grpc bindings generator for Java and a few minor supporting changes i… (#4553)

* grpc bindings generator for Java and a few minor supporting changes in improvements

* restored formatting before my previous changes for ease of review

* Fixed grpc java code generation bug resulting in duplicate extractor declarations in case the same is used in more than a single RPC method

CMakeLists.txt

@@ -60,6 +60,8 @@ set(FlatBuffers_Compiler_SRCS
   grpc/src/compiler/cpp_generator.cc
   grpc/src/compiler/go_generator.h
   grpc/src/compiler/go_generator.cc
+  grpc/src/compiler/java_generator.h
+  grpc/src/compiler/java_generator.cc
 )
 
 set(FlatHash_SRCS

grpc/src/compiler/java_generator.cc

+/*
+ * Copyright 2016 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "java_generator.h"
+
+#include <algorithm>
+#include <iostream>
+#include <iterator>
+#include <map>
+#include <utility>
+#include <vector>
+
+// just to get flatbuffer_version_string()
+#include <flatbuffers/flatbuffers.h>
+#include <flatbuffers/util.h>
+#define to_string flatbuffers::NumToString
+
+// Stringify helpers used solely to cast GRPC_VERSION
+#ifndef STR
+#define STR(s) #s
+#endif
+
+#ifndef XSTR
+#define XSTR(s) STR(s)
+#endif
+
+#ifndef FALLTHROUGH_INTENDED
+#define FALLTHROUGH_INTENDED
+#endif
+
+typedef grpc_generator::Printer Printer;
+typedef std::map<grpc::string, grpc::string> VARS;
+typedef grpc_generator::Service ServiceDescriptor;
+typedef grpc_generator::CommentHolder
+    DescriptorType;  // base class of all 'descriptors'
+typedef grpc_generator::Method MethodDescriptor;
+
+namespace grpc_java_generator {
+// Generates imports for the service
+void GenerateImports(grpc_generator::File* file,
+                     grpc_generator::Printer* printer, VARS& vars) {
+  vars["filename"] = file->filename();
+  printer->Print(
+      vars,
+      "//Generated by flatc compiler (version $flatc_version$) on " __DATE__
+      " " __TIME__ "  \n");
+  printer->Print("//If you make any local changes, they will be lost\n");
+  printer->Print(vars, "//source: $filename$.fbs\n\n");
+  printer->Print(vars, "package $Package$;\n\n");
+  vars["Package"] = vars["Package"] + ".";
+  if (file->additional_headers() != "") {
+    printer->Print(file->additional_headers().c_str());
+    printer->Print("\n\n");
+  }
+}
+
+// Adjust a method name prefix identifier to follow the JavaBean spec:
+//   - decapitalize the first letter
+//   - remove embedded underscores & capitalize the following letter
+static string MixedLower(const string& word) {
+  string w;
+  w += (string::value_type)tolower(word[0]);
+  bool after_underscore = false;
+  for (size_t i = 1; i < word.length(); ++i) {
+    if (word[i] == '_') {
+      after_underscore = true;
+    } else {
+      w += after_underscore ? (string::value_type)toupper(word[i]) : word[i];
+      after_underscore = false;
+    }
+  }
+  return w;
+}
+
+// Converts to the identifier to the ALL_UPPER_CASE format.
+//   - An underscore is inserted where a lower case letter is followed by an
+//     upper case letter.
+//   - All letters are converted to upper case
+static string ToAllUpperCase(const string& word) {
+  string w;
+  for (size_t i = 0; i < word.length(); ++i) {
+    w += (string::value_type)toupper(word[i]);
+    if ((i < word.length() - 1) && islower(word[i]) && isupper(word[i + 1])) {
+      w += '_';
+    }
+  }
+  return w;
+}
+
+static inline string LowerMethodName(const MethodDescriptor* method) {
+  return MixedLower(method->name());
+}
+
+static inline string MethodPropertiesFieldName(const MethodDescriptor* method) {
+  return "METHOD_" + ToAllUpperCase(method->name());
+}
+
+static inline string MethodPropertiesGetterName(
+    const MethodDescriptor* method) {
+  return MixedLower("get_" + method->name() + "_method");
+}
+
+static inline string MethodIdFieldName(const MethodDescriptor* method) {
+  return "METHODID_" + ToAllUpperCase(method->name());
+}
+
+static inline string JavaClassName(VARS& vars, const string& name) {
+  // string name = google::protobuf::compiler::java::ClassName(desc);
+  return vars["Package"] + name;
+}
+
+static inline string ServiceClassName(const string& service_name) {
+  return service_name + "Grpc";
+}
+
+// TODO(nmittler): Remove once protobuf includes javadoc methods in
+// distribution.
+template <typename ITR>
+static void GrpcSplitStringToIteratorUsing(const string& full,
+                                           const char* delim, ITR& result) {
+  // Optimize the common case where delim is a single character.
+  if (delim[0] != '\0' && delim[1] == '\0') {
+    char c = delim[0];
+    const char* p = full.data();
+    const char* end = p + full.size();
+    while (p != end) {
+      if (*p == c) {
+        ++p;
+      } else {
+        const char* start = p;
+        while (++p != end && *p != c)
+          ;
+        *result++ = string(start, p - start);
+      }
+    }
+    return;
+  }
+
+  string::size_type begin_index, end_index;
+  begin_index = full.find_first_not_of(delim);
+  while (begin_index != string::npos) {
+    end_index = full.find_first_of(delim, begin_index);
+    if (end_index == string::npos) {
+      *result++ = full.substr(begin_index);
+      return;
+    }
+    *result++ = full.substr(begin_index, (end_index - begin_index));
+    begin_index = full.find_first_not_of(delim, end_index);
+  }
+}
+
+static void GrpcSplitStringUsing(const string& full, const char* delim,
+                                 std::vector<string>* result) {
+  std::back_insert_iterator<std::vector<string>> it(*result);
+  GrpcSplitStringToIteratorUsing(full, delim, it);
+}
+
+static std::vector<string> GrpcSplit(const string& full, const char* delim) {
+  std::vector<string> result;
+  GrpcSplitStringUsing(full, delim, &result);
+  return result;
+}
+
+// TODO(nmittler): Remove once protobuf includes javadoc methods in
+// distribution.
+static string GrpcEscapeJavadoc(const string& input) {
+  string result;
+  result.reserve(input.size() * 2);
+
+  char prev = '*';
+
+  for (string::size_type i = 0; i < input.size(); i++) {
+    char c = input[i];
+    switch (c) {
+      case '*':
+        // Avoid "/*".
+        if (prev == '/') {
+          result.append("&#42;");
+        } else {
+          result.push_back(c);
+        }
+        break;
+      case '/':
+        // Avoid "*/".
+        if (prev == '*') {
+          result.append("&#47;");
+        } else {
+          result.push_back(c);
+        }
+        break;
+      case '@':
+        // '@' starts javadoc tags including the @deprecated tag, which will
+        // cause a compile-time error if inserted before a declaration that
+        // does not have a corresponding @Deprecated annotation.
+        result.append("&#64;");
+        break;
+      case '<':
+        // Avoid interpretation as HTML.
+        result.append("&lt;");
+        break;
+      case '>':
+        // Avoid interpretation as HTML.
+        result.append("&gt;");
