Protocol Buffers - 语言独立性

概述

到目前为止，我们一直在使用 Java 来序列化和反序列化电影院数据。但是，Google Protocol Buffers 提供的关键功能之一是“语言独立性”。在本章中，我们将了解如何使用 Java 进行序列化，并使用 Python 进行反序列化。

继续我们从Protocol Buffers - 字符串章节开始的theater示例，以下是我们需要使用的语法，以指示 Protobuf 我们将创建不同的数据类型：

theater.proto

syntax = "proto3";
package theater;
option java_package = "com.tutorialspoint.theater";

message Theater {
   string name = 1;
   string address = 2;
  
   int32 total_capcity = 3;
   int64 mobile = 4;
   float base_ticket_price = 5;
  
   bool drive_in = 6;
   
   enum PAYMENT_SYSTEM { 
      CASH = 0;
      CREDIT_CARD = 1;
      DEBIT_CARD = 2;
      APP = 3;
   }
   PAYMENT_SYSTEM payment = 7;
   repeated string snacks = 8;
   map<string, int32> movieTicketPrice = 9;
   TheaterOwner owner = 10;
}
message TheaterOwner{
   string name = 1;
   string address = 2;
}

使用 Java 进行序列化

要使用 Protobuf，我们现在必须使用protoc二进制文件从这个“.proto”文件创建所需的类。让我们看看如何做到这一点：

protoc  --java_out=. theater.proto

这将在当前目录的com > tutorialspoint > theater文件夹中创建一个TheaterOuterClass.java类。我们在应用程序中使用此类，就像在Protocol Buffers - 基本应用章节中所做的那样。

使用从 Proto 文件创建的 Java 类

首先，我们将创建一个写入器来写入剧院信息：

TheaterWriter.java

package com.tutorialspoint.theater;

import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.tutorialspoint.theater.TheaterOuterClass.Theater;
import com.tutorialspoint.theater.TheaterOuterClass.TheaterOwner;
import com.tutorialspoint.theater.TheaterOuterClass.Theater.PAYMENT_SYSTEM;

public class TheaterWriter {
   public static void main(String[] args) throws IOException {
      TheaterOwner owner = TheaterOwner.newBuilder()
         .setName("Anthony Gonsalves")
         .setAddress("513, St Paul Street, West Coast, California")
         .build();
	    
      List<String> snacks = new ArrayList<>();
      snacks.add("Popcorn");
      snacks.add("Coke");
      snacks.add("Chips");
      snacks.add("Soda");
	        
      Map<String, Integer> ticketPrice = new HashMap<>();
      ticketPrice.put("Avengers Endgame", 700);
      ticketPrice.put("Captain America", 200);
      ticketPrice.put("Wonder Woman 1984", 400);
	   
      Theater theater = Theater.newBuilder()
         .setName("Silver Screener")
         .setAddress("212, Maple Street, LA, California")
         .setDriveIn(true)
         .setTotalCapcity(320)
         .setMobile(98234567189L)
         .setBaseTicketPrice(22.45f)
         .setPayment(PAYMENT_SYSTEM.CREDIT_CARD)
         .putAllMovieTicketPrice(ticketPrice)
         .addAllSnacks(snacks)
         .setOwner(owner)
         .build();
		
      String filename = "E:/theater_protobuf_output";
      System.out.println("Saving theater information to file: " + filename);
		
      try(FileOutputStream output = new FileOutputStream(filename)){
         theater.writeTo(output);
      }
      System.out.println("Saved theater information with following data to disk: \n" + theater);
   }
}

让我们编译项目。

mvn clean install

序列化 Java 对象

现在，编译后，让我们执行writer：

> java -cp .\target\protobuf-tutorial-1.0.jar com.tutorialspoint.theater.TheaterWriter

Saving theater information to file: E:/theater_protobuf_output
Saved theater information with following data to disk:
name: "Silver Screener"
address: "212, Maple Street, LA, California"
total_capcity: 320
mobile: 98234567189
base_ticket_price: 22.45
drive_in: true
payment: CREDIT_CARD
snacks: "Popcorn"
snacks: "Coke"
snacks: "Chips"
snacks: "Soda"
movieTicketPrice {
   key: "Avengers Endgame"
   value: 700
}
movieTicketPrice {
   key: "Captain America"
   value: 200
}
movieTicketPrice {
   key: "Wonder Woman 1984"
   value: 400
}
owner {
   name: "Anthony Gonsalves"
   address: "513, St Paul Street, West Coast, California"
}

使用 Python 反序列化序列化对象

从 proto 文件生成 Python 类

让我们为 Theater 类生成 Python 代码：

protoc  --python_out=. theater.proto

执行此命令后，您会在当前目录中注意到一个自动生成的类theater_pb2.py。此类将帮助我们反序列化Theater对象。

使用生成的 Python 类

现在，让我们编写数据读取器，它将使用 Java 读取包含序列化对象的文件：

theaterReader.py

import theater_pb2

filename = "E:/theater_protobuf_output";
print("Reading from file: " + filename)

theater = theater_pb2.Theater()

f = open(filename, "rb")
theater.ParseFromString(f.read())
f.close()

print("Read theater from disk: \n" + str(theater))

然后，让我们执行reader。

python theaterReader.py

Reading from file: E:/greeting_protobuf_output
Read theater from disk:
name: "Silver Screener"
address: "212, Maple Street, LA, California"
total_capcity: 320
mobile: 98234567189
base_ticket_price: 22.45
drive_in: true
payment: CREDIT_CARD
snacks: "Popcorn"
snacks: "Coke"
snacks: "Chips"
snacks: "Soda"
movieTicketPrice {
  key: "Wonder Woman 1984"
  value: 400
}
movieTicketPrice {
  key: "Captain America"
  value: 200
}
movieTicketPrice {
  key: "Avengers Endgame"
  value: 700
}
owner {
  name: "Anthony Gonsalves"
  address: "513, St Paul Street, West Coast, California"
}

因此，正如我们所看到的，Java 客户端写入的所有值都被正确地反序列化并由我们的 Python 客户端读取，这有效地意味着 Protobuf 是语言独立的。