lombok的基本使用教程

前言

lombok是一个编译级别的插件,它可以在项目编译的时候生成一些代码。在很多工具类的项目中都有这个功能。比如dagger。

通俗的说,lombok可以通过注解来标示生成getter settter等代码。我们自然可以通过编译器比如IDEA的Generate生成,为啥要用这个?

在项目开发阶段,一个class的属性是一直变化的,今天可能增加一个字段,明天可能删除一个字段。每次变化都需要修改对应的模板代码。另外,有的class的字段超级多,多到一眼看不完。如果加上模板代码,更难一眼看出来。更有甚者,由于字段太多,想要使用builder来创建。手动创建builder和字段和原来的类夹杂在一起,看起来真的难受。lombok的@Builder即可解决这个问题。

引入

引入就是加入lombok的jar包。

在maven中

直接加入依赖

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<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.16.20</version>
</dependency>

在gradle中

这里比较麻烦,需要添加一个编译时生成代码的插件。gradle里有几个这样的插件。但为了简化过程,lombok提供了新插件。

来源:官网github

首先,添加一个plugin

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plugins {
id 'io.franzbecker.gradle-lombok' version '1.11'
}

然后,就可以了。还可以配置lombok的版本:

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lombok { // optional: values below are the defaults
version = "1.16.20"
sha256 = ""
}

IntelIJ IDEA 插件

在IDEA里使用需要添加一个插件。在插件里搜索lombok,安装,重启。

IDEA里需要在设置中启用annotation processors。

如果升级了InteliJ IDEA, 可能出现lombok不能用了,右键更新lombok plugin,重启即可。

基本用法

Geeter Setter

最简单的,最常用的,最直观的使用就是getter setter方法。

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package com.test.lombok;

import lombok.AccessLevel;
import lombok.Getter;
import lombok.Setter;

import java.util.Date;

/**
* Created by Ryan Miao on 1/18/18.
*/
public class GetterSetterExample {
/**
* Age of the person. Water is wet.
*
* @param age New value for this person's age. Sky is blue.
* @return The current value of this person's age. Circles are round.
*/
@Getter
@Setter
private int age = 10;

@Getter
@Setter
private boolean active;

@Getter
@Setter
private Boolean none;

@Getter
@Setter
private Date date;

/**
* Name of the person.
* -- SETTER --
* Changes the name of this person.
*
* @param name The new value.
*/
@Setter(AccessLevel.PROTECTED) private String name;

@Override public String toString() {
return String.format("%s (age: %d)", name, age);
}

public static void main(String[] args) {
GetterSetterExample example = new GetterSetterExample();
example.setActive(true);
example.setAge(123);
example.setDate(new Date());
example.setName("abc");
example.setNone(false);

Date date = example.getDate();
Boolean none = example.getNone();
boolean active = example.isActive();

}
}

简单使用没有问题,深入一点可以看到有些特殊设定。比如javadoc.

  1. Getter声明创建getter方法;
  2. Setter声明创建setter方法;
  3. @Setter(AccessLevel.PROTECTED)可以添加参数,指定权限为私有;
  4. Attention!关于boolean的set前缀都是set,但getter不同,小写的boolean,即基本类型,前缀是is; Boolean,即包装类型,前缀是get

编译后的结果如下:

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

package com.test.lombok;

import java.util.Date;

public class GetterSetterExample {
private int age = 10;
private boolean active;
private Boolean none;
private Date date;
private String name;

public GetterSetterExample() {
}

public String toString() {
return String.format("%s (age: %d)", this.name, this.age);
}

public static void main(String[] args) {
GetterSetterExample example = new GetterSetterExample();
example.setActive(true);
example.setAge(123);
example.setDate(new Date());
example.setName("abc");
example.setNone(false);
Date date = example.getDate();
Boolean none = example.getNone();
boolean active = example.isActive();
}

public int getAge() {
return this.age;
}

public void setAge(int age) {
this.age = age;
}

public boolean isActive() {
return this.active;
}

public void setActive(boolean active) {
this.active = active;
}

public Boolean getNone() {
return this.none;
}

public void setNone(Boolean none) {
this.none = none;
}

public Date getDate() {
return this.date;
}

public void setDate(Date date) {
this.date = date;
}

protected void setName(String name) {
this.name = name;
}
}

ToString

虽然ToString在生产环境貌似没什么卵用。但是,很多情况下,我们还是需要这个的。因为记log。不想每次看log的时候是一串@地址,那就好好把toString()加上。

