How to filter stream data with multiple parameters?

Question

I have a list of sources from a JSON file stored in S3. I need to provide search filters on few fields of the list. I have created a Builder class with all the needed fields on which the data can be filtered.

Now I want to use Java streams and apply the filters on the data based on the parameters the users will provide. Users can provide all the 6 parameters or only pass 2 or 3 parameters based on their need. For example user provides only 2 parameters out of 6 I should be able to filter the data based on the 2 parameters given and ignore the 4 parameters where the value is null.

public class ListOfFields {
    private String country;
    @JsonProperty("product")
    private String product;
    private String transactionId;
    private String sourceBy;
    private String category;
    private String specialTag;
    private String organicTag;
    private String successTag;
    private String speedTag;
    private String foodTag;
    private String costPrice;
    private String fruitType;
    private String fruitVendorId;    
}

The below is the builder class

public class ProductClass {
    @Builder.Default
    private String country = 'UnitedStates';
    private String sourceBy;
    private Boolean specialTag;
    private String category;
    private Boolean priceTag;
    private String fruitType;
}

The below method where user can make a call to get the product

public String getProduct(ProductClass productQuery) {      
    List<ListOfFields> result = listOfFields // (the declaration is made before in the class as private List<ListOfFields> listOfFields;)
            .stream().filter(productQuery::match)
            .collect(Collectors.toList());

How do I come up with dynamic predicate as the match function above? I should be able to filter on the parameters provided by the user be it 1 or 2 or 3 or 4 ... and not using the parameters where the user did not pass any value in the filter criteria.

Naman · Accepted Answer · 2020-07-04 01:54:16Z

Considering the ProductClass as the input and null values for the absence of the keys. You can define the list of Predicates possible using a method that takes in the actual query parameter.

private static List<Predicate<ListOfFields>> predicates(ProductClass product) {
    return List.of(
            lof -> product.priceTag != null && product.priceTag,
            lof -> product.specialTag != null && product.specialTag,
            lof -> product.country != null && product.country.equals(lof.country),
            lof -> product.sourceBy != null && product.sourceBy.equals(lof.sourceBy),
            lof -> product.category != null && product.category.equals(lof.category),
            lof -> product.fruitType != null && product.fruitType.equals(lof.fruitType)
    );
}

Upon reaching this, the list could be reduced to represent a single Predicate such as:

private static Predicate<ListOfFields> matchAll(List<Predicate<ListOfFields>> queries) {
    return queries.stream()
            .reduce(Predicate::and)
            .orElse(p -> true);
}

Now one can easily make use of this predicate while streaming the objects of type ListOfFields --

List<ListOfFields> result = listOfFields.stream()
        .filter(matchAll(predicates(productQuery)))
        .collect(Collectors.toList());

Mrinal · Accepted Answer · 2020-07-04 01:53:09Z

1

You can use regular if statements for each parameter and apply filter which returns Stream.

Stream< ListOfFields> stream = listOfFields.stream();
if(first parameter exists) {
    stream = stream.filter(predicate for first parameter);
}
if(second parameter exists) {
    stream = stream.filter(predicate for second parameter);
}
...
List< ListOfFields> result = stream.collect(Collectors.toList());

answered Jul 4, 2020 at 1:53

Mrinal

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