jdbc-custom-conversions.adoc

Custom Conversions

Spring Data JDBC allows registration of custom converters to influence how values are mapped in the database. Currently, converters are only applied on property-level.

Writing a Property by Using a Registered Spring Converter

The following example shows an implementation of a Converter that converts from a Boolean object to a String value:

import org.springframework.core.convert.converter.Converter;

@WritingConverter
public class BooleanToStringConverter implements Converter<Boolean, String> {

    @Override
    public String convert(Boolean source) {
        return source != null && source ? "T" : "F";
    }
}

There are a couple of things to notice here: Boolean and String are both simple types hence Spring Data requires a hint in which direction this converter should apply (reading or writing). By annotating this converter with @WritingConverter you instruct Spring Data to write every Boolean property as String in the database.

Reading by Using a Spring Converter

The following example shows an implementation of a Converter that converts from a String to a Boolean value:

@ReadingConverter
public class StringToBooleanConverter implements Converter<String, Boolean> {

    @Override
    public Boolean convert(String source) {
        return source != null && source.equalsIgnoreCase("T") ? Boolean.TRUE : Boolean.FALSE;
    }
}

There are a couple of things to notice here: String and Boolean are both simple types hence Spring Data requires a hint in which direction this converter should apply (reading or writing). By annotating this converter with @ReadingConverter you instruct Spring Data to convert every String value from the database that should be assigned to a Boolean property.

Registering Spring Converters with the JdbcConverter

class MyJdbcConfiguration extends AbstractJdbcConfiguration {

    // …

	@Override
    protected List<?> userConverters() {
		return Arrays.asList(new BooleanToStringConverter(), new StringToBooleanConverter());
	}

}

Note

In previous versions of Spring Data JDBC it was recommended to directly overwrite AbstractJdbcConfiguration.jdbcCustomConversions(). This is no longer necessary or even recommended, since that method assembles conversions intended for all databases, conversions registered by the Dialect used and conversions registered by the user. If you are migrating from an older version of Spring Data JDBC and have AbstractJdbcConfiguration.jdbcCustomConversions() overwritten conversions from your Dialect will not get registered.

JdbcValue

Value conversion uses JdbcValue to enrich values propagated to JDBC operations with a java.sql.Types type. Register a custom write converter if you need to specify a JDBC-specific type instead of using type derivation. This converter should convert the value to JdbcValue which has a field for the value and for the actual JDBCType.

{spring-data-commons-docs}/custom-conversions.adoc