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lombok使用总结

作者：Monodyee | 2024-05-31 06:06:17

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import lombok.val依赖

前提

这篇文章主要介绍lombok的使用，至于lombok的源码和原理暂不探究，可以看上一篇文章插件化注解处理API去了解lombok的基本原理。参考资料：

简介

Project Lombok是一个java库，它可以自动插入到编辑器中，并构建工具，使java更加丰富。再也不用getter或equals方法了。尽早访问未来的java特性，比如val等等。这个就是lombok的官方简介(例如Jdk9中新增的val关键字在lombok中很早就出现了)。lombok实际上是基于JSR-269的插件化注解处理API，在编译期间对使用了特定注解的类、方法、属性或者代码片段进行动态修改，添加或者实现其自定义功能的类库。

安装

maven依赖

在项目中使用到lombok的注解必须引入其依赖：

  1. <dependency>
  2.     <groupId>org.projectlombok</groupId>
  3.     <artifactId>lombok</artifactId>
  4.     <version>${version}</version>
  5. </dependency>

当前的最新版本为:1.16.20。

插件

如果不为IDE安装lombok的插件，IDE无法识别lombok编译期动态生成的代码，表现为代码块标红，因此需要安装其插件，插件地址：https://projectlombok.org/download。

下载完成后，将会得到一个jar包lombok-xx.xx.xx.jar，直接使用命令java -jar lombok-xx.xx.xx.jar运行即可，然后按照指引安装到IDEA、eclipse或者myeclipse。

lombok注解

@val

@val用于声明修饰符为final的局部变量类型，使用的时候不需要编写实际的类型，这一点依赖于编译器的类型推导。@val的作用域是局部变量。举例如下：

使用lombok：

  1.  
  2.  import java.util.ArrayList;
  3. import java.util.HashMap;
  4. import lombok.val;
  5.  
  6. public class ValExample {
  7.   public String example() {
  8.     val example = new ArrayList<String>();
  9.     example.add("Hello, World!");
  10.     val foo = example.get(0);
  11.     return foo.toLowerCase();
  12.   }
  13. }

相当于原生Java：

  1.  
  2.  import java.util.ArrayList;
  3. import java.util.HashMap;
  4. import java.util.Map;
  5.  
  6. public class ValExample {
  7.   public String example() {
  8.     final ArrayList<String> example = new ArrayList<String>();
  9.     example.add("Hello, World!");
  10.     final String foo = example.get(0);
  11.     return foo.toLowerCase();
  12.   }
  13. }

@var

@var的功能类似于@val，不过@var修饰的是非final修饰的局部变量。

@NonNull

@NonNull的作用域是属性(field)、方法参数或、构造函数参数以及局部变量(LOCAL_VARIABLE)，为这些参数添加一个空检查语句，基本格式是：if(param == null) {throw new NullPointerException("param ");}。

使用lombok：

  1. import lombok.NonNull;
  2.  
  3. public class NonNullExample extends Something {
  4.   private String name;
  5.   
  6.   public NonNullExample(@NonNull Person person) {
  7.     super("Hello");
  8.     this.name = person.getName();
  9.   }
  10. }

相当于原生Java：

  1. import lombok.NonNull;
  2.  
  3. public class NonNullExample extends Something {
  4.   private String name;
  5.   
  6.   public NonNullExample(@NonNull Person person) {
  7.     super("Hello");
  8.     if (person == null) {
  9.       throw new NullPointerException("person");
  10.     }
  11.     this.name = person.getName();
  12.   }
  13. }

@Cleanup

你可以使用@Cleanup来确保在代码执行路径退出当前范围之前自动清理给定的资源，一般使用在流的局部变量的关闭。可以通过value()指定关闭资源的方法名，注意，关闭资源的方法必须是无参void方法，默认的关闭资源方法名称是"close"。

使用lombok：

  1. import lombok.Cleanup;
  2. import java.io.*;
  3.  
  4. public class CleanupExample {
  5.   public static void main(String[] args) throws IOException {
  6.     @Cleanup InputStream in = new FileInputStream(args[0]);
  7.     @Cleanup OutputStream out = new FileOutputStream(args[1]);
  8.     byte[] b = new byte[10000];
  9.     while (true) {
  10.       int r = in.read(b);
  11.       if (r == -1) break;
  12.       out.write(b, 0, r);
  13.     }
  14.   }
  15. }

