codegen.xml

<customTypes>
  <customType>
    <name>Instant</name>
    <type>java.time.Instant</type>
    <binding>InstantBinding</binding>
  </customType>
</customTypes>
<forcedTypes>
  <forcedType>
    <name>Instant</name>
    <expression>.*DATEZ.*</expression>
    <types>TIMESTAMP\(6\)\ WITH\ TIME\ ZONE</types>
  </forcedType>
</forcedTypes>

ddl.sql

CREATE TABLE z (
  id    NUMBER(19) GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
  datez TIMESTAMP WITH TIME ZONE NOT NULL
);

InstantAwareGenerator.java

public class InstantAwareGenerator extends JavaGenerator {

  @Override
  protected String getJavaTypeReference(Database db, DataTypeDefinition type) {
    if (type.getUserType().equals("java.time.Instant")) {
      // TODO Not very type safe
      return "new org.jooq.impl.DefaultDataType<Object>(org.jooq.SQLDialect.ORACLE12C, Object.class, \"timestamp with time zone\")";
    } else {
      return super.getJavaTypeReference(db, type);
    }
  }
}

InstantBinding.java

public class InstantBinding implements Binding<Object, Instant> {

  private final Converter<Object, Instant> converter;

  public InstantBinding() {
    this.converter = new InstantConverter();
  }

  @Override
  public Converter<Object, Instant> converter() {
    return converter;
  }

  @Override
  public void sql(BindingSQLContext<Instant> ctx) throws SQLException {
    ctx.render().sql(ctx.variable());

  }

  @Override
  public void register(BindingRegisterContext<Instant> ctx) throws SQLException {
    ctx.statement().registerOutParameter(ctx.index(), Types.TIMESTAMP_WITH_TIMEZONE);
  }

  @Override
  public void set(BindingSetStatementContext<Instant> ctx) throws SQLException {
    PreparedStatement stmt = ctx.statement();
    Connection con = stmt.getConnection();
    if (con.isWrapperFor(OracleConnection.class)){
      OracleConnection oracleConnection= con.unwrap(OracleConnection.class);
      TIMESTAMPTZ t = new TIMESTAMPTZ(oracleConnection, Timestamp.from(ctx.value()), InstantConverter.UTC);
      stmt.setObject(ctx.index(),t);
    } else{
      throw new UnsupportedOperationException();
    }

  }

  @Override
  public void get(BindingGetResultSetContext<Instant> ctx) throws SQLException {
    ResultSet rs = ctx.resultSet();
    Object t = rs.getObject(ctx.index());
    Connection con = ctx.configuration().connectionProvider().acquire();
    if (con.isWrapperFor(OracleConnection.class)){
      OracleConnection oracleConnection= con.unwrap(OracleConnection.class);
      TIMESTAMPTZ tz = (TIMESTAMPTZ) t;
      Timestamp ts = tz.timestampValue(oracleConnection);
      ctx.value(ts.toInstant());
    }
  }

  @Override
  public void get(BindingGetStatementContext<Instant> ctx) throws SQLException {
    throw new SQLFeatureNotSupportedException();
  }

  @Override
  public void set(BindingSetSQLOutputContext<Instant> ctx) throws SQLException {
    throw new SQLFeatureNotSupportedException();
  }

  @Override
  public void get(BindingGetSQLInputContext<Instant> ctx) throws SQLException {
    throw new SQLFeatureNotSupportedException();
  }
}