使用Lombok的@Builder 注解时，属性有默认值，会有什么坑🥶

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发布于 2025-02-26 12:48:59

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在 java 中使用 Lombok的注解@Builder时，对象属性有默认值时会碰到默认值不会生效的坑。

Lombok 测试版本 1.18.28：

示例代码：

package com;


import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.EqualsAndHashCode;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;
import lombok.ToString;


@Getter
@Setter
@ToString
@EqualsAndHashCode
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class Demo {

   private String name;
   private boolean bTest1 = true;
   private Boolean bTest2 = true;


   public static void main(String[] args) {
      Demo demo = new DemoBuilder().build();
      System.out.println("lombok Builder 生成的对象： "+demo);
      System.out.println("默认构造函数生成的对象：  "+new Demo());
   }
}

代码中使用Lombok 的@Builder 注解生成的DemoBuilder，生成一个对象：

看一下对象中的属性默认值，使用DemoBuilder（第一行）与java默认构造函数（第二行）new对象后有什么不同结果：

使用DemoBuilder构造的java对象属性初始化完全和java的默认构造函数初始化的不一样，非常坑。

要想弄明白怎么回事，只能去看Lombok的@Builder是如何编译生成java代码（可跳过直接看重点截图）：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com;

import java.io.PrintStream;

public class Demo {
    private String name;
    private boolean bTest1 = true;
    private Boolean bTest2 = true;

    public static void main(String[] args) {
        Demo demo = (new DemoBuilder()).build();
        System.out.println("lombok Builder 生成的对象： " + demo);
        PrintStream var10000 = System.out;
        Demo var10001 = new Demo();
        var10000.println("默认构造函数生成的对象：  " + var10001);
    }

    public static DemoBuilder builder() {
        return new DemoBuilder();
    }

    public String getName() {
        return this.name;
    }

    public boolean isBTest1() {
        return this.bTest1;
    }

    public Boolean getBTest2() {
        return this.bTest2;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setBTest1(boolean bTest1) {
        this.bTest1 = bTest1;
    }

    public void setBTest2(Boolean bTest2) {
        this.bTest2 = bTest2;
    }

    public String toString() {
        String var10000 = this.getName();
        return "Demo(name=" + var10000 + ", bTest1=" + this.isBTest1() + ", bTest2=" + this.getBTest2() + ")";
    }

    public boolean equals(Object o) {
        if (o == this) {
            return true;
        } else if (!(o instanceof Demo)) {
            return false;
        } else {
            Demo other = (Demo)o;
            if (!other.canEqual(this)) {
                return false;
            } else if (this.isBTest1() != other.isBTest1()) {
                return false;
            } else {
                Object this$bTest2 = this.getBTest2();
                Object other$bTest2 = other.getBTest2();
                if (this$bTest2 == null) {
                    if (other$bTest2 != null) {
                        return false;
                    }
                } else if (!this$bTest2.equals(other$bTest2)) {
                    return false;
                }

                Object this$name = this.getName();
                Object other$name = other.getName();
                if (this$name == null) {
                    if (other$name != null) {
                        return false;
                    }
                } else if (!this$name.equals(other$name)) {
                    return false;
                }

                return true;
            }
        }
    }

    protected boolean canEqual(Object other) {
        return other instanceof Demo;
    }

    public int hashCode() {
        int PRIME = true;
        int result = 1;
        result = result * 59 + (this.isBTest1() ? 79 : 97);
        Object $bTest2 = this.getBTest2();
        result = result * 59 + ($bTest2 == null ? 43 : $bTest2.hashCode());
        Object $name = this.getName();
        result = result * 59 + ($name == null ? 43 : $name.hashCode());
        return result;
    }

    public Demo() {
    }

    public Demo(String name, boolean bTest1, Boolean bTest2) {
        this.name = name;
        this.bTest1 = bTest1;
        this.bTest2 = bTest2;
    }

    public static class DemoBuilder {
        private String name;
        private boolean bTest1;
        private Boolean bTest2;

        DemoBuilder() {
        }

        public DemoBuilder name(String name) {
            this.name = name;
            return this;
        }

        public DemoBuilder bTest1(boolean bTest1) {
            this.bTest1 = bTest1;
            return this;
        }

        public DemoBuilder bTest2(Boolean bTest2) {
            this.bTest2 = bTest2;
            return this;
        }

        public Demo build() {
            return new Demo(this.name, this.bTest1, this.bTest2);
        }

        public String toString() {
            return "Demo.DemoBuilder(name=" + this.name + ", bTest1=" + this.bTest1 + ", bTest2=" + this.bTest2 + ")";
        }
    }
}

Lombok的@Builder注解生成的 DemoBuilder构造函数如下：

就是一个java的普通对象，属性都来自我们自己写的对象，但是属性都是默认值初始化，所以我们使用new DemoBuilder().build()生成的对象，属性字段都是默认值。

