Sorting lists in Thymeleaf template using a custom comparator

Question

The Thymeleaf documentation states about sorting lists:

/*
 * Sort a copy of the given list. The members of the list must implement
 * comparable or you must define a comparator.
 */
${#lists.sort(list)}
${#lists.sort(list, comparator)}

In my document model, I have a list of maps with key value pairs (the published_content list from the JBake static page generator). In my template, I want to sort this list by comparing the value stored under a certain key in the maps.

In other words, the list variable has type List<Map<String, Object>> and I want to sort this list by comparing the value in each map stored under the key "mykey".

How can I formulate such a comparator in the template?

Answer 1

In Thymeleaf you need to use the full classname (include package). Something like:

<span th:each="doc : ${#lists.sort(documents, new com.mycompany.myapp.comparator.DocumentNameComparator())}">
    ...
</span>

Answer 2

The question is more related to a pure Java sorting issue, as you need a way to sort a list of maps, this was already answered here.

Related code:

public Comparator<Map<String, String>> mapComparator = new Comparator<Map<String, String>>() {
    public int compare(Map<String, String> m1, Map<String, String> m2) {
        return m1.get("name").compareTo(m2.get("name"));
    }
}

Collections.sort(list, mapComparator);

After having your list sorted working, using mapComparator, you could use the Thymeleaf expression ${#lists.sort(list, comparator)} as explained in the docs.