lombok详解

val 精简变量修饰，类似Scala，但是默认追加了final修饰符

val list = new ArrayList<String>();
//等同于
final ArrayList<String> list = new ArrayList<String>();

var 精简变量修饰，类似Scala，修饰变量

val list = new ArrayList<String>();
//等同于
ArrayList<String> list = new ArrayList<String>();

NonNull 修饰方法或者构造方法的参数，以及成员变量

public NonNullExample(@NonNull Person person) {
    super("Hello");
    this.name = person.getName();
}
//等同于
public NonNullExample(@NonNull Person person) {
    super("Hello");
    if (person == null) {
      throw new NullPointerException("person is marked @NonNull but is null");
    }
    this.name = person.getName();
}

Cleanup 修饰局部变量，用于关闭资源

默认触发修饰变量的close方法，但是如果目标对象没有close方法，可以直接指定关闭方法的名称 但是要求关闭方法不能有参数

@Cleanup("dispose") org.eclipse.swt.widgets.CoolBar bar = new CoolBar(parent, 0);

import lombok.Cleanup;
import java.io.*;

public class CleanupExample {
  public static void main(String[] args) throws IOException {
    @Cleanup InputStream in = new FileInputStream(args[0]);
    @Cleanup OutputStream out = new FileOutputStream(args[1]);
    byte[] b = new byte[10000];
    while (true) {
      int r = in.read(b);
      if (r == -1) break;
      out.write(b, 0, r);
    }
  }
}

等同于

---

import java.io.*;

public class CleanupExample {
  public static void main(String[] args) throws IOException {
    InputStream in = new FileInputStream(args[0]);
    try {
      OutputStream out = new FileOutputStream(args[1]);
      try {
        byte[] b = new byte[10000];
        while (true) {
          int r = in.read(b);
          if (r == -1) break;
          out.write(b, 0, r);
        }
      } finally {
        if (out != null) {
          out.close();
        }
      }
    } finally {
      if (in != null) {
        in.close();
      }
    }
  }
}

Getter/Setter 修饰成员变量或者类，已生成GetSet方法

• 当修饰类时，将生成类中所有的非静态成员变量的Get/Set类
• Getter/Setter都有AccessLevel参数，可设置生成的方法的修饰符(PUBLIC, PROTECTED, PACKAGE, and PRIVATE)
• 如果类被注解修饰，但是某个成员变量不想生成方法，可以设置AccessLevel参数值为NONE

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

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;
  
  /**
   * 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);
  }
}

等同于

---

public class GetterSetterExample {
  /**
   * Age of the person. Water is wet.
   */
  private int age = 10;

  /**
   * Name of the person.
   */
  private String name;
  
  @Override public String toString() {
    return String.format("%s (age: %d)", name, age);
  }
  
  /**
   * Age of the person. Water is wet.
   *
   * @return The current value of this person's age. Circles are round.
   */
  public int getAge() {
    return age;
  }
  
  /**
   * Age of the person. Water is wet.
   *
   * @param age New value for this person's age. Sky is blue.
   */
  public void setAge(int age) {
    this.age = age;
  }
  
  /**
   * Changes the name of this person.
   *
   * @param name The new value.
   */
  protected void setName(String name) {
    this.name = name;
  }
}

ToString 修饰类和方法，重写toString方法

• 默认格式类名(字段值1，字段值2)
• 可通过设置includeFieldNames=true，在字段值前面加上字段名:
• 默认所有非静态字段都会被打印，可以通过注解@ToString.Exclude来排除字段
• 如果只展示目标字段，可以在类的注解上追加参数onlyExplicitlyIncluded=true，然后在字段上加注解ToString.Include
• 如果需要打印父类的字段，可以设置参数callSuper=true
• 打印方法的输出，在方法上追加注解ToString.Include，注意必须是非静态方法，并且没有参数

import lombok.ToString;

@ToString
public class ToStringExample {
  private static final int STATIC_VAR = 10;
  private String name;
  private Shape shape = new Square(5, 10);
  private String[] tags;
  @ToString.Exclude private int id;
  
  public String getName() {
    return this.name;
  }
  
  @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;
    }
  }
}

等同于

---

import java.util.Arrays;