+        break;
+      case '&':
+        // Avoid interpretation as HTML.
+        result.append("&amp;");
+        break;
+      case '\\':
+        // Java interprets Unicode escape sequences anywhere!
+        result.append("&#92;");
+        break;
+      default:
+        result.push_back(c);
+        break;
+    }
+
+    prev = c;
+  }
+
+  return result;
+}
+
+static std::vector<string> GrpcGetDocLines(const string& comments) {
+  if (!comments.empty()) {
+    // TODO(kenton):  Ideally we should parse the comment text as Markdown and
+    //   write it back as HTML, but this requires a Markdown parser.  For now
+    //   we just use <pre> to get fixed-width text formatting.
+
+    // If the comment itself contains block comment start or end markers,
+    // HTML-escape them so that they don't accidentally close the doc comment.
+    string escapedComments = GrpcEscapeJavadoc(comments);
+
+    std::vector<string> lines = GrpcSplit(escapedComments, "\n");
+    while (!lines.empty() && lines.back().empty()) {
+      lines.pop_back();
+    }
+    return lines;
+  }
+  return std::vector<string>();
+}
+
+static std::vector<string> GrpcGetDocLinesForDescriptor(
+    const DescriptorType* descriptor) {
+  return descriptor->GetAllComments();
+  // return GrpcGetDocLines(descriptor->GetLeadingComments("///"));
+}
+
+static void GrpcWriteDocCommentBody(Printer* printer, VARS& vars,
+                                    const std::vector<string>& lines,
+                                    bool surroundWithPreTag) {
+  if (!lines.empty()) {
+    if (surroundWithPreTag) {
+      printer->Print(" * <pre>\n");
+    }
+
+    for (size_t i = 0; i < lines.size(); i++) {
+      // Most lines should start with a space.  Watch out for lines that start
+      // with a /, since putting that right after the leading asterisk will
+      // close the comment.
+      vars["line"] = lines[i];
+      if (!lines[i].empty() && lines[i][0] == '/') {
+        printer->Print(vars, " * $line$\n");
+      } else {
+        printer->Print(vars, " *$line$\n");
+      }
+    }
+
+    if (surroundWithPreTag) {
+      printer->Print(" * </pre>\n");
+    }
+  }
+}
+
+static void GrpcWriteDocComment(Printer* printer, VARS& vars,
+                                const string& comments) {
+  printer->Print("/**\n");
+  std::vector<string> lines = GrpcGetDocLines(comments);
+  GrpcWriteDocCommentBody(printer, vars, lines, false);
+  printer->Print(" */\n");
+}
+
+static void GrpcWriteServiceDocComment(Printer* printer, VARS& vars,
+                                       const ServiceDescriptor* service) {
+  printer->Print("/**\n");
+  std::vector<string> lines = GrpcGetDocLinesForDescriptor(service);
+  GrpcWriteDocCommentBody(printer, vars, lines, true);
+  printer->Print(" */\n");
+}
+
+void GrpcWriteMethodDocComment(Printer* printer, VARS& vars,
+                               const MethodDescriptor* method) {
+  printer->Print("/**\n");
+  std::vector<string> lines = GrpcGetDocLinesForDescriptor(method);
+  GrpcWriteDocCommentBody(printer, vars, lines, true);
+  printer->Print(" */\n");
+}
+
+//outputs static singleton extractor for type stored in "extr_type" and "extr_type_name" vars
+static void PrintTypeExtractor(Printer* p, VARS& vars) {
+  p->Print(
+    vars,
+    "private static volatile FlatbuffersUtils.FBExtactor<$extr_type$> "
+    "extractorOf$extr_type_name$;\n"
+    "private static FlatbuffersUtils.FBExtactor<$extr_type$> "
+    "getExtractorOf$extr_type_name$() {\n"
+    "    if (extractorOf$extr_type_name$ != null) return "
+    "extractorOf$extr_type_name$;\n"
+    "    synchronized ($service_class_name$.class) {\n"
+    "        if (extractorOf$extr_type_name$ != null) return "
+    "extractorOf$extr_type_name$;\n"
+    "        extractorOf$extr_type_name$ = new "
+    "FlatbuffersUtils.FBExtactor<$extr_type$>() {\n"
+    "            public $extr_type$ extract (ByteBuffer buffer) {\n"
+    "                return "
+    "$extr_type$.getRootAs$extr_type_name$(buffer);\n"
+    "            }\n"
+    "        };\n"
+    "        return extractorOf$extr_type_name$;\n"
+    "    }\n"
+    "}\n\n");
+}
+static void PrintMethodFields(Printer* p, VARS& vars,
+                              const ServiceDescriptor* service) {
+  p->Print("// Static method descriptors that strictly reflect the proto.\n");
+  vars["service_name"] = service->name();
+  
+  //set of names of rpc input- and output- types that were already encountered.
+  //this is needed to avoid duplicating type extractor since it's possible that
+  //the same type is used as an input or output type of more than a single RPC method
+  std::set<std::string> encounteredTypes;
+  
+  for (int i = 0; i < service->method_count(); ++i) {
+    auto method = service->method(i);
+    vars["arg_in_id"] = to_string((long)2 * i); //trying to make msvc 10 happy
+    vars["arg_out_id"] = to_string((long)2 * i + 1);
+    vars["method_name"] = method->name();
+    vars["input_type_name"] = method->get_input_type_name();
+    vars["output_type_name"] = method->get_output_type_name();
+    vars["input_type"] = JavaClassName(vars, method->get_input_type_name());
+    vars["output_type"] = JavaClassName(vars, method->get_output_type_name());
+    vars["method_field_name"] = MethodPropertiesFieldName(method.get());
+    vars["method_new_field_name"] = MethodPropertiesGetterName(method.get());
+    vars["method_method_name"] = MethodPropertiesGetterName(method.get());
+    bool client_streaming = method->ClientStreaming();
+    bool server_streaming = method->ServerStreaming();
+    if (client_streaming) {
+      if (server_streaming) {
+        vars["method_type"] = "BIDI_STREAMING";
+      } else {
+        vars["method_type"] = "CLIENT_STREAMING";
+      }
+    } else {
+      if (server_streaming) {
+        vars["method_type"] = "SERVER_STREAMING";
+      } else {
+        vars["method_type"] = "UNARY";
+      }
+    }
+
+    p->Print(
+        vars,
+        "@$ExperimentalApi$(\"https://github.com/grpc/grpc-java/issues/"
+        "1901\")\n"
+        "@$Deprecated$ // Use {@link #$method_method_name$()} instead. \n"
+        "public static final $MethodDescriptor$<$input_type$,\n"
+        "    $output_type$> $method_field_name$ = $method_method_name$();\n"
+        "\n"
+        "private static volatile $MethodDescriptor$<$input_type$,\n"
+        "    $output_type$> $method_new_field_name$;\n"
+        "\n");
+    
+    if (encounteredTypes.insert(vars["input_type_name"]).second) {
+      vars["extr_type"] = vars["input_type"];
+      vars["extr_type_name"] = vars["input_type_name"];
+      PrintTypeExtractor(p, vars);
+    }
+
+    if (encounteredTypes.insert(vars["output_type_name"]).second) {
+      vars["extr_type"] = vars["output_type"];
+      vars["extr_type_name"] = vars["output_type_name"];
+      PrintTypeExtractor(p, vars);
+    }
+    
+    p->Print(
+      vars,
+      "@$ExperimentalApi$(\"https://github.com/grpc/grpc-java/issues/"
