How to set size of string column using service.xml or Service Builder?

Pre-history: I get JDBCExceptionReporter data exception: string data, right truncation exception on update of entities.

I have found that this means, the data is too big for the specified varchar.

In the service.xml the column is specified like:

<column name="message" type="String"/>

I have found in Liferay's source code for ServiceBuilder this fragment:

else if (colType.equals("String")) {
    Map<String, String> hints = ModelHintsUtil.getHints(
        _packagePath + ".model." + entity.getName(), colName);

    int maxLength = 75;

    if (hints != null) {
        maxLength = GetterUtil.getInteger(
            hints.get("max-length"), maxLength);
    }

    if (col.isLocalized()) {
        maxLength = 4000;
    }

    if (maxLength < 4000) {
        sb.append("VARCHAR(" + maxLength + ")");
    }
    else if (maxLength == 4000) {
        sb.append("STRING");
    }
    else if (maxLength > 4000) {
        sb.append("TEXT");
    }
}

Now my question is, how can I define the max-length for my columns?