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;
  
  public String getName() {
    return this.name;
  }
  
  public static class Square extends Shape {
    private final int width, height;
    
    public Square(int width, int height) {
      this.width = width;
      this.height = height;
    }
    
    @Override public String toString() {
      return "Square(super=" + super.toString() + ", width=" + this.width + ", height=" + this.height + ")";
    }
  }
  
  @Override public String toString() {
    return "ToStringExample(" + this.getName() + ", " + this.shape + ", " + Arrays.deepToString(this.tags) + ")";
  }
}

EqualsAndHashCode 生成equals和hashCode方法

• 默认使用非静态和非transient修饰的字段
• 排除指定字段：注解@EqualsAndHashCode.Exclude
• 只选择指定字段：类注解@EqualsAndHashCode(onlyExplicitlyIncluded = true)，和字段注解@EqualsAndHashCode.Include
• 如果包含非Object父类，设置属性callSuper=true

import lombok.EqualsAndHashCode;

@EqualsAndHashCode
public class EqualsAndHashCodeExample {
  private transient int transientVar = 10;
  private String name;
  private double score;
  @EqualsAndHashCode.Exclude private Shape shape = new Square(5, 10);
  private String[] tags;
  @EqualsAndHashCode.Exclude private int id;
  
  public String getName() {
    return this.name;
  }
  
  @EqualsAndHashCode(callSuper=true)
  public static class Square extends Shape {
    private final int width, height;
    
    public Square(int width, int height) {
      this.width = width;
      this.height = height;
    }
  }
}

等同于

---

import java.util.Arrays;

public class EqualsAndHashCodeExample {
  private transient int transientVar = 10;
  private String name;
  private double score;
  private Shape shape = new Square(5, 10);
  private String[] tags;
  private int id;
  
  public String getName() {
    return this.name;
  }
  
  @Override public boolean equals(Object o) {
    if (o == this) return true;
    if (!(o instanceof EqualsAndHashCodeExample)) return false;
    EqualsAndHashCodeExample other = (EqualsAndHashCodeExample) o;
    if (!other.canEqual((Object)this)) return false;
    if (this.getName() == null ? other.getName() != null : !this.getName().equals(other.getName())) return false;
    if (Double.compare(this.score, other.score) != 0) return false;
    if (!Arrays.deepEquals(this.tags, other.tags)) return false;
    return true;
  }
  
  @Override public int hashCode() {
    final int PRIME = 59;
    int result = 1;
    final long temp1 = Double.doubleToLongBits(this.score);
    result = (result*PRIME) + (this.name == null ? 43 : this.name.hashCode());
    result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));
    result = (result*PRIME) + Arrays.deepHashCode(this.tags);
    return result;
  }
  
  protected boolean canEqual(Object other) {
    return other instanceof EqualsAndHashCodeExample;
  }
  
  public static class Square extends Shape {
    private final int width, height;
    
    public Square(int width, int height) {
      this.width = width;
      this.height = height;
    }
    
    @Override public boolean equals(Object o) {
      if (o == this) return true;
      if (!(o instanceof Square)) return false;
      Square other = (Square) o;
      if (!other.canEqual((Object)this)) return false;
      if (!super.equals(o)) return false;
      if (this.width != other.width) return false;
      if (this.height != other.height) return false;
      return true;
    }
    
    @Override public int hashCode() {
      final int PRIME = 59;
      int result = 1;
      result = (result*PRIME) + super.hashCode();
      result = (result*PRIME) + this.width;
      result = (result*PRIME) + this.height;
      return result;
    }
    
    protected boolean canEqual(Object other) {
      return other instanceof Square;
    }
  }
}

