文章目录
lombok_exploreval、var@NoNull@Cleanup@ToString@Getter、@Setter@EqualsAndHashCode@NoArgsConstructor、@AllArgsConstructor@RequiredArgsConstructor@Data@Value@Builder@SneakyThrows@Synchronized@With
lombok_explore
探索lombok在项目中的应用
val、var
val和var都表示定义一个变量，并且回进行类型推导
val: 定义的是final变量var: 定义的是非final变量
public class ValAndVarExample {
public void valExample(){
//相当于final String example = "Hello world";
val example = "hello world";
// example = "hello china"; //Cannot assign a value to final variable
System.out.println(example);
}
public void varExample(){
var example = "hello world";
example = "hello china";
System.out.println(example);
}
public static void main(String[] args) {
ValAndVarExample valAndVarExample = new ValAndVarExample();
valAndVarExample.valExample();
valAndVarExample.varExample();
}
}
@NoNull
用来指定某个方法入参不能为null。
public class NoNullExample {
/**
* 为空回抛出java.lang.NullPointerException: param is marked non-null but is null
* @param param
*/
public void example(@NonNull String param){
System.out.println(param);
}
public static void main(String[] args) {
NoNullExample noNullExample = new NoNullExample();
noNullExample.example(null);
}
}
会抛异常：
Exception in thread "main" java.lang.NullPointerException: param is marked non-null but is null
注意:NonNull仅仅会判断是不是null，而不会判断是不是空字符串。
lombok作用于编译期，此代码编译后的效果：
public class NoNullExample {
public NoNullExample() {
}
public void example(@NonNull String param) {
if (param == null) {
throw new NullPointerException("param is marked non-null but is null");
} else {
System.out.println(param);
}
}
public static void main(String[] args) {
NoNullExample noNullExample = new NoNullExample();
noNullExample.example((String)null);
}
}
@Cleanup
自动帮我们清理资源，比如InputStream、OutputStream，会自动的调用close方法。
public class CleanupExample {
public static void main(String[] args) throws IOException {
@Cleanup InputStream inputStream = new FileInputStream(args[0]);
byte[] bytes = new byte[1024];
inputStream.read(bytes);
}
}
编译后生成代码：
public class CleanupExample {
public CleanupExample() {
}
public static void main(String[] args) throws IOException {
FileInputStream inputStream = new FileInputStream(args[0]);
try {
byte[] bytes = new byte[1024];
inputStream.read(bytes);
} finally {
if (Collections.singletonList(inputStream).get(0) != null) {
inputStream.close();
}
}
}
}
如果某个资源没有close方法，那么我们可以指定某个方法来关闭资源，value属性默认为close:
@Target(ElementType.LOCAL_VARIABLE)
@Retention(RetentionPolicy.SOURCE)
public @interface Cleanup {
/** @return The name of the method that cleans up the resource. By default, 'close'. The method must not have any parameters. */
String value() default "close";
}
可以使用@Cleanup(value=“指定的方法”)，调用其他的方法，默认是close
@ToString
由Lombok重写toString()方法
@ToString
@Getter(value = AccessLevel.PRIVATE)
@Setter
@EqualsAndHashCode
public class CommonExample {
@ToString.Exclude private Integer id;
private String name;
private Integer age;
@EqualsAndHashCode.Exclude private String grade;
}
编译后格式为:
public String toString() {
return "CommonExample(name=" + this.getName() + ", age=" + this.getAge() + ", grade=" + this.getGrade() + ")";
}
@ToString.Exclude private Integer id; 已经将id排除
如果希望某个属性不参与重写的toString()方法中，可以利用@ToString.Exclude来标记。
@Getter、@Setter
由Lombok针对属性提供getter、setter方法，默认生成的方法是public，可以通过value属性来进行修改，比如:
@Getter(value = AccessLevel.PRIVATE)
@Setter
@EqualsAndHashCode
由Lombok重写equals()方法与hashCode()方法。
重写的equals()方法如下(编译后的结果):
public boolean equals(final Object o) {
//判断是否是当前对象本身进行比较
if (o == this) {
return true;
} else if (!(o instanceof CommonExample)) {
