lombok在java项目中的使用

时间:2022-07-23
本文章向大家介绍lombok在java项目中的使用，主要内容包括其使用实例、应用技巧、基本知识点总结和需要注意事项，具有一定的参考价值，需要的朋友可以参考一下。

lombok简介

IDEA配置lombok

lombok常用的注解

@Getter/@Setter

@ToString

@NonNull

@EqualsAndHashCode

@NoArgsConstructor@RequiredArgsConstructor@AllArgsConstructor

@Data

@Cleanup

@Builder

lombok简介

lombok是一个java类库，能够自动植入开发者的编译器来辅助java开发。使用lombok，可以使用一个注解来代替getter等方法的编写。使用起来非常简单，maven pom.xml文件中加入如下依赖，

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.12</version>
</dependency>
在实体类上加上注解@Data
@Data
public class Employee{

  private Long id;
  private String name;
  private String department;
  private Long number;
}

测试代码如下：

从图片中可以看出有编译错误代码，但是执行这个测试用例可以成功。

IDEA配置lombok

IDEA中安装lombok插件可以去除编译错误，跟安装普通插件一样，File->Settings->Plugins,如下图

重启后编译错误消失，注意点击下图中右下角的Enable按钮

lombok常用的注解

@Getter/@Setter

注解在类上，为所有非静态变量生产get和set方法

@ToString

注解在pojo类上面，为类生成toString方法，如果要在toString中排除一个变量，可以在该变量上面加上注解ToString.exclude,如果要在toString中打印出非静态变量，在非静态变量上增加@ToString.Include，如果要改变打印出的变量名称，在变量上加注解@ToString.Include(name = "username")，也可以通过@ToString.Include(rank = -1)来配置打印顺序，rank值越大越先打印 ·

如下示例：

@Setter
@ToString
public class ToStringExample {

    private static final int STATIC_VAR = 10;
    /**姓名**/
    private String name;
    private Square square = new Square(5, 10);
    private String[] tags;
    @ToString.Include(rank = 1)
    private static String password = "123456";
    @ToString.Exclude
    private int id;

    public String getName() {
        return this.name;
    }

    @ToString(callSuper=true)
    public static class Square {
        private final int width, height;

        public Square(int width, int height) {
            this.width = width;
            this.height = height;
        }
    }

    public static void main(String[] args){
        ToStringExample toStringExample = new ToStringExample();
        toStringExample.setName("jinjunzhu");
        toStringExample.setTags(new String[]{"123", "234"});
        System.out.println(toStringExample.toString());
    }
}点击并拖拽以移动

打印结果如下：

ToStringExample(password=123456, name=jinjunzhu, square=ToStringExample.Square(super=boot.lombok.ToStringExample$Square@446cdf90, width=5, height=10), tags=[123, 234])

@NonNull

检查借据是否为空，如果为空，抛出空指针异常

如下代码：

public class NonNullExample {

    private String name;

    public NonNullExample(@NonNull String name) {
        this.name = name;
    }

    public static void main(String[] args){
        NonNullExample nonNullExample = new NonNullExample(null);
    }
}点击并拖拽以移动

执行后结果如下：

@EqualsAndHashCode

为类生成equals(Object other)和hashcode()方法,默认为

non-static, non-transient生成，也可以用@EqualsAndHashCode.Include或@EqualsAndHashCode.Exclude来生成或不生成

如下2段代码等价

@EqualsAndHashCode
public class EqualsAndHashCodeExample {
    private transient int transientVar = 10;
    private String name;
    private double score;
    @EqualsAndHashCode.Exclude private Square shape = new Square(5, 10);
    private String[] tags;
    @EqualsAndHashCode.Exclude private int id;

    public String getName() {
        return this.name;
    }

    @EqualsAndHashCode()
    public static class Square {
        private final int width, height;

        public Square(int width, int height) {
            this.width = width;
            this.height = height;
        }
    }
}点击并拖拽以移动

这段代码等价于如下代码 

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 {
    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;
    }
  }
}点击并拖拽以移动

@NoArgsConstructor@RequiredArgsConstructor@AllArgsConstructor

@NoArgsConstructor产生一个无参构造函数

@RequiredArgsConstructor将为没有给变量生产一个只有一个参数的构造函数

@AllArgsConstructor将生成一个有所有变量的构造函数,其中的staticName属性指定生产一个静态构造函数的名称，代码如下：

@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;
    }

    public static void main(String[] args){
        ConstructorExample<User> constructorExample1 = new ConstructorExample<User>(1, 1, new User());
        ConstructorExample<User> constructorExample2 = ConstructorExample.of(new User());
    }
}点击并拖拽以移动

@Data

是 @ToString, @EqualsAndHashCode, @Getter on all fields, @Setter在所有非final变量和@RequiredArgsConstructor的汇集功能，也就是说能为POJO类所有变量生成getters方法, 为所有非final方法生产setters, toString, equals和hashCode方法代码如下：

@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;
    }
}点击并拖拽以移动

@Cleanup

用于代码执行完成后自动释放资源，代码如下：

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);
        }
    }
}

@Builder

引入一个复杂的构造函数，代码如下：

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

    public static void main(String args){
        BuilderExample.builder().created(System.currentTimeMillis()).age(30).name("jinjunzhu");
    }
}

还有一些不常用的变量，不一一介绍了，大家参考如下链接：

https://projectlombok.org/features/all

文中源码地址：

https://github.com/jinjunzhu/spring-boot-mybatis.git

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