相当于原生Java：

  1. import java.io.*;
  2.  
  3. public class CleanupExample {
  4.   public static void main(String[] args) throws IOException {
  5.     InputStream in = new FileInputStream(args[0]);
  6.     try {
  7.       OutputStream out = new FileOutputStream(args[1]);
  8.       try {
  9.         byte[] b = new byte[10000];
  10.         while (true) {
  11.           int r = in.read(b);
  12.           if (r == -1) break;
  13.           out.write(b, 0, r);
  14.         }
  15.       } finally {
  16.         if (out != null) {
  17.           out.close();
  18.         }
  19.       }
  20.     } finally {
  21.       if (in != null) {
  22.         in.close();
  23.       }
  24.     }
  25.   }
  26. }

@Getter/@Setter

@Getter/@Setter作用域是属性或者类。@Getter为指定属性或者类中的所有属性生成Getter方法，@Setter指定非final属性或者类中的所有非final属性生成Setter方法。可以通过@Getter/@Setter的value()中的AccessLevel属性来指定生成的方法的修饰符，可以通过@Getter的布尔值属性lazy来指定是否延迟加载。

使用lombok：

  1.  
  2.  import lombok.AccessLevel;
  3. import lombok.Getter;
  4. import lombok.Setter;
  5.  
  6. public class GetterSetterExample {
  7.   /**
  8.    * Age of the person. Water is wet.
  9.    * 
  10.    * @param age New value for this person's age. Sky is blue.
  11.    * @return The current value of this person's age. Circles are round.
  12.    */
  13.   @Getter @Setter private int age = 10;
  14.   
  15.   /**
  16.    * Name of the person.
  17.    * -- SETTER --
  18.    * Changes the name of this person.
  19.    * 
  20.    * @param name The new value.
  21.    */
  22.   @Setter(AccessLevel.PROTECTED) private String name;
  23.   
  24.   @Override public String toString() {
  25.     return String.format("%s (age: %d)", name, age);
  26.   }
  27. }

相当于原生Java：

  1. public class GetterSetterExample {
  2.   /**
  3.    * Age of the person. Water is wet.
  4.    */
  5.   private int age = 10;
  6.  
  7.   /**
  8.    * Name of the person.
  9.    */
  10.   private String name;
  11.   
  12.   @Override public String toString() {
  13.     return String.format("%s (age: %d)", name, age);
  14.   }
  15.   
  16.   /**
  17.    * Age of the person. Water is wet.
  18.    *
  19.    * @return The current value of this person's age. Circles are round.
  20.    */
  21.   public int getAge() {
  22.     return age;
  23.   }
  24.   
  25.   /**
  26.    * Age of the person. Water is wet.
  27.    *
  28.    * @param age New value for this person's age. Sky is blue.
  29.    */
  30.   public void setAge(int age) {
  31.     this.age = age;
  32.   }
  33.   
  34.   /**
  35.    * Changes the name of this person.
  36.    *
  37.    * @param name The new value.
  38.    */
  39.   protected void setName(String name) {
  40.     this.name = name;
  41.   }
  42. }

@ToString

@ToString的作用域是类，主要作用是覆盖类中的toString方法。@ToString的属性比较多，简介如下：

  • includeFieldNames()：布尔值，默认为true，true表示拼接toString的时候使用属性名。
  • exclude()：字符串数组，默认为空，用于通过属性名排除拼接toString时使用的属性。
  • of()：exclude()属性的对立属性，意思就是include。
  • callSuper()：布尔值，默认为false，是否调用父类的属性。
  • doNotUseGetters()：布尔值，默认为false，true表示拼接toString的时候使用属性值而不是其Getter方法。

下面是官方例子：

使用lombok：

  1. import lombok.ToString;
  2.  
  3. @ToString(exclude="id")
  4. public class ToStringExample {
  5.   private static final int STATIC_VAR = 10;
  6.   private String name;
  7.   private Shape shape = new Square(5, 10);
  8.   private String[] tags;
  9.   private int id;
  10.   
  11.   public String getName() {
  12.     return this.name;
  13.   }
  14.   
  15.   @ToString(callSuper=true, includeFieldNames=true)
  16.   public static class Square extends Shape {
  17.     private final int width, height;
  18.     
  19.     public Square(int width, int height) {
  20.       this.width = width;
  21.       this.height = height;
  22.     }
  23.   }
  24. }

