SpringBoot - Lombok使用详解2(@Setter、@Getter、@ToString、@EqualsAndHashCode)

作者: hangge 发布时间: 2019-10-10 浏览: 153 次 编辑

四、Lombok 注解详解(1)

1,@Setter 和 @Getter

(1)这两个注解用于生成 settergetter 方法,可以用在类或者属性上:

  • 如果用在属性上:则只为该属性提供 settergetter 方法
  • 如果是用在类上:则为这个类所有属性供 settergetter方法

(2)下面我们在一个类上添加 @Setter @Getter 注解:

package com.example.demo;
 
import lombok.Getter;
import lombok.Setter;
 
@Getter
@Setter
public class User {
    private String name;
    private Integer age;
}

(3)然后我们就可以直接使用它的 settergetter 方法了:

User user = new User();
user.setName("hangge");
user.setAge(123);
user.getName();
user.getAge();

2,@Getter(lazy=true)

(1)该标注用于生成一个 lazy 版的 getter,它会在第一次调用这个 getter 时计算一次值,然后从那里开始缓存它。如果计算该值需要大量 CPU,或者该值占用大量内存,这可能很有用。

注意Lombok 会自动去管理线程安全的问题,所以不会存在重复赋值的问题。

(2)要使用此功能,需要创建一个 private final 变量,并且使用运行成本高的表达式对其进行初始化,同时使用 @Getter(lazy=true) 注解进行标注。

// 使用注解
public class GetterLazyExample {
    @Getter(lazy=true) private final double[] cached = expensive();
 
    private double[] expensive() {
        double[] result = new double[1000000];
        for (int i = 0; i < result.length; i++) {
            result[i] = Math.asin(i);
        }
        return result;
    }
}
 
// 不使用注解
public class GetterLazyExample {
    private final java.util.concurrent.AtomicReference<java.lang.Object> cached =
            new java.util.concurrent.AtomicReference<java.lang.Object>();
 
    public double[] getCached() {
        java.lang.Object value = this.cached.get();
        if (value == null) {
            synchronized(this.cached) {
                value = this.cached.get();
                if (value == null) {
                    final double[] actualValue = expensive();
                    value = actualValue == null ? this.cached : actualValue;
                    this.cached.set(value);
                }
            }
        }
        return (double[])(value == this.cached ? null : value);
    }
 
    private double[] expensive() {
        double[] result = new double[1000000];
        for (int i = 0; i < result.length; i++) {
            result[i] = Math.asin(i);
        }
        return result;
    }
}

3,@ToString

(1)@ToString 注解在类上, 为类提供 toString() 方法:
  • 默认情况下,它会按顺序(以逗号分隔)打印这个类名称以及每个字段。
  • 可以这样设置不包含哪些字段:@ToString(exclude = "id") 或者 @ToString(exclude = {"id","name"})
package com.example.demo;
 
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;
 
@Getter
@Setter
@ToString
public class User {
    private String name;
    private Integer age;
}

(2)下面是一个简单的测试样例:

User user = new User();
user.setName("hangge");
user.setAge(123);
System.out.println(user.toString());

原文:SpringBoot - Lombok使用详解2(@Setter、@Getter、@ToString、@EqualsAndHashCode)

4,@EqualsAndHashCode

(1)当其注解在类上,为该类提供 hashCode() equals() 方法:

  • 默认情况下,它将使用所有非静态,非 transient 字段。
  • 可以通过在可选的 exclude 参数中来排除更多字段。
  • 也可以通过在 parameter 参数中命名它们来准确指定希望使用哪些字段。
package com.amos.lombok;
 
import lombok.EqualsAndHashCode;
 
@EqualsAndHashCode
public class EqualsAndHashCodeExample {
 
    private transient int transientVar = 10;
    private String name;
    private double score;
 
    /**
     * 不包含该字段
     */
    @EqualsAndHashCode.Exclude
    private Shape shape = new Square(5, 10);
    private String[] tags;
 
    /**
     * 不包含该字段
     */
    @EqualsAndHashCode.Exclude
    private int id;
 
    public String getName() {
        return this.name;
    }
 
    @EqualsAndHashCode(callSuper = true)
    public static class Square extends Shape {
        private final int width, height;
 
        public Square(int width, int height) {
            this.width = width;
            this.height = height;
        }
    }
 
    public static class Shape {
    }
}

(2)上面编译后会变成如下代码:

package com.amos.lombok;
 
import java.util.Arrays;
 
public class EqualsAndHashCodeExample {
    private transient int transientVar = 10;
    private String name;
    private double score;
    private EqualsAndHashCodeExample.Shape shape = new EqualsAndHashCodeExample.Square(5, 10);
    private String[] tags;
    private int id;
 
    public EqualsAndHashCodeExample() {
    }
 
    public String getName() {
        return this.name;
    }
 
    public boolean equals(final Object o) {
        if (o == this) {
            return true;
        } else if (!(o instanceof EqualsAndHashCodeExample)) {
            return false;
        } else {
            EqualsAndHashCodeExample other = (EqualsAndHashCodeExample)o;
            if (!other.canEqual(this)) {
                return false;
            } else {
                label31: {
                    Object this$name = this.getName();
                    Object other$name = other.getName();
                    if (this$name == null) {
                        if (other$name == null) {
                            break label31;
                        }
                    } else if (this$name.equals(other$name)) {
                        break label31;
                    }
 
                    return false;
                }
 
                if (Double.compare(this.score, other.score) != 0) {
                    return false;
                } else {
                    return Arrays.deepEquals(this.tags, other.tags);
                }
            }
        }
    }
 
    protected boolean canEqual(final Object other) {
        return other instanceof EqualsAndHashCodeExample;
    }
 
    public int hashCode() {
        int PRIME = true;
        int result = 1;
        Object $name = this.getName();
        int result = result * 59 + ($name == null ? 43 : $name.hashCode());
        long $score = Double.doubleToLongBits(this.score);
        result = result * 59 + (int)($score >>> 32 ^ $score);
        result = result * 59 + Arrays.deepHashCode(this.tags);
        return result;
    }
 
    public static class Shape {
        public Shape() {
        }
    }
 
    public static class Square extends EqualsAndHashCodeExample.Shape {
        private final int width;
        private final int height;
 
        public Square(int width, int height) {
            this.width = width;
            this.height = height;
        }
 
        public boolean equals(final Object o) {
            if (o == this) {
                return true;
            } else if (!(o instanceof EqualsAndHashCodeExample.Square)) {
                return false;
            } else {
                EqualsAndHashCodeExample.Square other = (EqualsAndHashCodeExample.Square)o;
                if (!other.canEqual(this)) {
                    return false;
                } else if (!super.equals(o)) {
                    return false;
                } else if (this.width != other.width) {
                    return false;
                } else {
                    return this.height == other.height;
                }
            }
        }
 
        protected boolean canEqual(final Object other) {
            return other instanceof EqualsAndHashCodeExample.Square;
        }
 
        public int hashCode() {
            int PRIME = true;
            int result = super.hashCode();
            result = result * 59 + this.width;
            result = result * 59 + this.height;
            return result;
        }
    }
}


原文出自:www.hangge.com 转载请保留原文链接:https://www.hangge.com/blog/cache/detail_2492.html