Protocol Buffers In Java

Protocol buffers are a flexible, efficient, automated mechanism for serializing structured data

Define how you want your data to be structured 

Use special generated source code to easily write and read structured data to and from a variety of data streams . 

Data serializing format defining protocol buffer in .proto file

protocol buffer is small logical record & contain key-val pair and a uniquely number :

a example is following 

package tutorial;

option java_package = "com.example.tutorial";
option java_outer_classname = "AddressBookProtos";

message Person {
  required string name = 1;
  required int32 id = 2;
  optional string email = 3;

  enum PhoneType {
    MOBILE = 0;
    HOME = 1;
    WORK = 2;
  }

  message PhoneNumber {
    required string number = 1;
    optional PhoneType type = 2 [default = HOME];
  }

  repeated PhoneNumber phone = 4;
}

message AddressBook {
  repeated Person person = 1;
}

Once defined .proto format file and could user proto compiler to generate java classes 

ProtoBuf Data Type:

Protocol Buffers fields as one of following:

• required: a well-formed message must have exactly one of this field.

• optional: a well-formed message can have zero or one of this field (but not more than one). 

• repeated: this field can be repeated any number of times (including zero) in a well-formed message. 

Comments should use C-style // syntax.

Compiler  generates a .java source file , special Builder Class to Create Message Instance

Code Style :

Use CamelCase for message names 

Use underscore_separated_names for field names

Use CamelCase for enum type names and CAPITALS_WITH_UNDERSCORES for value names

use CamelCase for both the service name and any RPC method names

Protocol Buffers Compiler Command 

protobuf   protoc --help
Usage: protoc [OPTION] PROTO_FILES
Parse PROTO_FILES and generate output based on the options given:
  -IPATH, --proto_path=PATH   Specify the directory in which to search for
                              imports.  May be specified multiple times;
                              directories will be searched in order.  If not
                              given, the current working directory is used.
  --version                   Show version info and exit.
  -h, --help                  Show this text and exit.
  --encode=MESSAGE_TYPE       Read a text-format message of the given type
                              from standard input and write it in binary
                              to standard output.  The message type must
                              be defined in PROTO_FILES or their imports.
  --decode=MESSAGE_TYPE       Read a binary message of the given type from
                              standard input and write it in text format
                              to standard output.  The message type must
                              be defined in PROTO_FILES or their imports.
  --decode_raw                Read an arbitrary protocol message from
                              standard input and write the raw tag/value
                              pairs in text format to standard output.  No
                              PROTO_FILES should be given when using this
                              flag.
  -oFILE,                     Writes a FileDescriptorSet (a protocol buffer,
    --descriptor_set_out=FILE defined in descriptor.proto) containing all of
                              the input files to FILE.
  --include_imports           When using --descriptor_set_out, also include
                              all dependencies of the input files in the
                              set, so that the set is self-contained.
  --include_source_info       When using --descriptor_set_out, do not strip
                              SourceCodeInfo from the FileDescriptorProto.
                              This results in vastly larger descriptors that
                              include information about the original
                              location of each decl in the source file as
                              well as surrounding comments.
  --error_format=FORMAT       Set the format in which to print errors.
                              FORMAT may be 'gcc' (the default) or 'msvs'
                              (Microsoft Visual Studio format).
  --plugin=EXECUTABLE         Specifies a plugin executable to use.
                              Normally, protoc searches the PATH for
                              plugins, but you may specify additional
                              executables not in the path using this flag.
                              Additionally, EXECUTABLE may be of the form
                              NAME=PATH, in which case the given plugin name
                              is mapped to the given executable even if
                              the executable's own name differs.
  --cpp_out=OUT_DIR           Generate C++ header and source.
  --java_out=OUT_DIR          Generate Java source file.
  --python_out=OUT_DIR        Generate Python source file.

Java Code Example:

package com.example.tutorial;

import com.example.tutorial.AddressBookProtos.AddressBook;
import com.example.tutorial.AddressBookProtos.Person;
import com.example.tutorial.AddressBookProtos.Person.PhoneNumber;
import com.example.tutorial.AddressBookProtos.Person.PhoneType;

public class Examples {
	public static void main(String[] args) {
		AddressBook.Builder addressBookBuilder = AddressBook.newBuilder();
		Person.Builder personBuilder = Person.newBuilder();
		PhoneNumber.Builder phoneBuilder = PhoneNumber.newBuilder();
		phoneBuilder.setNumber("13728369472");
		phoneBuilder.setType(PhoneType.WORK);

		personBuilder.setName("darion");
		personBuilder.setId(0);
		personBuilder.setEmail("darion.yaphet@gmail.com");
		personBuilder.setPhone(0, phoneBuilder);

		addressBookBuilder.setPerson(0, personBuilder);
	}
}

Java RPC Service Examples: 

Protocol Buffer as Following :

package echo;

message EchoRequest
{
  required string message = 1;
};

message EchoResponse
{
  required string response = 1;
};

service EchoService
{
  rpc Echo(EchoRequest) returns (EchoResponse);
};

參考文獻：

https://developers.google.com/protocol-buffers/