Package org.apache.juneau.commons.utils

Class PredicateUtils

java.lang.Object
org.apache.juneau.commons.utils.PredicateUtils
public final class PredicateUtils extends Object
Utility methods for composing Predicate instances.

  • Method Summary

    Modifier and Type
    Method
    Description
    static <T> void
    consumeIf(Predicate<T> predicate, Consumer<T> consumer, T value)
    Consumes the specified value if the predicate is null or matches the specified value.
    static <T> Predicate<T>
    distinctByKey(Function<? super T,?> keyExtractor)
    Returns a predicate that filters out duplicate elements based on a key extractor function.
    static <T> Function<T,T>
    peek()
    Returns a function that prints the input value to stderr and returns it unchanged.
    static <T> Function<T,T>
    peek(String message, Function<T,?> formatter)
    Returns a function that prints the input value to stderr using a custom formatter and returns it unchanged.
    static <T> boolean
    test(Predicate<T> predicate, T value)
    Returns true if the specified predicate is null or matches the specified value.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Method Details

    • consumeIf

      public static <T> void consumeIf(Predicate<T> predicate, Consumer<T> consumer, T value)
      Consumes the specified value if the predicate is null or matches the specified value.
      Type Parameters:
      T - The type being consumed.
      Parameters:
      predicate - The predicate. Can be null (treated as an always-match).
      consumer - The consumer. Must not be null when the predicate matches.
      value - The value. Can be null.

    • peek

      public static <T> Function<T,T> peek()
      Returns a function that prints the input value to stderr and returns it unchanged.
      Type Parameters:
      T - The type of value.
      Returns:
      A function that prints and returns the value.

    • peek

      public static <T> Function<T,T> peek(String message, Function<T,?> formatter)
      Returns a function that prints the input value to stderr using a custom formatter and returns it unchanged.
      Type Parameters:
      T - The type of value.
      Parameters:
      message - A format string using {0} as placeholder for the formatted value. Must not be null.
      formatter - A function to extract/format the value for display. Must not be null.
      Returns:
      A function that prints and returns the value.

    • test

      public static <T> boolean test(Predicate<T> predicate, T value)
      Returns true if the specified predicate is null or matches the specified value.
      Type Parameters:
      T - The type being tested.
      Parameters:
      predicate - The predicate. Can be null (returns true).
      value - The value to test. Can be null.
      Returns:
      true if the specified predicate is null or matches the specified value.

    • distinctByKey

      public static <T> Predicate<T> distinctByKey(Function<? super T,?> keyExtractor)
      Returns a predicate that filters out duplicate elements based on a key extractor function.

      This is useful for filtering streams to keep only the first occurrence of each unique key.

      Example:

      // Filter a stream to keep only methods with unique signatures Stream<Method> methods = ...; Stream<Method> unique = methods .filter(PredicateUtils.distinctByKey(Method::getName));

      Type Parameters:
      T - The element type.
      Parameters:
      keyExtractor - A function that extracts the key from each element. Must not be null.
      Returns:
      A predicate that returns true for the first occurrence of each unique key, and false for subsequent occurrences with the same key.