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Lombok为啥这么牛逼?SpringBoot和IDEA官方都要支持它

程序员文章站 2022-03-15 08:15:50
最近 idea 2020最后一个版本发布了 ,已经内置了lombok插件,springboot 2.1.x之后的版本也在starter中内置了lombok依赖。为什么他们都要支持lombok呢?今天我...

最近 idea 2020最后一个版本发布了 ,已经内置了lombok插件,springboot 2.1.x之后的版本也在starter中内置了lombok依赖。为什么他们都要支持lombok呢?今天我来讲讲lombok的使用,看看它有何神奇之处!

lombok简介

lombok是一款java代码功能增强库,在github上已有9.8k+star。它会自动集成到你的编辑器和构建工具中,从而使你的java代码更加生动有趣。通过lombok的注解,你可以不用再写getter、setter、equals等方法,lombok将在编译时为你自动生成。

lombok集成

首先我们需要在idea中安装好lombok插件,如果你使用的是最新版idea 2020.3,则lombok插件已经内置,无需安装。

Lombok为啥这么牛逼?SpringBoot和IDEA官方都要支持它

之后在项目的pom.xml文件中添加lombok依赖,springboot 2.1.x版本后无需指定lombok版本,springboot在 spring-boot-dependencies 中已经内置。

<!--lombok依赖-->
<dependency>
 <groupid>org.projectlombok</groupid>
 <artifactid>lombok</artifactid>
 <optional>true</optional>
</dependency>

lombok使用

lombok中有很多注解,这些注解使得我们可以更加方便的编写java代码,下面介绍下这些注解的使用。

val

使用val注解可以取代任意类型作为局部变量,这样我们就不用写复杂的arraylist和map.entry类型了,具体例子如下。

/**
 * created by macro on 2020/12/16.
 */
public class valexample {

 public static void example() {
 //val代替arraylist<string>和string类型
 val example = new arraylist<string>();
 example.add("hello world!");
 val foo = example.get(0);
 system.out.println(foo.tolowercase());
 }

 public static void example2() {
 //val代替map.entry<integer,string>类型
 val map = new hashmap<integer, string>();
 map.put(0, "zero");
 map.put(5, "five");
 for (val entry : map.entryset()) {
  system.out.printf("%d: %s\n", entry.getkey(), entry.getvalue());
 }
 }

 public static void main(string[] args) {
 example();
 example2();
 }
}

当我们使用了val注解后,lombok会从局部变量的初始化表达式推断出具体类型,编译后会生成如下代码。

public class valexample {
 public valexample() {
 }

 public static void example() {
 arraylist<string> example = new arraylist();
 example.add("hello world!");
 string foo = (string)example.get(0);
 system.out.println(foo.tolowercase());
 }

 public static void example2() {
 hashmap<integer, string> map = new hashmap();
 map.put(0, "zero");
 map.put(5, "five");
 iterator var1 = map.entryset().iterator();

 while(var1.hasnext()) {
  entry<integer, string> entry = (entry)var1.next();
  system.out.printf("%d: %s\n", entry.getkey(), entry.getvalue());
 }

 }
}

@nonnull

在方法上使用@nonnull注解可以做非空判断,如果传入空值的话会直接抛出nullpointerexception。

/**
 * created by macro on 2020/12/16.
 */
public class nonnullexample {
 private string name;
 public nonnullexample(@nonnull string name){
 this.name = name;
 }

 public static void main(string[] args) {
 new nonnullexample("test");
 //会抛出nullpointerexception
 new nonnullexample(null);
 }
}

编译后会在构造器中添加非空判断,具体代码如下。

public class nonnullexample {
 private string name;

 public nonnullexample(@nonnull string name) {
 if (name == null) {
  throw new nullpointerexception("name is marked non-null but is null");
 } else {
  this.name = name;
 }
 }

 public static void main(string[] args) {
 new nonnullexample("test");
 new nonnullexample((string)null);
 }
}

@cleanup

当我们在java中使用资源时,不可避免地需要在使用后关闭资源。使用@cleanup注解可以自动关闭资源。

/**
 * created by macro on 2020/12/16.
 */
public class cleanupexample {
 public static void main(string[] args) throws ioexception {
 string instr = "hello world!";
 //使用输入输出流自动关闭,无需编写try catch和调用close()方法
 @cleanup bytearrayinputstream in = new bytearrayinputstream(instr.getbytes("utf-8"));
 @cleanup bytearrayoutputstream out = new bytearrayoutputstream();
 byte[] b = new byte[1024];
 while (true) {
  int r = in.read(b);
  if (r == -1) break;
  out.write(b, 0, r);
 }
 string outstr = out.tostring("utf-8");
 system.out.println(outstr);
 }
}