//判断当前对象是否属于当前类型
return false;
} else {
CommonExample other = (CommonExample)o;
if (!other.canEqual(this)) {
return false;
} else {
//当前对象是当前类型，开始比较属性值
//id是否相等
label47: {
Object this$id = this.getId();
Object other$id = other.getId();
if (this$id == null) {
if (other$id == null) {
break label47;
}
} else if (this$id.equals(other$id)) {
break label47;
}
return false;
}
//age是否相等
Object this$age = this.getAge();
Object other$age = other.getAge();
if (this$age == null) {
if (other$age != null) {
return false;
}
} else if (!this$age.equals(other$age)) {
return false;
}
//name是否相等
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;
}
//如果上面的属性都相等，则返回true
return true;
}
}
}
//判断当前对象是否属于当前类型
protected boolean canEqual(final Object other) {
return other instanceof CommonExample;
}
仔细看并不难，就是比较两个对象的各个属性是否相等，属性全部相等，两个对象才相等。
重写的hashCode()方法如下（编译后的结果）:
public int hashCode() {
int PRIME = true;
int result = 1;
Object $id = this.getId();
int result = result * 59 + ($id == null ? 43 : $id.hashCode());
Object $age = this.getAge();
result = result * 59 + ($age == null ? 43 : $age.hashCode());
Object $name = this.getName();
result = result * 59 + ($name == null ? 43 : $name.hashCode());
return result;
}
就是利用各个属性的hashCode来生成整个对象的hashCode。
如果希望某个属性不参与重写的equals()方法hashCode()方法中，可以利用@EqualsAndHashCode.Exclude来标记。
@NoArgsConstructor、@AllArgsConstructor
由Lombok生成无参的构造方法、全部参数的构造方法，比如:
@NoArgsConstructor
@AllArgsConstructor
public class ConstructorExample {
@NonNull private Integer x;
@NonNull private Integer y;
private String description;
public static void main(String[] args) {
//Exception in thread "main" java.lang.NullPointerException: x is marked non-null but is null
// new ConstructorExample(null, null, "");
}
}
编译后的代码：
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
package com.adun.explore.example;
import lombok.NonNull;
public class ConstructorExample {
@NonNull
private Integer x;
@NonNull
private Integer y;
private String description;
public static void main(String[] args) {
}
//无参构造器
public ConstructorExample() {
}
//全参构造器
public ConstructorExample(@NonNull final Integer x, @NonNull final Integer y, final String description) {
if (x == null) {
throw new NullPointerException("x is marked non-null but is null");
} else if (y == null) {
throw new NullPointerException("y is marked non-null but is null");
} else {
this.x = x;
this.y = y;
this.description = description;
}
}
}
加在属性上的@NonNull会影响到构造方法，会在构造方法中判断对应参数是否为null。
@RequiredArgsConstructor
会针对必要属性，也就是加了@NonNull的属性生成一个构造方法，比如:
@RequiredArgsConstructor
public class ConstructorExample {
@NonNull private Integer x;
@NonNull private Integer y;
private String description;
public static void main(String[] args) {
//Exception in thread "main" java.lang.NullPointerException: x is marked non-null but is null
// new ConstructorExample(null, null, "");
}
}
编译后的代码：
public class ConstructorExample {
@NonNull
private Integer x;
@NonNull
private Integer y;
private String description;
public static void main(String[] args) {
}
//必要属性的构造器
public ConstructorExample(@NonNull final Integer x, @NonNull final Integer y) {
if (x == null) {
throw new NullPointerException("x is marked non-null but is null");
} else if (y == null) {
throw new NullPointerException("y is marked non-null but is null");
} else {
this.x = x;
this.y = y;
}
}
}
我们还可以利用@RequiredArgsConstructor的staticName来指定生成一个static方法，该方法可以用来构造出一个对象，比如:
@RequiredArgsConstructor(staticName = "of")
public class ConstructorExample {
@NonNull private Integer x;
@NonNull private Integer y;
