How do a LDAP search/authenticate against this LDAP in Java

Another approach is using UnboundID. Its api is very readable and shorter

Create a Ldap Connection

public static LDAPConnection getConnection() throws LDAPException {
    // host, port, username and password
    return new LDAPConnection("com.example.local", 389, "[email protected]", "admin");
}

Get filter result

public static List<SearchResultEntry> getResults(LDAPConnection connection, String baseDN, String filter) throws LDAPSearchException {
    SearchResult searchResult;

    if (connection.isConnected()) {
        searchResult = connection.search(baseDN, SearchScope.ONE, filter);

        return searchResult.getSearchEntries();
    }

    return null;
}

Get all Oragnization Units and Containers

String baseDN = "DC=com,DC=example,DC=local";
String filter = "(&(|(objectClass=organizationalUnit)(objectClass=container)))";

LDAPConnection connection = getConnection();        
List<SearchResultEntry> results = getResults(connection, baseDN, filter);

Get a specific Organization Unit

String baseDN = "DC=com,DC=example,DC=local";
String dn = "CN=Users,DC=com,DC=example,DC=local";

String filterFormat = "(&(|(objectClass=organizationalUnit)(objectClass=container))(distinguishedName=%s))";
String filter = String.format(filterFormat, dn);

LDAPConnection connection =  getConnection();

List<SearchResultEntry> results = getResults(connection, baseDN, filter);

Get all users under an Organizational Unit

String baseDN = "CN=Users,DC=com,DC=example,DC=local";
String filter = "(&(objectClass=user)(!(objectCategory=computer)))";

LDAPConnection connection =  getConnection();       
List<SearchResultEntry> results = getResults(connection, baseDN, filter);

Get a specific user under an Organization Unit

String baseDN = "CN=Users,DC=com,DC=example,DC=local";
String userDN = "CN=abc,CN=Users,DC=com,DC=example,DC=local";

String filterFormat = "(&(objectClass=user)(distinguishedName=%s))";
String filter = String.format(filterFormat, userDN);

LDAPConnection connection =  getConnection();
List<SearchResultEntry> results = getResults(connection, baseDN, filter);

Display result

for (SearchResultEntry e : results) {
    System.out.println("name: " + e.getAttributeValue("name"));
}