Protocol Buffers - 語言獨立性

概述

到目前為止，我們一直在使用 Java 來序列化和反序列化電影院資料。但是，Google Protocol Buffers 提供的關鍵功能之一是“語言獨立性”。在本章中，我們將瞭解如何使用 Java 進行序列化，並使用 Python 進行反序列化。

繼續我們從Protocol Buffers - 字串章節開始的theater示例，以下是我們需要使用的語法，以指示 Protobuf 我們將建立不同的資料型別：

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 進行序列化

要使用 Protobuf，我們現在必須使用protoc二進位制檔案從這個“.proto”檔案建立所需的類。讓我們看看如何做到這一點：

protoc  --java_out=. theater.proto

這將在當前目錄的com > tutorialspoint > theater資料夾中建立一個TheaterOuterClass.java類。我們在應用程式中使用此類，就像在Protocol Buffers - 基本應用章節中所做的那樣。

使用從 Proto 檔案建立的 Java 類

首先，我們將建立一個寫入器來寫入劇院資訊：

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);
   }
}

讓我們編譯專案。

mvn clean install

序列化 Java 物件

現在，編譯後，讓我們執行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 反序列化序列化物件

從 proto 檔案生成 Python 類

讓我們為 Theater 類生成 Python 程式碼：

protoc  --python_out=. theater.proto

執行此命令後，您會在當前目錄中注意到一個自動生成的類theater_pb2.py。此類將幫助我們反序列化Theater物件。

使用生成的 Python 類

現在，讓我們編寫資料讀取器，它將使用 Java 讀取包含序列化物件的檔案：

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))

然後，讓我們執行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，正如我們所看到的，Java 客戶端寫入的所有值都被正確地反序列化並由我們的 Python 客戶端讀取，這有效地意味著 Protobuf 是語言獨立的。