[ 
https://issues.apache.org/jira/browse/SPARK-22198?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Akos Tomasits updated SPARK-22198:
----------------------------------
    Description: 
It is not possible to create proper Java custom Transformer by extending 
UnaryTransformer or Transformer.

The built-in Params (e.g. defined in HasInputColumn trait) cannot be used and 
custom Params cannot be added.

It seems that the method 'uid()' is called during object creation before the 
provided 'uid' constructor parameter could be set.

This leads to the following error:
{quote}java.lang.IllegalArgumentException: requirement failed: Param 
<prefix>_1563950936fa__inputCol does not belong to <prefix>_d4105b75c4aa.
{quote}
If you extend UnaryTransformer and try to use it e.g. through CrossValidator, 
you will need to explicitly include a constructor, which receives a String 
parameter. As I saw in the source of built in transformers, this parameter is a 
'uid', which should be set in the object. However, it is not possible to do it 
in time, because the uid() method is invoked (and its result might be used) 
before this constructor finishes.

Sample class:
{quote}public class TextCleaner extends UnaryTransformer<String, String, 
TextCleaner>
 implements Serializable, DefaultParamsWritable, 
DefaultParamsReadable<TextCleaner> {

private static final long serialVersionUID = 2658543236303100458L;

private static final String sparkUidPrefix = "TextCleaner";

private final String sparkUid;

public TextCleaner() {
 sparkUid = 
org.apache.spark.ml.util.Identifiable$.MODULE$.randomUID(sparkUidPrefix);
 }

public TextCleaner(String uid) {
 sparkUid = uid;
 }

@Override
 public String uid() { // This method is called by parent class, before object 
creation finishes
 return sparkUid;
 }

...
{quote}

  was:
It is not possible to create proper Java custom Transformer by extending 
UnaryTransformer.

It seems that the method 'uid()' is called during object creation before the 
provided 'uid' constructor parameter could be set.

This leads to the following error:

{quote}
 java.lang.IllegalArgumentException: requirement failed: Param 
<prefix>_1563950936fa__inputCol does not belong to <prefix>_d4105b75c4aa.
{quote}

If you extend UnaryTransformer and try to use it e.g. through CrossValidator, 
you will need to explicitly include a constructor, which receives a String 
parameter. As I saw in the source of built in transformers, this parameter is a 
'uid', which should be set in the object. However, it is not possible to do it 
in time, because the uid() method is invoked (and its result might be used) 
before this constructor finishes.

Sample class:

{quote}
public class TextCleaner extends UnaryTransformer<String, String, TextCleaner>
                implements Serializable, DefaultParamsWritable, 
DefaultParamsReadable<TextCleaner> \{

    private static final long serialVersionUID = 2658543236303100458L;
    
    private static final String sparkUidPrefix = "TextCleaner";
    
    private final String sparkUid;

    public TextCleaner() \{
                sparkUid = 
org.apache.spark.ml.util.Identifiable$.MODULE$.randomUID(sparkUidPrefix);
        }

        public TextCleaner(String uid) \{
             sparkUid = uid;
        }
    
    @Override
    public String uid() \{ // This method is called by parent class, before 
object creation finishes
          return sparkUid;
    }

    ...
{quote}



> Java incompatibility when extending UnaryTransformer or Transformer
> -------------------------------------------------------------------
>
>                 Key: SPARK-22198
>                 URL: https://issues.apache.org/jira/browse/SPARK-22198
>             Project: Spark
>          Issue Type: Bug
>          Components: Java API, ML
>    Affects Versions: 2.2.0
>            Reporter: Akos Tomasits
>            Priority: Major
>
> It is not possible to create proper Java custom Transformer by extending 
> UnaryTransformer or Transformer.
> The built-in Params (e.g. defined in HasInputColumn trait) cannot be used and 
> custom Params cannot be added.
> It seems that the method 'uid()' is called during object creation before the 
> provided 'uid' constructor parameter could be set.
> This leads to the following error:
> {quote}java.lang.IllegalArgumentException: requirement failed: Param 
> <prefix>_1563950936fa__inputCol does not belong to <prefix>_d4105b75c4aa.
> {quote}
> If you extend UnaryTransformer and try to use it e.g. through CrossValidator, 
> you will need to explicitly include a constructor, which receives a String 
> parameter. As I saw in the source of built in transformers, this parameter is 
> a 'uid', which should be set in the object. However, it is not possible to do 
> it in time, because the uid() method is invoked (and its result might be 
> used) before this constructor finishes.
> Sample class:
> {quote}public class TextCleaner extends UnaryTransformer<String, String, 
> TextCleaner>
>  implements Serializable, DefaultParamsWritable, 
> DefaultParamsReadable<TextCleaner> {
> private static final long serialVersionUID = 2658543236303100458L;
> private static final String sparkUidPrefix = "TextCleaner";
> private final String sparkUid;
> public TextCleaner() {
>  sparkUid = 
> org.apache.spark.ml.util.Identifiable$.MODULE$.randomUID(sparkUidPrefix);
>  }
> public TextCleaner(String uid) {
>  sparkUid = uid;
>  }
> @Override
>  public String uid() { // This method is called by parent class, before 
> object creation finishes
>  return sparkUid;
>  }
> ...
> {quote}



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