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package com.test.lombok;

import lombok.Setter;
import lombok.ToString;


/**
* Created by Ryan Miao on 1/18/18.
*/
@Setter
@ToString(exclude="id")
public class ToStringExample {
private static final int STATIC_VAR = 10;
private String name;
private Shape shape = new Square(5, 10);
private String[] tags;
private int id;


@ToString(callSuper=true, includeFieldNames=true)
public static class Square extends Shape {
private final int width, height;

public Square(int width, int height) {
this.width = width;
this.height = height;
}
}

@ToString
public static class Shape {
private int color;

}

public static void main(String[] args) {
final ToStringExample example = new ToStringExample();
example.setId(1);
example.setName("abc");
example.setTags(new String[]{"a","b","c"});

final Shape shape = new Square(1,2);
example.setShape(shape);

System.out.println(example.toString());
}
}

1.@ToString最简单使用即可

打印结果如下:

ToStringExample(name=abc, shape=ToStringExample.Square(super=ToStringExample.Shape(color=0), width=1, height=2), tags=[a, b, c])

编译后的代码如下:

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

package com.test.lombok;

import java.util.Arrays;

public class ToStringExample {
private static final int STATIC_VAR = 10;
private String name;
private ToStringExample.Shape shape = new ToStringExample.Square(5, 10);
private String[] tags;
private int id;

public ToStringExample() {
}

public static void main(String[] args) {
ToStringExample example = new ToStringExample();
example.setId(1);
example.setName("abc");
example.setTags(new String[]{"a", "b", "c"});
ToStringExample.Shape shape = new ToStringExample.Square(1, 2);
example.setShape(shape);
System.out.println(example.toString());
}

public void setName(String name) {
this.name = name;
}

public void setShape(ToStringExample.Shape shape) {
this.shape = shape;
}

public void setTags(String[] tags) {
this.tags = tags;
}

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

public String toString() {
return "ToStringExample(name=" + this.name + ", shape=" + this.shape + ", tags=" + Arrays.deepToString(this.tags) + ")";
}

public static class Shape {
private int color;

public Shape() {
}

public String toString() {
return "ToStringExample.Shape(color=" + this.color + ")";
}
}

public static class Square extends ToStringExample.Shape {
private final int width;
private final int height;

public Square(int width, int height) {
this.width = width;
this.height = height;
}

public String toString() {
return "ToStringExample.Square(super=" + super.toString() + ", width=" + this.width + ", height=" + this.height + ")";
}
}
}

@EqualsAndHashCode

equals()和hashCode()在Java中有着举足轻重的基地作用,虽然通常很少关注。但是,这个必须不可省。不知道有几个可以手写出来的。

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package com.test.lombok;

import lombok.EqualsAndHashCode;

/**
* Created by Ryan Miao on 1/18/18.
*/
@EqualsAndHashCode(exclude={"id", "shape"})
public class EqualsAndHashCodeExample {
private transient int transientVar = 10;
private String name;
private double score;
private ToStringExample.Shape shape = new Square(5, 10);
private String[] tags;
private int id;

public String getName() {
return this.name;
}

@EqualsAndHashCode(callSuper=true)
public static class Square extends ToStringExample.Shape {
private final int width, height;

public Square(int width, int height) {
this.width = width;
this.height = height;
}
}

public static void main(String[] args) {
EqualsAndHashCodeExample example = new EqualsAndHashCodeExample();
EqualsAndHashCodeExample example1 = new EqualsAndHashCodeExample();
boolean equals = example.equals(example1);
boolean b = example.canEqual(example);
int i = example.hashCode();
}
}

编译后的结果为:

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

package com.test.lombok;

import com.test.lombok.ToStringExample.Shape;
import java.util.Arrays;

public class EqualsAndHashCodeExample {
private transient int transientVar = 10;
private String name;
private double score;
private Shape shape = new EqualsAndHashCodeExample.Square(5, 10);
private String[] tags;
private int id;

public EqualsAndHashCodeExample() {
}

public String getName() {
return this.name;
}

public static void main(String[] args) {
EqualsAndHashCodeExample example = new EqualsAndHashCodeExample();
EqualsAndHashCodeExample example1 = new EqualsAndHashCodeExample();
example.equals(example1);
boolean b = example.canEqual(example);
int i = example.hashCode();
}

public boolean equals(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(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 Square extends Shape {
private final int width;
private final int height;

public Square(int width, int height) {
this.width = width;
this.height = height;
}

public boolean equals(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(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;
}
}
}