+      "1901\")\n"
+      "public static $MethodDescriptor$<$input_type$,\n"
+      "    $output_type$> $method_method_name$() {\n"
+      "  $MethodDescriptor$<$input_type$, $output_type$> "
+      "$method_new_field_name$;\n"
+      "  if (($method_new_field_name$ = "
+      "$service_class_name$.$method_new_field_name$) == null) {\n"
+      "    synchronized ($service_class_name$.class) {\n"
+      "      if (($method_new_field_name$ = "
+      "$service_class_name$.$method_new_field_name$) == null) {\n"
+      "        $service_class_name$.$method_new_field_name$ = "
+      "$method_new_field_name$ = \n"
+      "            $MethodDescriptor$.<$input_type$, "
+      "$output_type$>newBuilder()\n"
+      "            .setType($MethodType$.$method_type$)\n"
+      "            .setFullMethodName(generateFullMethodName(\n"
+      "                \"$Package$$service_name$\", \"$method_name$\"))\n"
+      "            .setSampledToLocalTracing(true)\n"
+      "            .setRequestMarshaller(FlatbuffersUtils.marshaller(\n"
+      "                $input_type$.class, "
+      "getExtractorOf$input_type_name$()))\n"
+      "            .setResponseMarshaller(FlatbuffersUtils.marshaller(\n"
+      "                $output_type$.class, "
+      "getExtractorOf$output_type_name$()))\n");
+
+    //            vars["proto_method_descriptor_supplier"] = service->name() +
+    //            "MethodDescriptorSupplier";
+    p->Print(vars, "                .setSchemaDescriptor(null)\n");
+    //"                .setSchemaDescriptor(new
+    //$proto_method_descriptor_supplier$(\"$method_name$\"))\n");
+
+    p->Print(vars, "                .build();\n");
+    p->Print(vars,
+             "        }\n"
+             "      }\n"
+             "   }\n"
+             "   return $method_new_field_name$;\n"
+             "}\n");
+
+    p->Print("\n");
+  }
+}
+enum StubType {
+  ASYNC_INTERFACE = 0,
+  BLOCKING_CLIENT_INTERFACE = 1,
+  FUTURE_CLIENT_INTERFACE = 2,
+  BLOCKING_SERVER_INTERFACE = 3,
+  ASYNC_CLIENT_IMPL = 4,
+  BLOCKING_CLIENT_IMPL = 5,
+  FUTURE_CLIENT_IMPL = 6,
+  ABSTRACT_CLASS = 7,
+};
+
+enum CallType { ASYNC_CALL = 0, BLOCKING_CALL = 1, FUTURE_CALL = 2 };
+
+static void PrintBindServiceMethodBody(Printer* p, VARS& vars,
+                                       const ServiceDescriptor* service);
+
+// Prints a client interface or implementation class, or a server interface.
+static void PrintStub(Printer* p, VARS& vars, const ServiceDescriptor* service,
+                      StubType type) {
+  const string service_name = service->name();
+  vars["service_name"] = service_name;
+  vars["abstract_name"] = service_name + "ImplBase";
+  string stub_name = service_name;
+  string client_name = service_name;
+  CallType call_type = ASYNC_CALL;
+  bool impl_base = false;
+  bool interface = false;
+  switch (type) {
+    case ABSTRACT_CLASS:
+      call_type = ASYNC_CALL;
+      impl_base = true;
+      break;
+    case ASYNC_CLIENT_IMPL:
+      call_type = ASYNC_CALL;
+      stub_name += "Stub";
+      break;
+    case BLOCKING_CLIENT_INTERFACE:
+      interface = true;
+      FALLTHROUGH_INTENDED;
+    case BLOCKING_CLIENT_IMPL:
+      call_type = BLOCKING_CALL;
+      stub_name += "BlockingStub";
+      client_name += "BlockingClient";
+      break;
+    case FUTURE_CLIENT_INTERFACE:
+      interface = true;
+      FALLTHROUGH_INTENDED;
+    case FUTURE_CLIENT_IMPL:
+      call_type = FUTURE_CALL;
+      stub_name += "FutureStub";
+      client_name += "FutureClient";
+      break;
+    case ASYNC_INTERFACE:
+      call_type = ASYNC_CALL;
+      interface = true;
+      break;
+    default:
+      GRPC_CODEGEN_FAIL << "Cannot determine class name for StubType: " << type;
+  }
+  vars["stub_name"] = stub_name;
+  vars["client_name"] = client_name;
+
+  // Class head
+  if (!interface) {
+    GrpcWriteServiceDocComment(p, vars, service);
+  }
+  if (impl_base) {
+    p->Print(vars,
+             "public static abstract class $abstract_name$ implements "
+             "$BindableService$ {\n");
+  } else {
+    p->Print(vars,
+             "public static final class $stub_name$ extends "
+             "$AbstractStub$<$stub_name$> {\n");
+  }
+  p->Indent();
+
+  // Constructor and build() method
+  if (!impl_base && !interface) {
+    p->Print(vars, "private $stub_name$($Channel$ channel) {\n");
+    p->Indent();
+    p->Print("super(channel);\n");
+    p->Outdent();
+    p->Print("}\n\n");
+    p->Print(vars,
+             "private $stub_name$($Channel$ channel,\n"
+             "    $CallOptions$ callOptions) {\n");
+    p->Indent();
+    p->Print("super(channel, callOptions);\n");
+    p->Outdent();
+    p->Print("}\n\n");
+    p->Print(vars,
+             "@$Override$\n"
+             "protected $stub_name$ build($Channel$ channel,\n"
+             "    $CallOptions$ callOptions) {\n");
+    p->Indent();
+    p->Print(vars, "return new $stub_name$(channel, callOptions);\n");
+    p->Outdent();
+    p->Print("}\n");
+  }
+
+  // RPC methods
+  for (int i = 0; i < service->method_count(); ++i) {
+    auto method = service->method(i);
+    vars["input_type"] = JavaClassName(vars, method->get_input_type_name());
+    vars["output_type"] = JavaClassName(vars, method->get_output_type_name());
+    vars["lower_method_name"] = LowerMethodName(&*method);
+    vars["method_method_name"] = MethodPropertiesGetterName(&*method);
+    bool client_streaming = method->ClientStreaming();
+    bool server_streaming = method->ServerStreaming();
+
+    if (call_type == BLOCKING_CALL && client_streaming) {
+      // Blocking client interface with client streaming is not available
+      continue;
+    }
+
+    if (call_type == FUTURE_CALL && (client_streaming || server_streaming)) {
+      // Future interface doesn't support streaming.
+      continue;
+    }
+
+    // Method signature
+    p->Print("\n");
+    // TODO(nmittler): Replace with WriteMethodDocComment once included by the
+    // protobuf distro.
+    if (!interface) {
+      GrpcWriteMethodDocComment(p, vars, &*method);
+    }
+    p->Print("public ");
+    switch (call_type) {
+      case BLOCKING_CALL:
+        GRPC_CODEGEN_CHECK(!client_streaming)
+            << "Blocking client interface with client streaming is unavailable";
+        if (server_streaming) {
+          // Server streaming
+          p->Print(vars,
+                   "$Iterator$<$output_type$> $lower_method_name$(\n"
+                   "    $input_type$ request)");
+        } else {
+          // Simple RPC
+          p->Print(vars,
+                   "$output_type$ $lower_method_name$($input_type$ request)");
+        }
+        break;
+      case ASYNC_CALL:
+        if (client_streaming) {
+          // Bidirectional streaming or client streaming
+          p->Print(vars,
+                   "$StreamObserver$<$input_type$> $lower_method_name$(\n"
+                   "    $StreamObserver$<$output_type$> responseObserver)");