编译后lombok会生成如下代码。

public class cleanupexample {
 public cleanupexample() {
 }

 public static void main(string[] args) throws ioexception {
 string instr = "hello world!";
 bytearrayinputstream in = new bytearrayinputstream(instr.getbytes("utf-8"));

 try {
  bytearrayoutputstream out = new bytearrayoutputstream();

  try {
  byte[] b = new byte[1024];

  while(true) {
   int r = in.read(b);
   if (r == -1) {
   string outstr = out.tostring("utf-8");
   system.out.println(outstr);
   return;
   }

   out.write(b, 0, r);
  }
  } finally {
  if (collections.singletonlist(out).get(0) != null) {
   out.close();
  }

  }
 } finally {
  if (collections.singletonlist(in).get(0) != null) {
  in.close();
  }

 }
 }
}

@getter/@setter

有了@getter/@setter注解,我们再也不用编写getter/setter方法了。试想下之前即使我们使用idea自动生成getter/setter方法,如果类属性的类型和名称改了,又要重新生成getter/setter方法也是一件很麻烦的事情。

/**
 * created by macro on 2020/12/17.
 */
public class gettersetterexample {
 @getter
 @setter
 private string name;
 @getter
 @setter(accesslevel.protected)
 private integer age;

 public static void main(string[] args) {
 gettersetterexample example = new gettersetterexample();
 example.setname("test");
 example.setage(20);
 system.out.printf("name:%s age:%d",example.getname(),example.getage());
 }
}

编译后lombok会生成如下代码。

public class gettersetterexample {
 private string name;
 private integer age;

 public gettersetterexample() {
 }

 public string getname() {
 return this.name;
 }

 public void setname(final string name) {
 this.name = name;
 }

 public integer getage() {
 return this.age;
 }

 protected void setage(final integer age) {
 this.age = age;
 }
}

@tostring

把所有类属性都编写到tostring方法中方便打印日志,是一件多么枯燥无味的事情。使用@tostring注解可以自动生成tostring方法,默认会包含所有类属性,使用@tostring.exclude注解可以排除属性的生成。

/**
 * created by macro on 2020/12/17.
 */
@tostring
public class tostringexample {
 @tostring.exclude
 private long id;
 private string name;
 private integer age;
 public tostringexample(long id,string name,integer age){
 this.id =id;
 this.name = name;
 this.age = age;
 }

 public static void main(string[] args) {
 tostringexample example = new tostringexample(1l,"test",20);
 //自动实现tostring方法,输出tostringexample(name=test, age=20)
 system.out.println(example);
 }
}

编译后lombok会生成如下代码。

public class tostringexample {
 private long id;
 private string name;
 private integer age;

 public tostringexample(long id, string name, integer age) {
 this.id = id;
 this.name = name;
 this.age = age;
 }

 public string tostring() {
 return "tostringexample(name=" + this.name + ", age=" + this.age + ")";
 }
}

@equalsandhashcode

使用@equalsandhashcode注解可以自动生成hashcode和equals方法,默认包含所有类属性,使用@equalsandhashcode.exclude可以排除属性的生成。

/**
 * created by macro on 2020/12/17.
 */
@getter
@setter
@equalsandhashcode
public class equalsandhashcodeexample {
 private long id;
 @equalsandhashcode.exclude
 private string name;
 @equalsandhashcode.exclude
 private integer age;

 public static void main(string[] args) {
 equalsandhashcodeexample example1 = new equalsandhashcodeexample();
 example1.setid(1l);
 example1.setname("test");
 example1.setage(20);
 equalsandhashcodeexample example2 = new equalsandhashcodeexample();
 example2.setid(1l);
 //equals方法只对比id,返回true
 system.out.println(example1.equals(example2));
 }
}

编译后lombok会生成如下代码。

public class equalsandhashcodeexample {
 private long id;
 private string name;
 private integer age;

 public equalsandhashcodeexample() {
 }

 public boolean equals(final 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 {
  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;
  }

  return true;
  }
 }
 }

 protected boolean canequal(final object other) {
 return other instanceof equalsandhashcodeexample;
 }

 public int hashcode() {
 int prime = true;
 int result = 1;
 object $id = this.getid();
 int result = result * 59 + ($id == null ? 43 : $id.hashcode());
 return result;
 }
}

