| /* |
| * 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(); |
| } |
| } |