相当于原生Java：

  1. import java.util.Arrays;
  2.  
  3. public class ToStringExample {
  4.   private static final int STATIC_VAR = 10;
  5.   private String name;
  6.   private Shape shape = new Square(5, 10);
  7.   private String[] tags;
  8.   private int id;
  9.   
  10.   public String getName() {
  11.     return this.getName();
  12.   }
  13.   
  14.   public static class Square extends Shape {
  15.     private final int width, height;
  16.     
  17.     public Square(int width, int height) {
  18.       this.width = width;
  19.       this.height = height;
  20.     }
  21.     
  22.     @Override public String toString() {
  23.       return "Square(super=" + super.toString() + ", width=" + this.width + ", height=" + this.height + ")";
  24.     }
  25.   }
  26.   
  27.   @Override public String toString() {
  28.     return "ToStringExample(" + this.getName() + ", " + this.shape + ", " + Arrays.deepToString(this.tags) + ")";
  29.   }
  30. }

@EqualsAndHashCode

@EqualsAndHashCode的作用域是类，用于生成equals()和hashCode()方法。此注解的属性比较多，不过和@ToString类似。举例如下：

使用lombok：

  1. import lombok.EqualsAndHashCode;
  2.  
  3. @EqualsAndHashCode(exclude={"id", "shape"})
  4. public class EqualsAndHashCodeExample {
  5.   private transient int transientVar = 10;
  6.   private String name;
  7.   private double score;
  8.   private Shape shape = new Square(5, 10);
  9.   private String[] tags;
  10.   private int id;
  11.   
  12.   public String getName() {
  13.     return this.name;
  14.   }
  15.   
  16.   @EqualsAndHashCode(callSuper=true)
  17.   public static class Square extends Shape {
  18.     private final int width, height;
  19.     
  20.     public Square(int width, int height) {
  21.       this.width = width;
  22.       this.height = height;
  23.     }
  24.   }
  25. }

相当于原生Java：

  1. import java.util.Arrays;
  2.  
  3. public class EqualsAndHashCodeExample {
  4.   private transient int transientVar = 10;
  5.   private String name;
  6.   private double score;
  7.   private Shape shape = new Square(5, 10);
  8.   private String[] tags;
  9.   private int id;
  10.   
  11.   public String getName() {
  12.     return this.name;
  13.   }
  14.   
  15.   @Override public boolean equals(Object o) {
  16.     if (o == this) return true;
  17.     if (!(o instanceof EqualsAndHashCodeExample)) return false;
  18.     EqualsAndHashCodeExample other = (EqualsAndHashCodeExample) o;
  19.     if (!other.canEqual((Object)this)) return false;
  20.     if (this.getName() == null ? other.getName() != null : !this.getName().equals(other.getName())) return false;
  21.     if (Double.compare(this.score, other.score) != 0) return false;
  22.     if (!Arrays.deepEquals(this.tags, other.tags)) return false;
  23.     return true;
  24.   }
  25.   
  26.   @Override public int hashCode() {
  27.     final int PRIME = 59;
  28.     int result = 1;
  29.     final long temp1 = Double.doubleToLongBits(this.score);
  30.     result = (result*PRIME) + (this.name == null ? 43 : this.name.hashCode());
  31.     result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));
  32.     result = (result*PRIME) + Arrays.deepHashCode(this.tags);
  33.     return result;
  34.   }
  35.   
  36.   protected boolean canEqual(Object other) {
  37.     return other instanceof EqualsAndHashCodeExample;
  38.   }
  39.   
  40.   public static class Square extends Shape {
  41.     private final int width, height;
  42.     
  43.     public Square(int width, int height) {
  44.       this.width = width;
  45.       this.height = height;
  46.     }
  47.     
  48.     @Override public boolean equals(Object o) {
  49.       if (o == this) return true;
  50.       if (!(o instanceof Square)) return false;
  51.       Square other = (Square) o;
  52.       if (!other.canEqual((Object)this)) return false;
  53.       if (!super.equals(o)) return false;
  54.       if (this.width != other.width) return false;
  55.       if (this.height != other.height) return false;
  56.       return true;
  57.     }
  58.     
  59.     @Override public int hashCode() {
  60.       final int PRIME = 59;
  61.       int result = 1;
  62.       result = (result*PRIME) + super.hashCode();
  63.       result = (result*PRIME) + this.width;
  64.       result = (result*PRIME) + this.height;
  65.       return result;
  66.     }
  67.     
  68.     protected boolean canEqual(Object other) {
  69.       return other instanceof Square;
  70.     }
  71.   }
  72. }

