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Section 13: simplify your code with Lombok

2022-06-25 20:30:00 【Entry station】

[TOC]

In the development process , It's usually defined as a lot of JavaBean, And then through IDE To generate its properties 、getter、setter、equals、hashcode、toString Method , When you want to add an attribute or change an attribute , For example, naming 、 Type, etc , We need to regenerate these methods mentioned above . Such repetitive work is meaningless ,Lombok The annotations inside can easily solve these problems .
lombok Implementation principle ： Mainly through the abstract syntax tree (AST), After compilation , Corresponding to the class with its annotation , Then the annotation compiler will automatically correspond to the annotations in the project lombok Annotation files in the syntax tree , And automatically compile the corresponding class to generate getter perhaps setter Method , To simplify the code

pom.xml add to lombok

<dependency>
  <groupId>org.projectlombok</groupId>
  <artifactId>lombok</artifactId>
  <optional>true</optional>
</dependency>

@Getter @Setter annotation

This pair of notes is well understood by name , Used in front of member variables , It is equivalent to generating the corresponding get and set Method , You can also specify access modifiers for the generated methods , Of course , The default is public, Take a look at the simple example below ： 
// Rumenz.java
/**
 * @className: Rumenz
 * @description: TODO  Class description 
 * @author:  Entry station  rumenz.com
 * @date: 2021/12/9
 **/
public class RumenzGetSet {
    @Getter @Setter
    private Integer id;
    @Getter @Setter
    private String name;

}

  • Equivalent to 

    public class RumenzGetSet {
  private Integer id;
  private String name;

  public Integer getId() {
      return id;
  }

  public void setId(Integer id) {
      this.id = id;
  }

  public String getName() {
      return name;
  }

  public void setName(String name) {
      this.name = name;
  }
}

@RestController
@RequestMapping("/rumenz")
public class RumenzController {

    @GetMapping("/index")
    public String index(){
        RumenzGetSet r=new RumenzGetSet();
        r.setId(1);
        r.setName(" Entry station ");

        return r.getId()+r.getName();
    }
}
visit http://127.0.0.1:8080/rumenz/index return 1 Entry station

@NonNull annotation

This annotation can be used in front of a member method or a constructor's parameter , A non null check about this parameter will be automatically generated , If the argument is null , Throw a null pointer exception , Take an example 
public class RumenzNonNull {
    @Getter @Setter @NonNull
    private Integer id;
    @Getter @Setter @NonNull
    private String name;
}

  • Equivalent to 

    public class RumenzNonNull {
  private Integer id;
  private String name;

  public Integer getId() {
      return id;
  }

  public void setId(Integer id) {
      if (id == null) throw new java.lang.NullPointerException("id");
      this.id = id;
  }

  public String getName() {
      return name;
  }

  public void setName(String name) {
      if (name == null) throw new java.lang.NullPointerException("name");
      this.name = name;
  }
}
@GetMapping("/index1")
public String index1(){
    RumenzNonNull r=new RumenzNonNull();
    r.setId(1);
    r.setName(null);

    return r.getId()+r.getName();
}
visit http://127.0.0.1:8080/rumenz/index1 Report errors java.lang.NullPointerException: name is marked non-null but is null

@ToString

@ToString
public class RumenzToString {

    @Getter @Setter
    private Integer id;

    @Getter @Setter
    private String name;

    @Override
    public String toString() {
        return "RumenzToString{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}
  • Equivalent to 
public class RumenzToString {

    private Integer id;

    private String name;


    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "RumenzToString{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}
@GetMapping("/index2")
public String index2(){
     RumenzToString r=new RumenzToString();
     r.setId(1);
     r.setName(" Entry station ");
     return r.toString();
}
visit http://127.0.0.1:8080/rumenz/index1 return RumenzToString{id=1, name=' Entry station '}

EqualsAndHashCode annotation 

@EqualsAndHashCode
public class RumenzEqualsAndHashCode {

    @Getter @Setter
    private Integer id;
    @Getter @Setter
    private String name;

}

  • Equivalent to 

    public class RumenzEqualsAndHashCode {
  private Integer id;
  private String name;

  public Integer getId() {
      return id;
  }

  public void setId(Integer id) {
      this.id = id;
  }

  public String getName() {
      return name;
  }

  public void setName(String name) {
      this.name = name;
  }

  @Override
  public boolean equals(Object o) {
      if (this == o) return true;
      if (!(o instanceof RumenzEqualsAndHashCode)) return false;
      RumenzEqualsAndHashCode that = (RumenzEqualsAndHashCode) o;
      return id.equals(that.id) &&
              name.equals(that.name);
  }

}
@GetMapping("/index3")
public String index3(){
    RumenzEqualsAndHashCode r1=new RumenzEqualsAndHashCode();
    r1.setId(1);
    r1.setName(" Entry station ");

    RumenzEqualsAndHashCode r2=new RumenzEqualsAndHashCode();
    r2.setId(1);
    r2.setName(" Entry station ");
    if(r1.equals(r2)){
    return " equal ";
    }
    return " It's not equal ";
}

