Class HttpJsonClientCall<RequestT,ResponseT> (2.19.2)

public abstract class HttpJsonClientCall<RequestT,ResponseT>

An instance of a call to a remote method. A call will send zero or more request messages to the server and receive zero or more response messages back.

Instances are created by a HttpJsonChannel and used by stubs to invoke their remote behavior.

#start must be called prior to calling any other methods, with the exception of #cancel. Whereas #cancel must not be followed by any other methods, but can be called more than once, while only the first one has effect.

Methods are potentially blocking but are designed to execute quickly. The implementations of this class are expected to be thread-safe.

There is a race between #cancel and the completion/failure of the RPC in other ways. If #cancel won the race, Listener.onClose() is called with statusCode corresponding to CANCELLED. Otherwise, Listener.onClose() is called with whatever status the RPC was finished. We ensure that at most one is called.


java.lang.Object > HttpJsonClientCall<RequestT,ResponseT>

Type Parameters




public HttpJsonClientCall()


cancel(String message, Throwable cause)

public abstract void cancel(String message, Throwable cause)

Prevent any further processing for this HttpJsonClientCall. No further messages may be sent or will be received. The server is not informed of cancellations. Cancellation is permitted even if previously #halfClosed. Cancelling an already cancel()ed ClientCall has no effect.

No other methods on this class can be called after this method has been called.


if not null, will appear as the description of the CANCELLED status


if not null, will appear as the cause of the CANCELLED status


public abstract void halfClose()

Close the call for request message sending. Incoming response messages are unaffected. This should be called when no more messages will be sent from the client.

request(int numMessages)

public abstract void request(int numMessages)

Requests up to the given number of messages from the call to be delivered to HttpJsonClientCall.Listener#onMessage(Object). No additional messages will be delivered.

Message delivery is guaranteed to be sequential in the order received. In addition, the listener methods will not be accessed concurrently. While it is not guaranteed that the same thread will always be used, it is guaranteed that only a single thread will access the listener at a time.

If called multiple times, the number of messages able to delivered will be the sum of the calls.

This method is safe to call from multiple threads without external synchronization.


the requested number of messages to be delivered to the listener. Must be non-negative.

sendMessage(RequestT message)

public abstract void sendMessage(RequestT message)

Send a request message to the server. May be called zero or more times but for unary and server streaming calls it must be called not more than once.


message to be sent to the server.

start(HttpJsonClientCall.Listener<ResponseT> responseListener, HttpJsonMetadata requestHeaders)

public abstract void start(HttpJsonClientCall.Listener<ResponseT> responseListener, HttpJsonMetadata requestHeaders)

Start a call, using responseListener for processing response messages.

It must be called prior to any other method on this class, except for #cancel which may be called at any time.


receives response messages


which can contain extra call metadata, e.g. authentication credentials.