Lombok为啥这么牛逼?SpringBoot和IDEA官方都要支持它

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。

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。

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。

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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