How to Filter Values in Java 8 Map and Throw Exceptions for Matches

How do I filter values in a Java 8 Map and throw an exception if a match is found?

Map<String, Integer> map = new HashMap<>();
map.put("apple", 1);
map.put("banana", 2);
map.put("citrus", 3);
String keyToCheck = "banana";
map.entrySet().stream()
    .filter(entry -> entry.getKey().equals(keyToCheck))
    .findFirst()
    .orElseThrow(() -> new IllegalArgumentException("Match found: " + keyToCheck));

In Java 8, you can use the Stream API to efficiently filter values in a Map. If you want to throw an exception when a specific value is found, you can do this using the `findFirst` method along with `orElseThrow`. This allows you to check the map's entries against a condition and easily handle exceptions for any matches found.

Map<String, Integer> map = new HashMap<>();
map.put("apple", 1);
map.put("banana", 2);
map.put("citrus", 3);

String keyToCheck = "banana";
map.entrySet().stream()
    .filter(entry -> entry.getKey().equals(keyToCheck))
    .findFirst()
    .orElseThrow(() -> new IllegalArgumentException("Match found: " + keyToCheck));

Causes

• Desired to enforce rules in data processing.
• Need to validate map entries against a specific condition.

Solutions

• Use the Map's entrySet() method to convert the map into a stream of entries.
• Filter the stream using a lambda expression that defines your condition.
• Use findFirst to check for the existence of an entry meeting the condition and handle it with orElseThrow.

Mistake: Forgetting to check for null key/value in the Map process.

Solution: Always check for null before filtering.

Mistake: Not using the correct method (`orElseThrow`) to throw exceptions when a match is found.

Solution: Ensure you are using `orElseThrow` to handle situations where the match exists.