@NoArgsConstructor, @RequiredArgsConstructor, @AllArgsConstructor

这三个注解的作用域都是类。@NoArgsConstructor作用是生成一个无参数的构造函数。@AllArgsConstructor作用是生成一个具有所有字段的构造函数。@RequiredArgsConstructor的作用是为每一个使用了final或者@NonNull修饰的属性都生成一个只有一个参数的构造函数。这三个注解都可以通过staticName()指定构造的命名，通过access()指定构造的修饰符。@NoArgsConstructor的属性force()默认值为false，当类中存在final属性的时候使用了@NoArgsConstructor会编译错误，如果force()值为true，那么会把final修饰的属性作为"无参数构造"的参数，并且把属性赋值为0、null或者false。

使用lombok：

  1. import lombok.AccessLevel;
  2. import lombok.RequiredArgsConstructor;
  3. import lombok.AllArgsConstructor;
  4. import lombok.NonNull;
  5.  
  6. @RequiredArgsConstructor(staticName = "of")
  7. @AllArgsConstructor(access = AccessLevel.PROTECTED)
  8. public class ConstructorExample<T> {
  9.   private int x, y;
  10.   @NonNull private T description;
  11.   
  12.   @NoArgsConstructor
  13.   public static class NoArgsExample {
  14.     @NonNull private String field;
  15.   }
  16. }

相当于原生Java：

  1.  
  2.  public class ConstructorExample<T> {
  3.   private int x, y;
  4.   @NonNull private T description;
  5.   
  6.   private ConstructorExample(T description) {
  7.     if (description == null) throw new NullPointerException("description");
  8.     this.description = description;
  9.   }
  10.   
  11.   public static <T> ConstructorExample<T> of(T description) {
  12.     return new ConstructorExample<T>(description);
  13.   }
  14.   
  15.   @java.beans.ConstructorProperties({"x", "y", "description"})
  16.   protected ConstructorExample(int x, int y, T description) {
  17.     if (description == null) throw new NullPointerException("description");
  18.     this.x = x;
  19.     this.y = y;
  20.     this.description = description;
  21.   }
  22.   
  23.   public static class NoArgsExample {
  24.     @NonNull private String field;
  25.     
  26.     public NoArgsExample() {
  27.     }
  28.   }
  29. }

@Data

@Data的作用域是类，相当于同时应用了@Getter、@Setter、@ToString、@EqualsAndHashCode、@RequiredArgsConstructor。如果已经显示自定义过构造函数，就不会再自动生成构造函数了。举例如下：

使用lombok：

  1. import lombok.AccessLevel;
  2. import lombok.Setter;
  3. import lombok.Data;
  4. import lombok.ToString;
  5.  
  6. @Data public class DataExample {
  7.   private final String name;
  8.   @Setter(AccessLevel.PACKAGE) private int age;
  9.   private double score;
  10.   private String[] tags;
  11.   
  12.   @ToString(includeFieldNames=true)
  13.   @Data(staticConstructor="of")
  14.   public static class Exercise<T> {
  15.     private final String name;
  16.     private final T value;
  17.   }
  18. }