+        } else {
+          // Server streaming or simple RPC
+          p->Print(vars,
+                   "void $lower_method_name$($input_type$ request,\n"
+                   "    $StreamObserver$<$output_type$> responseObserver)");
+        }
+        break;
+      case FUTURE_CALL:
+        GRPC_CODEGEN_CHECK(!client_streaming && !server_streaming)
+            << "Future interface doesn't support streaming. "
+            << "client_streaming=" << client_streaming << ", "
+            << "server_streaming=" << server_streaming;
+        p->Print(vars,
+                 "$ListenableFuture$<$output_type$> $lower_method_name$(\n"
+                 "    $input_type$ request)");
+        break;
+    }
+
+    if (interface) {
+      p->Print(";\n");
+      continue;
+    }
+    // Method body.
+    p->Print(" {\n");
+    p->Indent();
+    if (impl_base) {
+      switch (call_type) {
+          // NB: Skipping validation of service methods. If something is wrong,
+          // we wouldn't get to this point as compiler would return errors when
+          // generating service interface.
+        case ASYNC_CALL:
+          if (client_streaming) {
+            p->Print(vars,
+                     "return "
+                     "asyncUnimplementedStreamingCall($method_method_name$(), "
+                     "responseObserver);\n");
+          } else {
+            p->Print(vars,
+                     "asyncUnimplementedUnaryCall($method_method_name$(), "
+                     "responseObserver);\n");
+          }
+          break;
+        default:
+          break;
+      }
+    } else if (!interface) {
+      switch (call_type) {
+        case BLOCKING_CALL:
+          GRPC_CODEGEN_CHECK(!client_streaming)
+              << "Blocking client streaming interface is not available";
+          if (server_streaming) {
+            vars["calls_method"] = "blockingServerStreamingCall";
+            vars["params"] = "request";
+          } else {
+            vars["calls_method"] = "blockingUnaryCall";
+            vars["params"] = "request";
+          }
+          p->Print(vars,
+                   "return $calls_method$(\n"
+                   "    getChannel(), $method_method_name$(), "
+                   "getCallOptions(), $params$);\n");
+          break;
+        case ASYNC_CALL:
+          if (server_streaming) {
+            if (client_streaming) {
+              vars["calls_method"] = "asyncBidiStreamingCall";
+              vars["params"] = "responseObserver";
+            } else {
+              vars["calls_method"] = "asyncServerStreamingCall";
+              vars["params"] = "request, responseObserver";
+            }
+          } else {
+            if (client_streaming) {
+              vars["calls_method"] = "asyncClientStreamingCall";
+              vars["params"] = "responseObserver";
+            } else {
+              vars["calls_method"] = "asyncUnaryCall";
+              vars["params"] = "request, responseObserver";
+            }
+          }
+          vars["last_line_prefix"] = client_streaming ? "return " : "";
+          p->Print(vars,
+                   "$last_line_prefix$$calls_method$(\n"
+                   "    getChannel().newCall($method_method_name$(), "
+                   "getCallOptions()), $params$);\n");
+          break;
+        case FUTURE_CALL:
+          GRPC_CODEGEN_CHECK(!client_streaming && !server_streaming)
+              << "Future interface doesn't support streaming. "
+              << "client_streaming=" << client_streaming << ", "
+              << "server_streaming=" << server_streaming;
+          vars["calls_method"] = "futureUnaryCall";
+          p->Print(vars,
+                   "return $calls_method$(\n"
+                   "    getChannel().newCall($method_method_name$(), "
+                   "getCallOptions()), request);\n");
+          break;
+      }
+    }
+    p->Outdent();
+    p->Print("}\n");
+  }
+
+  if (impl_base) {
+    p->Print("\n");
+    p->Print(
+        vars,
+        "@$Override$ public final $ServerServiceDefinition$ bindService() {\n");
+    vars["instance"] = "this";
+    PrintBindServiceMethodBody(p, vars, service);
+    p->Print("}\n");
+  }
+
+  p->Outdent();
+  p->Print("}\n\n");
+}
+
+static bool CompareMethodClientStreaming(
+    const std::unique_ptr<const grpc_generator::Method>& method1,
+    const std::unique_ptr<const grpc_generator::Method>& method2) {
+  return method1->ClientStreaming() < method2->ClientStreaming();
+}
+
+// Place all method invocations into a single class to reduce memory footprint
+// on Android.
+static void PrintMethodHandlerClass(Printer* p, VARS& vars,
+                                    const ServiceDescriptor* service) {
+  // Sort method ids based on ClientStreaming() so switch tables are compact.
+  std::vector<std::unique_ptr<const grpc_generator::Method>> sorted_methods(
+      service->method_count());
+  for (int i = 0; i < service->method_count(); ++i) {
+    sorted_methods[i] = service->method(i);
+  }
+  stable_sort(sorted_methods.begin(), sorted_methods.end(),
+              CompareMethodClientStreaming);
+  for (size_t i = 0; i < sorted_methods.size(); i++) {
+    auto& method = sorted_methods[i];
+    vars["method_id"] = to_string(i);
+    vars["method_id_name"] = MethodIdFieldName(&*method);
+    p->Print(vars,
+             "private static final int $method_id_name$ = $method_id$;\n");
+  }
+  p->Print("\n");
+  vars["service_name"] = service->name() + "ImplBase";
+  p->Print(vars,
+           "private static final class MethodHandlers<Req, Resp> implements\n"
+           "    io.grpc.stub.ServerCalls.UnaryMethod<Req, Resp>,\n"
+           "    io.grpc.stub.ServerCalls.ServerStreamingMethod<Req, Resp>,\n"
+           "    io.grpc.stub.ServerCalls.ClientStreamingMethod<Req, Resp>,\n"
+           "    io.grpc.stub.ServerCalls.BidiStreamingMethod<Req, Resp> {\n"
+           "  private final $service_name$ serviceImpl;\n"
+           "  private final int methodId;\n"
+           "\n"
+           "  MethodHandlers($service_name$ serviceImpl, int methodId) {\n"
+           "    this.serviceImpl = serviceImpl;\n"
+           "    this.methodId = methodId;\n"
+           "  }\n\n");
+  p->Indent();
+  p->Print(vars,
+           "@$Override$\n"
+           "@java.lang.SuppressWarnings(\"unchecked\")\n"
+           "public void invoke(Req request, $StreamObserver$<Resp> "
+           "responseObserver) {\n"
+           "  switch (methodId) {\n");
+  p->Indent();
+  p->Indent();
+
+  for (int i = 0; i < service->method_count(); ++i) {
+    auto method = service->method(i);
+    if (method->ClientStreaming()) {
+      continue;
+    }
+    vars["method_id_name"] = MethodIdFieldName(&*method);
+    vars["lower_method_name"] = LowerMethodName(&*method);
+    vars["input_type"] = JavaClassName(vars, method->get_input_type_name());
+    vars["output_type"] = JavaClassName(vars, method->get_output_type_name());
+    p->Print(vars,
