Htykuut

I have a list of objects where a few records can have empty value property and a few can have null value property. Using Collectors.groupingBy I need both the records to be considered as same.

import java.util.ArrayList;

import java.util.List;

import java.util.Map;

import java.util.stream.Collectors;



class Code {

    private String type;

    private String description;



    public static void main(String args) {

        List<Code> codeList = new ArrayList<>();

        Code c = new Code();

        c.setDescription("abc");

        c.setType("");

        codeList.add(c);

        Code c1 = new Code();

        c1.setDescription("abc");

        c1.setType(null);

        codeList.add(c1);



        Map<String, List<Code>> codeMap = codeList.stream()

                                                  .collect(Collectors.groupingBy(code -> getGroupingKey(code)));

        System.out.println(codeMap);

        System.out.println(codeMap.size());



    }



    private static String getGroupingKey(Code code) {

        return code.getDescription() +

                "~" + code.getType();

    }



    public String getType() {

        return type;

    }



    public void setType(String type) {

        this.type = type;

    }



    public String getDescription() {

        return description;

    }



    public void setDescription(String description) {

        this.description = description;

    }

}

The result of codeMap will have two records since it considers the empty string and the null value in the Type property as different. How can I achieve getting a single record here by considering both the null and empty records as same.

You can modify your getGroupingKey method like this:

private static String getGroupingKey(Code code) {

    return code.getDescription() + "~" + (code.getType() == null ? "" : code.getType());

}

or like this:

private static String getGroupingKey(Code code) {

    return code.getDescription() + "~" + Optional.ofNullable(code.getType()).orElse("");

}

or you might as well modify your getType() method directly as in:

public String getType() {

    return type == null ? "" : type;

}

or:

public String getType() {

    return Optional.ofNullable(type).orElse("");

}

Either should work the same. Pick one depending on your requirements I guess..

If you add the following toString method to your Code class:

@Override

public String toString() {

    return "Code{" +

            "type='" + type + ''' +

            ", description='" + description + ''' +

            '}';

} 

.. with the modified getGroupingKey method (or the getType method) the output should be as follows:

{abc~=[Code{type='', description='abc'}, Code{type='null', description='abc'}]}

1

Edit: You can also considering initializing the type to an empty String instead of null, then you would not need to modify anything:

private String type = "";

That might be an option too..