How to silently truncate strings while storing them when they are longer than the column length definition?

Question

I have a web app, using EclipseLink and MySQL for storing data. Some of these data are strings, ie varchars in the DB. In the code of entities, the strings have attributes

Answer 1

There was already answer mentioned Converters, but I want to add more details. My answer also assumes Converters from JPA, not EclipseLink specific.

At first create this class - special type converter which responsibility will be to truncate value at the persistence moment:

import javax.persistence.AttributeConverter;
import javax.persistence.Convert;

@Convert
public class TruncatedStringConverter implements AttributeConverter {
  private static final int LIMIT = 999;

  @Override
  public String convertToDatabaseColumn(String attribute) {
    if (attribute == null) {
      return null;
    } else if (attribute.length() > LIMIT) {
      return attribute.substring(0, LIMIT);
    } else {
      return attribute;
    }
  }

  @Override
  public String convertToEntityAttribute(String dbData) {
    return dbData;
  }
}

Then you can use it in your entities like this:

@Entity(name = "PersonTable")
public class MyEntity {
    
    @Convert(converter = TruncatedStringConverter.class)
    private String veryLongValueThatNeedToBeTruncated;
 
    //...
}

Related article about JPA Converters: http://www.baeldung.com/jpa-attribute-converters