A Hibernate UserType defines a (custom) way how to save Java objects into the database. Basically, it defines how the object is serialized to be persisted in the database and how the object is (re)created from the serialized data stored in the database.

Here is a UserType that I’ve written to persist objects of type JSONObject. I’m using the JSON implementation from json.org; for other JSON libraries the UserType should be very similar.

package net.janjonas.example;

import java.io.Serializable;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Types;

import org.hibernate.HibernateException;
import org.hibernate.usertype.UserType;
import org.json.JSONException;
import org.json.JSONObject;

/**
 * Hibernate user type to persist JSONObject
 * 
 * @see http://www.json.org/javadoc/org/json/JSONObject.html
 * @see http://docs.jboss.org/hibernate/stable/annotations/api/org/hibernate/usertype/UserType.html
 * @author "Jan Jonas "
 */
public class JSONObjectUserType implements UserType {

  private static final int[] SQL_TYPES = { Types.LONGVARCHAR };
  
  @Override
  public Object assemble(Serializable cached, Object owner) throws HibernateException {
    return deepCopy(cached);
  }

  @Override
  public Object deepCopy(Object value) throws HibernateException {
    if (value == null) return value;
    try {
      return new JSONObject(((JSONObject)value).toString());
    } catch (JSONException e) {
      throw new RuntimeException(e);
    }
  }

  @Override
  public Serializable disassemble(Object value) throws HibernateException {
    return ((JSONObject)value).toString();
  }

  @Override
  public boolean equals(Object x, Object y) throws HibernateException {
    if (x == null) return (y != null);
    return (x.equals(y));
  }

  @Override
  public int hashCode(Object x) throws HibernateException {
    return ((JSONObject)x).toString().hashCode();
  }

  @Override
  public boolean isMutable() {
    return true;
  }

  @Override
  public Object nullSafeGet(ResultSet rs, String[] names, Object owner) throws HibernateException, SQLException {
    if (!rs.wasNull()) {
      try {
        return new JSONObject(rs.getString(names[0]));
      } catch (JSONException e) {
        throw new RuntimeException(e);
      }
    }
    return null;
  }

  @Override
  public void nullSafeSet(PreparedStatement st, Object value, int index) throws HibernateException, SQLException {
    if (value == null) {
      st.setNull(index, SQL_TYPES[0]);
    } else {
      st.setString(index, ((JSONObject)value).toString());
    }
  }

  @Override
  public Object replace(Object original, Object target, Object owner) throws HibernateException {
    return deepCopy(original);
  }

  @Override
  @SuppressWarnings("unchecked")
  public Class returnedClass() {
    return JSONObject.class;
  }

  @Override
  public int[] sqlTypes() {
    return SQL_TYPES;
  }

}