Lombok的@Data生成的hashCode和equals方法坑

谁践踏了优雅 2023-10-01 08:03 56阅读 0赞

一、场景复现

创建两个lombok的@Data注解的类Pig实例，放进HashMap当key，map里面的数据居然被覆盖了。

package com.mk;
     
    import lombok.Data;
    @Data
    public class Pig extends Animal{
        
        private String sex;
    }

package com.mk;
     
    import java.util.HashMap;
    import java.util.Map;
     
    public class TestLombok {
        
     
        public static void main( String[] args ) {
        
     
            Pig aPig = new Pig();
            aPig.setName("A");
            aPig.setColor("white");
            aPig.setSex("male");
     
            Pig bPig = new Pig();
            bPig.setName("B");
            bPig.setColor("black");
            bPig.setSex("male");
     
            Map<Pig, String> map = new HashMap<>();
            map.put(aPig, "1");
            map.put(bPig, "2");
            System.out.println("map.size():"+map.size());
            System.out.println("map.get(aPig):"+map.get(aPig));
            System.out.println("map.get(bPig):"+map.get(bPig));
            System.out.println("map.keySet().iterator().next().getName():" + map.keySet().iterator().next().getName());
     
            System.out.println("aPig.equals(bPig):"+aPig.equals(bPig));
     
        }
    }

运行结果：

map.size():1
    map.get(aPig):2
    map.get(bPig):2
    map.keySet().iterator().next().getName():A
    aPig.equals(bPig):true```

百思不得其解，明明没有重写hashcode和equals方法，却返回true

通过反编译生成的class，可以看得lombok帮类文件生成hashcode和equals方法。hashcode和equals方法使用类声明的所有属性方法生成的（**不包含继承的父类属性方法**）

//
    // Source code recreated from a .class file by IntelliJ IDEA
    // (powered by Fernflower decompiler)
    //
     
    package com.mk;
     
    public abstract class Animal {
        
        private String name;
        private String color;
     
        public Animal() {
        
        }
     
        public String getName() {
        
            return this.name;
        }
     
        public String getColor() {
        
            return this.color;
        }
     
        public void setName(String name) {
        
            this.name = name;
        }
     
        public void setColor(String color) {
        
            this.color = color;
        }
     
        public boolean equals(Object o) {
        
            if (o == this) {
        
                return true;
            } else if (!(o instanceof Animal)) {
        
                return false;
            } else {
        
                Animal other = (Animal)o;
                if (!other.canEqual(this)) {
        
                    return false;
                } else {
        
                    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;
                    }
     
                    Object this$color = this.getColor();
                    Object other$color = other.getColor();
                    if (this$color == null) {
        
                        if (other$color != null) {
        
                            return false;
                        }
                    } else if (!this$color.equals(other$color)) {
        
                        return false;
                    }
     
                    return true;
                }
            }
        }
     
        protected boolean canEqual(Object other) {
        
            return other instanceof Animal;
        }
     
        public int hashCode() {
        
            int PRIME = true;
            int result = 1;
            Object $name = this.getName();
            int result = result * 59 + ($name == null ? 43 : $name.hashCode());
            Object $color = this.getColor();
            result = result * 59 + ($color == null ? 43 : $color.hashCode());
            return result;
        }
     
        public String toString() {
        
            return "Animal(name=" + this.getName() + ", color=" + this.getColor() + ")";
        }
    }

//
    // Source code recreated from a .class file by IntelliJ IDEA
    // (powered by Fernflower decompiler)
    //
     
    package com.mk;
     
    public class Pig extends Animal {
        
        private String sex;
     
        public Pig() {
        
        }
     
        public String getSex() {
        
            return this.sex;
        }
     
        public void setSex(String sex) {
        
            this.sex = sex;
        }
     
        public boolean equals(Object o) {
        
            if (o == this) {
        
                return true;
            } else if (!(o instanceof Pig)) {
        
                return false;
            } else {
        
                Pig other = (Pig)o;
                if (!other.canEqual(this)) {
        
                    return false;
                } else {
        
                    Object this$sex = this.getSex();
                    Object other$sex = other.getSex();
                    if (this$sex == null) {
        
                        if (other$sex != null) {
        
                            return false;
                        }
                    } else if (!this$sex.equals(other$sex)) {
        
                        return false;
                    }
     
                    return true;
                }
            }
        }
     
        protected boolean canEqual(Object other) {
        
            return other instanceof Pig;
        }
     
        public int hashCode() {
        
            int PRIME = true;
            int result = 1;
            Object $sex = this.getSex();
            int result = result * 59 + ($sex == null ? 43 : $sex.hashCode());
            return result;
        }
     
        public String toString() {
        
            return "Pig(sex=" + this.getSex() + ")";
        }
    }

#### 二、解决方案 ####

（1）不使用lombok对子类进行生成属性方法

（2）lombok生成属性方法的子类不能使用map、set等集合使用的hashcode和equals方法。