Lombok 一个充满争议性的插件

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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>
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Eclipse 安装 Lombok 插件

1、官网下载 jar 包：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

@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();
    }
}
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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();
    }
}
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@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);
        }
    }
}
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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();
            }
        }
    }
}
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@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;

}
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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;
    }
}
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@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;
}
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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;
    }

}
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@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;

}
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相当于

public class User {
    private int id;
    private String name;

    public User() {
    }

    public String toString() {
        return "User(name=" + this.name + ")";
    }
}
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@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;

}
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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;
    }
}
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@Data

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

import lombok.Data;

@Data
public class User {

    private int id;
    private String name;

}
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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() + ")";
    }
}
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