| /* |
| * 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.api.functions; |
| |
| import org.apache.flink.streaming.api.functions.async.ResultFuture; |
| import org.apache.flink.table.api.types.DataType; |
| |
| /** |
| * Base class for a user-defined asynchronously table function (UDTF). This is similar to |
| * {@link TableFunction} but this function is asynchronously. |
| * |
| * <p>A user-defined table functions works on |
| * zero, one, or multiple scalar values as input and returns multiple rows as output. |
| * |
| * <p>The behavior of a {@link AsyncTableFunction} can be defined by implementing a custom evaluation |
| * method. An evaluation method must be declared publicly, not static and named "eval". |
| * Evaluation methods can also be overloaded by implementing multiple methods named "eval". |
| * |
| * <p>The first parameter of evaluation method must be {@link ResultFuture}, and the others are user |
| * defined input parameters like the "eval" method of {@link TableFunction}. |
| * |
| * <p>For each "eval", an async io operation can be triggered, and once it has been done, |
| * the result can be collected by calling {@link ResultFuture#complete}. For each async |
| * operation, its context is stored in the operator immediately after invoking "eval", |
| * avoiding blocking for each stream input as long as the internal buffer is not full. |
| * |
| * <p>{@link ResultFuture} can be passed into callbacks or futures to collect the result data. |
| * An error can also be propagate to the async IO operator by |
| * {@link ResultFuture#completeExceptionally(Throwable)}. |
| * |
| * <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 DataType} of the result type |
| * can be manually defined by overriding {@link #getResultType}. |
| * |
| * <p>Internally, the Table/SQL API code generation works with primitive values as much as possible. |
| * If a user-defined table 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. DATE/TIME is equal to int, TIMESTAMP is equal to long. |
| * |
| * <p>Example: |
| * |
| * {@code |
| * |
| * public class HBaseAsyncTableFunction extends AsyncTableFunction<String> { |
| * |
| * // implement an "eval" method with as many parameters as you want |
| * public void eval(ResultFuture<String> result, String rowkey) { |
| * Get get = new Get(Bytes.toBytes(rowkey)); |
| * ListenableFuture<Result> future = hbase.asyncGet(get); |
| * Futures.addCallback(future, new FutureCallback<Result>() { |
| * public void onSuccess(Result result) { |
| * List<String> ret = process(result); |
| * result.complete(ret); |
| * } |
| * public void onFailure(Throwable thrown) { |
| * result.completeExceptionally(thrown); |
| * } |
| * }); |
| * } |
| * |
| * // you can overload the eval method here ... |
| * } |
| * } |
| * |
| * <p>NOTE: the {@link AsyncTableFunction} is can not used as UDTF currently. It only used in |
| * temporal table join as a async lookup function |
| * |
| * @param <T> The type of the output row |
| */ |
| public abstract class AsyncTableFunction<T> extends CustomTypeDefinedFunction { |
| |
| // public void eval(ResultFuture<T> future, [user defined inputs]) |
| |
| } |