@NoArgsConstructor, @RequiredArgsConstructor, @AllArgsConstructor 生成构造函数

• NoArgsConstructor 注意有参数被final修饰的情况，需要加上参数(force = true)
• RequiredArgsConstructor 只对两类变量有效，一种是final修饰的并且没有初始化的变量，另外一类是NonNull注解修饰并且没有初始化的变量
• AllArgsConstructor 生成一个包括所有参数的构造方法，并且有NonNull注解的会进行非空检查
• @RequiredArgsConstructor(staticName="of") 生成一个私有的构造方法，并提供一个静态方法of包装私有构造方法
• 以上注解只对非static字段生效

import lombok.AccessLevel;
import lombok.RequiredArgsConstructor;
import lombok.AllArgsConstructor;
import lombok.NonNull;

@RequiredArgsConstructor(staticName = "of")
@AllArgsConstructor(access = AccessLevel.PROTECTED)
public class ConstructorExample<T> {
  private int x, y;
  @NonNull private T description;
  
  @NoArgsConstructor
  public static class NoArgsExample {
    @NonNull private String field;
  }
}

等同于

---

public class ConstructorExample<T> {
  private int x, y;
  @NonNull private T description;
  
  private ConstructorExample(T description) {
    if (description == null) throw new NullPointerException("description");
    this.description = description;
  }
  
  public static <T> ConstructorExample<T> of(T description) {
    return new ConstructorExample<T>(description);
  }
  
  @java.beans.ConstructorProperties({"x", "y", "description"})
  protected ConstructorExample(int x, int y, T description) {
    if (description == null) throw new NullPointerException("description");
    this.x = x;
    this.y = y;
    this.description = description;
  }
  
  public static class NoArgsExample {
    @NonNull private String field;
    
    public NoArgsExample() {
    }
  }
}

Data 大集合

• 相当于一个快捷方式，包括之前的toString,EqualsAndHashCode,所有字段的Getter,非final字段的Setter，和RequiredArgsConstructor
• Data无法像单个注解一样添加自定义属性，但是可以再次追加单个注解，以覆盖Data对应的方法
• 如果有任何同名的方法存在，Data不会再生成对应的方法
• 如果有任意一个构造方法，Data注解将不会生成RequiredArgsConstructor对应的构造方法

import lombok.AccessLevel;
import lombok.Setter;
import lombok.Data;
import lombok.ToString;

@Data public class DataExample {
  private final String name;
  @Setter(AccessLevel.PACKAGE) private int age;
  private double score;
  private String[] tags;
  
  @ToString(includeFieldNames=true)
  @Data(staticConstructor="of")
  public static class Exercise<T> {
    private final String name;
    private final T value;
  }
}

等同于

---

import java.util.Arrays;

public class DataExample {
  private final String name;
  private int age;
  private double score;
  private String[] tags;
  
  public DataExample(String name) {
    this.name = name;
  }
  
  public String getName() {
    return this.name;
  }
  
  void setAge(int age) {
    this.age = age;
  }
  
  public int getAge() {
    return this.age;
  }
  
  public void setScore(double score) {
    this.score = score;
  }
  
  public double getScore() {
    return this.score;
  }
  
  public String[] getTags() {
    return this.tags;
  }
  
  public void setTags(String[] tags) {
    this.tags = tags;
  }
  
  @Override public String toString() {
    return "DataExample(" + this.getName() + ", " + this.getAge() + ", " + this.getScore() + ", " + Arrays.deepToString(this.getTags()) + ")";
  }
  
  protected boolean canEqual(Object other) {
    return other instanceof DataExample;
  }
  
  @Override public boolean equals(Object o) {
    if (o == this) return true;
    if (!(o instanceof DataExample)) return false;
    DataExample other = (DataExample) o;
    if (!other.canEqual((Object)this)) return false;
    if (this.getName() == null ? other.getName() != null : !this.getName().equals(other.getName())) return false;
    if (this.getAge() != other.getAge()) return false;
    if (Double.compare(this.getScore(), other.getScore()) != 0) return false;
    if (!Arrays.deepEquals(this.getTags(), other.getTags())) return false;
    return true;
  }
  