private String description;
public static void main(String[] args) {
ConstructorExample.of(1, 2);
}
}
编译后生成的代码：
public class ConstructorExample {
@NonNull
private Integer x;
@NonNull
private Integer y;
private String description;
public static void main(String[] args) {
of(1, 2);
}
private ConstructorExample(@NonNull final Integer x, @NonNull final Integer y) {
if (x == null) {
throw new NullPointerException("x is marked non-null but is null");
} else if (y == null) {
throw new NullPointerException("y is marked non-null but is null");
} else {
this.x = x;
this.y = y;
}
}
public static ConstructorExample of(@NonNull final Integer x, @NonNull final Integer y) {
return new ConstructorExample(x, y);
}
}
@Data
@Data等价于@ToString、@EqualsAndHashCode、@Getter、@Setter、@RequiredArgsConstructor，所以一个类加了@Data注解，那么Lombok就会︰
重写toString()方法重写equals()和hashCode()方法生成getter、setter方法根据@NonNull标记的属性生成对应的构造方法
比如：
@Data
public class DataExample {
@NonNull private final String name;
private int age;
private double score;
}
编译后生成：
public class DataExample {
@NonNull
private final String name;
private int age;
private double score;
//@RequiredArgsConstructor
public DataExample(@NonNull final String name) {
if (name == null) {
throw new NullPointerException("name is marked non-null but is null");
} else {
this.name = name;
}
}
//@Getter
@NonNull
public String getName() {
return this.name;
}
public int getAge() {
return this.age;
}
public double getScore() {
return this.score;
}
//@Setter
public void setAge(final int age) {
this.age = age;
}
public void setScore(final double score) {
this.score = score;
}
//@EqualsAndHashCode
public boolean equals(final Object o) {
if (o == this) {
return true;
} else if (!(o instanceof DataExample)) {
return false;
} else {
DataExample other = (DataExample)o;
if (!other.canEqual(this)) {
return false;
} else if (this.getAge() != other.getAge()) {
return false;
} else if (Double.compare(this.getScore(), other.getScore()) != 0) {
return false;
} else {
Object this$name = this.getName();
Object other$name = other.getName();
if (this$name == null) {
if (other$name == null) {
return true;
}
} else if (this$name.equals(other$name)) {
return true;
}
return false;
}
}
}
protected boolean canEqual(final Object other) {
return other instanceof DataExample;
}
public int hashCode() {
int PRIME = true;
int result = 1;
int result = result * 59 + this.getAge();
long $score = Double.doubleToLongBits(this.getScore());
result = result * 59 + (int)($score >>> 32 ^ $score);
Object $name = this.getName();
result = result * 59 + ($name == null ? 43 : $name.hashCode());
return result;
}
//ToString
public String toString() {
return "DataExample(name=" + this.getName() + ", age=" + this.getAge() + ", score=" + this.getScore() + ")";
}
}
@Value
将一个类变得不可变，不能被继承、类中的属性也不能被修改。
会使得类变成final的会使得没有声明访问权限的属性变为私有的会使得属性变为final的、可以通过@NonFinal来标记某个属性不变成final同时还会生成getter、equals()、 hashCode()、toString()方法还会生成一个全属性的构造方法
@Value
public class ValueExample {
String name;
@NonFinal public int age;
public double score;
}
编译后生成的代码：
//会使得类变成final的
public final class ValueExample {
//会使得没有声明访问权限的属性变为私有的
private final String name;
//会使得属性变为final的、可以通过@NonFinal来标记某个属性不变成final
public int age;
public final double score;
//全参构造器
public ValueExample(final String name, final int age, final double score) {
this.name = name;
this.age = age;
this.score = score;
}
//Getter
public String getName() {
return this.name;
}
public int getAge() {
return this.age;
}
public double getScore() {
return this.score;
}
//equals()、 hashCode()
