Google Protobuf基础系列：Builder与build

1 Builder与build

• Builder：新建对象，不初始化；
• build：初始化对象。

2 生成协议

2.1 协议内容

syntax = "proto3";

message User {

    string username = 1;
    string sex = 2;
    int32 age = 3;
    Team team = 4;
    repeated Team team_list = 5;

    message Team {
        string ceo = 1;
        string cto = 2;
        string cfo = 3;
    }
}

2.2 协议版本

3.16.0-rc-2

2.3 构建命令

构建对象协议类：

protoc --proto_path=D:\java-basic-with-maven\src\main\java\com\monkey\java_study\proto  --java_out=D:\java-basic-with-maven\src\main\java\com\monkey\java_study\proto  D:\java-basic-with-maven\src\main\java\com\monkey\java_study\proto\user-from-proto.proto

3 样例

3.1 Builder构建对象最后build

先使用Builder构建对象，占位，添加属性。
最后输出时，初始化对象：build。

public static byte[] createObjectFromProto() throws InvalidProtocolBufferException {
     
        /**
         * 构建对象
         * Builder
         */
        UserFromProto.User.Builder userBuilder = UserFromProto.User.newBuilder();
        /**
         * 初始化
         * build
         */
        userBuilder.setAge(SIX)
                .setUsername("xiaoxiao")
                .setSex("male");

        List<UserFromProto.User.Team> teamList = new ArrayList<>();
        /**
         * 构建对象，不初始化
         * Builder
         */
        UserFromProto.User.Team.Builder team = UserFromProto.User.Team.newBuilder();
        team.setCeo("ceo");
        team.setCfo("cfo");
        /**
         * 构建对象，不初始化
         * Builder
         */
        UserFromProto.User.Team.Builder team1 = UserFromProto.User.Team.newBuilder();
        team1.setCeo("ceo2");
        team1.setCfo("cfo2");
        userBuilder.addTeamList(team);
        userBuilder.addTeamList(team1);
        /**
         * 添加列表：初始化对象
         */
        teamList.add(team.build());
        teamList.add(team1.build());
        userBuilder.addAllTeamList(teamList);
        logger.info("Proto创建的类：{}", userBuilder);
        Gson json = new Gson();
        logger.info("gson:{}", json.toJson(userBuilder));
        /**
         * 初始化对象
         * build
         */
        return userBuilder.build().toByteArray();
    }

3.2 build初始化对象添加其他属性

使用build初始化对象后，需要为该对象添加属性，使用newBuilder方法，重用当前初始化的对象，添加属性，并初始化：build。

public static byte[] createObjectByBuild() throws InvalidProtocolBufferException {
     

        /**
         * 构建对象，不初始化
         * Builder
         */
        UserFromProto.User.Builder user = UserFromProto.User.newBuilder()
                .setAge(100)
                .setSex("male");
        /**
         * 构建对象，并初始化
         * build
         */
        UserFromProto.User.Team team1 = UserFromProto.User.Team.newBuilder()
                .setCeo("ceo1")
                .build();
        /**
         * 使用初始化的对象，继续添加属性，并初始化
         * build
         */
        team1 = UserFromProto.User.Team.newBuilder(team1).setCfo("cfo1").build();

        List<UserFromProto.User.Team> teamList = new ArrayList<>();
        teamList.add(team1);
        user.addAllTeamList(teamList);
        /**
         * 初始化对象
         */
        logger.info(">>>>>>>>>>User:{}", user.build());
        return user.build().toByteArray();
    }

4 完整样例

package com.monkey.java_study.thirdparty;

import com.google.gson.Gson;
import com.google.protobuf.InvalidProtocolBufferException;
import com.monkey.java_study.common.entity.UserFromProto;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

import java.util.ArrayList;
import java.util.List;

import static com.monkey.java_study.common.constant.DigitalConstant.SIX;

