org.apache.flink.table.functions.AsyncTableFunction Maven / Gradle / Ivy
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*
* http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.flink.table.functions;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.table.annotation.DataTypeHint;
import org.apache.flink.table.annotation.FunctionHint;
import org.apache.flink.table.catalog.DataTypeFactory;
import org.apache.flink.table.connector.source.LookupTableSource;
import org.apache.flink.table.data.RowData;
import org.apache.flink.table.types.DataType;
import org.apache.flink.table.types.extraction.TypeInferenceExtractor;
import org.apache.flink.table.types.inference.TypeInference;
import org.apache.flink.types.Row;
import java.util.concurrent.CompletableFuture;
/**
* Base class for a user-defined asynchronous table function. A user-defined asynchronous table
* function maps zero, one, or multiple scalar values to zero, one, or multiple rows (or structured
* types).
*
* This kind of function is similar to {@link TableFunction} but is executed asynchronously.
*
*
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.
*
*
By default, input and output data types are automatically extracted using reflection. This
* includes the generic argument {@code T} of the class for determining an output data type. Input
* arguments are derived from one or more {@code eval()} methods. If the reflective information is
* not sufficient, it can be supported and enriched with {@link DataTypeHint} and {@link
* FunctionHint} annotations. See {@link TableFunction} for more examples how to annotate an
* implementation class.
*
*
Note: Currently, asynchronous table functions are only supported as the runtime implementation
* of {@link LookupTableSource}s for performing temporal joins. By default, input and output {@link
* DataType}s of {@link AsyncTableFunction} are derived similar to other {@link
* UserDefinedFunction}s using the logic above. However, for convenience, in a {@link
* LookupTableSource} the output type can simply be a {@link Row} or {@link RowData} in which case
* the input and output types are derived from the table's schema with default conversion.
*
*
The first parameter of the evaluation method must be a {@link CompletableFuture}. Other
* parameters specify user-defined input parameters like the "eval" method of {@link TableFunction}.
* The generic type of {@link CompletableFuture} must be {@link java.util.Collection} to collect
* multiple possible result values.
*
*
For each call to eval(), an async IO operation can be triggered, and once the
* operation has been done, the result can be collected by calling {@link
* CompletableFuture#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 CompletableFuture} can be passed into callbacks or futures to collect the result data.
* An error can also be propagated to the async IO operator by calling {@link
* CompletableFuture#completeExceptionally(Throwable)}.
*
*
For storing a user-defined function in a catalog, the class must have a default constructor
* and must be instantiable during runtime.
*
*
The following example shows how to perform an asynchronous request to Apache HBase:
*
*
{@code
* public class HBaseAsyncTableFunction extends AsyncTableFunction {
*
* // implement an "eval" method that takes a CompletableFuture as the first parameter
* // and ends with as many parameters as you want
* public void eval(CompletableFuture> 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 ...
* }
* }
*
* @param The type of the output row used during reflective extraction.
*/
@PublicEvolving
public abstract class AsyncTableFunction extends UserDefinedFunction {
@Override
public final FunctionKind getKind() {
return FunctionKind.ASYNC_TABLE;
}
@Override
@SuppressWarnings({"unchecked", "rawtypes"})
public TypeInference getTypeInference(DataTypeFactory typeFactory) {
return TypeInferenceExtractor.forAsyncTableFunction(typeFactory, (Class) getClass());
}
}