Issue java.io.StreamCorruptedException

I'm trying to make a simple select query but receive this error:

java.io.StreamCorruptedException: invalid stream header: 78780A1F 
at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:857)

In datamap I have a db-attribute of type CLOB that I want read as a simple String.

<db-entity name="DISC">
        <db-attribute name="DATE" type="TIMESTAMP" isMandatory="true" length="7"/>
        <db-attribute name="ID" type="INTEGER" isPrimaryKey="true" isMandatory="true"/>
        <db-attribute name="FLAG" type="VARCHAR" isMandatory="true"/>
        <db-attribute name="REQUEST" type="CLOB" isMandatory="false"/>
        <db-key-generator>
            <db-generator-type>ORACLE</db-generator-type>
            <db-generator-name>DISC_SEQ</db-generator-name>
            <db-key-cache-size>1</db-key-cache-size>
        </db-key-generator>
</db-entity>
<obj-entity name="Disc" className="it.pack.dao.Disc" dbEntityName="DISC">
        <obj-attribute name="date" type="java.time.LocalDateTime" db-attribute-path="DATE"/>
        <obj-attribute name="id" type="java.lang.Integer" db-attribute-path="ID"/>
        <obj-attribute name="flag" type="java.lang.String" db-attribute-path="FLAG"/>
        <obj-attribute name="request" type="java.lang.String" db-attribute-path="REQUEST"/>
</obj-entity>

I think that CLOB cannot map to java.lang.String but how can I read it?