lombok使用基础教程
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
<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。
首先，添加一个plugin
plugins {
id 'io.franzbecker.gradle-lombok' version '1.11'
}
然后，就可以了。还可以配置lombok的版本：
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
测试代码： https://github.com/Ryan-Miao/someTest/tree/master/src/main/java/com/test/lombok
Geter Setter
最简单的，最常用的，最直观的使用就是getter setter方法。
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.
Getter声明创建getter方法；Setter声明创建setter方法；@Setter(AccessLevel.PROTECTED)可以添加参数，指定权限为私有；- 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：
//
// 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。
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：
//
// 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。
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：
//
// 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。
@NoArgsConstructor
public static class NoArgsExample {
@NonNull private String field;
}
NonNull被忽略了
最终生成代码如下：
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。
@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：
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。
@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：
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。
@AllArgsConstructor(access = AccessLevel.PROTECTED)
public class ConstructorExample<T> {
private int x, y;
@NonNull
private T description;
}
最终生成代码如下：
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。
同@Data， @Value是一个集合体。包含Getter,AllArgsConstructor,ToString,EqualsAndHashCode。
/**
* 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
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。
/**
* 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：
//
// 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
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