net.jini.jeri

Interface OutboundRequestIterator

public interface OutboundRequestIterator

Produces OutboundRequest instances to use for attempting to send a particular request to a remote communication endpoint.

As long as hasNext returns true, the next method can be invoked to initiate an attempt to make the request. If successful, the next method returns an OutboundRequest to use to write the request data and read the response.

If the request communication attempt fails, such as if the next invocation throws an exception or if a subsequent I/O operation on the returned OutboundRequest or its streams throws an exception, then if hasNext returns true again, the next method can be invoked again to retry the request attempt. This process of retrying failed request attempts can repeat as long as hasNext returns true after the previous failed request attempt.

Note that it is the user's responsibility to abstain from retrying a request attempt if doing so might violate any applicable guarantees of at most once execution semantics (invoking getDeliveryStatus on the previous OutboundRequest might aid in making that determination).

A typical OutboundRequestIterator is likely to support making only one request attempt, in which case after one invocation of next (successful or not), hasNext will return false. Reasons that an OutboundRequestIterator might support multiple request attempts include:

• if the remote endpoint implementation features multiple communication mechanism alternatives to attempt or
• if the implementation can ascertain that the nature of the previous request attempt failure indicates that it would be very unlikely to reoccur in a subsequent attempt.

The hasNext method should not return true after successive failed request attempts indefinitely. The request retry mechanism provided by OutboundRequestIterator is not intended for implementing a strategy of general retry of the same communication mechanism after indeterminate failures.

Note that it is permitted, although unlikely, for an OutboundRequestIterator's hasNext method to never return true, in which case the OutboundRequestIterator does not support initiating even one attempt to send the request.

An OutboundRequestIterator is not guaranteed to be safe for concurrent use by multiple threads.

Since:

2.0

Author:

Sun Microsystems, Inc.

See Also:

Endpoint

Method Summary

Methods

Modifier and Type	Method and Description
boolean	hasNext() Returns true if this iterator supports making at least one more attempt to communicate the request, and false otherwise.
OutboundRequest	next() Initiates an attempt to communicate the request to the remote endpoint.

Method Detail

hasNext

boolean hasNext()

Returns true if this iterator supports making at least one more attempt to communicate the request, and false otherwise.

If this method returns true, then it is guaranteed that the next invocation of next on this iterator will not throw a NoSuchElementException.

If next has been invoked on this iterator and the previous invocation of next returned an OutboundRequest, then this method should not be invoked until that OutboundRequest has been used to attempt to communicate the request and a failure has occurred.

The security context in which this method is invoked may be used for subsequent verification of security permissions; see the next method specification for more details.

Returns:

true if this iterator supports making another attempt to communicate the request, and false otherwise

next

OutboundRequest next()
                     throws IOException

Initiates an attempt to communicate the request to the remote endpoint.

After an invocation of hasNext returns true, it is guaranteed that the next invocation of this method will not throw a NoSuchElementException.

If successful, this method returns an OutboundRequest to use to write the request data and read the response. Even if this method throws an IOException or a SecurityException, the iteration of attempts to communicate the request may continue with another invocation of hasNext.

The implementation verifies that the user's security context has all of the security permissions necessary to communicate the current request attempt with the remote endpoint and to satisfy any required constraints, as appropriate to the implementation of this interface. The implementation is allowed, however, to indicate failure of such a permission check by either throwing a SecurityException from this method or, after returning an OutboundRequest from this method, throwing a SecurityException from some subsequent operation on the OutboundRequest or its streams. If such a SecurityException is thrown, request data must not have been transmitted to the server (that is, if an OutboundRequest has been returned, its getDeliveryStatus method must return false), and the client's identity must not have been revealed to the server.

Also, the implementation of this method or the returned OutboundRequest must eventually verify that the client and server have the requisite principals and credentials to satisfy any required constraints and if not, throw an IOException. If such an IOException is thrown, request data must not have been transmitted to the server.

In verifying any such permission requirement or credential, the implementation is allowed to use the security context in effect for this or any previous invocation of a method on this iterator or the security context in effect for any operation on the OutboundRequest returned by this or any previous invocation of this method on this iterator. Therefore, this iterator and the OutboundRequest instances that it produces should be used in a uniform security context.

Returns:

the OutboundRequest to use to write the request data and read the response

Throws:

NoSuchElementException - if this iterator does not support making another attempt to communicate the request (that is, if hasNext would return false)

IOException - if an I/O exception occurs while performing this operation; in this event, the recipient may have received an indication of the request initiation attempt

SecurityException - if the user does not have the permissions necessary to communicate with the remote endpoint