构造函数@NoArgsConstructor, @RequiredArgsConstructor, @AllArgsConstructor

Java中class的一切起源于构造器。大家最喜欢的还是构造函数创建对象。这里有一点比较坑的是无参构造函数。当你自己添加一个带有参数的构造函数后,无参构造函数则别隐藏。通常也没啥问题,但当你使用jackson反序列化对象的时候就被恶心到了。jackson通过无参构造函数创建对象。因此,当你考虑这个class会用来序列化为json的时候,即必须手动添加一个无参数构造函数。

@NoArgsConstructor

当你想要创建一个valueobject,DDD中的值对象,要求实现Immutable,那么无参数构造器就不合适了。@NoArgsConstructor会生成一个空的构造器。如果你设置了final field,那么编译会报错。如果你强制执行创建无参数构造器。即,@NoArgsConstructor(force = true),那么final的field会初始化为0/false/null。通常适合与@Data集成。

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@NoArgsConstructor
public static class NoArgsExample {
@NonNull private String field;
}
  • NonNull被忽略了

最终生成代码如下:

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public static class NoArgsExample {
@NonNull
private String field;

public NoArgsExample() {
}
}

对于final的字段,我认为我不会用空构造器来做这件事。所以,感觉这个参数force=true不要也罢,鸡肋。

@RequiredArgsConstructor

一个class可以有很多属性,但你可能只关心其中的几个字段,那么可以使用@RequiredArgsConstructor@NonNull将标注这个字段不应为null,初始化的时候会检查是否为空,否则抛出NullPointException。在上面的无参构造函数中被忽略了。那么,对于关注的字段标注@NonNull, @RequiredArgsConstructor则会生成带有这些字段的构造器。

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@RequiredArgsConstructor
public class RequiredArgsExample {
@NonNull private String field;
private Date date;
private Integer integer;
private int i;
private boolean b;
private Boolean aBoolean;
}

最终生成结果:

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public class RequiredArgsExample {
@NonNull
private String field;
private Date date;
private Integer integer;
private int i;
private boolean b;
private Boolean aBoolean;

public RequiredArgsExample(@NonNull String field) {
if (field == null) {
throw new NullPointerException("field");
} else {
this.field = field;
}
}
}

只有@NonNull会生成构造器。其他默认,Java的class初始化默认为null.false,0.

lombok提供了另一种初始化做法,静态初始化。即私有构造器,使用静态方法创建对象。这种做法看起来简单,但通常用的不多。因为静态初始化的东西很难mock,对测试不够友好。

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@RequiredArgsConstructor(staticName = "of")
public static class RequiredArgsStaticExample {
@NonNull private String field;
private Date date;
private Integer integer;
private int i;
private boolean b;
private Boolean aBoolean;
}

最终生成代码如下:

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public class ConstructorExample<T> {
private int x;
private int y;
@NonNull
private T description;
private ConstructorExample(@NonNull T description) {
if (description == null) {
throw new NullPointerException("description");
} else {
this.description = description;
}
}
public static <T> ConstructorExample<T> of(@NonNull T description) {
return new ConstructorExample(description);
}
}

@AllArgsConstructor

想要初始化所有字段。

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@AllArgsConstructor(access = AccessLevel.PROTECTED)
public class ConstructorExample<T> {
private int x, y;
@NonNull
private T description;
}

最终生成代码如下:

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public class ConstructorExample<T> {
private int x;
private int y;
@NonNull
private T description;
protected ConstructorExample(int x, int y, @NonNull T description) {
if (description == null) {
throw new NullPointerException("description");
} else {
this.x = x;
this.y = y;
this.description = description;
}
}
}

