Getting UnSupportedOperationException when removing keyset values from a map-CodePudding

I have this below piece of method that iterates through a map and removes data based on certain criteria.

private Map<String, String> getSearchResultsWithoutOverUsedData(
    Map<String, String> searchDocumentResults
) {
    List<String> overUsedTestData = this.extractOverUsedTestData(
        searchDocumentResults
    );

    if (overUsedTestData.size() > 0) {
        this.deleteSearchResultsAboveThresholdUsage(overUsedTestData);
        searchDocumentResults.keySet().removeAll(overUsedTestData);
    }
    return searchDocumentResults;
}

When the line searchDocumentResults.keySet().removeAll(overUsedTestData); gets executed, it throws the following error sometimes.

java.lang.UnsupportedOperationException: null
    at java.util.Collections$UnmodifiableCollection.removeAll(Collections.java:1070) ~[?:1.8.0_302]
    at TestDataHandler.getSearchResultsWithoutOverUsedData(TestDataHandler.java:55) ~[MyService-1.0.jar:?]

As the parameter searchDocumentsResults is not final, I'm confused why its immutable. Any help to understand this would be much appreciated. Thanks in advance.

CodePudding user response：

If searchDocumentResults map happens to be immutable, you should create its copy first and then remove the overUsedTestData:

searchDocumentResults = new HashMap<>(searchDocumentResults);
searchDocumentResults.keySet().removeAll(overUsedTestData);

or using Stream API:

searchDocumentResults = searchDocumentResults.entrySet()
        .stream()
        .filter(e -> !overUsedTestData.contains(e.getKey()))
        .collect(Collectors.toMap(
            Map.Entry::getKey,
            Map.Entry::getValue
        ));