@Data annotation

  • 1） Generate a parameterless constructor ;
  • 2） Attribute set/get Method ;
  • 3）equals(), hashCode(), toString(), canEqual() Method .
@Data(staticConstructor="of")
public class RumenzData {


    private Integer id;

    private String name;

}
// Equivalent to 

public class RumenzData {
    private Integer id;
    private String name;

    private RumenzData() {
    }

    public static RumenzData of() {
        return new RumenzData();
    }

    public Integer getId() {
        return this.id;
    }

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

    public void setId(final Integer id) {
        this.id = id;
    }

    public void setName(final String name) {
        this.name = name;
    }

    public boolean equals(final Object o) {
        if (o == this) {
            return true;
        } else if (!(o instanceof RumenzData)) {
            return false;
        } else {
            RumenzData other = (RumenzData)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;
                }

                Object this$name = this.getName();
                Object other$name = other.getName();
                if (this$name == null) {
                    if (other$name != null) {
                        return false;
                    }
                } else if (!this$name.equals(other$name)) {
                    return false;
                }

                return true;
            }
        }
    }

    protected boolean canEqual(final Object other) {
        return other instanceof RumenzData;
    }

    public int hashCode() {
        int PRIME = true;
        int result = 1;
        Object $id = this.getId();
        int result = result * 59 + ($id == null ? 43 : $id.hashCode());
        Object $name = this.getName();
        result = result * 59 + ($name == null ? 43 : $name.hashCode());
        return result;
    }

    public String toString() {
        return "RumenzData(id=" + this.getId() + ", name=" + this.getName() + ")";
    }
}
@GetMapping("/index4")
public String index4(){
   RumenzData of = RumenzData.of();
   of.setName(" Entry station ");
   String name = of.getName();
   return name;
}

@Cleanup annotation

This annotation is used before the variable , It can guarantee that the resources represented by this variable will be automatically closed , The default is to call resources close() Method , If there are other ways to close the resource , You can use @Cleanup(“methodName”) To specify the method to call , Let's take the input-output stream as an example ： 
@GetMapping("/index5")
public String index5() throws IOException {

   File file = ResourceUtils.getFile("classpath:application.properties");
   @Cleanup  InputStream inputStream = new FileInputStream(file);

   byte b[]=new byte[(int) file.length()];
   inputStream.read(b);
   //@Cleanup  Instead of  inputStream.close();
   return new String(b);
}
Equivalent to 
@GetMapping({"/index5"})
public String index5() throws IOException {
        File file = ResourceUtils.getFile("classpath:application.properties");
        FileInputStream inputStream = new FileInputStream(file);

        String var4;
        try {
            byte[] b = new byte[(int)file.length()];
            inputStream.read(b);
            var4 = new String(b);
        } finally {
            if (Collections.singletonList(inputStream).get(0) != null) {
                inputStream.close();
            }

        }

        return var4;
}

@NoArgsConstructor annotation

@NoArgsConstructor Use on class , It can provide a parameterless constructor 
@NoArgsConstructor
public class RumenzNoArgsConstructor {
    private Integer id;
    private String name;
}
Equivalent to 

public class RumenzNoArgsConstructor {
    private Integer id;
    private String name;

    public RumenzNoArgsConstructor() {
    }
}

@RequiredArgsConstructor annotation

Appoint final Property generation and construction method 
@ToString
@RequiredArgsConstructor
public class RumenzRequiredArgsConstructor {
    private Integer id;
    private final String name;
}

// Equivalent to 

public class RumenzRequiredArgsConstructor {
    private Integer id;
    private final String name; //final

    public String toString() {
        return "RumenzRequiredArgsConstructor(id=" + this.id + ", name=" + this.name + ")";
    }

    public RumenzRequiredArgsConstructor(final String name) {
        this.name = name;
    }
}

@AllArgsConstructor annotation

All fields in the class generate a constructor with parameters . 
@ToString
@AllArgsConstructor
public class RumenzAllArgsConstructor {
    private  Integer id;
    private  String name;
}

// Equivalent to 

public class RumenzAllArgsConstructor {
    private Integer id;
    private String name;

    public String toString() {
        return "RumenzAllArgsConstructor(id=" + this.id + ", name=" + this.name + ")";
    }

    public RumenzAllArgsConstructor(final Integer id, final String name) {
        this.id = id;
        this.name = name;
    }
}

@Value annotation

  • 1） Parametric construction method ;
  • 2） Just add @Value annotation , There are no other restrictions , Then the class properties will be compiled into final Of , So only get Method , But not set Method .
@ToString
@Value
public class RumenzValue {
    private Integer id;
    private String name;
}