相当于原生Java：

  1. import java.util.Arrays;
  2.  
  3. public class DataExample {
  4.   private final String name;
  5.   private int age;
  6.   private double score;
  7.   private String[] tags;
  8.   
  9.   public DataExample(String name) {
  10.     this.name = name;
  11.   }
  12.   
  13.   public String getName() {
  14.     return this.name;
  15.   }
  16.   
  17.   void setAge(int age) {
  18.     this.age = age;
  19.   }
  20.   
  21.   public int getAge() {
  22.     return this.age;
  23.   }
  24.   
  25.   public void setScore(double score) {
  26.     this.score = score;
  27.   }
  28.   
  29.   public double getScore() {
  30.     return this.score;
  31.   }
  32.   
  33.   public String[] getTags() {
  34.     return this.tags;
  35.   }
  36.   
  37.   public void setTags(String[] tags) {
  38.     this.tags = tags;
  39.   }
  40.   
  41.   @Override public String toString() {
  42.     return "DataExample(" + this.getName() + ", " + this.getAge() + ", " + this.getScore() + ", " + Arrays.deepToString(this.getTags()) + ")";
  43.   }
  44.   
  45.   protected boolean canEqual(Object other) {
  46.     return other instanceof DataExample;
  47.   }
  48.   
  49.   @Override public boolean equals(Object o) {
  50.     if (o == this) return true;
  51.     if (!(o instanceof DataExample)) return false;
  52.     DataExample other = (DataExample) o;
  53.     if (!other.canEqual((Object)this)) return false;
  54.     if (this.getName() == null ? other.getName() != null : !this.getName().equals(other.getName())) return false;
  55.     if (this.getAge() != other.getAge()) return false;
  56.     if (Double.compare(this.getScore(), other.getScore()) != 0) return false;
  57.     if (!Arrays.deepEquals(this.getTags(), other.getTags())) return false;
  58.     return true;
  59.   }
  60.   
  61.   @Override public int hashCode() {
  62.     final int PRIME = 59;
  63.     int result = 1;
  64.     final long temp1 = Double.doubleToLongBits(this.getScore());
  65.     result = (result*PRIME) + (this.getName() == null ? 43 : this.getName().hashCode());
  66.     result = (result*PRIME) + this.getAge();
  67.     result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));
  68.     result = (result*PRIME) + Arrays.deepHashCode(this.getTags());
  69.     return result;
  70.   }
  71.   
  72.   public static class Exercise<T> {
  73.     private final String name;
  74.     private final T value;
  75.     
  76.     private Exercise(String name, T value) {
  77.       this.name = name;
  78.       this.value = value;
  79.     }
  80.     
  81.     public static <T> Exercise<T> of(String name, T value) {
  82.       return new Exercise<T>(name, value);
  83.     }
  84.     
  85.     public String getName() {
  86.       return this.name;
  87.     }
  88.     
  89.     public T getValue() {
  90.       return this.value;
  91.     }
  92.     
  93.     @Override public String toString() {
  94.       return "Exercise(name=" + this.getName() + ", value=" + this.getValue() + ")";
  95.     }
  96.     
  97.     protected boolean canEqual(Object other) {
  98.       return other instanceof Exercise;
  99.     }
  100.     
  101.     @Override public boolean equals(Object o) {
  102.       if (o == this) return true;
  103.       if (!(o instanceof Exercise)) return false;
  104.       Exercise<?> other = (Exercise<?>) o;
  105.       if (!other.canEqual((Object)this)) return false;
  106.       if (this.getName() == null ? other.getValue() != null : !this.getName().equals(other.getName())) return false;
  107.       if (this.getValue() == null ? other.getValue() != null : !this.getValue().equals(other.getValue())) return false;
  108.       return true;
  109.     }
  110.     
  111.     @Override public int hashCode() {
  112.       final int PRIME = 59;
  113.       int result = 1;
  114.       result = (result*PRIME) + (this.getName() == null ? 43 : this.getName().hashCode());
  115.       result = (result*PRIME) + (this.getValue() == null ? 43 : this.getValue().hashCode());
  116.       return result;
  117.     }
  118.   }
  119. }

@Value

@Value的作用域是类，和@Data类似，但是用于不可变类型。生成的类和所有字段都设置为final，所有字段都为private，自动生成Getter但是没有Setter，会生成初始化所有字段的构造函数。相当于同时应用了final、 @ToString、 @EqualsAndHashCode、 @AllArgsConstructor 、@FieldDefaults(makeFinal = true, level = AccessLevel.PRIVATE)和@Getter。

使用lombok：

  1. import lombok.AccessLevel;
  2. import lombok.experimental.NonFinal;
  3. import lombok.experimental.Value;
  4. import lombok.experimental.Wither;
  5. import lombok.ToString;
  6.  
  7. @Value public class ValueExample {
  8.   String name;
  9.   @Wither(AccessLevel.PACKAGE) @NonFinal int age;
  10.   double score;
  11.   protected String[] tags;
  12.   
  13.   @ToString(includeFieldNames=true)
  14.   @Value(staticConstructor="of")
  15.   public static class Exercise<T> {
  16.     String name;
  17.     T value;
  18.   }
  19. }

