Check if a Map Value contains a particular String and an element from the restricted List

user_7839821 0
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I have a map of some values like this:

Map<String, String> roleMap = new HashMap<>();
map.put(1,"A");
map.put(2,"B;C;D");
map.put(3,"A;C");

And the list of some restricted values:

List<String> restrictedList= List.of("B", "C");

I need to check if the value "A" is presented in each key of the map and not together with one of the values from restricted list, then throw some error.

I succeeded to do this but think it can be done better with streams fully and not a half job.

This is my solution:

map.forEach((key, value) -> {
    if (Arrays.stream(value.toString().split(";"))
        .anyMatch(role -> "A".contains(role))
            && CollectionUtils.containsAny(Arrays.asList(value.toString().split(";")), restrictedList)) {
        errorsList.add(String.format("%s combination can't be used with 'A'", value))
    };
});

The result of above scenario should output that key number 3 is invalid because only key number 3 contains "A and also some value from restricted list.

But I wonder how to implement it with streams?

I tried with filter() before anyMatch() but it doesn't work.

java-stream hashmap list java
3 Answers

I recommend extracting your condition checking to isInRestrictedList method.

Then you can use stream.filter map in a very simple and clean way like this:

List<String> errorsList = map.entrySet()
    .stream()
    .filter(entry -> isInRestrictedList(entry.getValue()))
    .map(entry -> String.format("key: %s, %s combination can't be used with 'A'", entry.getKey(), entry.getValue()))
    .collect(Collectors.toList());

private boolean isInRestrictedList(String value) {
    List<String> restrictedList = Arrays.asList("B", "C");
    List<String> source = Arrays.asList(value.split(";"));
    return source.contains("A") && CollectionUtils.containsAny(source, restrictedList);
}

The output of errorsList is key: 3, A;C combination can't be used with 'A'

user_54854540

You can create a stream over the values of the map and apply filter() operation on it twice:

  • to find out if the target string ("A") in your code is contained in the map value;
  • to determine whether there's an intersection between a particular map value and the given restricted list.

Both checks are making of anyMatch() operation.

In order to improve performance of checking against the restricted lists, it's being wrapped with a HashSet.

A string array is being created via split() operation from each value only once to reduce the overheads.

Target value ("A"), error message and delimiter (";") are being passed to the method dynamically and not hard-coded.

The code might look like this:

public static List<String> getErrorList(List<String> restricted,
                                        Map<String, String> map,
                                        String targetValue, // in your code "A"
                                        String errorMessage,
                                        String delimiter) {
    
    Set<String> restrictedSet = new HashSet<>(restricted); // list is being wrapped by the set to improve performance
    
    return map.values().stream()          // Stream<String>
        .map(str -> str.split(delimiter)) // Stream<String[]>
        .filter(arr -> Arrays.stream(arr).anyMatch(targetValue::equals))     // contain the target value
        .filter(arr -> Arrays.stream(arr).anyMatch(restrictedSet::contains)) // contains any of the restricted values
        .map(arr -> String.join(delimiter, arr))                             // Stream<String>
        .map(str -> String.format("%s %s %s", str, errorMessage, targetValue))
        .collect(Collectors.toList());
}

main() - demo

public static void main(String[] args) {
    Map<String, String> roleMap =
        Map.of("1","A", "2","B;C;D", "3","A;C");
    
    List<String> restrictedValues = List.of("B", "C");
    
    String errorMessage = " combination can't be used with ";
    String targetValue = "A";

    System.out.println(getErrorList(restrictedValues, roleMap, targetValue, errorMessage, ";"));
}

Output

[A;C  combination can't be used with  A]
user_179499450

You could do something like below to filter the keys which have invalid values according to your requierments and collect those keys to a list/set:

Map<Integer,String> map = new HashMap<>();
map.put(1,"A");
map.put(2,"B;C;D");
map.put(3,"A;C");

List<String> restrictedList= List.of("B", "C");

List<Integer> invalidKeys =  map.entrySet().stream()
        .filter(e -> Arrays.asList(e.getValue().split(";")).contains("A"))
        .filter(e -> Arrays.asList(e.getValue().split(";")).stream().anyMatch(restrictedList::contains))
        .map(Map.Entry::getKey)
        .collect(Collectors.toList());

System.out.println(invalidKeys);

If you want to avoid two filters and calling Arrays.asList twice, you could extract a predicate like below:

Predicate<String> containsRestrictedValueAndA = s -> {
    List<String> temp = Arrays.asList(s.split(";"));
    return temp.contains("A") && temp.stream().anyMatch(restrictedList::contains);
};

List<Integer> invalidKeys2 = map.entrySet().stream()
                .filter( e -> containsRestrictedValueAndA.test(e.getValue()))
                .map(Map.Entry::getKey)
                .collect(Collectors.toList());

System.out.println(invalidKeys2);
user_51769920
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