| /* |
| * 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.api.common.functions.InvalidTypesException; |
| import org.apache.flink.api.common.typeinfo.TypeInformation; |
| import org.apache.flink.api.java.typeutils.TypeExtractor; |
| import org.apache.flink.table.api.ValidationException; |
| |
| /** |
| * Base class for a user-defined scalar function. A user-defined scalar functions maps zero, one, |
| * or multiple scalar values to a new scalar value. |
| * |
| * <p>The behavior of a {@link ScalarFunction} can be defined by implementing a custom evaluation |
| * method. An evaluation method must be declared publicly and named <code>eval</code>. Evaluation |
| * methods can also be overloaded by implementing multiple methods named <code>eval</code>. |
| * |
| * <p>User-defined functions must have a default constructor and must be instantiable during runtime. |
| * |
| * <p>By default the result type of an evaluation method is determined by Flink's type extraction |
| * facilities. This is sufficient for basic types or simple POJOs but might be wrong for more |
| * complex, custom, or composite types. In these cases {@link TypeInformation} of the result type |
| * can be manually defined by overriding {@link ScalarFunction#getResultType}. |
| * |
| * <p>Internally, the Table/SQL API code generation works with primitive values as much as possible. |
| * If a user-defined scalar function should not introduce much overhead during runtime, it is |
| * recommended to declare parameters and result types as primitive types instead of their boxed |
| * classes. <code>DATE/TIME</code> is equal to <code>int</code>, <code>TIMESTAMP</code> is equal |
| * to <code>long</code>. |
| */ |
| @PublicEvolving |
| public abstract class ScalarFunction extends UserDefinedFunction { |
| |
| /** |
| * Returns the result type of the evaluation method with a given signature. |
| * |
| * <p>This method needs to be overridden in case Flink's type extraction facilities are not |
| * sufficient to extract the {@link TypeInformation} based on the return type of the evaluation |
| * method. Flink's type extraction facilities can handle basic types or |
| * simple POJOs but might be wrong for more complex, custom, or composite types. |
| * |
| * @param signature signature of the method the return type needs to be determined |
| * @return {@link TypeInformation} of result type or <code>null</code> if Flink should |
| * determine the type |
| */ |
| public TypeInformation<?> getResultType(Class<?>[] signature) { |
| return null; |
| } |
| |
| /** |
| * Returns {@link TypeInformation} about the operands of the evaluation method with a given |
| * signature. |
| * |
| * <p>In order to perform operand type inference in SQL (especially when <code>NULL</code> is |
| * used) it might be necessary to determine the parameter {@link TypeInformation} of an |
| * evaluation method. By default Flink's type extraction facilities are used for this but might |
| * be wrong for more complex, custom, or composite types. |
| * |
| * @param signature signature of the method the operand types need to be determined |
| * @return {@link TypeInformation} of operand types |
| */ |
| public TypeInformation<?>[] getParameterTypes(Class<?>[] signature) { |
| final TypeInformation<?>[] types = new TypeInformation<?>[signature.length]; |
| for (int i = 0; i < signature.length; i++) { |
| try { |
| types[i] = TypeExtractor.getForClass(signature[i]); |
| } catch (InvalidTypesException e) { |
| throw new ValidationException( |
| "Parameter types of scalar function " + this.getClass().getCanonicalName() + |
| " cannot be automatically determined. Please provide type information manually."); |
| } |
| } |
| return types; |
| } |
| } |