+             "case $method_id_name$:\n"
+             "  serviceImpl.$lower_method_name$(($input_type$) request,\n"
+             "      ($StreamObserver$<$output_type$>) responseObserver);\n"
+             "  break;\n");
+  }
+  p->Print(
+      "default:\n"
+      "  throw new AssertionError();\n");
+
+  p->Outdent();
+  p->Outdent();
+  p->Print(
+      "  }\n"
+      "}\n\n");
+
+  p->Print(vars,
+           "@$Override$\n"
+           "@java.lang.SuppressWarnings(\"unchecked\")\n"
+           "public $StreamObserver$<Req> invoke(\n"
+           "    $StreamObserver$<Resp> responseObserver) {\n"
+           "  switch (methodId) {\n");
+  p->Indent();
+  p->Indent();
+
+  for (int i = 0; i < service->method_count(); ++i) {
+    auto method = service->method(i);
+    if (!method->ClientStreaming()) {
+      continue;
+    }
+    vars["method_id_name"] = MethodIdFieldName(&*method);
+    vars["lower_method_name"] = LowerMethodName(&*method);
+    vars["input_type"] = JavaClassName(vars, method->get_input_type_name());
+    vars["output_type"] = JavaClassName(vars, method->get_output_type_name());
+    p->Print(
+        vars,
+        "case $method_id_name$:\n"
+        "  return ($StreamObserver$<Req>) serviceImpl.$lower_method_name$(\n"
+        "      ($StreamObserver$<$output_type$>) responseObserver);\n");
+  }
+  p->Print(
+      "default:\n"
+      "  throw new AssertionError();\n");
+
+  p->Outdent();
+  p->Outdent();
+  p->Print(
+      "  }\n"
+      "}\n");
+
+  p->Outdent();
+  p->Print("}\n\n");
+}
+
+static void PrintGetServiceDescriptorMethod(Printer* p, VARS& vars,
+                                            const ServiceDescriptor* service) {
+  vars["service_name"] = service->name();
+  //        vars["proto_base_descriptor_supplier"] = service->name() +
+  //        "BaseDescriptorSupplier"; vars["proto_file_descriptor_supplier"] =
+  //        service->name() + "FileDescriptorSupplier";
+  //        vars["proto_method_descriptor_supplier"] = service->name() +
+  //        "MethodDescriptorSupplier"; vars["proto_class_name"] =
+  //        google::protobuf::compiler::java::ClassName(service->file());
+  //        p->Print(
+  //                 vars,
+  //                 "private static abstract class
+  //                 $proto_base_descriptor_supplier$\n" "    implements
+  //                 $ProtoFileDescriptorSupplier$,
+  //                 $ProtoServiceDescriptorSupplier$ {\n" "
+  //                 $proto_base_descriptor_supplier$() {}\n"
+  //                 "\n"
+  //                 "  @$Override$\n"
+  //                 "  public com.google.protobuf.Descriptors.FileDescriptor
+  //                 getFileDescriptor() {\n" "    return
+  //                 $proto_class_name$.getDescriptor();\n" "  }\n"
+  //                 "\n"
+  //                 "  @$Override$\n"
+  //                 "  public com.google.protobuf.Descriptors.ServiceDescriptor
+  //                 getServiceDescriptor() {\n" "    return
+  //                 getFileDescriptor().findServiceByName(\"$service_name$\");\n"
+  //                 "  }\n"
+  //                 "}\n"
+  //                 "\n"
+  //                 "private static final class
+  //                 $proto_file_descriptor_supplier$\n" "    extends
+  //                 $proto_base_descriptor_supplier$ {\n" "
+  //                 $proto_file_descriptor_supplier$() {}\n"
+  //                 "}\n"
+  //                 "\n"
+  //                 "private static final class
+  //                 $proto_method_descriptor_supplier$\n" "    extends
+  //                 $proto_base_descriptor_supplier$\n" "    implements
+  //                 $ProtoMethodDescriptorSupplier$ {\n" "  private final
+  //                 String methodName;\n"
+  //                 "\n"
+  //                 "  $proto_method_descriptor_supplier$(String methodName)
+  //                 {\n" "    this.methodName = methodName;\n" "  }\n"
+  //                 "\n"
+  //                 "  @$Override$\n"
+  //                 "  public com.google.protobuf.Descriptors.MethodDescriptor
+  //                 getMethodDescriptor() {\n" "    return
+  //                 getServiceDescriptor().findMethodByName(methodName);\n" "
+  //                 }\n"
+  //                 "}\n\n");
+
+  p->Print(
+      vars,
+      "private static volatile $ServiceDescriptor$ serviceDescriptor;\n\n");
+
+  p->Print(vars,
+           "public static $ServiceDescriptor$ getServiceDescriptor() {\n");
+  p->Indent();
+  p->Print(vars, "$ServiceDescriptor$ result = serviceDescriptor;\n");
+  p->Print("if (result == null) {\n");
+  p->Indent();
+  p->Print(vars, "synchronized ($service_class_name$.class) {\n");
+  p->Indent();
+  p->Print("result = serviceDescriptor;\n");
+  p->Print("if (result == null) {\n");
+  p->Indent();
+
+  p->Print(vars,
+           "serviceDescriptor = result = "
+           "$ServiceDescriptor$.newBuilder(SERVICE_NAME)");
+  p->Indent();
+  p->Indent();
+  p->Print(vars, "\n.setSchemaDescriptor(null)");
+  for (int i = 0; i < service->method_count(); ++i) {
+    auto method = service->method(i);
+    vars["method_method_name"] = MethodPropertiesGetterName(&*method);
+    p->Print(vars, "\n.addMethod($method_method_name$())");
+  }
+  p->Print("\n.build();\n");
+  p->Outdent();
+  p->Outdent();
+
+  p->Outdent();
+  p->Print("}\n");
+  p->Outdent();
+  p->Print("}\n");
+  p->Outdent();
+  p->Print("}\n");
+  p->Print("return result;\n");
+  p->Outdent();
+  p->Print("}\n");
+}
+
+static void PrintBindServiceMethodBody(Printer* p, VARS& vars,
+                                       const ServiceDescriptor* service) {
+  vars["service_name"] = service->name();
+  p->Indent();
+  p->Print(vars,
+           "return "
+           "$ServerServiceDefinition$.builder(getServiceDescriptor())\n");
+  p->Indent();
+  p->Indent();
+  for (int i = 0; i < service->method_count(); ++i) {
+    auto method = service->method(i);
+    vars["lower_method_name"] = LowerMethodName(&*method);
+    vars["method_method_name"] = MethodPropertiesGetterName(&*method);
+    vars["input_type"] = JavaClassName(vars, method->get_input_type_name());
+    vars["output_type"] = JavaClassName(vars, method->get_output_type_name());
+    vars["method_id_name"] = MethodIdFieldName(&*method);
+    bool client_streaming = method->ClientStreaming();
+    bool server_streaming = method->ServerStreaming();
+    if (client_streaming) {
+      if (server_streaming) {
+        vars["calls_method"] = "asyncBidiStreamingCall";
+      } else {
+        vars["calls_method"] = "asyncClientStreamingCall";
+      }
+    } else {
+      if (server_streaming) {
+        vars["calls_method"] = "asyncServerStreamingCall";
+      } else {
+        vars["calls_method"] = "asyncUnaryCall";
+      }
+    }
+    p->Print(vars, ".addMethod(\n");
+    p->Indent();
+    p->Print(vars,
+             "$method_method_name$(),\n"
+             "$calls_method$(\n");
