Java – LDAP connection leak in this code

Can anyone explain why this code randomly "leaks" LDAP connections? I can see that the number of established TCP / IP connections increases over time, and this can cause problems at some stage I tried to play with com sun. jndi. ldap. Connect environment properties (enable pool, disable it, etc.) but it doesn't seem to help@ H_ 404_ 7@@H_ 301_ 8@ @H_ 404_ 7@ this means that my bad code has a bug How can I do better and ensure that I never "leak" LDAP connections@ H_ 301_ 8@ @H_ 404_ 7@@H_ 301_ 8@

import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingEnumeration;
import javax.naming.NamingException;
import javax.naming.directory.Attributes;
import javax.naming.directory.InitialDirContext;
import javax.naming.directory.SearchControls;
import javax.naming.directory.SearchResult;

public class LdapUtil {
    private String ldap_context = "ou=myunit,dc=com";
    protected static String ldap_server = "ldap://ldapserver:389/";
    private String ldap_prefix = "(&(uid=";
    private String ldap_postfix = ")(objectclass=inetOrgPerson))";
    private String[] ldap_attributes = {"uid","departmentNumber","cn","postOffice@R_150_2419@","mail"};
    private Properties ldap_properties;
    private SearchControls ldap_searchcontrols;
        private static String ldap_principal = "uid=bind_account,cn=users,ou=myunit,dc=com";
        private static String ldap_credentials = "qwerty";

    private List<String> getUserAttributes(final String userId) {
        List<String> UserAttributes = new ArrayList<String>();
        InitialDirContext ctx = null;
        NamingEnumeration<SearchResult> resultsEnum = null;
        NamingEnumeration<String> atrEnum = null;

        // Connect the LDAP
        try {
        ctx = new InitialDirContext(this.ldap_properties);
        // Prepare the query string
        String query = this.ldap_prefix+ userId+ this.ldap_postfix;
        // Query!
        resultsEnum = ctx.search(this.ldap_context,query,this.ldap_searchcontrols);

        // Enumerate the results
        while (resultsEnum.hasMore()) {
            SearchResult sr = (SearchResult) resultsEnum.nextElement();

            // Get all the attributes for a hit
            Attributes atr = sr.getAttributes();
            // Enumerate the attributes
            atrEnum = atr.getIDs();

            while (atrEnum.hasMore()) {
                    String nextid = atrEnum.nextElement();
                    String nextattribute = atr.get(nextid).toString();
                    UserAttributes.add(nextattribute);
            }

        }
        } catch ( Exception eom ) {
            System.out.println("LDAP exception");
        } finally {
            try {
                if (atrEnum!=null)
                atrEnum.close();
                if (resultsEnum!=null)
                resultsEnum.close();
                if (ctx!=null)
                ctx.close();
            } catch (NamingException eo) {
                // nothing
            } catch (NullPointerException eo) {
                // Nothing
            }
        } 
        return UserAttributes;
    }


    /*
     * Parses the LDAP search results and searches for selected attribute.
     */
    private String getAttribute (final List<String> attributes,final String attribuutti) {
        String result = null;
        // Let's go through all attributes
        for (int i = 0; i < attributes.size(); i++) {
            String attribute = attributes.get(i).toString();
            // Look for match
            if (attribute.startsWith(attribuutti)) {
                // Return the value after the space
                int k = attribute.indexOf(" ");
                result = attribute.substring(k+1,attribute.length());
            }
        }
        return result;
    }


    public LdapUtil(String remoteuser) {

        // Pre-initialize LDAP connection related properties
        this.ldap_properties = new Properties();
        this.ldap_properties.put(Context.INITIAL_CONTEXT_FACTORY,"com.sun.jndi.ldap.LdapCtxFactory");
        this.ldap_properties.put(Context.PROVIDER_URL,ldap_server) ;
        this.ldap_properties.put(Context.REFERRAL,"follow" );
        this.ldap_properties.put(Context.Security_AUTHENTICATION,"simple");
        this.ldap_properties.put(Context.Security_PRINCIPAL,ldap_principal);
        this.ldap_properties.put(Context.Security_CREDENTIALS,ldap_credentials);
        this.ldap_properties.put("com.sun.jndi.ldap.read.timeout","10000");
        this.ldap_properties.put("com.sun.jndi.ldap.connect.timeout","10000");
        // Tried with both pooling and without - doesn't solve problems
        this.ldap_properties.put("com.sun.jndi.ldap.connect.pool","false");

        // Pre-initialize LDAP search controls
        this.ldap_searchcontrols = new SearchControls();
        this.ldap_searchcontrols.setSearchScope(SearchControls.SUBTREE_SCOPE);
        this.ldap_searchcontrols.setReturningAttributes(this.ldap_attributes);

            // The List for attributes
        List<String> attributes = null;

        attributes = getUserAttributes(remoteuser);
    }

}

Solution

An obvious problem is that your finally block is wrong F close throws an exception and will not call the following close method Always write this Code: @ h_ 404_ 7@@H_ 301_ 8@ @H_ 404_ 7@@H_ 301_ 8@

final Res res = acquire();
try {
    use(res);
} finally {
    res.release();
}