# Interface HttpResponse.PushPromiseHandler<T>

Type Parameters:
  `T` - the push promise response body type

Enclosing interface:
  `HttpResponse<T>`

public static interface HttpResponse.PushPromiseHandler<T>
A handler for push promises.

A push promise is a synthetic request sent by an HTTP/2 server when retrieving an initiating client-sent request. The server has determined, possibly through inspection of the initiating request, that the client will likely need the promised resource, and hence pushes a synthetic push request, in the form of a push promise, to the client. The client can choose to accept or reject the push promise request.

A push promise request may be received up to the point where the response body of the initiating client-sent request has been fully received. The delivery of a push promise response, however, is not coordinated with the delivery of the response to the initiating client-sent request.

Since:
  11

## Method Summary

Modifier and Type
Method
Description
`void`
`applyPushPromise(HttpRequest initiatingRequest, HttpRequest pushPromiseRequest, Function<HttpResponse.BodyHandler<T>, CompletableFuture<HttpResponse<T>>> acceptor)`
Notification of an incoming push promise.
`static <T> HttpResponse.PushPromiseHandler<T>`
`of(Function<HttpRequest, HttpResponse.BodyHandler<T>> pushPromiseHandler, ConcurrentMap<HttpRequest, CompletableFuture<HttpResponse<T>>> pushPromisesMap)`
Returns a push promise handler that accumulates push promises, and their responses, into the given map.

## Method Details

### applyPushPromise

void applyPushPromise(HttpRequest initiatingRequest, HttpRequest pushPromiseRequest, Function<HttpResponse.BodyHandler<T>, CompletableFuture<HttpResponse<T>>> acceptor)
Notification of an incoming push promise.

This method is invoked once for each push promise received, up to the point where the response body of the initiating client-sent request has been fully received.

A push promise is accepted by invoking the given `acceptor` function. The `acceptor` function must be passed a non-null `BodyHandler`, that is to be used to handle the promise's response body. The acceptor function will return a `CompletableFuture` that completes with the promise's response.

If the `acceptor` function is not successfully invoked, then the push promise is rejected. The `acceptor` function will throw an `IllegalStateException` if invoked more than once.

Parameters:
  `initiatingRequest` - the initiating client-send request
  `pushPromiseRequest` - the synthetic push request
  `acceptor` - the acceptor function that must be successfully invoked to accept the push promise

### of

static <T> HttpResponse.PushPromiseHandler<T> of(Function<HttpRequest, HttpResponse.BodyHandler<T>> pushPromiseHandler, ConcurrentMap<HttpRequest, CompletableFuture<HttpResponse<T>>> pushPromisesMap)
Returns a push promise handler that accumulates push promises, and their responses, into the given map.

Entries are added to the given map for each push promise accepted. The entry's key is the push request, and the entry's value is a `CompletableFuture` that completes with the response corresponding to the key's push request. A push request is rejected / cancelled if there is already an entry in the map whose key is equal to it. A push request is rejected / cancelled if it does not have the same origin as its initiating request.

Entries are added to the given map as soon as practically possible when a push promise is received and accepted. That way code, using such a map like a cache, can determine if a push promise has been issued by the server and avoid making, possibly, unnecessary requests.

The delivery of a push promise response is not coordinated with the delivery of the response to the initiating client-sent request. However, when the response body for the initiating client-sent request has been fully received, the map is guaranteed to be fully populated, that is, no more entries will be added. The individual `CompletableFutures` contained in the map may or may not already be completed at this point.

Type Parameters:
  `T` - the push promise response body type
Parameters:
  `pushPromiseHandler` - the body handler to use for push promises
  `pushPromisesMap` - a map to accumulate push promises into
Returns:
  a push promise handler