  @Override public int hashCode() {
    final int PRIME = 59;
    int result = 1;
    final long temp1 = Double.doubleToLongBits(this.getScore());
    result = (result*PRIME) + (this.getName() == null ? 43 : this.getName().hashCode());
    result = (result*PRIME) + this.getAge();
    result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));
    result = (result*PRIME) + Arrays.deepHashCode(this.getTags());
    return result;
  }
  
  public static class Exercise<T> {
    private final String name;
    private final T value;
    
    private Exercise(String name, T value) {
      this.name = name;
      this.value = value;
    }
    
    public static <T> Exercise<T> of(String name, T value) {
      return new Exercise<T>(name, value);
    }
    
    public String getName() {
      return this.name;
    }
    
    public T getValue() {
      return this.value;
    }
    
    @Override public String toString() {
      return "Exercise(name=" + this.getName() + ", value=" + this.getValue() + ")";
    }
    
    protected boolean canEqual(Object other) {
      return other instanceof Exercise;
    }
    
    @Override public boolean equals(Object o) {
      if (o == this) return true;
      if (!(o instanceof Exercise)) return false;
      Exercise<?> other = (Exercise<?>) o;
      if (!other.canEqual((Object)this)) return false;
      if (this.getName() == null ? other.getValue() != null : !this.getName().equals(other.getName())) return false;
      if (this.getValue() == null ? other.getValue() != null : !this.getValue().equals(other.getValue())) return false;
      return true;
    }
    
    @Override public int hashCode() {
      final int PRIME = 59;
      int result = 1;
      result = (result*PRIME) + (this.getName() == null ? 43 : this.getName().hashCode());
      result = (result*PRIME) + (this.getValue() == null ? 43 : this.getValue().hashCode());
      return result;
    }
  }
}

Value修饰类，生成一个final类，并且成员变量全是private final修饰

• Value是个快捷方式，完整的注解：final @ToString @EqualsAndHashCode @AllArgsConstructor @FieldDefaults(makeFinal = true, level = AccessLevel.PRIVATE) @Getter
• 在修饰类和成员变量的同时，Value会生成toString、equals、hashCode方法，还有包括所有参数的构造方法以及所有成员变量的get方法
• 如果有任何自定义的构造方法，Value将不会再生成一个所有参数的构造方法

import lombok.AccessLevel;
import lombok.experimental.NonFinal;
import lombok.experimental.Value;
import lombok.experimental.Wither;
import lombok.ToString;

@Value public class ValueExample {
  String name;
  @Wither(AccessLevel.PACKAGE) @NonFinal int age;
  double score;
  protected String[] tags;
  
  @ToString(includeFieldNames=true)
  @Value(staticConstructor="of")
  public static class Exercise<T> {
    String name;
    T value;
  }
}

等同于

---

import java.util.Arrays;

public final class ValueExample {
  private final String name;
  private int age;
  private final double score;
  protected final String[] tags;
  
  @java.beans.ConstructorProperties({"name", "age", "score", "tags"})
  public ValueExample(String name, int age, double score, String[] tags) {
    this.name = name;
    this.age = age;
    this.score = score;
    this.tags = tags;
  }
  
  public String getName() {
    return this.name;
  }
  
  public int getAge() {
    return this.age;
  }
  
  public double getScore() {
    return this.score;
  }
  
  public String[] getTags() {
    return this.tags;
  }
  
  @java.lang.Override
  public boolean equals(Object o) {
    if (o == this) return true;
    if (!(o instanceof ValueExample)) return false;
    final ValueExample other = (ValueExample)o;
    final Object this$name = this.getName();
    final Object other$name = other.getName();
    if (this$name == null ? other$name != null : !this$name.equals(other$name)) return false;
    if (this.getAge() != other.getAge()) return false;
    if (Double.compare(this.getScore(), other.getScore()) != 0) return false;
    if (!Arrays.deepEquals(this.getTags(), other.getTags())) return false;
    return true;
  }
  
