Flat Buffers - 数字



概述

数字包括 flatbuffers 类型,例如 **int、short、float、double**,它们是 Flat Buffers 的基本构建块。它分别翻译为我们使用的语言(例如 Java、Python 等)中的 **int、short float、double**。

继续我们从 Flat Buffers - 字符串 章节中的 **theater** 示例,以下是我们需要使用的语法,以便指示 Flat Buffers 我们将创建 **数字** −

theater.fbs

namespace com.tutorialspoint.theater;

table Theater {
   total_capcity:int;
   mobile:long;
   base_ticket_price:float;
}
root_type Theater;

现在我们的 **表格** 包含 **数值** 属性。默认值为 0 或 0.0(视情况而定)。

从 FBS 文件创建 Java 类

要使用 Flat Buffers,我们现在必须使用 **flatc** 二进制文件从这个“.fbs”文件创建所需的类。让我们看看如何做到这一点 −

flatc  --java theater.fbs

这将在当前目录中的 **com > tutorialspoint > theater** 文件夹中创建一个 Theater.java 类。我们类似于在 Flat Buffers - 模式 章节中所做的那样,在我们的应用程序中使用此类。

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使用从 fbs 文件创建的 Java 类

首先让我们创建一个 **写入器** 来写入 **theater** 信息 −

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 totalCapacity = 320; 
      long mobile = 98234567189L;
      float baseTicketPrice = 22.45f;

      // create theater FlatBuffers using startTheater() method
      Theater.startTheater(builder);
      // add details to the Theater FlatBuffer
      Theater.addTotalCapcity(builder, totalCapacity);
      Theater.addMobile(builder, mobile);
      Theater.addBaseTicketPrice(builder, baseTicketPrice);

      // 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);
   }
}	

接下来,我们将有一个 **读取器** 来读取 **theater** 信息 −

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("Total Capacity: " + theater.totalCapcity() 
            + "\n" + "Mobile: " + theater.mobile()
            + "\n" + "Base Ticket Price: " + theater.baseTicketPrice());
      }
   }
}

编译项目

现在我们已经设置了 **读取器** 和 **写入器**,让我们编译项目。

mvn clean install

序列化 Java 对象

现在,编译后,让我们首先执行 **写入器** −

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:
24

反序列化序列化对象

现在,让我们执行 **读取器** 以从同一文件读取 −

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

Reading from file theater_flatbuffers_output
Total Capacity: 320
Mobile: 98234567189
Base Ticket Price: 22.45

因此,正如我们所看到的,我们能够通过将二进制数据反序列化为 **Theater** 对象来读取序列化的字符串。现在让我们在下一章 Flat Buffers - bool 中查看 **数字**。

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