Lombok提供了注解@Builder.Default，可以解决上面的问题（可跳过直接看重点截图）：

package com;


import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.EqualsAndHashCode;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;
import lombok.ToString;


@Getter
@Setter
@ToString
@EqualsAndHashCode
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class Demo {

   private String name;

   @Builder.Default
   private boolean bTest1 = true;

   @Builder.Default
   private Boolean bTest2 = true;


   public static void main(String[] args) {
      Demo demo = new DemoBuilder().build();
      System.out.println("lombok Builder 生成的对象： "+demo);
      System.out.println("默认构造函数生成的对象：  "+new Demo());
   }
}

在属性上使用注解@Builder.Default：

我们可以下生成的java代码实现方式（可跳过直接看重点截图）：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com;

import java.io.PrintStream;

public class Demo {
    private String name;
    private boolean bTest1;
    private Boolean bTest2;

    public static void main(String[] args) {
        Demo demo = (new DemoBuilder()).build();
        System.out.println("lombok Builder 生成的对象： " + demo);
        PrintStream var10000 = System.out;
        Demo var10001 = new Demo();
        var10000.println("默认构造函数生成的对象：  " + var10001);
    }

    private static boolean $default$bTest1() {
        return true;
    }

    private static Boolean $default$bTest2() {
        return true;
    }

    public static DemoBuilder builder() {
        return new DemoBuilder();
    }

    public String getName() {
        return this.name;
    }

    public boolean isBTest1() {
        return this.bTest1;
    }

    public Boolean getBTest2() {
        return this.bTest2;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setBTest1(boolean bTest1) {
        this.bTest1 = bTest1;
    }

    public void setBTest2(Boolean bTest2) {
        this.bTest2 = bTest2;
    }

    public String toString() {
        String var10000 = this.getName();
        return "Demo(name=" + var10000 + ", bTest1=" + this.isBTest1() + ", bTest2=" + this.getBTest2() + ")";
    }

    public boolean equals(Object o) {
        if (o == this) {
            return true;
        } else if (!(o instanceof Demo)) {
            return false;
        } else {
            Demo other = (Demo)o;
            if (!other.canEqual(this)) {
                return false;
            } else if (this.isBTest1() != other.isBTest1()) {
                return false;
            } else {
                Object this$bTest2 = this.getBTest2();
                Object other$bTest2 = other.getBTest2();
                if (this$bTest2 == null) {
                    if (other$bTest2 != null) {
                        return false;
                    }
                } else if (!this$bTest2.equals(other$bTest2)) {
                    return false;
                }

                Object this$name = this.getName();
                Object other$name = other.getName();
                if (this$name == null) {
                    if (other$name != null) {
                        return false;
                    }
                } else if (!this$name.equals(other$name)) {
                    return false;
                }

                return true;
            }
        }
    }

    protected boolean canEqual(Object other) {
        return other instanceof Demo;
    }

    public int hashCode() {
        int PRIME = true;
        int result = 1;
        result = result * 59 + (this.isBTest1() ? 79 : 97);
        Object $bTest2 = this.getBTest2();
        result = result * 59 + ($bTest2 == null ? 43 : $bTest2.hashCode());
        Object $name = this.getName();
        result = result * 59 + ($name == null ? 43 : $name.hashCode());
        return result;
    }

    public Demo() {
        this.bTest1 = $default$bTest1();
        this.bTest2 = $default$bTest2();
    }

    public Demo(String name, boolean bTest1, Boolean bTest2) {
        this.name = name;
        this.bTest1 = bTest1;
        this.bTest2 = bTest2;
    }

    public static class DemoBuilder {
        private String name;
        private boolean bTest1$set;
        private boolean bTest1$value;
        private boolean bTest2$set;
        private Boolean bTest2$value;

        DemoBuilder() {
        }

        public DemoBuilder name(String name) {
            this.name = name;
            return this;
        }

        public DemoBuilder bTest1(boolean bTest1) {
            this.bTest1$value = bTest1;
            this.bTest1$set = true;
            return this;
        }

        public DemoBuilder bTest2(Boolean bTest2) {
            this.bTest2$value = bTest2;
            this.bTest2$set = true;
            return this;
        }

        public Demo build() {
            boolean bTest1$value = this.bTest1$value;
            if (!this.bTest1$set) {
                bTest1$value = Demo.$default$bTest1();
            }

            Boolean bTest2$value = this.bTest2$value;
            if (!this.bTest2$set) {
                bTest2$value = Demo.$default$bTest2();
            }

            return new Demo(this.name, bTest1$value, bTest2$value);
        }

        public String toString() {
            return "Demo.DemoBuilder(name=" + this.name + ", bTest1$value=" + this.bTest1$value + ", bTest2$value=" + this.bTest2$value + ")";
        }
    }
}

在生成的java类中，实现了两个获取属性默认值的静态方法：