  @java.lang.Override
  public int hashCode() {
    final int PRIME = 59;
    int result = 1;
    final Object $name = this.getName();
    result = result * PRIME + ($name == null ? 43 : $name.hashCode());
    result = result * PRIME + this.getAge();
    final long $score = Double.doubleToLongBits(this.getScore());
    result = result * PRIME + (int)($score >>> 32 ^ $score);
    result = result * PRIME + Arrays.deepHashCode(this.getTags());
    return result;
  }
  
  @java.lang.Override
  public String toString() {
    return "ValueExample(name=" + getName() + ", age=" + getAge() + ", score=" + getScore() + ", tags=" + Arrays.deepToString(getTags()) + ")";
  }
  
  ValueExample withAge(int age) {
    return this.age == age ? this : new ValueExample(name, age, score, tags);
  }
  
  public static final class Exercise<T> {
    private final String name;
    private final T value;
    
    private Exercise(String name, T value) {
      this.name = name;
      this.value = value;
    }
    
    public static <T> Exercise<T> of(String name, T value) {
      return new Exercise<T>(name, value);
    }
    
    public String getName() {
      return this.name;
    }
    
    public T getValue() {
      return this.value;
    }
    
    @java.lang.Override
    public boolean equals(Object o) {
      if (o == this) return true;
      if (!(o instanceof ValueExample.Exercise)) return false;
      final Exercise<?> other = (Exercise<?>)o;
      final Object this$name = this.getName();
      final Object other$name = other.getName();
      if (this$name == null ? other$name != null : !this$name.equals(other$name)) return false;
      final Object this$value = this.getValue();
      final Object other$value = other.getValue();
      if (this$value == null ? other$value != null : !this$value.equals(other$value)) return false;
      return true;
    }
    
    @java.lang.Override
    public int hashCode() {
      final int PRIME = 59;
      int result = 1;
      final Object $name = this.getName();
      result = result * PRIME + ($name == null ? 43 : $name.hashCode());
      final Object $value = this.getValue();
      result = result * PRIME + ($value == null ? 43 : $value.hashCode());
      return result;
    }
    
    @java.lang.Override
    public String toString() {
      return "ValueExample.Exercise(name=" + getName() + ", value=" + getValue() + ")";
    }
  }
}

Builder 构造者模式生成实体类，可修饰类，构造方法和一般方法

类似

Person.builder().name("Adam Savage").city("San Francisco").job("Mythbusters").job("Unchained Reaction").build();

• 当一个方法被Builder注解修饰（以下简称target)，会有七个要素生成
  • 一个内部静态类叫做 FooBuilder ，有着和静态方法一样的类型参数(以下简称builder)
  • 在builder里，target方法的每一个参数都对应了一个私有的非静态非final的成员变量
  • 在builder里，包含一个package范围的私有无参的空构造方法
  • 在builder里，每一个target的参数都对应了一个类似setter的方法，但是这个setter方法跟target方法的参数名一样，并且返回了builder自身，以形成链式结构
  • 在builder里，包含一个build方法，用对应的参数调用target方法，最终生成target方法的返回值
  • 在builder里，包含一个合理的toString实现
  • 在target方法所在的类，会包含一个builder方法，他会创建类builder的实例
• 以上的7个要素如果在检测到有同名的要素时会自动跳过（只对比名称）
• 当Builder作用于类时，请确保该类没有任何显性的构造函数。如果有任意显性构造函数，请直接将Builder作用于构造函数上
• 当Builder和Value同时作用于一个类时，Builder想要生成的Package范围的构造函数会覆盖Value想要生成的private范围的构造函数
• 如果参数的值需要从某个字段或者方法获取，可以在字段或者参数上添加注解@Builder.ObtainVia(method = "")
• Builder可配置的方面包括
  • 静态内部类的名称(默认是type + “Builder”)
  • build方法的名称
  • builder方法的名称
  • 是否需要toBuilder()方法
  • 生成元素的访问范围
  • 如果你的构造链方法需要一个前缀，比如Person.builder().setName
• 关于以上配置项，下面是个实例
  @Builder(builderClassName = "HelloWorldBuilder", buildMethodName = "execute", builderMethodName = "helloWorld", toBuilder = true, access = AccessLevel.PRIVATE, setterPrefix = "set")
• 当Builder注解作用于类，某些成员变量不需要set的时候，可以设置成员变量默认值
  成员变量上用注解@Builder.Default实现
  @Builder.Default private final long created = System.currentTimeMillis();
• @Singular 注解作用于参数或者成员变量时，会吧对应参数当做集合。
  • 不会生成setter而会生成两个adder方法，一个新增单个，一个新增整个集合
  • 还会生成一个clear方法，一旦build方法被调用，生成的集合不能再被修改
  • 可指定新增单个的方法名@Singular("axis") List<Line> axes;
  • 如果追加的集合为null会抛出异常，可设置忽略空集合@Singular(ignoreNullCollections = true)

