充满争议的 Lombok

Dear 丶 2022-10-12 15:56 85阅读 0赞

Lombok 一个充满争议性的插件，不能否认它的神奇，大量的让我们偷懒了，不过在减少代码量的同时，当某一个模块使用 Lombok 后，其余依赖此模块的其他代码都需要引入 Lombok 依赖。实际应用时酌情使用

# 简介 #

> Project Lombok is a java library that automatically plugs into your editor and build tools, spicing up your java.  
> Never write another getter or equals method again, with one annotation your class has a fully featured builder, Automate your logging variables, and much more.

Lombok 是一种 Java 实用工具，可用来帮助开发人员消除 Java 的冗长，尤其是对于简单的 Java 对象（POJO）。它通过注释实现这一目的。通过在开发环境中实现 Lombok，开发人员可以节省构建诸如 hashCode() 和 equals() 这样的方法以及以往用来分类各种 accessor 和 mutator 的大量时间。

--------------------

# 安装 #

## IDEA 安装 Lombok 插件 ##

1、Setting → Plugin，搜索 Lombok 安装即可

![image-20210705100759659][]

IDEA 2020.3 版本开始已经内置 Lombok 插件，

![image-20210705101817840][]

2、导入 Lombok 依赖

<dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.12</version>
        <scope>provided</scope>
     </dependency>

## Eclipse 安装 Lombok 插件 ##

1、官网下载 jar 包：[https://projectlombok.org/download][https_projectlombok.org_download]

2、双击 lombak.jar 包

3、点击 Install / Update

![image-20210705101735574][]

4、点击Quit Installer，完成安装  
![image-20210705100326948][]

5、安装完成之后，确认 eclipse 安装路径下是否多了一个 lombok.jar 包，并且配置文件 eclipse.ini 中是否添加了如下内容：  
\-javaagent:D:\\eclipse-jee-2021-03-R-win32-x86\_64\\eclipse\\lombok.jar

--------------------

# Lombok 常用注解说明 #

[Lombok注解文档][Lombok]

> @NonNull
> 
> @Cleanup
> 
> @Getter and @Setter
> 
> @AllArgsConstructor
> 
> @RequiredArgsConstructor
> 
> @NoArgsConstructor
> 
> @ToString
> 
> @EqualsAndHashCode
> 
> @Data

## @NonNull ##

用在成员方法或者构造方法的参数前面，会自动产生一个关于此参数的非空检查，如果参数为空，则抛出一个空指针异常

import lombok.NonNull;
    
    public class NonNullExample extends Something { 
        private String name;
    
        public NonNullExample(@NonNull Person person) { 
            this.name = person.getName();
        }
    }

相当于

import lombok.NonNull;
    
    public class NonNullExample extends Something { 
        private String name;
    
        public NonNullExample(@NonNull Person person) { 
            if (person == null) { 
                throw new NullPointerException("person is marked @NonNull but is null");
            }
            this.name = person.getName();
        }
    }

## @Cleanup ##

用在变量前面，可以保证此变量代表的资源会被自动关闭，默认是调用资源的close()方法

import lombok.Cleanup;
    import java.io.*;
    
    public class CleanupExample { 
        public static void main(String[] args) throws IOException { 
            @Cleanup InputStream in = new FileInputStream(args[0]);
            @Cleanup OutputStream out = new FileOutputStream(args[1]);
            byte[] b = new byte[10000];
            while (true) { 
                int r = in.read(b);
                if (r == -1) break;
                out.write(b, 0, r);
            }
        }
    }

相当于

import java.io.*;
    
    public class CleanupExample { 
        public static void main(String[] args) throws IOException { 
            InputStream in = new FileInputStream(args[0]);
            try { 
                OutputStream out = new FileOutputStream(args[1]);
                try { 
                    byte[] b = new byte[10000];
                    while (true) { 
                        int r = in.read(b);
                        if (r == -1) break;
                        out.write(b, 0, r);
                    }
                } finally { 
                    if (out != null) { 
                        out.close();
                    }
                }
            } finally { 
                if (in != null) { 
                    in.close();
                }
            }
        }
    }

## @Getter and @Setter ##

在成员变量前面，相当于为成员变量生成对应的 get 和 set 方法，还可以为生成的方法指定访问修饰符，默认为public

在类上，可以为此类里的所有**非静态**成员变量生成对应的 get 和 set 方法。

import lombok.AccessLevel;
    import lombok.Getter;
    import lombok.Setter;
    
    public class GetterSetterExample { 
    
        @Getter 
        @Setter 
        private int age;
    
