Protocol Buffers - 巢狀類

概述

在這裡，我們將瞭解如何建立巢狀類。Protobuf 將其轉換為巢狀的Java類。

繼續我們從Protocol Buffers - 字串章節開始的劇院示例，以下是我們需要使用的語法，以指示 Protobuf 我們將建立一個重複的 -

theater.proto

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

message Theater {
   TheaterOwner owner = 10;
}
message TheaterOwner{
   string name = 1;
   string address = 2;
}

現在我們的訊息類包含一個巢狀類，即關於劇院所有者資訊。

從 Proto 檔案建立 Java 類

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，類似於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

TheaterWriter.java

package com.tutorialspoint.theater;

import java.io.FileOutputStream;
import java.io.IOException;

import com.tutorialspoint.theater.TheaterOuterClass.Theater;
import com.tutorialspoint.theater.TheaterOuterClass.TheaterOwner;

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();
	    
      Theater theater = Theater.newBuilder()
         .setOwner(owner)
         .build();
		
      String filename = "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);
   }
}

接下來，我們將有一個讀取器來讀取劇院資訊 -

TheaterReader.java

package com.tutorialspoint.theater;

import java.io.FileInputStream;
import java.io.IOException;

import com.tutorialspoint.theater.TheaterOuterClass.Theater;
import com.tutorialspoint.theater.TheaterOuterClass.Theater.Builder;

public class TheaterReader{
   public static void main(String[] args) throws IOException {
      Builder theaterBuilder = Theater.newBuilder();

      String filename = "theater_protobuf_output";
      System.out.println("Reading from file " + filename);
        
      try(FileInputStream input = new FileInputStream(filename)) {
         Theater theater = theaterBuilder.mergeFrom(input).build();
         System.out.println(theater);
      }
   }
}

編譯專案

現在我們已經設定了讀取器和寫入器，讓我們編譯專案。

mvn clean install

序列化 Java 物件

現在，編譯後，讓我們先執行寫入器 -

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

Saving theater information to file: theater_protobuf_output
Saved theater information with following data to disk:
owner {
   name: "Anthony Gonsalves"
   address: "513, St Paul Street, West Coast, California"
}

反序列化序列化物件

現在，讓我們執行讀取器以從同一檔案讀取 -

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

Reading from file theater_protobuf_output
owner {
   name: "Anthony Gonsalves"
   address: "513, St Paul Street, West Coast, California"
}

因此，正如我們所看到的，我們能夠透過將二進位制資料反序列化為劇院物件來讀取序列化的巢狀類。