import lombok.Builder;
import lombok.Singular;
import java.util.Set;

@Builder
public class BuilderExample {
  @Builder.Default private long created = System.currentTimeMillis();
  private String name;
  private int age;
  @Singular private Set<String> occupations;
}

等同于

---

import java.util.Set;

public class BuilderExample {
  private long created;
  private String name;
  private int age;
  private Set<String> occupations;
  
  BuilderExample(String name, int age, Set<String> occupations) {
    this.name = name;
    this.age = age;
    this.occupations = occupations;
  }
  
  private static long $default$created() {
    return System.currentTimeMillis();
  }
  
  public static BuilderExampleBuilder builder() {
    return new BuilderExampleBuilder();
  }
  
  public static class BuilderExampleBuilder {
    private long created;
    private boolean created$set;
    private String name;
    private int age;
    private java.util.ArrayList<String> occupations;
    
    BuilderExampleBuilder() {
    }
    
    public BuilderExampleBuilder created(long created) {
      this.created = created;
      this.created$set = true;
      return this;
    }
    
    public BuilderExampleBuilder name(String name) {
      this.name = name;
      return this;
    }
    
    public BuilderExampleBuilder age(int age) {
      this.age = age;
      return this;
    }
    
    public BuilderExampleBuilder occupation(String occupation) {
      if (this.occupations == null) {
        this.occupations = new java.util.ArrayList<String>();
      }
      
      this.occupations.add(occupation);
      return this;
    }
    
    public BuilderExampleBuilder occupations(Collection<? extends String> occupations) {
      if (this.occupations == null) {
        this.occupations = new java.util.ArrayList<String>();
      }

      this.occupations.addAll(occupations);
      return this;
    }
    
    public BuilderExampleBuilder clearOccupations() {
      if (this.occupations != null) {
        this.occupations.clear();
      }
      
      return this;
    }

    public BuilderExample build() {
      // complicated switch statement to produce a compact properly sized immutable set omitted.
      Set<String> occupations = ...;
      return new BuilderExample(created$set ? created : BuilderExample.$default$created(), name, age, occupations);
    }
    
    @java.lang.Override
    public String toString() {
      return "BuilderExample.BuilderExampleBuilder(created = " + this.created + ", name = " + this.name + ", age = " + this.age + ", occupations = " + this.occupations + ")";
    }
  }
}

SneakyThrows checked Exception不用再try catch

不推荐

Synchronized 用户成员方法或者静态方法

关键字synchronized锁的是this，但是该注解锁的是不同的对象

import lombok.Synchronized;

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");
  }
}

等同于

---

public class SynchronizedExample {
  private static final Object $LOCK = new Object[0];
  private final Object $lock = new Object[0];
  private final Object readLock = new Object();
  
  public static void hello() {
    synchronized($LOCK) {
      System.out.println("world");
    }
  }
  
  public int answerToLife() {
    synchronized($lock) {
      return 42;
    }
  }
  
  public void foo() {
    synchronized(readLock) {
      System.out.println("bar");
    }
  }
}

