How many backslash needed to get user’s groups?

Recently, I had to check the performance of AD domain controller when checking user’s groups. As many of you already know, the filter would be:

    (member:1.2.840.113556.1.4.1941:=%dn)

Somehow, the filter did not give any results back. Later I realized the comma within the dn could be the culprit. The format of the dn was as following:

    CN=LastName\, FirstName,OU=Users,DC=mycorp,DC=com 

Eventually, here is the Java code I figured out when checking LDAP server with JNDI:

    String sFilterPattern = "(member:1.2.840.113556.1.4.1941:=%dn)";		
    String sDN = "CN=LastName\\\\\\\\, FirstName,OU=Users,DC=mycorp,DC=com";   // 8 backslash
    sFilter = sFilter.replaceFirst("%dn", sDN);

When I dynamically obtained user’s dn and then used the dn to construct above filter, I had to patch extra backslashes using the following:

    String sUserDN = method-to-return-user-dn();
    String sDN = sUserDN.replaceFirst("\\\\", "\\\\\\\\\\\\\\\\");            // 16 backslash   
    ... ...