NamingEnumeration hasMoreElements method takes a lot of time when returning false for LDAP

问题

I am trying to search a LDAP server(Active Directory). When I parse the search results, the hasMoreElements method of NamingEnumeration takes around 15-20 seconds to execute when it returns false. It is not the case when it is returning true. Is there a way to solve this issue?

Code:

SearchControls ctrl = new SearchControls();
ctrl.setSearchScope(SearchControls.SUBTREE_SCOPE);
String searchFilter = "(&(objectClass=user("uid"="abc"))";
NamingEnumeration ne = dirContext.search("ldap://abc:389/dc=abc,dc=xy", searchFilter,ctrl);

if (ne != null) {
    while (ne.hasMoreElements()) {
        //parse results
    }

回答1:

The NamingEnumeration does some cleanup when calling hasMoreElements() the last time. It also checks if there are additional referrals is the context-property Context.REFERRAL is set to "follow". In one case in our software this caused exactly the behaviour as described: The last call to hasMoreElements() (or to hasMore() or calling next() more often than allowed) caused up to 40 seconds as referrals are searched in the LDAP context. The solution is to not set Context.REFERRAL to "follow".

回答2:

AD has a default limit of number of objects it returns in an LDAP query. I think it is in the 1000 object range.

If you hit 1001, you get 1000 returned, then an error, so I could see this being the case.

Count how many objects you get back in a test, and betcha you beat 1000 and then fail.

来源：https://stackoverflow.com/questions/1150201/namingenumeration-hasmoreelements-method-takes-a-lot-of-time-when-returning-fals