+    p->Indent();
+    p->Print(vars,
+             "new MethodHandlers<\n"
+             "  $input_type$,\n"
+             "  $output_type$>(\n"
+             "    $instance$, $method_id_name$)))\n");
+    p->Outdent();
+    p->Outdent();
+  }
+  p->Print(".build();\n");
+  p->Outdent();
+  p->Outdent();
+  p->Outdent();
+}
+
+static void PrintService(Printer* p, VARS& vars,
+                         const ServiceDescriptor* service,
+                         bool disable_version) {
+  vars["service_name"] = service->name();
+  vars["service_class_name"] = ServiceClassName(service->name());
+  vars["grpc_version"] = "";
+#ifdef GRPC_VERSION
+  if (!disable_version) {
+    vars["grpc_version"] = " (version " XSTR(GRPC_VERSION) ")";
+  }
+#else
+  (void)disable_version;
+#endif
+  // TODO(nmittler): Replace with WriteServiceDocComment once included by
+  // protobuf distro.
+  GrpcWriteServiceDocComment(p, vars, service);
+  p->Print(vars,
+           "@$Generated$(\n"
+           "    value = \"by gRPC proto compiler$grpc_version$\",\n"
+           "    comments = \"Source: $file_name$.fbs\")\n"
+           "public final class $service_class_name$ {\n\n");
+  p->Indent();
+  p->Print(vars, "private $service_class_name$() {}\n\n");
+
+  p->Print(vars,
+           "public static final String SERVICE_NAME = "
+           "\"$Package$$service_name$\";\n\n");
+
+  PrintMethodFields(p, vars, service);
+
+  // TODO(nmittler): Replace with WriteDocComment once included by protobuf
+  // distro.
+  GrpcWriteDocComment(
+      p, vars,
+      " Creates a new async stub that supports all call types for the service");
+  p->Print(vars,
+           "public static $service_name$Stub newStub($Channel$ channel) {\n");
+  p->Indent();
+  p->Print(vars, "return new $service_name$Stub(channel);\n");
+  p->Outdent();
+  p->Print("}\n\n");
+
+  // TODO(nmittler): Replace with WriteDocComment once included by protobuf
+  // distro.
+  GrpcWriteDocComment(
+      p, vars,
+      " Creates a new blocking-style stub that supports unary and streaming "
+      "output calls on the service");
+  p->Print(vars,
+           "public static $service_name$BlockingStub newBlockingStub(\n"
+           "    $Channel$ channel) {\n");
+  p->Indent();
+  p->Print(vars, "return new $service_name$BlockingStub(channel);\n");
+  p->Outdent();
+  p->Print("}\n\n");
+
+  // TODO(nmittler): Replace with WriteDocComment once included by protobuf
+  // distro.
+  GrpcWriteDocComment(
+      p, vars,
+      " Creates a new ListenableFuture-style stub that supports unary calls "
+      "on the service");
+  p->Print(vars,
+           "public static $service_name$FutureStub newFutureStub(\n"
+           "    $Channel$ channel) {\n");
+  p->Indent();
+  p->Print(vars, "return new $service_name$FutureStub(channel);\n");
+  p->Outdent();
+  p->Print("}\n\n");
+
+  PrintStub(p, vars, service, ABSTRACT_CLASS);
+  PrintStub(p, vars, service, ASYNC_CLIENT_IMPL);
+  PrintStub(p, vars, service, BLOCKING_CLIENT_IMPL);
+  PrintStub(p, vars, service, FUTURE_CLIENT_IMPL);
+
+  PrintMethodHandlerClass(p, vars, service);
+  PrintGetServiceDescriptorMethod(p, vars, service);
+  p->Outdent();
+  p->Print("}\n");
+}
+
+void PrintStaticImports(Printer* p) {
+  p->Print(
+      "import java.nio.ByteBuffer;\n"
+      "import static "
+      "io.grpc.MethodDescriptor.generateFullMethodName;\n"
+      "import static "
+      "io.grpc.stub.ClientCalls.asyncBidiStreamingCall;\n"
+      "import static "
+      "io.grpc.stub.ClientCalls.asyncClientStreamingCall;\n"
+      "import static "
+      "io.grpc.stub.ClientCalls.asyncServerStreamingCall;\n"
+      "import static "
+      "io.grpc.stub.ClientCalls.asyncUnaryCall;\n"
+      "import static "
+      "io.grpc.stub.ClientCalls.blockingServerStreamingCall;\n"
+      "import static "
+      "io.grpc.stub.ClientCalls.blockingUnaryCall;\n"
+      "import static "
+      "io.grpc.stub.ClientCalls.futureUnaryCall;\n"
+      "import static "
+      "io.grpc.stub.ServerCalls.asyncBidiStreamingCall;\n"
+      "import static "
+      "io.grpc.stub.ServerCalls.asyncClientStreamingCall;\n"
+      "import static "
+      "io.grpc.stub.ServerCalls.asyncServerStreamingCall;\n"
+      "import static "
+      "io.grpc.stub.ServerCalls.asyncUnaryCall;\n"
+      "import static "
+      "io.grpc.stub.ServerCalls.asyncUnimplementedStreamingCall;\n"
+      "import static "
+      "io.grpc.stub.ServerCalls.asyncUnimplementedUnaryCall;\n\n");
+}
+
+void GenerateService(const grpc_generator::Service* service,
+                     grpc_generator::Printer* printer, VARS& vars,
+                     bool disable_version) {
+  // All non-generated classes must be referred by fully qualified names to
+  // avoid collision with generated classes.
+  vars["String"] = "java.lang.String";
+  vars["Deprecated"] = "java.lang.Deprecated";
+  vars["Override"] = "java.lang.Override";
+  vars["Channel"] = "io.grpc.Channel";
+  vars["CallOptions"] = "io.grpc.CallOptions";
+  vars["MethodType"] = "io.grpc.MethodDescriptor.MethodType";
+  vars["ServerMethodDefinition"] = "io.grpc.ServerMethodDefinition";
+  vars["BindableService"] = "io.grpc.BindableService";
+  vars["ServerServiceDefinition"] = "io.grpc.ServerServiceDefinition";
+  vars["ServiceDescriptor"] = "io.grpc.ServiceDescriptor";
+  vars["ProtoFileDescriptorSupplier"] =
+      "io.grpc.protobuf.ProtoFileDescriptorSupplier";
+  vars["ProtoServiceDescriptorSupplier"] =
+      "io.grpc.protobuf.ProtoServiceDescriptorSupplier";
+  vars["ProtoMethodDescriptorSupplier"] =
+      "io.grpc.protobuf.ProtoMethodDescriptorSupplier";
+  vars["AbstractStub"] = "io.grpc.stub.AbstractStub";
+  vars["MethodDescriptor"] = "io.grpc.MethodDescriptor";
+  vars["NanoUtils"] = "io.grpc.protobuf.nano.NanoUtils";
+  vars["StreamObserver"] = "io.grpc.stub.StreamObserver";
+  vars["Iterator"] = "java.util.Iterator";
+  vars["Generated"] = "javax.annotation.Generated";
+  vars["ListenableFuture"] =
+      "com.google.common.util.concurrent.ListenableFuture";
+  vars["ExperimentalApi"] = "io.grpc.ExperimentalApi";
+
+  PrintStaticImports(printer);
+
+  PrintService(printer, vars, service, disable_version);
+}
+
+grpc::string GenerateServiceSource(
+    grpc_generator::File* file, const grpc_generator::Service* service,
+    grpc_java_generator::Parameters* parameters) {
+  grpc::string out;
+  auto printer = file->CreatePrinter(&out);
+  VARS vars;
+  vars["flatc_version"] = grpc::string(
+      FLATBUFFERS_STRING(FLATBUFFERS_VERSION_MAJOR) "." FLATBUFFERS_STRING(
+          FLATBUFFERS_VERSION_MINOR) "." FLATBUFFERS_STRING(FLATBUFFERS_VERSION_REVISION));
+
+  vars["file_name"] = file->filename();
+
+  if (!parameters->package_name.empty()) {
+    vars["Package"] = parameters->package_name;  // ServiceJavaPackage(service);
+  }
+  GenerateImports(file, &*printer, vars);
+  GenerateService(service, &*printer, vars, false);
+  return out;
+}
+
+}  // namespace grpc_java_generator

