Package org.javers.core.diff.custom

Interface CustomValueComparator<T>

Type Parameters:

T - Value Type

All Known Subinterfaces:

CustomPropertyComparator<T,C>, CustomValueToStringTemplate<T>

All Known Implementing Classes:

BigDecimalComparatorWithFixedEquals, CustomBigDecimalComparator, NullAsBlankStringComparator

public interface CustomValueComparator<T>

A custom comparator for ValueType classes to be used instead of default Object.equals(Object).

Example implementation: CustomBigDecimalComparator

Usage:

 JaversBuilder.javers()
              .registerValue(BigDecimal.class, new CustomBigDecimalComparator(2))
              .build()
 

See Also:

http://javers.org/documentation/domain-configuration/#ValueType, https://javers.org/documentation/diff-configuration/#custom-comparators

Method Summary

Modifier and Type	Method	Description
boolean	equals(T a, T b)	Called by Javers to compare two Values.
default boolean	handlesNulls()	This flag is used to indicate to Javers whether a comparator implementation wants to handle nulls.
java.lang.String	toString(T value)	This method has two roles.

Method Detail

equals

boolean equals(T a,
               T b)

Called by Javers to compare two Values.

Parameters:

a - not null if handlesNulls() returns false

b - not null if handlesNulls() returns false

toString

java.lang.String toString(T value)

This method has two roles. First, it is used when Values are compared in hashing contexts. Second, it is used to build Entity Ids from Values.

Hashcode role

When a Value class has custom toString(), it is used instead of Object.hashCode() when comparing Values in hashing contexts, so:

• Sets with Values
• Lists with Values compared as ListCompareAlgorithm.AS_SET
• Maps with Values as keys

Custom toString() implementation should be aligned with custom equals(Object, Object) in the same way like Object.hashCode() should be aligned with Object.equals(Object).

Entity Id role

Each Value can serve as an Entity Id.
When a Value has custom toString() function, it is used for creating InstanceId for Entities. If a Value doesn't have a custom toString() , default ReflectionUtil.reflectiveToString(Object)) is used.

See full example CustomToStringExample.groovy.

Parameters:

value - not null if handlesNulls() returns false

handlesNulls

default boolean handlesNulls()

This flag is used to indicate to Javers whether a comparator implementation wants to handle nulls.

By default, the flag is false and Javers checks if both values are non-null before calling a comparator.
If any of given values is null — Javers compares them using the standard Java logic:

• null == null
• null != non-null

If the flag is true — Javers skips that logic and allows a comparator to handle nulls on its own. In that case, a comparator holds responsibility for null-safety.

See Also:

NullAsBlankStringComparator