FlatBuffers - 字符串

概述

FlatBuffers 字符串在使用的语言（例如 Java、Python 等）中转换为字符串。继续以剧院为例，以下是指示 FlatBuffers 创建字符串所需的语法：

theater.fbs

namespace com.tutorialspoint.theater;

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

现在我们的表格包含两个字符串属性。每个属性的默认值为 null。

从 fbs 文件创建 Java 类

要使用 FlatBuffers，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。让我们看看如何操作：

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。我们在应用程序中使用此类，类似于Flat Buffers - Schema章节中所做的那样。

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剧院信息：

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 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);
   }
}

接下来，我们将有一个读取器来读取剧院信息：

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("Name: " + theater.name() + "\n" + "Address: " + theater.address());
      }
   }
}

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:
72

反序列化已序列化的对象

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
Name: Silver Screener
Address: 212, Maple Street, LA, California

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剧院对象来读取已序列化的字符串。现在让我们在下一章Flat Buffers - Numbers中查看数字。

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