An endpoint that my application interacts with allows you to specify which fields are returned in the JSON result. My application will then map the JSON to a POJO using Jackson. Quite often I add more fields in one place and forget to add it in the other which results in problems. I wrote a unit test to help make the process easier but I feel like there could be room for improvements.

Here's what I have so far:

private static final String[] POTENTIAL_FIELDS = new String[] { "field1", "field2" };

public void checkFields() {
    // get all constant fields
    Set<String> constantFields = Arrays.stream(POTENTIAL_FIELDS)

    // get all private fields
    Set<String> reflectFields = Arrays.stream(FieldsModel.class.getDeclaredFields())
            .filter((field) -> !Modifier.isStatic(field.getModifiers()))
            .map(field -> field.getName().toLowerCase())

    Set<String> symmetricDifference = Sets.symmetricDifference(constantFields, reflectFields);

    // check if there's a difference
    if (!symmetricDifference.isEmpty()) {
        Assert.fail(String.format("Difference: %s\n", String.join(",", symmetricDifference)));

private static class FieldsModel {
    private int field1;
    private String field2;

The only non-standard imports are FieldsModel which is what the name suggests, and Sets which is from Guava (com.google.coom.collect.Sets). Here is a direct link to the method I used.

  • \$\begingroup\$ "Here's what I have so far" Does it work like you want it? \$\endgroup\$ – Mast Jul 29 at 16:36
  • \$\begingroup\$ Yes it does, it has the desired effect. I just was wondering if there was a more efficient way to find the disjunctive union than Guava's symmetricDifference or if I did something weird with Assert.fail(...) \$\endgroup\$ – Michael Ziluck Jul 29 at 16:37
  • \$\begingroup\$ Do you know how Sets.symmetricDifference works? Is the algorithm available in literature or how do you suggest we can compare it to other methods? \$\endgroup\$ – dfhwze Jul 29 at 18:46
  • 1
    \$\begingroup\$ @dfhwze Just edited my post to provide a direct link to that method. \$\endgroup\$ – Michael Ziluck Jul 29 at 18:55
  • 1
    \$\begingroup\$ @dfhwze Edited again to include those \$\endgroup\$ – Michael Ziluck Jul 29 at 19:33
  1. If you are using only one class there is no need to use ArrayList for POTENTIAL_FIELDS and then after converting it to set. Class will have a unique field name.
  2. If the number of class fields are not large then no need to worried about performance.
  • \$\begingroup\$ In the comments on my original question, they asked me to add in POTENTIAL_FIELDS so testers didn't need to. In the actual code, it's in a separate class. Also, where do you see an ArrayList? \$\endgroup\$ – Michael Ziluck Aug 2 at 12:51

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