相当于原生Java：

  1. import java.util.Arrays;
  2.  
  3. public final class ValueExample {
  4.   private final String name;
  5.   private int age;
  6.   private final double score;
  7.   protected final String[] tags;
  8.   
  9.   @java.beans.ConstructorProperties({"name", "age", "score", "tags"})
  10.   public ValueExample(String name, int age, double score, String[] tags) {
  11.     this.name = name;
  12.     this.age = age;
  13.     this.score = score;
  14.     this.tags = tags;
  15.   }
  16.   
  17.   public String getName() {
  18.     return this.name;
  19.   }
  20.   
  21.   public int getAge() {
  22.     return this.age;
  23.   }
  24.   
  25.   public double getScore() {
  26.     return this.score;
  27.   }
  28.   
  29.   public String[] getTags() {
  30.     return this.tags;
  31.   }
  32.   
  33.   @java.lang.Override
  34.   public boolean equals(Object o) {
  35.     if (o == this) return true;
  36.     if (!(o instanceof ValueExample)) return false;
  37.     final ValueExample other = (ValueExample)o;
  38.     final Object this$name = this.getName();
  39.     final Object other$name = other.getName();
  40.     if (this$name == null ? other$name != null : !this$name.equals(other$name)) return false;
  41.     if (this.getAge() != other.getAge()) return false;
  42.     if (Double.compare(this.getScore(), other.getScore()) != 0) return false;
  43.     if (!Arrays.deepEquals(this.getTags(), other.getTags())) return false;
  44.     return true;
  45.   }
  46.   
  47.   @java.lang.Override
  48.   public int hashCode() {
  49.     final int PRIME = 59;
  50.     int result = 1;
  51.     final Object $name = this.getName();
  52.     result = result * PRIME + ($name == null ? 43 : $name.hashCode());
  53.     result = result * PRIME + this.getAge();
  54.     final long $score = Double.doubleToLongBits(this.getScore());
  55.     result = result * PRIME + (int)($score >>> 32 ^ $score);
  56.     result = result * PRIME + Arrays.deepHashCode(this.getTags());
  57.     return result;
  58.   }
  59.   
  60.   @java.lang.Override
  61.   public String toString() {
  62.     return "ValueExample(name=" + getName() + ", age=" + getAge() + ", score=" + getScore() + ", tags=" + Arrays.deepToString(getTags()) + ")";
  63.   }
  64.   
  65.   ValueExample withAge(int age) {
  66.     return this.age == age ? this : new ValueExample(name, age, score, tags);
  67.   }
  68.   
  69.   public static final class Exercise<T> {
  70.     private final String name;
  71.     private final T value;
  72.     
  73.     private Exercise(String name, T value) {
  74.       this.name = name;
  75.       this.value = value;
  76.     }
  77.     
  78.     public static <T> Exercise<T> of(String name, T value) {
  79.       return new Exercise<T>(name, value);
  80.     }
  81.     
  82.     public String getName() {
  83.       return this.name;
  84.     }
  85.     
  86.     public T getValue() {
  87.       return this.value;
  88.     }
  89.     
  90.     @java.lang.Override
  91.     public boolean equals(Object o) {
  92.       if (o == this) return true;
  93.       if (!(o instanceof ValueExample.Exercise)) return false;
  94.       final Exercise<?> other = (Exercise<?>)o;
  95.       final Object this$name = this.getName();
  96.       final Object other$name = other.getName();
  97.       if (this$name == null ? other$name != null : !this$name.equals(other$name)) return false;
  98.       final Object this$value = this.getValue();
  99.       final Object other$value = other.getValue();
  100.       if (this$value == null ? other$value != null : !this$value.equals(other$value)) return false;
  101.       return true;
  102.     }
  103.     
  104.     @java.lang.Override
  105.     public int hashCode() {
  106.       final int PRIME = 59;
  107.       int result = 1;
  108.       final Object $name = this.getName();
  109.       result = result * PRIME + ($name == null ? 43 : $name.hashCode());
  110.       final Object $value = this.getValue();
  111.       result = result * PRIME + ($value == null ? 43 : $value.hashCode());
  112.       return result;
  113.     }
  114.     
  115.     @java.lang.Override
  116.     public String toString() {
  117.       return "ValueExample.Exercise(name=" + getName() + ", value=" + getValue() + ")";
  118.     }
  119.   }
  120. }

@Builder

@Builder的作用域是类，使用此注解后类中新增一个成员类(Builder)将会使用构建者模式，编译时增加了一个Builder内部类和全字段的构造器。@Builder.Default用于指定Builder中的属性的默认值，@Singular用于告诉lombok当前属性类型是集合类型，lombok会为信任的集合类型添加"adder"方法而不是"setter"方法。

使用lombok：

  1. import lombok.Builder;
  2. import lombok.Singular;
  3. import java.util.Set;
  4.  
  5. @Builder
  6. public class BuilderExample {
  7.   @Builder.Default private long created = System.currentTimeMillis();
  8.   private String name;
  9.   private int age;
  10.   @Singular private Set<String> occupations;
  11. }