grpc/src/compiler/java_generator.h

+/*
+ * Copyright 2016 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef NET_GRPC_COMPILER_JAVA_GENERATOR_H_
+#define NET_GRPC_COMPILER_JAVA_GENERATOR_H_
+
+#include <stdlib.h>  // for abort()
+#include <iostream>
+#include <map>
+#include <string>
+
+#include "src/compiler/schema_interface.h"
+
+class LogMessageVoidify {
+ public:
+  LogMessageVoidify() {}
+  // This has to be an operator with a precedence lower than << but
+  // higher than ?:
+  void operator&(std::ostream&) {}
+};
+
+class LogHelper {
+  std::ostream* os_;
+
+ public:
+  LogHelper(std::ostream* os) : os_(os) {}
+#if defined(_MSC_VER)
+#pragma warning(push)
+#pragma warning( \
+    disable : 4722)  // the flow of control terminates in a destructor
+  // (needed to compile ~LogHelper where destructor emits abort intentionally -
+  // inherited from grpc/java code generator).
+#endif
+  ~LogHelper() {
+    *os_ << std::endl;
+    ::abort();
+  }
+#if defined(_MSC_VER)
+#pragma warning(pop)
+#endif
+  std::ostream& get_os() const { return *os_; }
+};
+
+// Abort the program after logging the mesage if the given condition is not
+// true. Otherwise, do nothing.
+#define GRPC_CODEGEN_CHECK(x)                                            \
+  (x) ? (void)0                                                          \
+      : LogMessageVoidify() & LogHelper(&std::cerr).get_os()             \
+                                  << "CHECK FAILED: " << __FILE__ << ":" \
+                                  << __LINE__ << ": "
+
+// Abort the program after logging the mesage.
+#define GRPC_CODEGEN_FAIL GRPC_CODEGEN_CHECK(false)
+
+using namespace std;
+
+namespace grpc_java_generator {
+struct Parameters {
+  //        //Defines the custom parameter types for methods
+  //        //eg: flatbuffers uses flatbuffers.Builder as input for the client
+  //        and output for the server grpc::string custom_method_io_type;
+
+  // Package name for the service
+  grpc::string package_name;
+};
+
+// Return the source of the generated service file.
+grpc::string GenerateServiceSource(grpc_generator::File* file,
+                                   const grpc_generator::Service* service,
+                                   grpc_java_generator::Parameters* parameters);
+
+}  // namespace grpc_java_generator
+
+#endif  // NET_GRPC_COMPILER_JAVA_GENERATOR_H_

