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Lombok基本使用

程序员文章站 2022-07-10 17:50:43
一、Lombok是什么官网:https://projectlombok.org/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 fea...

一、Lombok是什么

官网:https://projectlombok.org/

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.

翻译:Lombok是一种Java 使用工具,可用来帮助开发人员消除 Java中的冗长代码,尤其是对于简单的Java对象(POJO),它通过注解实现这一目的

使用Lombok前:

/**
 * #Description :  用户类
 * #Date: 2020/11/11 00:11
 * @author : tiankun
 */
public class User implements Serializable {
    private Integer id;        
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    public User() {
    }

    public User(Integer id, String username, Date birthday, String sex, String address) {
        this.id = id;
        this.username = username;
        this.birthday = birthday;
        this.sex = sex;
        this.address = address;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", birthday=" + birthday +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

使用Lombok后

/**
 * #Description :  用户类
 * #Date: 2020/11/11 00:11
 * @author : tiankun
 */
@Data
public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;
}

 

二、Lombok原理

JSR269规范:插件化注解处理API(Pluggable Annotation Processing API)

JDK6 提供的特性,在 Javac 编译期利用注解做一些事情

@Data 源码

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.SOURCE)    // 源代码级别
public @interface Data {
    String staticConstructor() default "";
}

Lombok基本使用

 

@Data 注解,在我们编译后,它会把Get,Set等方法添加到我们的class文件中

用@Data注解,User编译后的Class文件

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.tk.domain;

import java.io.Serializable;
import java.util.Date;

public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    public User() {
    }

    public Integer getId() {
        return this.id;
    }

    public String getUsername() {
        return this.username;
    }

    public Date getBirthday() {
        return this.birthday;
    }

    public String getSex() {
        return this.sex;
    }

    public String getAddress() {
        return this.address;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    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 {
                label71: {
                    Object this$id = this.getId();
                    Object other$id = other.getId();
                    if (this$id == null) {
                        if (other$id == null) {
                            break label71;
                        }
                    } else if (this$id.equals(other$id)) {
                        break label71;
                    }

                    return false;
                }

                Object this$username = this.getUsername();
                Object other$username = other.getUsername();
                if (this$username == null) {
                    if (other$username != null) {
                        return false;
                    }
                } else if (!this$username.equals(other$username)) {
                    return false;
                }

                label57: {
                    Object this$birthday = this.getBirthday();
                    Object other$birthday = other.getBirthday();
                    if (this$birthday == null) {
                        if (other$birthday == null) {
                            break label57;
                        }
                    } else if (this$birthday.equals(other$birthday)) {
                        break label57;
                    }

                    return false;
                }

                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;
                }

                Object this$address = this.getAddress();
                Object other$address = other.getAddress();
                if (this$address == null) {
                    if (other$address == null) {
                        return true;
                    }
                } else if (this$address.equals(other$address)) {
                    return true;
                }

                return false;
            }
        }
    }

    protected boolean canEqual(Object other) {
        return other instanceof User;
    }

    public int hashCode() {
        int PRIME = true;
        int result = 1;
        Object $id = this.getId();
        int result = result * 59 + ($id == null ? 43 : $id.hashCode());
        Object $username = this.getUsername();
        result = result * 59 + ($username == null ? 43 : $username.hashCode());
        Object $birthday = this.getBirthday();
        result = result * 59 + ($birthday == null ? 43 : $birthday.hashCode());
        Object $sex = this.getSex();
        result = result * 59 + ($sex == null ? 43 : $sex.hashCode());
        Object $address = this.getAddress();
        result = result * 59 + ($address == null ? 43 : $address.hashCode());
        return result;
    }

    public String toString() {
        return "User(id=" + this.getId() + ", username=" + this.getUsername() + ", birthday=" + this.getBirthday() + ", sex=" + this.getSex() + ", address=" + this.getAddress() + ")";
    }
}

 

三、安装

 

1、导入jar包 / 资源

安装lombok插件的前提就是需要下载lombok,jar。

官网下载jar包

当然也如果是Maven项目直接可以在maven中导入,版本随你意,我使用的就是maven

<!-- lombok-->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.12</version>
</dependency>

2、安装lombok插件

2.1 Eclipse

在下载完lombok.jar。右键点击。打开方式选择——》java(TM) Platform  SE binary 

Lombok基本使用

 

Lombok基本使用

 

’插件安装成功,然后把你的lombok.jar导入到你项目中去(如果没有安装插件,则使用lombok,jar包中的注解不起作用)

 

2.2 IDEA

直接在 Setting-> Plugins 里面搜索 lombok下载 重启即可

Lombok基本使用

 

四、Lombok的常用注解

Lombok基本使用

 

1、Getter、Setter

①、字段上:对该字段进行操作

②、类上:对类中所有的字段进行操作

public class User implements Serializable {
    @Setter()
    @Getter(AccessLevel.PRIVATE)     //指定修饰符    默认是 AccessLevel.PUBLIC
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;
}

