休眠如何在属性上使用String.intern [英] How to have hibernate use String.intern on attributes

问题描述

对于某些实体，我们需要将成千上万个独立实体的负载永久保存在内存中.它们的许多属性来自一组有限的字符串(尽管不够有限，无法将其放入枚举中).休眠是否可以将String.intern用于这些属性以节省空间?

For some entities we need to keep loads (thousands) of detached enties permanently in memory. Many of their attributes are from a limited set of strings (though not limited enough to put it into an enumeration). Is it possible to have hibernate use String.intern for those attributes to save space?

理想情况下，应该通过注释来起作用，我可以在每个属性或易于更改的属性上加上注释，而不会因实现问题而使源代码过于混乱.

Ideally that should work via an annotation I could put on each of those attributes, or something easily changeable, without confusing the source code too much by this implementation concern.

推荐答案

正如您所建议的那样，使用JPA属性转换器是完全可行的.您可以通过在转换器上使用 autoApply = true 在常规级别上执行此操作，也可以使用 @Convert 批注在逐字段级别上进行操作.

As you suggest yourself, it's perfectly doable with a JPA attribute converter. You could do it on a general level by using autoApply = true on the converter, or you could do it on a field by field level with the @Convert annotation.

import javax.persistence.AttributeConverter;
import javax.persistence.Converter;

@Converter(autoApply = true)
public class StringInternConverter implements AttributeConverter<String, String> {
    @Override
    public String convertToDatabaseColumn(String attribute) {
        return attribute;
    }

    @Override
    public String convertToEntityAttribute(String dbData) {
        return dbData != null? dbData.intern(): null;
    }
}

在Hibernate 5.2.10上进行了测试，就像一个魅力一样！

Tested with Hibernate 5.2.10 and works like a charm!

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