@xxconstructor

使用@xxconstructor注解可以自动生成构造方法,有@noargsconstructor、@requiredargsconstructor和@allargsconstructor三个注解可以使用。

  • @noargsconstructor:生成无参构造函数。
  • @requiredargsconstructor:生成包含必须参数的构造函数,使用@nonnull注解的类属性为必须参数。
  • @allargsconstructor:生成包含所有参数的构造函数。
/**
 * created by macro on 2020/12/17.
 */
@noargsconstructor
@requiredargsconstructor(staticname = "of")
@allargsconstructor
public class constructorexample {
 @nonnull
 private long id;
 private string name;
 private integer age;

 public static void main(string[] args) {
 //无参构造器
 constructorexample example1 = new constructorexample();
 //全部参数构造器
 constructorexample example2 = new constructorexample(1l,"test",20);
 //@nonnull注解的必须参数构造器
 constructorexample example3 = constructorexample.of(1l);
 }
}

编译后lombok会生成如下代码。

public class constructorexample {
 @nonnull
 private long id;
 private string name;
 private integer age;

 public constructorexample() {
 }

 private constructorexample(@nonnull final long id) {
 if (id == null) {
  throw new nullpointerexception("id is marked non-null but is null");
 } else {
  this.id = id;
 }
 }

 public static constructorexample of(@nonnull final long id) {
 return new constructorexample(id);
 }

 public constructorexample(@nonnull final long id, final string name, final integer age) {
 if (id == null) {
  throw new nullpointerexception("id is marked non-null but is null");
 } else {
  this.id = id;
  this.name = name;
  this.age = age;
 }
 }
}

@data

@data是一个方便使用的组合注解,是@tostring、@equalsandhashcode、@getter、@setter和@requiredargsconstructor的组合体。

/**
 * created by macro on 2020/12/17.
 */
@data
public class dataexample {
 @nonnull
 private long id;
 @equalsandhashcode.exclude
 private string name;
 @equalsandhashcode.exclude
 private integer age;

 public static void main(string[] args) {
 //@requiredargsconstructor已生效
 dataexample example1 = new dataexample(1l);
 //@getter @setter已生效
 example1.setname("test");
 example1.setage(20);
 //@tostring已生效
 system.out.println(example1);
 dataexample example2 = new dataexample(1l);
 //@equalsandhashcode已生效
 system.out.println(example1.equals(example2));
 }
}

编译后lombok会生成如下代码。

public class dataexample {
 @nonnull
 private long id;
 private string name;
 private integer age;

 public dataexample(@nonnull final long id) {
 if (id == null) {
  throw new nullpointerexception("id is marked non-null but is null");
 } else {
  this.id = id;
 }
 }

 @nonnull
 public long getid() {
 return this.id;
 }

 public string getname() {
 return this.name;
 }

 public integer getage() {
 return this.age;
 }

 public void setid(@nonnull final long id) {
 if (id == null) {
  throw new nullpointerexception("id is marked non-null but is null");
 } else {
  this.id = id;
 }
 }

 public void setname(final string name) {
 this.name = name;
 }

 public void setage(final integer age) {
 this.age = age;
 }

 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 {
  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;
  }

  return true;
  }
 }
 }

 protected boolean canequal(final object other) {
 return other instanceof dataexample;
 }

 public int hashcode() {
 int prime = true;
 int result = 1;
 object $id = this.getid();
 int result = result * 59 + ($id == null ? 43 : $id.hashcode());
 return result;
 }

 public string tostring() {
 return "dataexample(id=" + this.getid() + ", name=" + this.getname() + ", age=" + this.getage() + ")";
 }
}

@value

使用@value注解可以把类声明为不可变的,声明后此类相当于final类,无法被继承,其属性也会变成final属性。

/**
 * created by macro on 2020/12/17.
 */
@value
public class valueexample {
 private long id;
 private string name;
 private integer age;

 public static void main(string[] args) {
 //只能使用全参构造器
 valueexample example = new valueexample(1l,"test",20);
 // example.setname("andy") //没有生成setter方法,会报错
 // example.name="andy" //字段被设置为final类型,会报错
 }
}

编译后lombok会生成如下代码。

public final class valueexample {
 private final long id;
 private final string name;
 private final integer age;

 public static void main(string[] args) {
 new valueexample(1l, "test", 20);
 }

 public valueexample(final long id, final string name, final integer age) {
 this.id = id;
 this.name = name;
 this.age = age;
 }

 public long getid() {
 return this.id;
 }

 public string getname() {
 return this.name;
 }

 public integer getage() {
 return this.age;
 }
}

@builder

使用@builder注解可以通过建造者模式来创建对象,建造者模式加链式调用,创建对象太方便了!