Lombok基本使用

 

特殊情况:

1、如果字段是被 static修饰的,则不会生成该字段的 Getter、Setter方法

2、如果字段是被finnal 修饰的,则只会生成 Get方法 不会生成 Set 方法

Lombok基本使用

Lombok基本使用

 

如果我们不想某个字段被生成Getter,Setter方法,可以使用参数: AccessLevel.NONE 来设置

Lombok基本使用

Lombok基本使用

 

2、ToString

static修饰的变量 不会被打印输出, final修饰的的变量可以被打印输出

  • of    只打印 {} 中的字段
  • exclude      打印除了 { } 中的所有字段
@Getter
@Setter
@ToString(of = {"id"})
//@ToString(exclude = {"name"})
public class User implements Serializable {
    static String  s = "";
    final String ss = "";
    private Integer id;
    private String name;


    public static void main(String[] args) {
        User user = new User();
        user.setId(18);
        user.setName("田坤");
        System.out.println(user);
    }
}
User(id=18)

Lombok基本使用

 

3、EqualsAndHashCode

帮我们生成 hashCodo 和 equals 方法

  • of    只操作 {} 中的字段
  • exclude      操作除了 { } 中的所有字段

lombok帮我们生成的 equals 和 hashCode方法

 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 {
                label47: {
                    Object this$ss = this.getSs();
                    Object other$ss = other.getSs();
                    if (this$ss == null) {
                        if (other$ss == null) {
                            break label47;
                        }
                    } else if (this$ss.equals(other$ss)) {
                        break label47;
                    }

                    return false;
                }

                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$name = this.getName();
                Object other$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;
        Object $ss = this.getSs();
        int result = result * 59 + ($ss == null ? 43 : $ss.hashCode());
        Object $id = this.getId();
        result = result * 59 + ($id == null ? 43 : $id.hashCode());
        Object $name = this.getName();
        result = result * 59 + ($name == null ? 43 : $name.hashCode());
        return result;
    }

 

4、NonNull

NonNull 表示修饰的变量不能为空,如果为空则会抛出一个异常

    @NonNull
    private String name;

    public void test(@NonNull String str){

    }

编译后 lombok 在class文件中帮我们做的事:

    public void setName(@NonNull String name) {
        if (name == null) {
            throw new NullPointerException("name is marked non-null but is null");
        } else {
            this.name = name;
        }
    }    
    
    public void test(@NonNull String str) {
        if (str == null) {
            throw new NullPointerException("str is marked non-null but is null");
        }
    }
 

5、Constructor

  • @NoArgsConstructor           生成无参的构造函数
  • @RequiredArgsConstructor     生成部分参数的构造函数
    • 只识别 @NonNull 修饰的字段 和 没有初始值的 final 修饰的字段
  • @AllArgsConstructor            生成全参的构造函数
@RequiredArgsConstructor
public class User implements Serializable {
    static String  s = "";
    final String ss;
    private Integer id;
    @NonNull private String name;
}

编译后的class文件

    public User(String ss, @NonNull String name) {
        if (name == null) {
            throw new NullPointerException("name is marked non-null but is null");
        } else {
            this.ss = ss;
            this.name = name;
        }
    }

 

6、Data

     集四个职责于一身

  • Getter、Setter
  • ToString
  • EqualsAndHashCode
  • RequiredArgsConstructor

 

7、Builder

可以使用 链式编程 来传入参数和调用方法

Lombok基本使用

@Builder
@ToString
public class User implements Serializable {
    static String  s = "";
    final String ss;
    private Integer id;
    private String name;
}

class Test{
    public static void main(String[] args) {
        User user = User.builder().id(11).name("田坤").build();
        System.out.println(user);
    }
}

 

8、Log 启用日志

https://www.jianshu.com/p/42b1bcb994a8

9、Val  (@Value)

一个未定义的类型

    val map = new HashMap<String,String>();

 

10、Clearup

自动关闭一些资源

public void demo(){
        //创建源
        System.out.println();
        File srcFile = new File("D:/WorkSpace/IdeaWorksSpace/javabase/IO/src/part2/ave1.jpg");
        File destFile = new File("D:/WorkSpace/IdeaWorksSpace/javabase/IO/src/part2/ave1Copy.jpg");
        //选择流
        @Cleanup InputStream is = null;
        @Cleanup OutputStream os = null;
        //操作
        try {
            is = new FileInputStream(srcFile);
            os = new FileOutputStream(destFile);
            //缓存容器
            byte[] flush = new byte[1024];
            int len = -1;
            while ((len = is.read(flush))!= -1){
                os.write(flush,0,len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

@Cleanup 最后会帮我们关闭 InputStream 和 OutputStream ,他也是在编译后在 finally里面 关闭资源;

 

 

 

 

 

 

 

 

 

 

 

 

本文地址:https://blog.csdn.net/qq_41965731/article/details/109614145

相关标签: Java高级框架