If the value of the enum map does not exist, deserialization is not performed

1. 前言

1. Enumerations are often used in development,when using it,It may happen that the passed value is not among the values ​​defined by the enumeration,则报错如下(无法转换)：
   
2. The reason for this isThe corresponding value does not exist in the enumeration,Therefore, normal object conversion assignment cannot be performed,There are generally two places where the scene often occurs：
   一、controllerWhen the layer interface is called externally;
   二、mybatisWhen the query result is deserialized.
3. I had an idea one day,Why when deserializing,No value is passed in and not when enumerating the mapped values,不报错,自动赋值为null呢？

2. 先说结论

1. 在controllerWhen the layer interface receives parameters,是使用objectMapper进行反序列化的,And there is a configuration inside：READ_UNKNOWN_ENUM_VALUES_AS_NULL,意思就是：Get an unrecognized enumeration value and assign it tonull,不报错;
   在springboot中可在yml配置文件中写：

   spring:
     jackson:
       deserialization:
         READ_UNKNOWN_ENUM_VALUES_AS_NULL: true
   

2. 在mybatisWhen the query results are reversed,可以使用mybatis的类型处理器TypeHandler,to judge when deserializing.
   在配置文件中指定The default enumeration type handler：

   mybatis:
     configuration:
       default-enum-type-handler: com.example.csdn.enum_test.MyEnumTypeHandler
   

   // 自定义枚举处理器,继承mybatis自带的EnumTypeHandler,Simplify the code to be written for optimization
   // @MappedTypes is meant to indicate thatTypeHandlerThe implementation class can handleJava 类型的集合
   // @MappedTypes({Enum.class})的意思是：Only the enumeration type will go to the following processor
   @MappedTypes({
         Enum.class})
   public class MyEnumTypeHandler<E extends Enum<E>> extends EnumTypeHandler<E> {
         
   
   	// corresponding to the enumeration typeclass对象
       private final Class<E> type;
   
       public MyEnumTypeHandler(Class<E> type) {
         
           super(type);
           this.type = type;
       }
   
       @Override
       public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
         
           String s = rs.getString(columnName);
           // Get all the enumeration values
           final Field[] declaredFields = type.getFields();
           // If the value is taken from the library,One of the enumeration values ​​exists
           // 则 directly to enumeration,否则,directly responsible fornull
           return Arrays.stream(declaredFields).anyMatch(field -> field.getName().equals(s))
                   ? Enum.valueOf(type, s) : null;
       }
   }
   

3. 解释一下: Those who really have this need can consider using the above method,This operation is not recommended in other cases,After all, if the other party passed on something inexplicable,You also don't know what illegal content the other party is passing,直接转null了,而且在controller层dtoAn enumeration is defined in the object,Also a check,directly against the rules,error earlier.

3. 代码验证

1. controllerThe layer interface encountered an enumeration map value that does not exist

1. 在配置文件中配置：

   spring:
     jackson:
       deserialization:
         READ_UNKNOWN_ENUM_VALUES_AS_NULL: true
   

2. 代码:

   @Data
   public class testDto {
         
       private String name;
       private test_enum pwd;
   }
   
   
   public enum test_enum {
         
       A, B, C,
   }
   
   @RestController
   public class EnumController {
         
   
       @PostMapping("/enum/test")
       public void test2(@RequestBody testDto testDto){
         
           System.out.println(testDto);
       }
   }
   

   

2. mybatisThe enum map value in does not exist

1. 在Without a custom type handler下：

   
   

2. In the case of adding a custom processor：
   配置文件中配置：

   mybatis:
     configuration:
       default-enum-type-handler: com.example.csdn.enum_test.MyEnumTypeHandler
   

   @MappedTypes({
         Enum.class})
   public class MyEnumTypeHandler<E extends Enum<E>> extends EnumTypeHandler<E> {
         
   
   	// corresponding to the enumeration typeclass对象
       private final Class<E> type;
   
       public MyEnumTypeHandler(Class<E> type) {
         
           super(type);
           this.type = type;
       }
   
       @Override
       public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
         
           String s = rs.getString(columnName);
           // Get all the enumeration values
           final Field[] declaredFields = type.getFields();
           // If the value is taken from the library,One of the enumeration values ​​exists
           // 则 directly to enumeration,否则,directly responsible fornull
           return Arrays.stream(declaredFields).anyMatch(field -> field.getName().equals(s))
                   ? Enum.valueOf(type, s) : null;
       }
   }