1// Protocol Buffers - Google's data interchange format
2// Copyright 2008 Google Inc.  All rights reserved.
3// http://code.google.com/p/protobuf/
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30
31package com.google.protobuf;
32
33/**
34 * Abstract base interface for protocol-buffer-based RPC services.  Services
35 * themselves are abstract classes (implemented either by servers or as
36 * stubs), but they subclass this base interface.  The methods of this
37 * interface can be used to call the methods of the service without knowing
38 * its exact type at compile time (analogous to the Message interface).
39 *
40 * <p>Starting with version 2.3.0, RPC implementations should not try to build
41 * on this, but should instead provide code generator plugins which generate
42 * code specific to the particular RPC implementation.  This way the generated
43 * code can be more appropriate for the implementation in use and can avoid
44 * unnecessary layers of indirection.
45 *
46 * @author kenton@google.com Kenton Varda
47 */
48public interface Service {
49  /**
50   * Get the {@code ServiceDescriptor} describing this service and its methods.
51   */
52  Descriptors.ServiceDescriptor getDescriptorForType();
53
54  /**
55   * <p>Call a method of the service specified by MethodDescriptor.  This is
56   * normally implemented as a simple {@code switch()} that calls the standard
57   * definitions of the service's methods.
58   *
59   * <p>Preconditions:
60   * <ul>
61   *   <li>{@code method.getService() == getDescriptorForType()}
62   *   <li>{@code request} is of the exact same class as the object returned by
63   *       {@code getRequestPrototype(method)}.
64   *   <li>{@code controller} is of the correct type for the RPC implementation
65   *       being used by this Service.  For stubs, the "correct type" depends
66   *       on the RpcChannel which the stub is using.  Server-side Service
67   *       implementations are expected to accept whatever type of
68   *       {@code RpcController} the server-side RPC implementation uses.
69   * </ul>
70   *
71   * <p>Postconditions:
72   * <ul>
73   *   <li>{@code done} will be called when the method is complete.  This may be
74   *       before {@code callMethod()} returns or it may be at some point in
75   *       the future.
76   *   <li>The parameter to {@code done} is the response.  It must be of the
77   *       exact same type as would be returned by
78   *       {@code getResponsePrototype(method)}.
79   *   <li>If the RPC failed, the parameter to {@code done} will be
80   *       {@code null}.  Further details about the failure can be found by
81   *       querying {@code controller}.
82   * </ul>
83   */
84  void callMethod(Descriptors.MethodDescriptor method,
85                  RpcController controller,
86                  Message request,
87                  RpcCallback<Message> done);
88
89  /**
90   * <p>{@code callMethod()} requires that the request passed in is of a
91   * particular subclass of {@code Message}.  {@code getRequestPrototype()}
92   * gets the default instances of this type for a given method.  You can then
93   * call {@code Message.newBuilderForType()} on this instance to
94   * construct a builder to build an object which you can then pass to
95   * {@code callMethod()}.
96   *
97   * <p>Example:
98   * <pre>
99   *   MethodDescriptor method =
100   *     service.getDescriptorForType().findMethodByName("Foo");
101   *   Message request =
102   *     stub.getRequestPrototype(method).newBuilderForType()
103   *         .mergeFrom(input).build();
104   *   service.callMethod(method, request, callback);
105   * </pre>
106   */
107  Message getRequestPrototype(Descriptors.MethodDescriptor method);
108
109  /**
110   * Like {@code getRequestPrototype()}, but gets a prototype of the response
111   * message.  {@code getResponsePrototype()} is generally not needed because
112   * the {@code Service} implementation constructs the response message itself,
113   * but it may be useful in some cases to know ahead of time what type of
114   * object will be returned.
115   */
116  Message getResponsePrototype(Descriptors.MethodDescriptor method);
117}
118