With用于成员变量或者类上，表示可修改类中的任何或者指定字段，即使该字段是final

其实就是clone了一个当前类，并修改对应成员变量的值

import lombok.AccessLevel;
import lombok.NonNull;
import lombok.With;

public class WithExample {
  @With(AccessLevel.PROTECTED) @NonNull private final String name;
  @With private final int age;
  
  public WithExample(String name, int age) {
    if (name == null) throw new NullPointerException();
    this.name = name;
    this.age = age;
  }
}

import lombok.NonNull;

public class WithExample {
  private @NonNull final String name;
  private final int age;

  public WithExample(String name, int age) {
    if (name == null) throw new NullPointerException();
    this.name = name;
    this.age = age;
  }

  protected WithExample withName(@NonNull String name) {
    if (name == null) throw new java.lang.NullPointerException("name");
    return this.name == name ? this : new WithExample(name, age);
  }

  public WithExample withAge(int age) {
    return this.age == age ? this : new WithExample(name, age);
  }
}

Getter(lazy=true) 修饰private final 成员变量，获取一次，并缓存，之后都取缓存

当一个成员变量的计算需要消耗大量资源，可以将它设置为private final，并加上该注解
这个注解会在第一次计算后缓存结果，他要求计算方法是非线程安全的

import lombok.Getter;

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;
  }
}

等同于

---

public class GetterLazyExample {
  private final java.util.concurrent.AtomicReference<java.lang.Object> cached = new java.util.concurrent.AtomicReference<java.lang.Object>();
  
  public double[] getCached() {
    java.lang.Object value = this.cached.get();
    if (value == null) {
      synchronized(this.cached) {
        value = this.cached.get();
        if (value == null) {
          final double[] actualValue = expensive();
          value = actualValue == null ? this.cached : actualValue;
          this.cached.set(value);
        }
      }
    }
    return (double[])(value == this.cached ? null : value);
  }
  
  private double[] expensive() {
    double[] result = new double[1000000];
    for (int i = 0; i < result.length; i++) {
      result[i] = Math.asin(i);
    }
    return result;
  }
}

Log修饰类，增加成员变量log

多个注解，以适配多种Logger:

• @CommonsLog
  private static final org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory.getLog(LogExample.class);
• @Flogger
  private static final com.google.common.flogger.FluentLogger log = com.google.common.flogger.FluentLogger.forEnclosingClass();
• @JBossLog private static final org.jboss.logging.Logger log = org.jboss.logging.Logger.getLogger(LogExample.class);
• @Log
  private static final java.util.logging.Logger log = java.util.logging.Logger.getLogger(LogExample.class.getName());
• @Log4j
  private static final org.apache.log4j.Logger log = org.apache.log4j.Logger.getLogger(LogExample.class);
• @Log4j2
  private static final org.apache.logging.log4j.Logger log = org.apache.logging.log4j.LogManager.getLogger(LogExample.class);
• @Slf4j
  private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(LogExample.class);
• @XSlf4j
  private static final org.slf4j.ext.XLogger log = org.slf4j.ext.XLoggerFactory.getXLogger(LogExample.class);
• @CustomLog
  可自定义log，详情参考结尾的官方链接

import lombok.extern.java.Log;
import lombok.extern.slf4j.Slf4j;

@Log
public class LogExample {
  
  public static void main(String... args) {
    log.severe("Something's wrong here");
  }
}

@Slf4j
public class LogExampleOther {
  
  public static void main(String... args) {
    log.error("Something else is wrong here");
  }
}

@CommonsLog(topic="CounterLog")
public class LogExampleCategory {

  public static void main(String... args) {
    log.error("Calling the 'CounterLog' with a message");
  }
}

相当于

---

public class LogExample {
  private static final java.util.logging.Logger log = java.util.logging.Logger.getLogger(LogExample.class.getName());
  
  public static void main(String... args) {
    log.severe("Something's wrong here");
  }
}

public class LogExampleOther {
  private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(LogExampleOther.class);
  
  public static void main(String... args) {
    log.error("Something else is wrong here");
  }
}

public class LogExampleCategory {
  private static final org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory.getLog("CounterLog");

  public static void main(String... args) {
    log.error("Calling the 'CounterLog' with a message");
  }
}

详细参考 lombok官方文档