/* * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.flink.table.functions; import org.apache.flink.annotation.PublicEvolving; import org.apache.flink.table.utils.EncodingUtils; import java.io.Serializable; /** * Base class for all user-defined functions such as scalar functions, table functions, * or aggregation functions. */ @PublicEvolving public abstract class UserDefinedFunction implements Serializable { /** * Returns a unique, serialized representation for this function. */ public final String functionIdentifier() { final String md5 = EncodingUtils.hex(EncodingUtils.md5(EncodingUtils.encodeObjectToString(this))); return getClass().getCanonicalName().replace('.', '$').concat("$").concat(md5); } /** * Setup method for user-defined function. It can be used for initialization work. * By default, this method does nothing. */ public void open(FunctionContext context) throws Exception { // do nothing } /** * Tear-down method for user-defined function. It can be used for clean up work. * By default, this method does nothing. */ public void close() throws Exception { // do nothing } /** * Returns information about the determinism of the function's results. * * @return <code>true</code> if and only if a call to this function is guaranteed to * always return the same result given the same parameters. <code>true</code> is * assumed by default. If the function is not pure functional like * <code>random(), date(), now(), ...</code> this method must return <code>false</code>. */ public boolean isDeterministic() { return true; } /** * Returns the name of the UDF that is used for plan explain and logging. */ @Override public String toString() { return getClass().getSimpleName(); } }