public boolean equals(final Object o) {
if (o == this) {
return true;
} else if (!(o instanceof ValueExample)) {
return false;
} else {
ValueExample other = (ValueExample)o;
if (this.getAge() != other.getAge()) {
return false;
} else if (Double.compare(this.getScore(), other.getScore()) != 0) {
return false;
} else {
Object this$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;
}
}
}
public int hashCode() {
int PRIME = true;
int result = 1;
int result = result * 59 + this.getAge();
long $score = Double.doubleToLongBits(this.getScore());
result = result * 59 + (int)($score >>> 32 ^ $score);
Object $name = this.getName();
result = result * 59 + ($name == null ? 43 : $name.hashCode());
return result;
}
//toString
public String toString() {
return "ValueExample(name=" + this.getName() + ", age=" + this.getAge() + ", score=" + this.getScore() + ")";
}
}
@Builder
可以让我们通过构造者模式来构造对象，比如:
@Builder
@ToString
public class BuilderExample {
@Builder.Default private long id=3;
private String name;
private int age;
@Singular private Set
public static void main(String[] args) {
BuilderExample example = BuilderExample.builder()
.age(18)
.friend("tom")
.friend("jack")
.build();
System.out.println(example);
}
}
@Builder.Default使得默认值生效，不然id的值不会是默认的3@Singular使得可以向对应集合中多次添加元素
编译后的代码：
//使用建造者模式
public class BuilderExample {
private long id;
private String name;
private int age;
private Set
public static void main(String[] args) {
BuilderExample example = builder().age(18).friend("tom").friend("jack").build();
System.out.println(example);
}
private static long $default$id() {
return 3L;
}
BuilderExample(final long id, final String name, final int age, final Set
this.id = id;
this.name = name;
this.age = age;
this.friends = friends;
}
public static BuilderExample.BuilderExampleBuilder builder() {
return new BuilderExample.BuilderExampleBuilder();
}
public String toString() {
return "BuilderExample(id=" + this.id + ", name=" + this.name + ", age=" + this.age + ", friends=" + this.friends + ")";
}
public static class BuilderExampleBuilder {
private boolean id$set;
private long id$value;
private String name;
private int age;
private ArrayList
BuilderExampleBuilder() {
}
public BuilderExample.BuilderExampleBuilder id(final long id) {
this.id$value = id;
this.id$set = true;
return this;
}
public BuilderExample.BuilderExampleBuilder name(final String name) {
this.name = name;
return this;
}
public BuilderExample.BuilderExampleBuilder age(final int age) {
this.age = age;
return this;
}
public BuilderExample.BuilderExampleBuilder friend(final String friend) {
if (this.friends == null) {
this.friends = new ArrayList();
}
this.friends.add(friend);
//返回对象的本身
return this;
}
public BuilderExample.BuilderExampleBuilder friends(final Collection friends) {
if (friends == null) {
throw new NullPointerException("friends cannot be null");
} else {
if (this.friends == null) {
this.friends = new ArrayList();
}
this.friends.addAll(friends);
return this;
}
}
public BuilderExample.BuilderExampleBuilder clearFriends() {
if (this.friends != null) {
this.friends.clear();
}
return this;
}
public BuilderExample build() {
Set friends;
switch(this.friends == null ? 0 : this.friends.size()) {
case 0:
friends = Collections.emptySet();
break;
case 1:
friends = Collections.singleton(this.friends.get(0));
break;
default:
Set
friends.addAll(this.friends);
friends = Collections.unmodifiableSet(friends);
}
long id$value = this.id$value;
if (!this.id$set) {
id$value = BuilderExample.$default$id();
}
