVLET_PATH
The name of the request attribute under which the original servlet path is made available to the target of a dispatch(String) or dispatch(ServletContext,String)

Method Summary

Modifier and Type Method and Description void addListener(AsyncListener listener) Registers the given AsyncListener with the most recent asynchronous cycle that was started by a call to one of the ServletRequest.startAsync() methods. void addListener(AsyncListener listener, ServletRequest servletRequest, ServletResponse servletResponse) Registers the given AsyncListener with the most recent asynchronous cycle that was started by a call to one of the ServletRequest.startAsync() methods. void complete() Completes the asynchronous operation that was started on the request that was used to initialze this AsyncContext, closing the response that was used to initialize this AsyncContext. T createListener(Class clazz) Instantiates the given AsyncListener class. void dispatch() Dispatches the request and response objects of this AsyncContext to the servlet container. void dispatch(ServletContext context, String path) Dispatches the request and response objects of this AsyncContext to the given path scoped to the given context. void dispatch(String path) Dispatches the request and response objects of this AsyncContext to the given path. ServletRequest getRequest() Gets the request that was used to initialize this AsyncContext by calling ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse). ServletResponse getResponse() Gets the response that was used to initialize this AsyncContext by calling ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse). long getTimeout() Gets the timeout (in milliseconds) for this AsyncContext. boolean hasOriginalRequestAndResponse() Checks if this AsyncContext was initialized with the original or application-wrapped request and response objects. void setTimeout(long timeout) Sets the timeout (in milliseconds) for this AsyncContext. void start(Runnable run) Causes the container to dispatch a thread, possibly from a managed thread pool, to run the specified Runnable.

Field Detail

###ASYNC_REQUEST_URI

static final String ASYNC_REQUEST_URI

The name of the request attribute under which the original request URI is made available to the target of a dispatch(String) or dispatch(ServletContext,String)

ASYNC_CONTEXT_PATH

static final String ASYNC_CONTEXT_PATH

The name of the request attribute under which the original context path is made available to the target of a dispatch(String) or dispatch(ServletContext,String)

ASYNC_PATH_INFO

static final String ASYNC_PATH_INFO

The name of the request attribute under which the original path info is made available to the target of a dispatch(String) or dispatch(ServletContext,String)

ASYNC_SERVLET_PATH

static final String ASYNC_SERVLET_PATH

The name of the request attribute under which the original servlet path is made available to the target of a dispatch(String) or dispatch(ServletContext,String)

ASYNC_QUERY_STRING

static final String ASYNC_QUERY_STRING

The name of the request attribute under which the original query string is made available to the target of a dispatch(String) or dispatch(ServletContext,String)

Method Detail

getRequest

ServletRequest getRequest()

Gets the request that was used to initialize this AsyncContext by calling ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse).

Returns:

the request that was used to initialize this AsyncContext

Throws:

IllegalStateException - if complete() or any of the dispatch() methods has been called in the asynchronous cycle

getResponse

ServletResponse getResponse()

Gets the response that was used to initialize this AsyncContext by calling ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse).

Returns:

the response that was used to initialize this AsyncContext

Throws:

IllegalStateException - if complete() or any of the dispatch() methods has been called in the asynchronous cycle
我感觉是让ServletRequest和ServletResponse能够异步执行，ServletRequest和ServletResponse只是一个请求和响应而已，如果想要封装这两个对象让他们可以在异步的环境中运行，不会有两个线程同时使用到了ServletRequest和ServletResponse

hasOriginalRequestAndResponse

boolean hasOriginalRequestAndResponse()

Checks if this AsyncContext was initialized with the original or application-wrapped request and response objects.
This information may be used by filters invoked in the outbound direction, after a request was put into asynchronous mode, to determine whether any request and/or response wrappers that they added during their inbound invocation need to be preserved for the duration of the asynchronous operation, or may be released.

Returns:

true if this AsyncContext was initialized with the original request and response objects by calling ServletRequest.startAsync(), or if it was initialized by calling ServletRequest.startAsync(ServletRequest, ServletResponse), and neither the ServletRequest nor ServletResponse arguments carried any application-provided wrappers; false otherwise

dispatch

void dispatch()

Dispatches the request and response objects of this AsyncContext to the servlet container.
If the asynchronous cycle was started with ServletRequest.startAsync(ServletRequest, ServletResponse), and the request passed is an instance of HttpServletRequest, then the dispatch is to the URI returned by HttpServletRequest.getRequestURI(). Otherwise, the dispatch is to the URI of the request when it was last dispatched by the container.
The following sequence illustrates how this will work:

