Comparing Java Lists Without Implementing equals

In Java, there are several ways to compare whether two Lists have the same values regardless of order, such as sorting followed by using equals, or executing containsAll in both directions, etc. All of these methods require us to implement the equals and hashCode methods for the element classes in the list.

However, there are special cases where it’s not convenient for us to implement the equals method of a class — for example, when it comes from an ancient third-party JAR package where modifying the code could bring many unknown issues. What should we do in such situations?

Actually, it’s quite simple. The all-powerful Apache Commons already thought of this, so they added externally supplied equals and hashCode methods in commons-collections4. Even the equals and hashCode methods themselves don’t need to be written by us — they can be implemented using the commons-lang package. The specific code is as follows:

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-collections4</artifactId>
    <version>4.1</version>
</dependency>
<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.5</version>
</dependency>

public static <T> boolean isEqualCollection(Collection<T> l1, Collection<T> l2, final String... exludedFields) {
    Equator<T> equator = generateEquator(exludedFields);
    return CollectionUtils.isEqualCollection(l1, l2, equator);
}

private static  <T> Equator<T> generateEquator(final String... exludedFields) {
    Equator<T> equator = new Equator<T>() {
        @Override
        public boolean equate(T o1, T o2) {
            if (o1 == null && o2 == null) {
                return true;
            }
            if (o1 == null || o2 == null) {
                return false;
            }
            if (o1.getClass() != o2.getClass()) {
                return false;
            }
            return EqualsBuilder.reflectionEquals(o1, o2, exludedFields);
        }

        @Override
        public int hash(T o) {
            return HashCodeBuilder.reflectionHashCode(o, exludedFields);
        }
    };
    return equator;
}

Source: https://lichuanyang.top/en/posts/28720/