return new BuilderExample(id$value, this.name, this.age, friends);
}
public String toString() {
return "BuilderExample.BuilderExampleBuilder(id$value=" + this.id$value + ", name=" + this.name + ", age=" + this.age + ", friends=" + this.friends + ")";
}
}
}
@SneakyThrows
自动捕获并抛出异常，比如:
public class SneakyThrowsExample {
@SneakyThrows
public String utf8ToString(byte[] bytes){
return new String(bytes,"UTF-8");
}
}
我们手动抛出异常：
public class SneakyThrowsExample {
public String utf8ToString(byte[] bytes){
try {
return new String(bytes,"UTF-8");
} catch (UnsupportedEncodingException e) {
throw new RuntimeException(e);
}
}
那么用Lombok，就只需要加上@SneakyThrows就可以了，它会来帮我们抛出异常，比如:
编译后生成的代码：
生成代码会抛出Throwable ，慎用
public class SneakyThrowsExample {
public SneakyThrowsExample() {
}
public String utf8ToString(byte[] bytes) {
try {
return new String(bytes, "UTF-8");
} catch (Throwable var3) {
throw var3;
}
}
}
使用时切记需要指定异常
public class SneakyThrowsExample {
@SneakyThrows(UnsupportedEncodingException.class)
public String utf8ToString(byte[] bytes){
return new String(bytes,"UTF-8");
}
}
编译生成：
public class SneakyThrowsExample {
public SneakyThrowsExample() {
}
public String utf8ToString(byte[] bytes) {
try {
return new String(bytes, "UTF-8");
} catch (UnsupportedEncodingException var3) {
throw var3;
}
}
}
@Synchronized
其实就是帮我们加锁，比如:
public class SynchronizedExample {
private final Object readLock = new Object();
@Synchronized
public static void hello(){
System.out.println("world");
}
@Synchronized
public int answerToLife(){
return 42;
}
@Synchronized("readLock")
public void foo(){
System.out.println("bar");
}
}
编译生成的代码：
package com.adun.explore.example;
public class SynchronizedExample {
//三个锁对象
private static final Object $LOCK = new Object[0];
private final Object $lock = new Object[0];
private final Object readLock = new Object();
public SynchronizedExample() {
}
public static void hello() {
synchronized($LOCK) {
System.out.println("world");
}
}
public int answerToLife() {
synchronized(this.$lock) {
return 42;
}
}
public void foo() {
synchronized(this.readLock) {
System.out.println("bar");
}
}
}
@With
一旦修改对应的属性，就会生成一个新的对象，比如:
@AllArgsConstructor
public class WithExample {
private String name;
@With private final int age;
public static void main(String[] args) {
WithExample example = new WithExample("adun", 18);
System.out.println(example);
//age相同
WithExample withExample = example.withAge(18);
System.out.println(withExample);
}
}
运行结果：
com.adun.explore.example.WithExample@2f0e140b
com.adun.explore.example.WithExample@2f0e140b
@AllArgsConstructor
public class WithExample {
private String name;
@With private final int age;
public static void main(String[] args) {
WithExample example = new WithExample("adun", 18);
System.out.println(example);
//age不同
WithExample withExample = example.withAge(19);
System.out.println(withExample);
}
}
com.adun.explore.example.WithExample@2f0e140b
com.adun.explore.example.WithExample@7440e464
编译生成的代码：
package com.adun.explore.example;
public class WithExample {
private String name;
private final int age;
public static void main(String[] args) {
WithExample example = new WithExample("adun", 18);
System.out.println(example);
WithExample withExample = example.withAge(19);
System.out.println(withExample);
}
public WithExample(final String name, final int age) {
this.name = name;
this.age = age;
}
//@With生成的方法
public WithExample withAge(final int age) {
return this.age == age ? this : new WithExample(this.name, age);
}
}
源码地址
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