             // REQUEST dispatch to /url/A             AsyncContext ac = request.startAsync();             ...             ac.dispatch(); // ASYNC dispatch to /url/A             // REQUEST to /url/A             // FORWARD dispatch to /url/B             request.getRequestDispatcher("/url/B").forward(request,response);             // Start async operation from within the target of the FORWARD             // dispatch             ac = request.startAsync();             ...             ac.dispatch(); // ASYNC dispatch to /url/A             // REQUEST to /url/A             // FORWARD dispatch to /url/B             request.getRequestDispatcher("/url/B").forward(request,response);             // Start async operation from within the target of the FORWARD             // dispatch             ac = request.startAsync(request,response);             ...             ac.dispatch(); // ASYNC dispatch to /url/B

This method returns immediately after passing the request and response objects to a container managed thread, on which the dispatch operation will be performed. If this method is called before the container-initiated dispatch that called startAsync has returned to the container, the dispatch operation will be delayed until after the container-initiated dispatch has returned to the container.
The dispatcher type of the request is set to DispatcherType.ASYNC. Unlike forward dispatches, the response buffer and headers will not be reset, and it is legal to dispatch even if the response has already been committed.
Control over the request and response is delegated to the dispatch target, and the response will be closed when the dispatch target has completed execution, unless ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse) are called.
Any errors or exceptions that may occur during the execution of this method must be caught and handled by the container, as follows:

• Invoke, at their onError method, all AsyncListener instances registered with the ServletRequest for which this AsyncContext was created, and make the caught Throwable available via AsyncEvent.getThrowable().
• If none of the listeners called complete() or any of the dispatch() methods, perform an error dispatch with a status code equal to HttpServletResponse.SC_INTERNAL_SERVER_ERROR, and make the above Throwable available as the value of the RequestDispatcher.ERROR_EXCEPTION request attribute.
  
  • If no matching error page was found, or the error page did not call complete() or any of the dispatch() methods, call complete().
    There can be at most one asynchronous dispatch operation per asynchronous cycle, which is started by a call to one of the ServletRequest.startAsync() methods. Any attempt to perform an additional asynchronous dispatch operation within the same asynchronous cycle will result in an IllegalStateException. If startAsync is subsequently called on the dispatched request, then any of the dispatch or complete() methods may be called.
    Throws:
    IllegalStateException - if one of the dispatch methods has been called and the startAsync method has not been called during the resulting dispatch, or if complete() was called

dispatch

void dispatch(String path)

Dispatches the request and response objects of this AsyncContext to the given path.
The path parameter is interpreted in the same way as in ServletRequest.getRequestDispatcher(String), within the scope of the ServletContext from which this AsyncContext was initialized.
All path related query methods of the request must reflect the dispatch target, while the original request URI, context path, path info, servlet path, and query string may be recovered from the ASYNC_REQUEST_URI, ASYNC_CONTEXT_PATH, ASYNC_PATH_INFO, ASYNC_SERVLET_PATH, and ASYNC_QUERY_STRING attributes of the request. These attributes will always reflect the original path elements, even under repeated dispatches.
There can be at most one asynchronous dispatch operation per asynchronous cycle, which is started by a call to one of the ServletRequest.startAsync() methods. Any attempt to perform an additional asynchronous dispatch operation within the same asynchronous cycle will result in an IllegalStateException. If startAsync is subsequently called on the dispatched request, then any of the dispatch or complete() methods may be called.
See dispatch() for additional details, including error handling.

Parameters:

path - the path of the dispatch target, scoped to the ServletContext from which this AsyncContext was initialized
Throws:
IllegalStateException - if one of the dispatch methods has been called and the startAsync method has not been called during the resulting dispatch, or if complete() was called
###See Also:
ServletRequest.getDispatcherType()

dispatch

            void dispatch(ServletContext context,                        String path)

Dispatches the request and response objects of this AsyncContext to the given path scoped to the given context.
The path parameter is interpreted in the same way as in ServletRequest.getRequestDispatcher(String), except that it is scoped to the given context.
All path related query methods of the request must reflect the dispatch target, while the original request URI, context path, path info, servlet path, and query string may be recovered from the ASYNC_REQUEST_URI, ASYNC_CONTEXT_PATH, ASYNC_PATH_INFO, ASYNC_SERVLET_PATH, and ASYNC_QUERY_STRING attributes of the request. These attributes will always reflect the original path elements, even under repeated dispatches.
There can be at most one asynchronous dispatch operation per asynchronous cycle, which is started by a call to one of the ServletRequest.startAsync() methods. Any attempt to perform an additional asynchronous dispatch operation within the same asynchronous cycle will result in an IllegalStateException. If startAsync is subsequently called on the dispatched request, then any of the dispatch or complete() methods may be called.
See dispatch() for additional details, including error handling.