// Equivalent to 

public final class RumenzValue {
    private final Integer id;
    private final String name;

    public RumenzValue(final Integer id, final String name) {
        this.id = id;
        this.name = name;
    }

    public Integer getId() {
        return this.id;
    }

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

    public boolean equals(final Object o) {
        if (o == this) {
            return true;
        } else if (!(o instanceof RumenzValue)) {
            return false;
        } else {
            RumenzValue other = (RumenzValue)o;
            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;
            }

            Object this$name = this.getName();
            Object other$name = other.getName();
            if (this$name == null) {
                if (other$name != null) {
                    return false;
                }
            } else if (!this$name.equals(other$name)) {
                return false;
            }

            return true;
        }
    }

    public int hashCode() {
        int PRIME = true;
        int result = 1;
        Object $id = this.getId();
        int result = result * 59 + ($id == null ? 43 : $id.hashCode());
        Object $name = this.getName();
        result = result * 59 + ($name == null ? 43 : $name.hashCode());
        return result;
    }

    public String toString() {
        return "RumenzValue(id=" + this.getId() + ", name=" + this.getName() + ")";
    }
}

@SneakyThrows annotation

This annotation is used for methods , You can use the code in the method try-catch The sentences are wrapped up , Catch the exception and in catch of use Lombok.sneakyThrow(e) Throw an exception , have access to @SneakyThrows(Exception.class) Specifies which exception to throw , A very simple note , Just look at an example ： 

@SneakyThrows
@GetMapping("/index9")
public String index9() {

        // Use @SneakyThrows You don't have to throw an exception explicitly 
        File file = ResourceUtils.getFile("classpath:application.properties");
        @Cleanup  InputStream inputStream = new FileInputStream(file);

        byte b[]=new byte[(int) file.length()];
        inputStream.read(b);
        //@Cleanup  Instead of  inputStream.close();
        return new String(b);
}

// Equivalent to 

@GetMapping({"/index9"})
public String index9() {
        try {
            File file = ResourceUtils.getFile("classpath:application.properties");
            FileInputStream inputStream = new FileInputStream(file);

            String var4;
            try {
                byte[] b = new byte[(int)file.length()];
                inputStream.read(b);
                var4 = new String(b);
            } finally {
                if (Collections.singletonList(inputStream).get(0) != null) {
                    inputStream.close();
                }

            }

            return var4;
        } catch (Throwable var9) {
            throw var9;
        }
}

@Synchronized annotation

synchronized Is an important keyword in thread safety , It is a kind of synchronous lock , Mainly used to ensure that at the same time , Only one thread can execute a method or a block of code . In general use synchronized To lock the code block , Not the way , Because locking code blocks is more efficient . 
public class RumenzSynchronized {

    private final Object readLock = new Object();

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

    @Synchronized
    public int answerToLife() {
        return 110;
    }

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

// Equivalent to 

public class RumenzSynchronized {
    private static final Object $LOCK = new Object[0];
    private final Object $lock = new Object[0];
    private final Object readLock = new Object();

    public RumenzSynchronized() {
    }

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

    public int answerToLife() {
        synchronized(this.$lock) {
            return 110;
        }
    }

    public void foo() {
        synchronized(this.readLock) {
            System.out.println(" Entry station ");
        }
    }
}

@Builder annotation

Used in class 、 Constructors 、 On the way , Provide you with complex builder APIs 
@ToString
@Builder
public class RumenzBuilder {
    private Integer id;
    private String name;
}

// Equivalent to 

public class RumenzBuilder {
    private Integer id;
    private String name;

    RumenzBuilder(final Integer id, final String name) {
        this.id = id;
        this.name = name;
    }

    public static RumenzBuilder.RumenzBuilderBuilder builder() {
        return new RumenzBuilder.RumenzBuilderBuilder();
    }

    public String toString() {
        return "RumenzBuilder(id=" + this.id + ", name=" + this.name + ")";
    }

    public static class RumenzBuilderBuilder {
        private Integer id;
        private String name;

        RumenzBuilderBuilder() {
        }

        public RumenzBuilder.RumenzBuilderBuilder id(final Integer id) {
            this.id = id;
            return this;
        }

        public RumenzBuilder.RumenzBuilderBuilder name(final String name) {
            this.name = name;
            return this;
        }

        public RumenzBuilder build() {
            return new RumenzBuilder(this.id, this.name);
        }

        public String toString() {
            return "RumenzBuilder.RumenzBuilderBuilder(id=" + this.id + ", name=" + this.name + ")";
        }
    }
}

@GetMapping("/index11")
public String index11() {
    RumenzBuilder rb=RumenzBuilder.builder().id(1).name(" Entry station ").build();
    return rb.toString();
}

@SuperBuilder

When an entity class has an integration relationship , Need to use @SuperBuilder, Otherwise, it will be called .builder All will report wrong. .

@Builder The construction of parent class member properties is not supported ,@SuperBuilder The emergence of annotations , To solve this problem .

Use @Builder or @SuperBuilder When the annotation , Null parameter constructors are not created by default , If you have an additional need to use null or full parameter constructors , You need to add the following comments to both the subclass and the parent class ：

The source code address of this summary :
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