Interface Service

public interface Service

Abstract base interface for protocol-buffer-based RPC services. Services themselves are abstract classes (implemented either by servers or as stubs), but they subclass this base interface. The methods of this interface can be used to call the methods of the service without knowing its exact type at compile time (analogous to the Message interface).

Starting with version 2.3.0, RPC implementations should not try to build on this, but should instead provide code generator plugins which generate code specific to the particular RPC implementation. This way the generated code can be more appropriate for the implementation in use and can avoid unnecessary layers of indirection.

Methods

callMethod(Descriptors.MethodDescriptor method, RpcController controller, Message request, RpcCallback<Message> done)

public abstract void callMethod(Descriptors.MethodDescriptor method, RpcController controller, Message request, RpcCallback<Message> done)

Call a method of the service specified by MethodDescriptor. This is normally implemented as a simple switch() that calls the standard definitions of the service's methods.

Preconditions:

  • method.getService() == getDescriptorForType()
  • request is of the exact same class as the object returned by getRequestPrototype(method).
  • controller is of the correct type for the RPC implementation being used by this Service. For stubs, the "correct type" depends on the RpcChannel which the stub is using. Server-side Service implementations are expected to accept whatever type of RpcController the server-side RPC implementation uses.

Postconditions:

  • done will be called when the method is complete. This may be before callMethod() returns or it may be at some point in the future.
  • The parameter to done is the response. It must be of the exact same type as would be returned by getResponsePrototype(method).
  • If the RPC failed, the parameter to done will be null. Further details about the failure can be found by querying controller.
Parameters
NameDescription
methodDescriptors.MethodDescriptor
controllerRpcController
requestMessage
doneRpcCallback<Message>

getDescriptorForType()

public abstract Descriptors.ServiceDescriptor getDescriptorForType()

Get the ServiceDescriptor describing this service and its methods.

Returns
TypeDescription
Descriptors.ServiceDescriptor

getRequestPrototype(Descriptors.MethodDescriptor method)

public abstract Message getRequestPrototype(Descriptors.MethodDescriptor method)

callMethod() requires that the request passed in is of a particular subclass of Message. getRequestPrototype() gets the default instances of this type for a given method. You can then call Message.newBuilderForType() on this instance to construct a builder to build an object which you can then pass to callMethod().

Example:

MethodDescriptor method = service.getDescriptorForType().findMethodByName("Foo"); Message request = stub.getRequestPrototype(method).newBuilderForType() .mergeFrom(input).build(); service.callMethod(method, request, callback);

Parameter
NameDescription
methodDescriptors.MethodDescriptor
Returns
TypeDescription
Message

getResponsePrototype(Descriptors.MethodDescriptor method)

public abstract Message getResponsePrototype(Descriptors.MethodDescriptor method)

Like getRequestPrototype(), but gets a prototype of the response message. getResponsePrototype() is generally not needed because the Service implementation constructs the response message itself, but it may be useful in some cases to know ahead of time what type of object will be returned.

Parameter
NameDescription
methodDescriptors.MethodDescriptor
Returns
TypeDescription
Message