/**
 * created by macro on 2020/12/17.
 */
@builder
@tostring
public class builderexample {
 private long id;
 private string name;
 private integer age;

 public static void main(string[] args) {
 builderexample example = builderexample.builder()
  .id(1l)
  .name("test")
  .age(20)
  .build();
 system.out.println(example);
 }
}

编译后lombok会生成如下代码。

public class builderexample {
 private long id;
 private string name;
 private integer age;

 builderexample(final long id, final string name, final integer age) {
 this.id = id;
 this.name = name;
 this.age = age;
 }

 public static builderexample.builderexamplebuilder builder() {
 return new builderexample.builderexamplebuilder();
 }

 public string tostring() {
 return "builderexample(id=" + this.id + ", name=" + this.name + ", age=" + this.age + ")";
 }

 public static class builderexamplebuilder {
 private long id;
 private string name;
 private integer age;

 builderexamplebuilder() {
 }

 public builderexample.builderexamplebuilder id(final long id) {
  this.id = id;
  return this;
 }

 public builderexample.builderexamplebuilder name(final string name) {
  this.name = name;
  return this;
 }

 public builderexample.builderexamplebuilder age(final integer age) {
  this.age = age;
  return this;
 }

 public builderexample build() {
  return new builderexample(this.id, this.name, this.age);
 }

 public string tostring() {
  return "builderexample.builderexamplebuilder(id=" + this.id + ", name=" + this.name + ", age=" + this.age + ")";
 }
 }
}

@sneakythrows

还在手动捕获并抛出异常?使用@sneakythrows注解自动实现试试!

/**
 * created by macro on 2020/12/17.
 */
public class sneakythrowsexample {

 //自动抛出异常,无需处理
 @sneakythrows(unsupportedencodingexception.class)
 public static byte[] str2byte(string str){
 return str.getbytes("utf-8");
 }

 public static void main(string[] args) {
 string str = "hello world!";
 system.out.println(str2byte(str).length);
 }
}

编译后lombok会生成如下代码。

public class sneakythrowsexample {
 public sneakythrowsexample() {
 }

 public static byte[] str2byte(string str) {
 try {
  return str.getbytes("utf-8");
 } catch (unsupportedencodingexception var2) {
  throw var2;
 }
 }
}

@synchronized

当我们在多个线程中访问同一资源时,往往会出现线程安全问题,以前我们往往使用synchronized关键字修饰方法来实现同步访问。使用@synchronized注解同样可以实现同步访问。

package com.macro.mall.tiny.example;

import lombok.*;

/**
 * created by macro on 2020/12/17.
 */
@data
public class synchronizedexample {
 @nonnull
 private integer count;

 @synchronized
 @sneakythrows
 public void reducecount(integer id) {
 if (count > 0) {
  thread.sleep(500);
  count--;
  system.out.println(string.format("thread-%d count:%d", id, count));
 }
 }

 public static void main(string[] args) {
 //添加@synchronized三个线程可以同步调用reducecount方法
 synchronizedexample example = new synchronizedexample(20);
 new reducethread(1, example).start();
 new reducethread(2, example).start();
 new reducethread(3, example).start();
 }


 @requiredargsconstructor
 static class reducethread extends thread {
 @nonnull
 private integer id;
 @nonnull
 private synchronizedexample example;

 @override
 public void run() {
  while (example.getcount() > 0) {
  example.reducecount(id);
  }
 }
 }
}

编译后lombok会生成如下代码。

public class synchronizedexample {
 private final object $lock = new object[0];
 @nonnull
 private integer count;

 public void reducecount(integer id) {
 try {
  synchronized(this.$lock) {
  if (this.count > 0) {
   thread.sleep(500l);
   integer var3 = this.count;
   integer var4 = this.count = this.count - 1;
   system.out.println(string.format("thread-%d count:%d", id, this.count));
  }