include/flatbuffers/idl.h

@@ -346,6 +346,7 @@ struct RPCCall {
   std::string name;
   SymbolTable<Value> attributes;
   StructDef *request, *response;
+  std::vector<std::string> rpc_comment;
 };
 
 struct ServiceDef : public Definition {
@@ -843,6 +844,12 @@ bool GenerateCppGRPC(const Parser &parser,
 bool GenerateGoGRPC(const Parser &parser,
                     const std::string &path,
                     const std::string &file_name);
+    
+// Generate GRPC Java classes.
+// See idl_gen_grpc.cpp
+bool GenerateJavaGRPC(const Parser &parser,
+                      const std::string &path,
+                      const std::string &file_name);
 
 }  // namespace flatbuffers
 

src/flatc.cpp

@@ -18,7 +18,8 @@
 
 #include <list>
 
-#define FLATC_VERSION "1.8.0 (" __DATE__ ")"
+#define FLATC_VERSION "1.8.0 (" __DATE__ " " __TIME__ ")"
+
 
 namespace flatbuffers {
 

src/flatc_main.cpp

@@ -67,7 +67,7 @@ int main(int argc, const char *argv[]) {
       "Generate Go files for tables/structs",
       flatbuffers::GeneralMakeRule },
     { flatbuffers::GenerateGeneral,  "-j", "--java", "Java", true,
-      nullptr,
+      flatbuffers::GenerateJavaGRPC,
       flatbuffers::IDLOptions::kJava,
       "Generate Java classes for tables/structs",
       flatbuffers::GeneralMakeRule },

src/idl_gen_grpc.cpp

@@ -23,6 +23,7 @@
 
 #include "src/compiler/cpp_generator.h"
 #include "src/compiler/go_generator.h"
+#include "src/compiler/java_generator.h"
 
 #if defined(_MSC_VER)
 #pragma warning(push)
@@ -53,7 +54,7 @@ class FlatBufMethod : public grpc_generator::Method {
     return "";
   }
   std::vector<grpc::string> GetAllComments() const {
-    return std::vector<grpc::string>();
+    return method_->rpc_comment;
   }
 
   std::string name() const { return method_->name; }
@@ -110,7 +111,7 @@ class FlatBufService : public grpc_generator::Service {
     return "";
   }
   std::vector<grpc::string> GetAllComments() const {
-    return std::vector<grpc::string>();
+    return service_->doc_comment;
   }
 
   std::string name() const { return service_->name; }
@@ -187,7 +188,8 @@ class FlatBufFile : public grpc_generator::File {
  public:
   enum Language {
     kLanguageGo,
-    kLanguageCpp
+    kLanguageCpp,
+    kLanguageJava
   };
 
   FlatBufFile(
@@ -229,6 +231,9 @@ class FlatBufFile : public grpc_generator::File {
       case kLanguageGo: {
         return "import \"github.com/google/flatbuffers/go\"";
       }
+      case kLanguageJava: {
+        return "import com.google.flatbuffers.grpc.FlatbuffersUtils;";
+      }
     }
     return "";
   }
@@ -328,9 +333,50 @@ bool GenerateCppGRPC(const Parser &parser,
                                source_code, false);
 }
 
+class JavaGRPCGenerator : public flatbuffers::BaseGenerator {
+ public:
+  JavaGRPCGenerator(const Parser& parser, const std::string& path,
+                    const std::string& file_name)
+      : BaseGenerator(parser, path, file_name, "", "." /*separator*/),
+        parser_(parser),
+        path_(path),
+        file_name_(file_name) {}
+
+  bool generate() {
+    FlatBufFile file(parser_, file_name_, FlatBufFile::kLanguageJava);
+    grpc_java_generator::Parameters p;
+    for (int i = 0; i < file.service_count(); i++) {
+      auto service = file.service(i);
+      const Definition* def = parser_.services_.vec[i];
+      p.package_name =
+          def->defined_namespace->GetFullyQualifiedName("");  // file.package();
+      std::string output =
+          grpc_java_generator::GenerateServiceSource(&file, service.get(), &p);
+      std::string filename =
+          NamespaceDir(*def->defined_namespace) + def->name + "Grpc.java";
+      if (!flatbuffers::SaveFile(filename.c_str(), output, false)) return false;
+    }
+    return true;
+  }
+
+ protected:
+  const Parser& parser_;
+  const std::string &path_, &file_name_;
+};
+
+bool GenerateJavaGRPC(const Parser& parser, const std::string& path,
+                      const std::string& file_name) {
+  int nservices = 0;
+  for (auto it = parser.services_.vec.begin(); it != parser.services_.vec.end();
+       ++it) {
+    if (!(*it)->generated) nservices++;
+  }
+  if (!nservices) return true;
+  return JavaGRPCGenerator(parser, path, file_name).generate();
+}
+
 }  // namespace flatbuffers
 
 #if defined(_MSC_VER)
 #pragma warning(pop)
 #endif
-

src/idl_parser.cpp

@@ -1645,6 +1645,7 @@ CheckedError Parser::ParseService() {
   ECHECK(ParseMetaData(&service_def.attributes));
   EXPECT('{');
   do {
+    std::vector<std::string> rpc_comment = doc_comment_;
     auto rpc_name = attribute_;
     EXPECT(kTokenIdentifier);
     EXPECT('(');
@@ -1660,6 +1661,7 @@ CheckedError Parser::ParseService() {
     rpc.name = rpc_name;
     rpc.request = reqtype.struct_def;
     rpc.response = resptype.struct_def;
+    rpc.rpc_comment = rpc_comment;
     if (service_def.calls.Add(rpc_name, &rpc))
       return Error("rpc already exists: " + rpc_name);
     ECHECK(ParseMetaData(&rpc.attributes));