FlatBuffers - 字串

概述

FlatBuffers 字串在使用的語言（例如 Java、Python 等）中轉換為字串。繼續以劇院為例，以下是指示 FlatBuffers 建立字串所需的語法：

theater.fbs

namespace com.tutorialspoint.theater;

table Theater {
   name:string;
   address:string;
}
root_type Theater;

現在我們的表格包含兩個字串屬性。每個屬性的預設值為 null。

從 fbs 檔案建立 Java 類

要使用 FlatBuffers，我們現在必須使用flatc二進位制檔案從這個“.fbs”檔案建立所需的類。讓我們看看如何操作：

flatc  --java theater.fbs

這將在當前目錄中的com > tutorialspoint > theater資料夾中建立一個 Theater.java 類。我們在應用程式中使用此類，類似於Flat Buffers - Schema章節中所做的那樣。

使用從 fbs 檔案建立的 Java 類

首先，讓我們建立一個寫入器來寫入劇院資訊：

TheaterWriter.java

package com.tutorialspoint.theater;

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

import com.google.flatbuffers.FlatBufferBuilder;

public class TheaterWriter {
   public static void main(String[] args) throws FileNotFoundException, IOException {
      // create a flat buffer builder
      // it will be used to create Theater FlatBuffer
      FlatBufferBuilder builder = new FlatBufferBuilder(1024);

      int name = builder.createString("Silver Screener");
      int address = builder.createString("212, Maple Street, LA, California");

      // create theater FlatBuffers using startTheater() method
      Theater.startTheater(builder);
      // add the name and address to the Theater FlatBuffer
      Theater.addName(builder, name);
      Theater.addAddress(builder, address);

      // mark end of data being entered in Greet FlatBuffer
      int theater = Theater.endTheater(builder);

      // finish the builder
      builder.finish(theater);

      // get the bytes to be stored
      byte[] data = builder.sizedByteArray();

      String filename = "theater_flatbuffers_output";
      System.out.println("Saving theater to file: " + filename);
      // write the builder content to the file named theater_flatbuffers_output
      try(FileOutputStream output = new FileOutputStream(filename)){
         output.write(data);
      }
      System.out.println("Saved theater 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.FileNotFoundException;
import java.io.IOException;
import java.nio.ByteBuffer;

public class TheaterReader {
   public static void main(String[] args) throws FileNotFoundException, IOException {

      String filename = "theater_flatbuffers_output";
      System.out.println("Reading from file " + filename);
      try(FileInputStream input = new FileInputStream(filename)) {
         // get the serialized data
         byte[] data = input.readAllBytes();
         ByteBuffer buf = ByteBuffer.wrap(data);
         // read the root object in serialized data
         Theater theater = Theater.getRootAsTheater(buf);
         // print theater values 
         System.out.println("Name: " + theater.name() + "\n" + "Address: " + theater.address());
      }
   }
}

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\flatbuffers-tutorial-1.0.jar com.tutorialspoint.theater.TheaterWriter

Saving theater to file: theater_flatbuffers_output
Saved theater with following data to disk:
72

反序列化已序列化的物件

現在，讓我們執行讀取器以從同一檔案讀取：

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

Reading from file theater_flatbuffers_output
Name: Silver Screener
Address: 212, Maple Street, LA, 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已序列化的字串。現在讓我們在下一章Flat Buffers - Numbers中檢視數字。