  }
 } catch (throwable var7) {
  throw var7;
 }
 }
}

@with

使用@with注解可以实现对原对象进行克隆,并改变其一个属性,使用时需要指定全参构造方法。

@with
@allargsconstructor
public class withexample {
 private long id;
 private string name;
 private integer age;

 public static void main(string[] args) {
 withexample example1 = new withexample(1l, "test", 20);
 withexample example2 = example1.withage(22);
 //将原对象进行clone并设置age,返回false
 system.out.println(example1.equals(example2));
 }
}

编译后lombok会生成如下代码。

public class withexample {
 private long id;
 private string name;
 private integer age;

 public withexample withid(final long id) {
 return this.id == id ? this : new withexample(id, this.name, this.age);
 }

 public withexample withname(final string name) {
 return this.name == name ? this : new withexample(this.id, name, this.age);
 }

 public withexample withage(final integer age) {
 return this.age == age ? this : new withexample(this.id, this.name, age);
 }

 public withexample(final long id, final string name, final integer age) {
 this.id = id;
 this.name = name;
 this.age = age;
 }
}

@getter(lazy=true)

当我们获取某一个属性比较消耗资源时,可以给@getter添加 lazy=true 属性实现懒加载,会生成double check lock 样板代码对属性进行懒加载。

/**
 * created by macro on 2020/12/17.
 */
public class getterlazyexample {
 @getter(lazy = true)
 private final double[] cached = expensive();

 private double[] expensive() {
 double[] result = new double[1000000];
 for (int i = 0; i < result.length; i++) {
  result[i] = math.asin(i);
 }
 return result;
 }

 public static void main(string[] args) {
 //使用double check lock 样板代码对属性进行懒加载
 getterlazyexample example = new getterlazyexample();
 system.out.println(example.getcached().length);
 }
}

编译后lombok会生成如下代码。

public class getterlazyexample {
 private final atomicreference<object> cached = new atomicreference();

 public getterlazyexample() {
 }

 private double[] expensive() {
 double[] result = new double[1000000];

 for(int i = 0; i < result.length; ++i) {
  result[i] = math.asin((double)i);
 }

 return result;
 }

 public double[] getcached() {
 object value = this.cached.get();
 if (value == null) {
  synchronized(this.cached) {
  value = this.cached.get();
  if (value == null) {
   double[] actualvalue = this.expensive();
   value = actualvalue == null ? this.cached : actualvalue;
   this.cached.set(value);
  }
  }
 }

 return (double[])((double[])(value == this.cached ? null : value));
 }
}

@log

使用@log注解,可以直接生成日志对象log,通过log对象可以直接打印日志。

/**
 * created by macro on 2020/12/17.
 */
@log
public class logexample {
 public static void main(string[] args) {
 log.info("level info");
 log.warning("level warning");
 log.severe("level severe");
 }
}

编译后lombok会生成如下代码。

public class logexample {
 private static final logger log = logger.getlogger(logexample.class.getname());

 public logexample() {
 }

 public static void main(string[] args) {
 log.info("level info");
 log.warning("level warning");
 log.severe("level severe");
 }
}

@slf4j

使用lombok生成日志对象时,根据使用日志实现的不同,有多种注解可以使用。比如@log、@log4j、@log4j2、@slf4j等。

/**
 * created by macro on 2020/12/17.
 */
@slf4j
public class logslf4jexample {
 public static void main(string[] args) {
 log.info("level:{}","info");
 log.warn("level:{}","warn");
 log.error("level:{}", "error");
 }
}

编译后lombok会生成如下代码。

public class logslf4jexample {
 private static final logger log = loggerfactory.getlogger(logslf4jexample.class);

 public logslf4jexample() {
 }

 public static void main(string[] args) {
 log.info("level:{}", "info");
 log.warn("level:{}", "warn");
 log.error("level:{}", "error");
 }
}

lombok原理

如果idea不安装lombok插件的话,我们打开使用lombok的项目是无法通过编译的。装了以后idea才会提示我们lombok为我们生成的方法和属性。

使用了@data注解以后,查看类结构可以发现getter、setter、tostring等方法。

Lombok为啥这么牛逼?SpringBoot和IDEA官方都要支持它

打开target目录下的 .class 文件,我们可以看到lombok为我们生成的代码,可见lombok是通过解析注解,然后在编译时生成代码来实现java代码的功能增强的。

Lombok为啥这么牛逼?SpringBoot和IDEA官方都要支持它 

参考资料

官方文档:https://projectlombok.org/features/all

项目源码地址

https://github.com/macrozheng/mall-learning/tree/master/mall-tiny-lombok

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