org.apache.flink.table.api.functions.AsyncTableFunction Maven / Gradle / Ivy
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*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
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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.
*
* A user-defined table functions works on
* zero, one, or multiple scalar values as input and returns multiple rows as output.
*
*
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".
*
*
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}.
*
*
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.
*
*
{@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)}.
*
*
User-defined functions must have a default constructor and must be instantiable during
* runtime.
*
*
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}.
*
*
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.
*
*
Example:
*
* {@code
*
* public class HBaseAsyncTableFunction extends AsyncTableFunction {
*
* // implement an "eval" method with as many parameters as you want
* public void eval(ResultFuture result, String rowkey) {
* Get get = new Get(Bytes.toBytes(rowkey));
* ListenableFuture future = hbase.asyncGet(get);
* Futures.addCallback(future, new FutureCallback() {
* public void onSuccess(Result result) {
* List ret = process(result);
* result.complete(ret);
* }
* public void onFailure(Throwable thrown) {
* result.completeExceptionally(thrown);
* }
* });
* }
*
* // you can overload the eval method here ...
* }
* }
*
* NOTE: the {@link AsyncTableFunction} is can not used as UDTF currently. It only used in
* temporal table join as a async lookup function
*
* @param The type of the output row
*/
public abstract class AsyncTableFunction extends CustomTypeDefinedFunction {
// public void eval(ResultFuture future, [user defined inputs])
}