Protocol Buffers - Numbers

Overview

Numbers include protobuf types like int32, int64, float, double, which are basic building blocks of Protobuf. It translates to int, long float, double, respectively, in the languages that we use, for example, Java, Python, etc.

Continuing with our theater example from Protocol Buffers - String chapter, following is the syntax that we need to have to instruct Protobuf that we will be creating numbers −

theater.proto

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

message Theater {
   int32 total_capcity = 3;
   int64 mobile = 4;
   float base_ticket_price = 5;
}

Now our class/message contains numerical attributes. Each of them also has a position which is what Protobuf uses while serialization and deserialization. Each attribute of a member needs to have a unique number assigned.

Creating Java Classes from Proto File

To use Protobuf, we will now have to use protoc binary to create the required classes from this ".proto" file. Let us see how to do that −

protoc  --java_out=. theater.proto

This will create a TheaterOuterClass.java class in com > tutorialspoint > theater folder in current directory. We're using this class in our application similar to as done in Protocol Buffers - Basic App chapter.

Using Java Classes created from Proto File

TheaterWriter.java

package com.tutorialspoint.theater;

import java.io.FileOutputStream;
import java.io.IOException;
import com.tutorialspoint.theater.TheaterOuterClass.Theater;

public class TheaterWriter{
   public static void main(String[] args) throws IOException {
      Theater theater = Theater.newBuilder()
         .setTotalCapcity(320)
         .setMobile(98234567189L)
         .setBaseTicketPrice(22.45f)
         .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);
   }
}

Next, we will have a reader to read the theater information −

TheaterReader.java

package com.tutorialspoint.theater;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import com.tutorialspoint.greeting.Greeting.Greet;
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.getBaseTicketPrice());
         System.out.println(theater);
      }
   }
}

Compile the project

Now that we have set up the reader and the writer, let us compile the project.

mvn clean install

Serialize the Java Object

Now, post compilation, let us execute the writer first −

> 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:
total_capcity: 320
mobile: 98234567189
base_ticket_price: 22.45

Deserialize the Serialized Object

Now, let us execute the reader to read from the same file −

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

Reading from file theater_protobuf_output
22.45
total_capcity: 320
mobile: 98234567189
base_ticket_price: 22.45

So, as we see, we are able to read the serialized int, float, and long by deserializing the binary data to Theater object. In the next chapter Protocol Buffers - bool , we will look at the Boolean type.