/**
 * Google proto数据序列化测试.
 *
 * @author xindaqi
 * @date 2021-05-08 9:59
 */
public class GoogleProtoTest {
     

    private static final Logger logger = LogManager.getLogger(GoogleProtoTest.class);

    /**
     * 通过Google protobuf创建类
     *
     * @return 对象字节数组
     * @throws InvalidProtocolBufferException
     */
    public static byte[] createObjectFromProto() throws InvalidProtocolBufferException {
     
        /**
         * 构建对象
         * Builder
         */
        UserFromProto.User.Builder userBuilder = UserFromProto.User.newBuilder();
        /**
         * 初始化
         * build
         */
        userBuilder.setAge(SIX)
                .setUsername("xiaoxiao")
                .setSex("male");

        List<UserFromProto.User.Team> teamList = new ArrayList<>();
        /**
         * 构建对象，不初始化
         * Builder
         */
        UserFromProto.User.Team.Builder team = UserFromProto.User.Team.newBuilder();
        team.setCeo("ceo");
        team.setCfo("cfo");
        /**
         * 构建对象，不初始化
         * Builder
         */
        UserFromProto.User.Team.Builder team1 = UserFromProto.User.Team.newBuilder();
        team1.setCeo("ceo2");
        team1.setCfo("cfo2");
        userBuilder.addTeamList(team);
        userBuilder.addTeamList(team1);
        /**
         * 添加列表：初始化对象
         */
        teamList.add(team.build());
        teamList.add(team1.build());
        userBuilder.addAllTeamList(teamList);
        logger.info("Proto创建的类：{}", userBuilder);
        Gson json = new Gson();
        logger.info("gson:{}", json.toJson(userBuilder));
        /**
         * 初始化对象
         * build
         */
        return userBuilder.build().toByteArray();
    }

    public static byte[] createObjectByBuild() throws InvalidProtocolBufferException {
     

        /**
         * 构建对象，不初始化
         * Builder
         */
        UserFromProto.User.Builder user = UserFromProto.User.newBuilder()
                .setAge(100)
                .setSex("male");
        /**
         * 构建对象，并初始化
         * build
         */
        UserFromProto.User.Team team1 = UserFromProto.User.Team.newBuilder()
                .setCeo("ceo1")
                .build();
        /**
         * 使用初始化的对象，继续添加属性，并初始化
         * build
         */
        team1 = UserFromProto.User.Team.newBuilder(team1).setCfo("cfo1").build();

        List<UserFromProto.User.Team> teamList = new ArrayList<>();
        teamList.add(team1);
        user.addAllTeamList(teamList);
        /**
         * 初始化对象
         */
        logger.info(">>>>>>>>>>User:{}", user.build());
        return user.build().toByteArray();
    }

    /**
     * 解析字节数组，转换为对象
     *
     * @param params 字节数组
     * @throws InvalidProtocolBufferException
     */
    public static void parseObjectFromProto(byte[] params) throws InvalidProtocolBufferException {
     
        logger.info("入参：" + params);
        UserFromProto.User user = UserFromProto.User.parseFrom(params);
        logger.info("Proto解析字节结果：" + user);
        logger.info("username: " + user.getUsername());
        logger.info("cto:" + user.getTeam().getCto());
        List<UserFromProto.User.Team> teamList = user.getTeamListList();
        logger.info("team list:" + teamList);
    }

    public static void main(String[] args) {
     
        try {
     
            byte[] params = createObjectFromProto();
            parseObjectFromProto(params);
            createObjectByBuild();

        } catch(InvalidProtocolBufferException ipe) {
     
            throw new RuntimeException(ipe);
        } catch(Exception e) {
     
            throw new RuntimeException(e);
        }

    }
}

5 小结

• Builder构建对象，占位，不初始化；
• build：初始化对象，此时可以使用相关属性；
• newBuilder：添加属性或者重用初始化的对象，继续添加属性。