必用项@Data

@Data是一个集合体。包含Getter,Setter,RequiredArgsConstructor,ToString,EqualsAndHashCode

不可变对象valueobject @Value

这个看起来很美好,就是可以帮忙生成一个不可变对象。对于所有的字段都将生成final的。但我感觉有点失控。注解的优势应该是所见即所得,可以通过字面量来传递消息。而@Value字段给字段加final会让人困惑,因为这更改了我们的定义。当我想声明一个Immutable对象的时候,我会显示的给字段加一个限定final。

@Data@Value是一个集合体。包含Getter,AllArgsConstructor,ToString,EqualsAndHashCode

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/**
* Created by Ryan Miao on 1/18/18.
*/
@Value
public class Room {
@NonNull
private String id;
private String name;
private boolean active;
private Date createTime;

}

编译后

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public final class Room {
@NonNull
private final String id;
private final String name;
private final boolean active;
private final Date createTime;

public Room(@NonNull String id, String name, boolean active, Date createTime) {
if (id == null) {
throw new NullPointerException("id");
} else {
this.id = id;
this.name = name;
this.active = active;
this.createTime = createTime;
}
}

@NonNull
public String getId() {
return this.id;
}

public String getName() {
return this.name;
}

public boolean isActive() {
return this.active;
}

public Date getCreateTime() {
return this.createTime;
}

public boolean equals(Object o) {
if (o == this) {
return true;
} else if (!(o instanceof Room)) {
return false;
} else {
Room other = (Room)o;
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;
}

label41: {
Object this$name = this.getName();
Object other$name = other.getName();
if (this$name == null) {
if (other$name == null) {
break label41;
}
} else if (this$name.equals(other$name)) {
break label41;
}

return false;
}

if (this.isActive() != other.isActive()) {
return false;
} else {
Object this$createTime = this.getCreateTime();
Object other$createTime = other.getCreateTime();
if (this$createTime == null) {
if (other$createTime != null) {
return false;
}
} else if (!this$createTime.equals(other$createTime)) {
return false;
}

return true;
}
}
}

public int hashCode() {
int PRIME = true;
int result = 1;
Object $id = this.getId();
int result = result * 59 + ($id == null ? 43 : $id.hashCode());
Object $name = this.getName();
result = result * 59 + ($name == null ? 43 : $name.hashCode());
result = result * 59 + (this.isActive() ? 79 : 97);
Object $createTime = this.getCreateTime();
result = result * 59 + ($createTime == null ? 43 : $createTime.hashCode());
return result;
}

public String toString() {
return "Room(id=" + this.getId() + ", name=" + this.getName() + ", active=" + this.isActive() + ", createTime=" + this.getCreateTime() + ")";
}
}

最喜欢的项 @Builder

对于喜欢builder模式的人来说,声明式简化对象创建流程让一切看得美好。但是,手动复制字段,手动创建方法很让人不喜。@Builder解决了刚需。

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/**
* Created by Ryan Miao on 1/18/18.
*/
@Data
@Builder(toBuilder = true)
public class Room {
@NonNull
private String id;
private String name;
private boolean active;
private Date createTime;
@Singular
private Set<String> occupations;

public static void main(String[] args) {
Room room = Room.builder().active(true)
.name("name")
.id("id")
.createTime(new Date())
.occupation("1")
.occupation("2")
.build();

Assert.assertEquals(2, room.getOccupations().size());

}
}

这才是我们想要的建造者。对应生成的代码为:

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

package com.test.lombok;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.LinkedHashSet;
import java.util.Set;
import lombok.NonNull;
import org.junit.Assert;

public class Room {
@NonNull
private String id;
private String name;
private boolean active;
private Date createTime;
private Set<String> occupations;

public static void main(String[] args) {
Room room = builder().active(true).name("name").id("id").createTime(new Date()).occupation("1").occupation("2").build();
Assert.assertEquals(2L, (long)room.getOccupations().size());
}

Room(@NonNull String id, String name, boolean active, Date createTime, Set<String> occupations) {
if (id == null) {
throw new NullPointerException("id");
} else {
this.id = id;
this.name = name;
this.active = active;
this.createTime = createTime;
this.occupations = occupations;
}
}

public static Room.RoomBuilder builder() {
return new Room.RoomBuilder();
}

public Room.RoomBuilder toBuilder() {
return (new Room.RoomBuilder()).id(this.id).name(this.name).active(this.active).createTime(this.createTime).occupations(this.occupations);
}

