Java 建造者Builder 模式代码示例

/**
 * 用户实体，多属性，部分字段可选，使用内部Builder
 */
public class User {
    // 必填
    private final Long id;
    private final String username;
    // 可选字段
    private String password;
    private String email;
    private Integer age;
    private String address;

    // 私有构造器，只能通过Builder构建对象
    private User(Builder builder) {
        this.id = builder.id;
        this.username = builder.username;
        this.password = builder.password;
        this.email = builder.email;
        this.age = builder.age;
        this.address = builder.address;
    }

    // 静态建造者
    public static class Builder {
        // 必填参数放这里
        private final Long id;
        private final String username;
        // 可选参数，默认值
        private String password;
        private String email;
        private Integer age;
        private String address;

        // 构造方法接收【必填参数】
        public Builder(Long id, String username) {
            this.id = id;
            this.username = username;
        }

        // 链式set方法，返回this
        public Builder password(String password) {
            this.password = password;
            return this;
        }

        public Builder email(String email) {
            this.email = email;
            return this;
        }

        public Builder age(Integer age) {
            this.age = age;
            return this;
        }

        public Builder address(String address) {
            this.address = address;
            return this;
        }

        // 执行构建，返回目标对象，可以在这里做参数校验
        public User build() {
            // 可以在这里做参数校验，必填项校验
            if (username == null || username.isBlank()) {
                throw new IllegalArgumentException("用户名不能为空");
            }
            return new User(this);
        }
    }

    // getter，没有setter，对象不可变（final）
    public Long getId() { return id; }
    public String getUsername() { return username; }
    public String getPassword() { return password; }
    public String getEmail() { return email; }
    public Integer getAge() { return age; }
    public String getAddress() { return address; }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", email='" + email + '\'' +
                ", age=" + age +
                ", address='" + address + '\'' +
                '}';
    }
}

public class TestBuilder {
    public static void main(String[] args) {
        // 链式构建对象，可选字段按需设置
        User user = new User.Builder(1001L, "zhangsan")
                .password("123456")
                .age(28)
                .email("zhangsan@test.com")
                .address("南京市江宁区")
                .build();

        System.out.println(user);

        // 只传必填，可选全部不传
        User simpleUser = new User.Builder(1002L, "lisi")
                .build();
        System.out.println(simpleUser);
    }
}

// 产品：电脑
class Computer {
    private String cpu;
    private String memory;
    private String disk;
    private String system;

    public void setCpu(String cpu) { this.cpu = cpu; }
    public void setMemory(String memory) { this.memory = memory; }
    public void setDisk(String disk) { this.disk = disk; }
    public void setSystem(String system) { this.system = system; }

    @Override
    public String toString() {
        return "Computer{" +
                "cpu='" + cpu + '\'' +
                ", memory='" + memory + '\'' +
                ", disk='" + disk + '\'' +
                ", system='" + system + '\'' +
                '}';
    }
}

// 抽象建造者
abstract class ComputerBuilder {
    protected Computer computer = new Computer();
    public abstract void buildCpu();
    public abstract void buildMemory();
    public abstract void buildDisk();
    public abstract void buildSystem();
    public Computer getResult() {
        return computer;
    }
}

// 具体建造者：游戏本
class GameBookBuilder extends ComputerBuilder{
    @Override
    public void buildCpu() { computer.setCpu("i9‑14900HX"); }
    @Override
    public void buildMemory() { computer.setMemory("32G"); }
    @Override
    public void buildDisk() { computer.setDisk("2T SSD"); }
    @Override
    public void buildSystem() { computer.setSystem("Windows11"); }
}

// 具体建造者：办公本
class OfficeBookBuilder extends ComputerBuilder{
    @Override
    public void buildCpu() { computer.setCpu("i5‑1340P"); }
    @Override
    public void buildMemory() { computer.setMemory("16G"); }
    @Override
    public void buildDisk() { computer.setDisk("512G SSD"); }
    @Override
    public void buildSystem() { computer.setSystem("Windows11"); }
}

// 指挥者Director：统一组装流程，隔离客户端与构建步骤
class Director {
    public Computer construct(ComputerBuilder builder){
        builder.buildCpu();
        builder.buildMemory();
        builder.buildDisk();
        builder.buildSystem();
        return builder.getResult();
    }
}

// 测试
public class GofBuilderDemo {
    public static void main(String[] args) {
        Director director = new Director();
        // 构建游戏本
        Computer gamePc = director.construct(new GameBookBuilder());
        System.out.println(gamePc);
        // 构建办公本
        Computer officePc = director.construct(new OfficeBookBuilder());
        System.out.println(officePc);
    }
}

<!-- maven依赖 lombok -->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <optional>true</optional>
</dependency>

import lombok.Builder;
import lombok.ToString;

@Builder
@ToString
public class UserLombok {
    private Long id;
    private String username;
    private String password;
    private String email;
    private Integer age;
}

UserLombok user = UserLombok.builder()
        .id(1003L)
        .username("wangwu")
        .age(22)
        .build();
System.out.println(user);