相当于原生Java：

  1.  
  2.  import java.util.Set;
  3.  
  4. public class BuilderExample {
  5.   private long created;
  6.   private String name;
  7.   private int age;
  8.   private Set<String> occupations;
  9.   
  10.   BuilderExample(String name, int age, Set<String> occupations) {
  11.     this.name = name;
  12.     this.age = age;
  13.     this.occupations = occupations;
  14.   }
  15.   
  16.   private static long $default$created() {
  17.     return System.currentTimeMillis();
  18.   }
  19.   
  20.   public static BuilderExampleBuilder builder() {
  21.     return new BuilderExampleBuilder();
  22.   }
  23.   
  24.   public static class BuilderExampleBuilder {
  25.     private long created;
  26.     private boolean created$set;
  27.     private String name;
  28.     private int age;
  29.     private java.util.ArrayList<String> occupations;
  30.     
  31.     BuilderExampleBuilder() {
  32.     }
  33.     
  34.     public BuilderExampleBuilder created(long created) {
  35.       this.created = created;
  36.       this.created$set = true;
  37.       return this;
  38.     }
  39.     
  40.     public BuilderExampleBuilder name(String name) {
  41.       this.name = name;
  42.       return this;
  43.     }
  44.     
  45.     public BuilderExampleBuilder age(int age) {
  46.       this.age = age;
  47.       return this;
  48.     }
  49.     
  50.     public BuilderExampleBuilder occupation(String occupation) {
  51.       if (this.occupations == null) {
  52.         this.occupations = new java.util.ArrayList<String>();
  53.       }
  54.       
  55.       this.occupations.add(occupation);
  56.       return this;
  57.     }
  58.     
  59.     public BuilderExampleBuilder occupations(Collection<? extends String> occupations) {
  60.       if (this.occupations == null) {
  61.         this.occupations = new java.util.ArrayList<String>();
  62.       }
  63.  
  64.       this.occupations.addAll(occupations);
  65.       return this;
  66.     }
  67.     
  68.     public BuilderExampleBuilder clearOccupations() {
  69.       if (this.occupations != null) {
  70.         this.occupations.clear();
  71.       }
  72.       
  73.       return this;
  74.     }
  75.  
  76.     public BuilderExample build() {
  77.       // complicated switch statement to produce a compact properly sized immutable set omitted.
  78.       Set<String> occupations = ...;
  79.       return new BuilderExample(created$set ? created : BuilderExample.$default$created(), name, age, occupations);
  80.     }
  81.     
  82.     @java.lang.Override
  83.     public String toString() {
  84.       return "BuilderExample.BuilderExampleBuilder(created = " + this.created + ", name = " + this.name + ", age = " + this.age + ", occupations = " + this.occupations + ")";
  85.     }
  86.   }
  87. }

@Synchronized

@Synchronized的作用域是方法，用于方法同步，使用此注解后，方法体中的代码块自动包含在一个synchronize块中。synchronize块加锁的对象一定是类中的一个成员属性，可以通过@Synchronized的value()指定，如果不存在则由lombok新建，一般是private final Object $lock = new Object[0];。

使用lombok：

  1. import lombok.Synchronized;
  2.  
  3. public class SynchronizedExample {
  4.   private final Object readLock = new Object();
  5.   
  6.   @Synchronized
  7.   public static void hello() {
  8.     System.out.println("world");
  9.   }
  10.   
  11.   @Synchronized
  12.   public int answerToLife() {
  13.     return 42;
  14.   }
  15.   
  16.   @Synchronized("readLock")
  17.   public void foo() {
  18.     System.out.println("bar");
  19.   }
  20. }

相当于原生Java：

  1.  
  2.  public class SynchronizedExample {
  3.   private static final Object $LOCK = new Object[0];
  4.   private final Object $lock = new Object[0];
  5.   private final Object readLock = new Object();
  6.   
  7.   public static void hello() {
  8.     synchronized($LOCK) {
  9.       System.out.println("world");
  10.     }
  11.   }
  12.   
  13.   public int answerToLife() {
  14.     synchronized($lock) {
  15.       return 42;
  16.     }
  17.   }
  18.   
  19.   public void foo() {
  20.     synchronized(readLock) {
  21.       System.out.println("bar");
  22.     }
  23.   }
  24. }

@SneakyThrows

@SneakyThrows的作用域是构造或者方法，用于自动捕获(隐藏)检查异常。我们知道，java对于检查异常，需要在编码时进行捕获，或者抛出。该注解的作用是将检查异常包装为运行时异常，那么编码时就无需处理异常了。

