Getting Started with Protocol Buffers: Serialize and Deserialize Objects in Java

Protocol Buffers overview

Protocol Buffers (protobuf) is a language‑independent, platform‑independent, extensible method for serializing structured data. Compared with XML, protobuf messages are 3–10 × smaller, 20–100 × faster to parse, and have a simpler syntax.

Defining a .proto file

A .proto file declares the data structures to be serialized. Each message type contains fields identified by unique numeric tags (e.g., =1). In protobuf 2 the keywords required and optional indicate mandatory or optional fields; protobuf 3 removes these keywords. Example of a simple Person message (protobuf 2 syntax):

message Person {
    required string name = 1;
    required int32 id = 2;
    optional string email = 3;
    enum PhoneType {
        MOBILE = 0;
        HOME = 1;
        WORK = 2;
    }
    message PhoneNumber {
        required string number = 1;
        optional PhoneType type = 2 [default = HOME];
    }
    repeated PhoneNumber phone = 4;
}

Compiling the .proto file

The protobuf compiler protoc translates a .proto file into language‑specific source files. The compiler can be downloaded from the official releases page:

https://github.com/protocolbuffers/protobuf/releases

After extracting the archive, add protoc.exe (or the platform binary) to the system PATH. Running protoc without arguments prints the usage message, confirming a successful installation.

Java project setup

Create a Gradle (or Maven) project and add the protobuf Java runtime libraries. Example build.gradle snippet (version 3.13.0):

dependencies {
    compile ([group: 'com.google.protobuf', name: 'protobuf-java', version: '3.13.0'],
             [group: 'com.google.protobuf', name: 'protobuf-java-util', version: '3.13.0'])
}

The dependencies are resolved from Maven Central.

Student.proto example

Place the schema file under src/main/protobuf with the following content:

syntax = "proto3";
package com.badao.protobuf;
option optimize_for = SPEED;
option java_package = "com.badao.protobuf";
option java_outer_classname = "DataInfo";

message Student {
    string name = 1;
    int32 age = 2;
    string address = 3;
}

The optimize_for = SPEED option generates code prioritising runtime speed (at the cost of larger binary size). java_package sets the generated Java package, and java_outer_classname defines the outer class name ( DataInfo).

Generating Java classes

From the project’s terminal run:

protoc --java_out=src/main/java src/main/protobuf/Student.proto

The command creates DataInfo.java containing the nested class Student in the directory src/main/java/com/badao/protobuf.

Serialization and deserialization

Example Java program that builds a Student instance, serializes it to a byte array, and parses it back:

package com.badao.protobuf;

import com.google.protobuf.InvalidProtocolBufferException;

public class ProtobufTest {
    public static void main(String[] args) throws InvalidProtocolBufferException {
        DataInfo.Student student = DataInfo.Student.newBuilder()
                .setName("公众号:霸道的程序猿")
                .setAge(100)
                .setAddress("中国")
                .build();
        byte[] bytes = student.toByteArray();
        DataInfo.Student student1 = DataInfo.Student.parseFrom(bytes);
        System.out.println(student1.getName());
        System.out.println(student1.getAge());
        System.out.println(student1.getAddress());
    }
}

The builder pattern is required to set fields. toByteArray() produces the protobuf binary representation; parseFrom reconstructs the object from the byte array. Running the program prints the original field values, confirming successful round‑trip serialization.