        @Setter(AccessLevel.PROTECTED)
        private String name;
    
    }

相当于

public class GetterSetterExample { 
    
        private int age;
    
        private String name;
    
        public int getAge() { 
            return age;
        }
    
        public void setAge(int age) { 
            this.age = age;
        }
    
        protected void setName(String name) { 
            this.name = name;
        }
    }

## @AllArgsConstructor / @NoArgsConstructor ##

在类上使用，为该类产生全参构造方法和无参构造方法

import lombok.AllArgsConstructor;
    import lombok.NoArgsConstructor;
    
    @AllArgsConstructor
    @NoArgsConstructor
    public class User { 
        private int id;
        private String name;
        private String password;
    }

相当于

public class User { 
        private int id;
        private String name;
        private String password;
    
        public User() { 
        }
    
        public User(int id, String name, String password) { 
            this.id = id;
            this.name = name;
            this.password = password;
        }
    
    }

## @ToString ##

在类上使用，生成 toString() 方法

*  @ToString.Exclude 排除指定字段
 *  @ToString.Include 包含指定字段

import lombok.ToString;
    
    @ToString
    public class User { 
    
        @ToString.Exclude
        private int id;
        private String name;
    
    }

相当于

public class User { 
        private int id;
        private String name;
    
        public User() { 
        }
    
        public String toString() { 
            return "User(name=" + this.name + ")";
        }
    }

## @EqualsAndHashCode ##

生成 equals() 和 hashCode() 方法，以及 canEqual() 方法用来判断某个对象是否是当前类的实例，生成方法时只会使用类中的 **非静态** 和 **非transient** 成员变量

*  @EqualsAndHashCode.Exclude 排除指定字段
 *  @EqualsAndHashCode.Include 包含指定字段

import lombok.EqualsAndHashCode;
    
    @EqualsAndHashCode
    public class User {
    
        private  int id;
        private String name;
    
    }

相当于

public class User { 
        private int id;
        private String name;
    
        public User() { 
        }
    
        public boolean equals(Object o) { 
            if (o == this) { 
                return true;
            } else if (!(o instanceof User)) { 
                return false;
            } else { 
                User other = (User)o;
                if (!other.canEqual(this)) { 
                    return false;
                } else if (this.id != other.id) { 
                    return false;
                } else { 
                    Object this$name = this.name;
                    Object other$name = other.name;
                    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 User;
        }
    
        public int hashCode() { 
            int PRIME = true;
            int result = 1;
            int result = result * 59 + this.id;
            Object $name = this.name;
            result = result * 59 + ($name == null ? 43 : $name.hashCode());
            return result;
        }
    }

## @Data ##

包含了 @Getter and @Setter 、@ToString、@EqualsAndHashCode、@NoArgsConstructor

import lombok.Data;
    
    @Data
    public class User { 
    
        private int id;
        private String name;
    
    }

相当于

public class User { 
        private int id;
        private String name;
    
        public User() { 
        }
    
        public int getId() { 
            return this.id;
        }
    
        public String getName() { 
            return this.name;
        }
    
        public void setId(int id) { 
            this.id = id;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public boolean equals(Object o) { 
            if (o == this) { 
                return true;
            } else if (!(o instanceof User)) { 
                return false;
            } else { 
                User other = (User)o;
                if (!other.canEqual(this)) { 
                    return false;
                } else if (this.getId() != other.getId()) { 
                    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;
                    }
    
                    return true;
                }
            }
        }
    
        protected boolean canEqual(Object other) { 
            return other instanceof User;
        }
    
        public int hashCode() { 
            int PRIME = true;
            int result = 1;
            int result = result * 59 + this.getId();
            Object $name = this.getName();
            result = result * 59 + ($name == null ? 43 : $name.hashCode());
            return result;
        }
    
        public String toString() { 
            return "User(id=" + this.getId() + ", name=" + this.getName() + ")";
        }
    }

[image-20210705100759659]: /images/20221005/39659db06be44d3aa23b41bdba3c7a3e.png
[image-20210705101817840]: /images/20221005/985842c2279f4cfdb63db2b69742ab4f.png
[https_projectlombok.org_download]: https://projectlombok.org/download
[image-20210705101735574]: /images/20221005/9b5b733ba4634947ab9635b03961a21d.png
[image-20210705100326948]: /images/20221005/e728f545a47e4122b4f99917f0661e3f.png
[Lombok]: https://projectlombok.org/features/all