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https://issues.apache.org/jira/browse/FLINK-5571?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15860828#comment-15860828
]
ASF GitHub Bot commented on FLINK-5571:
---------------------------------------
Github user godfreyhe commented on a diff in the pull request:
https://github.com/apache/flink/pull/3176#discussion_r100478286
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/functions/UserDefinedFunction.scala
---
@@ -24,4 +24,19 @@ package org.apache.flink.table.functions
* User-defined functions must have a default constructor and must be
instantiable during runtime.
*/
trait UserDefinedFunction {
--- End diff --
The Scala wrapper class can be abstract class.
MathTrait.scala
```Scala
trait MathTrait {
def sum(x: Int, y: Int) = x + y
}
```
MathTraitWrapper.scala
```Scala
abstract class MathTraitWrapper extends MathTrait {
}
```
JavaMath.java
```Java
public class JavaMath extends MathTraitWrapper {
public static void main(String[] args) {
new JavaMath();
}
public JavaMath() {
System.out.println(sum(2, 2));
}
}
```
This code works as expected, printing the number 4 when it is run.
> add open and close methods for UserDefinedFunction in TableAPI & SQL
> --------------------------------------------------------------------
>
> Key: FLINK-5571
> URL: https://issues.apache.org/jira/browse/FLINK-5571
> Project: Flink
> Issue Type: New Feature
> Components: Table API & SQL
> Reporter: godfrey he
> Assignee: godfrey he
>
> Currently, a User Defined Function (UDF) in table API & SQL works on zero,
> one, or multiple values in custom evaluation method. Many UDFs need more
> complex features, e.g. report metrics, get parameters from job configuration,
> or get extra data from distribute cache file, etc. Adding open and close
> methods in UserDefinedFunction class can solve this problem. The code cloud
> look like:
> {code}
> trait UserDefinedFunction {
> def open(context: UDFContext): Unit = {}
> def close(): Unit = {}
> }
> {code}
> UDFContext contains the information about metric reporters, job parameters,
> distribute cache, etc. The code cloud look like:
> {code}
> class UDFContext(context: RuntimeContext) {
> def getMetricGroup: MetricGroup = ???
> def getDistributedCacheFile(name: String): File = ???
> def getJobParameter(key: String, default: String): String = ???
> }
> {code}
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