提示：不过这并不是友好的编码方式，因为你编写的api的使用者，不能显式的获知需要处理检查异常。

使用lombok：

  1. import lombok.SneakyThrows;
  2.  
  3. public class SneakyThrowsExample implements Runnable {
  4.   @SneakyThrows(UnsupportedEncodingException.class)
  5.   public String utf8ToString(byte[] bytes) {
  6.     return new String(bytes, "UTF-8");
  7.   }
  8.   
  9.   @SneakyThrows
  10.   public void run() {
  11.     throw new Throwable();
  12.   }
  13. }

相当于原生Java：

  1. import lombok.Lombok;
  2.  
  3. public class SneakyThrowsExample implements Runnable {
  4.   public String utf8ToString(byte[] bytes) {
  5.     try {
  6.       return new String(bytes, "UTF-8");
  7.     } catch (UnsupportedEncodingException e) {
  8.       throw Lombok.sneakyThrow(e);
  9.     }
  10.   }
  11.   
  12.   public void run() {
  13.     try {
  14.       throw new Throwable();
  15.     } catch (Throwable t) {
  16.       throw Lombok.sneakyThrow(t);
  17.     }
  18.   }
  19. }

@Log

@Log的作用域是类，用于生成日志API句柄。目前支持的类型如下：

  1. @CommonsLog 
  2. 相当于在类中定义了：private static final org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory.getLog(LogExample.class);
  3. @JBossLog
  4. 相当于在类中定义了：private static final org.jboss.logging.Logger log = org.jboss.logging.Logger.getLogger(LogExample.class);
  5. @Log
  6. 相当于在类中定义了：private static final java.util.logging.Logger log = java.util.logging.Logger.getLogger(LogExample.class.getName());
  7. @Log4j
  8. 相当于在类中定义了：private static final org.apache.log4j.Logger log = org.apache.log4j.Logger.getLogger(LogExample.class);
  9. @Log4j2
  10. 相当于在类中定义了：private static final org.apache.logging.log4j.Logger log = org.apache.logging.log4j.LogManager.getLogger(LogExample.class);
  11. @Slf4j
  12. 相当于在类中定义了：private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(LogExample.class);
  13. @XSlf4j
  14. 相当于在类中定义了：private static final org.slf4j.ext.XLogger log = org.slf4j.ext.XLoggerFactory.getXLogger(LogExample.class);

使用lombok：

  1. import lombok.extern.java.Log;
  2. import lombok.extern.slf4j.Slf4j;
  3.  
  4. @Log
  5. public class LogExample {
  6.   
  7.   public static void main(String... args) {
  8.     log.error("Something's wrong here");
  9.   }
  10. }
  11.  
  12. @Slf4j
  13. public class LogExampleOther {
  14.   
  15.   public static void main(String... args) {
  16.     log.error("Something else is wrong here");
  17.   }
  18. }
  19.  
  20. @CommonsLog(topic="CounterLog")
  21. public class LogExampleCategory {
  22.  
  23.   public static void main(String... args) {
  24.     log.error("Calling the 'CounterLog' with a message");
  25.   }
  26. }

相当于原生Java：

  1.  
  2.  public class LogExample {
  3.   private static final java.util.logging.Logger log = java.util.logging.Logger.getLogger(LogExample.class.getName());
  4.   
  5.   public static void main(String... args) {
  6.     log.error("Something's wrong here");
  7.   }
  8. }
  9.  
  10. public class LogExampleOther {
  11.   private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(LogExampleOther.class);
  12.   
  13.   public static void main(String... args) {
  14.     log.error("Something else is wrong here");
  15.   }
  16. }
  17.  
  18. public class LogExampleCategory {
  19.   private static final org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory.getLog("CounterLog");
  20.  
  21.   public static void main(String... args) {
  22.     log.error("Calling the 'CounterLog' with a message");
  23.   }
  24. }

小结

其实从实现的角度来看，lombok并不是一个十分奇特的框架，它用到的技术已经是"很老的"Jdk6的一个特性，但是它表现出来的特性确实令人感觉它就是奇技淫巧。毕竟是奇技淫巧，很多不了解的人就会望然生畏，觉得使用了它很可能会导致系统出现无法预知的BUG之类(这里吐槽一下，笔者所在的公司禁用lombok)。其实，基于插件化注解处理API生成代码是位于编译期间，如果出现任何问题，很明显编译是不可能通过的。如果觉得lombok有问题，大可以去翻看每一个编译后的文件，看它们有没有表现异常。lombok在日常编码中可以极大提高效率，因此它一定是百益而无一害的。

（全文完）

转载于:https://www.cnblogs.com/throwable/p/9139922.html

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