
- FlatBuffers 教程
- FlatBuffers - 首页
- FlatBuffers - 简介
- FlatBuffers - Schema
- FlatBuffers - 结构
- FlatBuffers - 表格
- FlatBuffers - 字符串
- FlatBuffers - 数字
- FlatBuffers - 布尔值
- FlatBuffers - 枚举
- FlatBuffers - 向量
- FlatBuffers - 结构体
- FlatBuffers - 联合体
- FlatBuffers - 嵌套表格
- FlatBuffers - 默认值
- FlatBuffers - JSON 转二进制
- FlatBuffers - 二进制转 JSON
- FlatBuffers - 可变缓冲区
- FlatBuffers - 向后兼容性
- FlatBuffers - 语言无关性
- FlatBuffers 有用资源
- FlatBuffers - 快速指南
- FlatBuffers - 有用资源
- FlatBuffers - 讨论
FlatBuffers - 向量
概述
向量数据类型是FlatBuffers的复合数据类型之一。它等同于我们使用的语言(例如Java等)中的数组或列表。
继续我们从FlatBuffers - 字符串章节的剧院示例,以下是我们需要使用的语法,以指示FlatBuffers我们将创建一个向量:
theater.fbs
namespace com.tutorialspoint.theater; table Theater { snacks:[string]; // vector of strings tickets:[float]; // vector of floats } root_type Theater;
现在我们的表格包含字符串和浮点数的向量属性。
从fbs文件创建Java类
要使用FlatBuffers,我们现在必须使用flatc二进制文件从此“.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FlatBuffers - Schema章节中所做的。
使用从fbs文件创建的Java类
创建和写入向量
为了创建一个向量,我们需要首先准备标量类型数组的偏移量,然后我们可以将向量添加到flat buffer中。
// create data for an array of strings int popcorn = builder.createString("Popcorn"); int coke = builder.createString("Coke"); int chips = builder.createString("Chips"); int soda = builder.createString("Soda"); // create array for snacks int[] snacks = {popcorn, coke, chips, soda}; // create offset for snacks vector int snacksVector = Theater.createSnacksVector(builder, snacks); // add details to the Theater FlatBuffer Theater.addSnacks(builder, snacksVector);
以下示例代码显示了创建字符串和整数向量的过程。
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); // create data for an array of strings int popcorn = builder.createString("Popcorn"); int coke = builder.createString("Coke"); int chips = builder.createString("Chips"); int soda = builder.createString("Soda"); // create array for snacks int[] snacks = {popcorn, coke, chips, soda}; // create array for tickets float[] tickets = {100.0f, 100.f, 200.f}; // create offset for snacks vector int snacksVector = Theater.createSnacksVector(builder, snacks); // create offset for tickets vector int ticketsVector = Theater.createTicketsVector(builder, tickets); // create theater FlatBuffers using startTheater() method Theater.startTheater(builder); // add details to the Theater FlatBuffer Theater.addSnacks(builder, snacksVector); Theater.addTickets(builder, ticketsVector); // 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); } }
读取向量
为了读取向量,我们有方法来获取向量的长度和通过索引获取条目,如下所示。
// iterate snacks vector of length determined by snacksLength() method for(int i = 0; i < theater.snacksLength(); i++ ) { // get a snack by its index System.out.print(" " + theater.snacks(i)); }
以下示例代码显示了读取字符串和整数向量的过程。
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("Snacks: "); for(int i = 0; i < theater.snacksLength(); i++ ) { System.out.print(" " + theater.snacks(i)); } System.out.println("\nTickets: "); for(int i = 0; i < theater.ticketsLength(); i++ ) { System.out.print(" " + theater.tickets(i)); } } } }
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 information to file: theater_flatbuffers_output Saved theater information with following data to disk: 96
反序列化序列化的对象
现在,让我们执行读取器从同一文件读取:
java -cp .\target\flatbuffers-tutorial-1.0.jar com.tutorialspoint.theater.TheaterReader Reading from file theater_flatbuffers_output Snacks: Popcorn Coke Chips Soda Tickets: 100.0 100.0 200.0
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向量。在下一章FlatBuffers - 结构体中,我们将了解结构体,一种复合类型。
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