Parameters:

context - the ServletContext of the dispatch target
path - the path of the dispatch target, scoped to the given ServletContext

Throws:

IllegalStateException - if one of the dispatch methods has been called and the startAsync method has not been called during the resulting dispatch, or if complete() was called

complete

void complete()

Completes the asynchronous operation that was started on the request that was used to initialze this AsyncContext, closing the response that was used to initialize this AsyncContext.
Any listeners of type AsyncListener that were registered with the ServletRequest for which this AsyncContext was created will be invoked at their onComplete method.
It is legal to call this method any time after a call to ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse), and before a call to one of the dispatch methods of this class. If this method is called before the container-initiated dispatch that called startAsync has returned to the container, then the call will not take effect (and any invocations of AsyncListener.onComplete(AsyncEvent) will be delayed) until after the container-initiated dispatch has returned to the container.

start

            void start(Runnable run)

Causes the container to dispatch a thread, possibly from a managed thread pool, to run the specified Runnable. The container may propagate appropriate contextual information to the Runnable.

Parameters:

run - the asynchronous handler

addListener

            void addListener(AsyncListener listener)

Registers the given AsyncListener with the most recent asynchronous cycle that was started by a call to one of the ServletRequest.startAsync() methods.
The given AsyncListener will receive an AsyncEvent when the asynchronous cycle completes successfully, times out, results in an error, or a new asynchronous cycle is being initiated via one of the ServletRequest.startAsync() methods.
AsyncListener instances will be notified in the order in which they were added.
If ServletRequest.startAsync(ServletRequest, ServletResponse) or ServletRequest.startAsync() is called, the exact same request and response objects are available from the AsyncEvent when the AsyncListener is notified.

Parameters:

listener - the AsyncListener to be registered

Throws:

IllegalStateException - if this method is called after the container-initiated dispatch, during which one of the ServletRequest.startAsync() methods was called, has returned to the container

addListener

            void addListener(AsyncListener listener,                           ServletRequest servletRequest,                           ServletResponse servletResponse)

Registers the given AsyncListener with the most recent asynchronous cycle that was started by a call to one of the ServletRequest.startAsync() methods.
The given AsyncListener will receive an AsyncEvent when the asynchronous cycle completes successfully, times out, results in an error, or a new asynchronous cycle is being initiated via one of the ServletRequest.startAsync() methods.
AsyncListener instances will be notified in the order in which they were added.
The given ServletRequest and ServletResponse objects will be made available to the given AsyncListener via the getSuppliedRequest and getSuppliedResponse methods, respectively, of the AsyncEvent delivered to it. These objects should not be read from or written to, respectively, at the time the AsyncEvent is delivered, because additional wrapping may have occurred since the given AsyncListener was registered, but may be used in order to release any resources associated with them.

Parameters:

listener - the AsyncListener to be registered
servletRequest - the ServletRequest that will be included in the AsyncEvent
servletResponse - the ServletResponse that will be included in the AsyncEvent

Throws:

IllegalStateException - if this method is called after the container-initiated dispatch, during which one of the ServletRequest.startAsync() methods was called, has returned to the container

createListener

            <T extends AsyncListener> T createListener(Class<T> clazz)                                                   throws ServletException

Instantiates the given AsyncListener class.
The returned AsyncListener instance may be further customized before it is registered with this AsyncContext via a call to one of the addListener methods.
The given AsyncListener class must define a zero argument constructor, which is used to instantiate it.
This method supports resource injection if the given clazz represents a Managed Bean. See the Java EE platform and JSR 299 specifications for additional details about Managed Beans and resource injection.
This method supports any annotations applicable to AsyncListener.

Parameters:

clazz - the AsyncListener class to instantiate

Returns:

the new AsyncListener instance

Throws:

ServletException - if the given clazz fails to be instantiated

setTimeout

            void setTimeout(long timeout)

Sets the timeout (in milliseconds) for this AsyncContext.
The timeout applies to this AsyncContext once the container-initiated dispatch during which one of the ServletRequest.startAsync() methods was called has returned to the container.
The timeout will expire if neither the complete() method nor any of the dispatch methods are called. A timeout value of zero or less indicates no timeout.
If setTimeout(long) is not called, then the container’s default timeout, which is available via a call to getTimeout(), will apply.
The default value is 30000 ms.

Parameters:

timeout - the timeout in milliseconds

Throws:

IllegalStateException - if this method is called after the container-initiated dispatch, during which one of the ServletRequest.startAsync() methods was called, has returned to the container

getTimeout

            long getTimeout()

Gets the timeout (in milliseconds) for this AsyncContext.
This method returns the container’s default timeout for asynchronous operations, or the timeout value passed to the most recent invocation of setTimeout(long).
A timeout value of zero or less indicates no timeout.

Returns:

            the timeout in milliseconds