lombok的@Builder注解的坑

1.导致无参构造丢失

• 单独使用@Data注解，是会生成无参数构造方法。
• 单独使用@Builder注解，发现生成了全属性的构造方法。

@Data和@Builder一起用：我们发现没有了默认的构造方法。如果用@NoArgsConstructor注解会报错！

直接加上这4个注解

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@Data @Builder @AllArgsConstructor @NoArgsConstructor

2.@Builder注解导致默认值失效

 

 

解决： 只需要在字段上面加上@Builder.Default注解即可,但是这样 new 出来得对象，默认值丢失

 

 

 

3.原因分析

我们使用注解的方式，底层本质就是反射帮我们生成了一系列的setter、getter，所以我们直接打开编译后的target包下面的.class文件，上面的所有原因一目了然！

我们想知道@Data、@Builder等注解底层到底做了什么，直接编译当前文件，即可在生成的.class字节码文件查看具体代码便知道了

@Builder 生成了一个内部类PersonBuilder，并针对每一个属性生成一个同名方法，builder()方法，将每个属性的值塞回到Person类中返回

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public class Person {     private Integer id;     private String value;       private static String $default$value() {         return "yes";     }       public static Person.PersonBuilder builder() {         return new Person.PersonBuilder();     }       public Integer getId() {         return this.id;     }       public String getValue() {         return this.value;     }       public void setId(final Integer id) {         this.id = id;     }       public void setValue(final String value) {         this.value = value;     }       public boolean equals(final Object o) {         if (o == this) {             return true;         } else if (!(o instanceof Person)) {             return false;         } else {             Person other = (Person)o;             if (!other.canEqual(this)) {                 return false;             } else {                 Object this$id = this.getId();                 Object other$id = other.getId();                 if (this$id == null) {                     if (other$id != null) {                         return false;                     }                 } else if (!this$id.equals(other$id)) {                     return false;                 }                   Object this$value = this.getValue();                 Object other$value = other.getValue();                 if (this$value == null) {                     if (other$value != null) {                         return false;                     }                 } else if (!this$value.equals(other$value)) {                     return false;                 }                   return true;             }         }     }       protected boolean canEqual(final Object other) {         return other instanceof Person;     }       public int hashCode() {         int PRIME = true;         int result = 1;         Object $id = this.getId();         int result = result * 59 + ($id == null ? 43 : $id.hashCode());         Object $value = this.getValue();         result = result * 59 + ($value == null ? 43 : $value.hashCode());         return result;     }       public Person(final Integer id, final String value) {         this.id = id;         this.value = value;     }       public Person() {     }       public String toString() {         return "Person(id=" + this.getId() + ", value=" + this.getValue() + ")";     }       public static class PersonBuilder {         private Integer id;         private boolean value$set;         private String value;           PersonBuilder() {         }           public Person.PersonBuilder id(final Integer id) {             this.id = id;             return this;         }           public Person.PersonBuilder value(final String value) {             this.value = value;             this.value$set = true;             return this;         }           public Person build() {             String value = this.value;             if (!this.value$set) {                 value = Person.$default$value();             }               return new Person(this.id, value);         }           public String toString() {             return "Person.PersonBuilder(id=" + this.id + ", value=" + this.value + ")";         }     } }