@NonNull
public String getId() {
return this.id;
}

public String getName() {
return this.name;
}

public boolean isActive() {
return this.active;
}

public Date getCreateTime() {
return this.createTime;
}

public Set<String> getOccupations() {
return this.occupations;
}

public void setId(@NonNull String id) {
if (id == null) {
throw new NullPointerException("id");
} else {
this.id = id;
}
}

public void setName(String name) {
this.name = name;
}

public void setActive(boolean active) {
this.active = active;
}

public void setCreateTime(Date createTime) {
this.createTime = createTime;
}

public void setOccupations(Set<String> occupations) {
this.occupations = occupations;
}

public boolean equals(Object o) {
if (o == this) {
return true;
} else if (!(o instanceof Room)) {
return false;
} else {
Room other = (Room)o;
if (!other.canEqual(this)) {
return false;
} else {
label63: {
Object this$id = this.getId();
Object other$id = other.getId();
if (this$id == null) {
if (other$id == null) {
break label63;
}
} else if (this$id.equals(other$id)) {
break label63;
}

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;
}

if (this.isActive() != other.isActive()) {
return false;
} else {
Object this$createTime = this.getCreateTime();
Object other$createTime = other.getCreateTime();
if (this$createTime == null) {
if (other$createTime != null) {
return false;
}
} else if (!this$createTime.equals(other$createTime)) {
return false;
}

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

return true;
}
}
}
}

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

public int hashCode() {
int PRIME = true;
int result = 1;
Object $id = this.getId();
int result = result * 59 + ($id == null ? 43 : $id.hashCode());
Object $name = this.getName();
result = result * 59 + ($name == null ? 43 : $name.hashCode());
result = result * 59 + (this.isActive() ? 79 : 97);
Object $createTime = this.getCreateTime();
result = result * 59 + ($createTime == null ? 43 : $createTime.hashCode());
Object $occupations = this.getOccupations();
result = result * 59 + ($occupations == null ? 43 : $occupations.hashCode());
return result;
}

public String toString() {
return "Room(id=" + this.getId() + ", name=" + this.getName() + ", active=" + this.isActive() + ", createTime=" + this.getCreateTime() + ", occupations=" + this.getOccupations() + ")";
}

public static class RoomBuilder {
private String id;
private String name;
private boolean active;
private Date createTime;
private ArrayList<String> occupations;

RoomBuilder() {
}

public Room.RoomBuilder id(String id) {
this.id = id;
return this;
}

public Room.RoomBuilder name(String name) {
this.name = name;
return this;
}

public Room.RoomBuilder active(boolean active) {
this.active = active;
return this;
}

public Room.RoomBuilder createTime(Date createTime) {
this.createTime = createTime;
return this;
}

public Room.RoomBuilder occupation(String occupation) {
if (this.occupations == null) {
this.occupations = new ArrayList();
}

this.occupations.add(occupation);
return this;
}

public Room.RoomBuilder occupations(Collection<? extends String> occupations) {
if (this.occupations == null) {
this.occupations = new ArrayList();
}

this.occupations.addAll(occupations);
return this;
}

public Room.RoomBuilder clearOccupations() {
if (this.occupations != null) {
this.occupations.clear();
}

return this;
}

public Room build() {
Set occupations;
switch(this.occupations == null ? 0 : this.occupations.size()) {
case 0:
occupations = Collections.emptySet();
break;
case 1:
occupations = Collections.singleton(this.occupations.get(0));
break;
default:
Set<String> occupations = new LinkedHashSet(this.occupations.size() < 1073741824 ? 1 + this.occupations.size() + (this.occupations.size() - 3) / 3 : 2147483647);
occupations.addAll(this.occupations);
occupations = Collections.unmodifiableSet(occupations);
}

return new Room(this.id, this.name, this.active, this.createTime, occupations);
}

public String toString() {
return "Room.RoomBuilder(id=" + this.id + ", name=" + this.name + ", active=" + this.active + ", createTime=" + this.createTime + ", occupations=" + this.occupations + ")";
}
}
}

总结

lombok还提供了其他几个注解,以及还有好多内置的参数没有讲解。但是,根据2-8原理,我们根本不需要。上面这几个足够了。更多的注解只会增加理解阅读难度。

参考

https://projectlombok.org/features/all

http://kriszhang.com/lombok/

Ryan Miao wechat
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