Refactor multiple If' statements in Java-8

Question

I need to validate mandatory fields in my class

For example, 9 fields must not be null.

I need to check if they are all null but I

Answer 1

As easy refactoring you could introduce two helper methods :

private String createErrorMsgIfObjectNull(Object o, String errorMessage) {
    return Objects.isNull(o) ?  errorMessage : "";
}

private String createErrorMsgIfStringEmpty(String s, String errorMessage) {
    return StringUtils.isEmpty(s) ?  errorMessage : "";
}

And use them in this way :

StringBuilder mandatoryExcessFields = new StringBuilder(MANDATORY_EXCESS_FIELDS.length);

mandatoryExcessFields.append(createErrorMsgIfObjectNull(excess.getAsOfDate(), MANDATORY_EXCESS_FIELDS[0]))
                     .append(createErrorMsgIfStringEmpty(excess.getStatus(), MANDATORY_EXCESS_FIELDS[1]))
                     .append(createErrorMsgIfObjectNull(excess.getLimit(), MANDATORY_EXCESS_FIELDS[2]))
                     // ...  

By checking the type of the object to test you could still go further. You would have a single helper method that will apply the processing according to the argument type :

private String createErrorMsgIfNullOrEmptyString(Object o, String errorMessage) {
    if (o instanceof String) {
        return StringUtils.isEmpty((String)o) ? errorMessage : "";
    }
    return Objects.isNull(o) ? errorMessage : "";
}

---

A Java 8 stream way would inline the helper in a filter and map() operations and would collect the String result :

List> objectAndErrorMessageList = new ArrayList<>();
int i = 0;
objectAndErrorMessageList.add(new SimpleImmutableEntry<>(excess.getAsOfDate(), MANDATORY_EXCESS_FIELDS[i++]));
objectAndErrorMessageList.add(new SimpleImmutableEntry<>(excess.getStatus(), MANDATORY_EXCESS_FIELDS[i++]));
// and so for

String globalErrorMsg = 
    objectAndErrorMessageList.stream()
                             .filter(e -> {
                                 Object objectToValid = e.getKey();
                                 if (objectToValid == null) {
                                     return true;
                                 }
                                 if (objectToValid instanceof String && StringUtils.isEmpty(objectToValid)) {
                                     return true;
                                 }
                                 return false;
                             })
                             .map(SimpleImmutableEntry::getValue)
                             .collect(Collectors.joining(""));