Java开发神器Lombok的安装与使用

秃头哥编程

发布于 2019-06-17 15:44:58

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发布于 2019-06-17 15:44:58

文章被收录于专栏：秃头哥编程

项目中经常使用bean，entity等类，绝大部分数据类类中都需要get、set、toString、equals和hashCode方法，虽然eclipse和idea开发环境下都有自动生成的快捷方式，但自动生成这些代码后，如果bean中的属性一旦有修改、删除或增加时，需要重新生成或删除get/set等方法，给代码维护增加负担。而使用了lombok则不一样，使用了lombok的注解(@Setter,@Getter,@ToString,@@RequiredArgsConstructor,@EqualsAndHashCode或@Data)之后，就不需要编写或生成get/set等方法，很大程度上减少了代码量，而且减少了代码维护的负担。故强烈建议项目中使用lombok，去掉bean中get、set、toString、equals和hashCode等方法的代码。

一、IDEA安装Lombok

安装过程如下图

安装完成后，重启IDEA即可。

二、在pom中添加依赖

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.16.20</version>
    <scope>provided</scope>
</dependency>

三、Lombok常用注解

1、@Getter/@Setter注解为属性自动生成get/set方法。

@Setter
@Getter
public class User {
    private Long id;
    private String name;
    private String password;
    private String salt;
    private Integer status;
    private String address;
    private String phone;
    private Date lasttime;
}

2、@ToString注解，生成一个toString方法，默认的toString格式为：ClassName(fieldName= fieleValue ,fieldName1=fieleValue)。

@ToString
public class User {
    private Long id;
    private String name;
    private String password;
    private String salt;
    private Integer status;
    private String address;
    private String phone;
    private Date lasttime;
}

@ToString和下面的代码含义一样

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", password='" + password + '\'' +
                ", salt='" + salt + '\'' +
                ", status=" + status +
                ", address='" + address + '\'' +
                ", phone='" + phone + '\'' +
                ", lasttime=" + lasttime +
                '}';
    }

3、Val将变量申明为final类型。

val defaultCount = new ArrayList<>();

// 下面的代码和上面的含义一样
final List<Integer> defaultCount = new ArrayList<>();

4、@NonNull注解能够为方法或构造函数的参数提供非空检查。

public void notNullExample(@NonNull String string) {
    //方法内的代码
}

//=>上面代码相当于如下：

public void notNullExample(String string) {
    if (string != null) {
        //方法内的代码相当于如下：
    } else {
        throw new NullPointerException("null");
    }
}

5、@NoArgsConstructor, @RequiredArgsConstructor, @AllArgsConstructor,这几个注解分别自动生成了无参构造器、指定参数的构造器和包含所有参数的构造器。

@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; 
  } 

}

//上面代码相当于如下：
@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 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() { 
    } 
  } 
}

6、@Builder注解提供了一种比较推崇的构建值对象的方式。

@Builder 
public class BuilderExample { 

  private String name; 
  private int age; 

  @Singular private Set<String> occupations; 

}

//上面代码相当于如下：

public class BuilderExample { 

  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; 
  } 

  public static BuilderExampleBuilder builder() { 
    return new BuilderExampleBuilder(); 
  } 

  public static class BuilderExampleBuilder { 

    private String name; 
    private int age; 
    private java.util.ArrayList<String> occupations;    

    BuilderExampleBuilder() { 
    } 

    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() {  
      Set<String> occupations = new HashSet<>(); 
      return new BuilderExample(name, age, occupations); 
    } 

    @verride 
    public String toString() { 
      return "BuilderExample.BuilderExampleBuilder(name = " + this.name + ", age = " + this.age + ", occupations = " + this.occupations + ")"; 
    } 
  } 
}

7、@Data注解作用比较全，其包含注解的集合@ToString，@EqualsAndHashCode，所有字段的@Getter和所有非final字段的@Setter, @RequiredArgsConstructor。其示例代码可以参考上面几个注解的组合。

8、@Synchronized注解类似Java中的Synchronized 关键字，但是可以隐藏同步锁。

public class SynchronizedExample { 

 private final Object readLock = new   Object(); 

 @Synchronized 
 public static void hello() { 
     System.out.println("world");   
 } 

 @Synchronized("readLock") 
 public void foo() { 
   System.out.println("bar"); 
 } 

//上面代码相当于如下：

 public class SynchronizedExample { 

  private static final Object $LOCK = new   Object[0]; 
  private final Object readLock = new   Object(); 

  public static void hello() { 
    synchronized($LOCK) { 
      System.out.println("world"); 
    } 
  }   

  public void foo() { 
    synchronized(readLock) { 
        System.out.println("bar");   
    } 
  } 

}

9、@Cleanup注解能够自动释放资源。

public   void jedisExample(String[] args) {
    try {
        @Cleanup Jedis jedis =   redisService.getJedis();
    } catch (Exception ex) {
        logger.error(“Jedis异常:”,ex)
    }

    //=>上面代码相当于如下：
    Jedis jedis= null;
    try {
        jedis = redisService.getJedis();
    } catch (Exception e) {
        logger.error(“Jedis异常:”,ex)
    } finally {
        if (jedis != null) {
            try {
                jedis.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

10、@EqualsAndHashCode注解，自动生成equals和hashCode方法。

@EqualsAndHashCode(exclude = {"id"}, callSuper =true)
public class LombokDemo extends Demo{
    private int id;
    private String name;
    private String gender;
}

//上面代码相当于如下：

public class LombokDemo extends Demo{

    private int id;
    private String name;
    private String gender;
    
    @Override
    public boolean equals(final Object o) {
        if (o == this) return true;
        if (o == null) return false;
        if (o.getClass() != this.getClass()) return false;
        if (!super.equals(o)) return false;
        final LombokDemo other = (LombokDemo)o;
        if (this.name == null ? other.name != null : !this.name.equals(other.name)) return false;
        if (this.gender == null ? other.gender != null : !this.gender.equals(other.gender)) return false;
        return true;
    }

    @Override
    public int hashCode() {
        final int PRIME = 31;
        int result = 1;
        result = result * PRIME + super.hashCode();
        result = result * PRIME + (this.name == null ? 0 : this.name.hashCode());
        result = result * PRIME + (this.gender == null ? 0 : this.gender.hashCode());
        return result;
    }

}

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原始发表：2019-06-07，如有侵权请联系 cloudcommunity@tencent.com 删除

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