With Java

In few lines you have a usable DirContextSource:

import net.sf.michaelo.dirctxsrc.DirContextSource;
import javax.naming.directory.DirContext;
[…]
DirContextSource.Builder builder = new DirContextSource.Builder("ldap://domain-name");
// Set the Active Directory site
builder.additionalProperty("net.sf.michaelo.activedirectory.site", "debln-01");
// Make it fail fast
builder.additionalProperty("dns.com.sun.jndi.dns.timeout.initial", "200")
       .additionalProperty("dns.com.sun.jndi.dns.timeout.retries", "2");
DirContextSource contextSource = builder.build();
// try and catch block omitted for the sake of brevity,
// handle NamingException appropriately
DirContext context = contextSource.getDirContext();
// Perform operations
context.close();
[…]

With a Servlet Container (Apache Tomcat)

Navigate in your server.xml to /Server/GlobalNamingResources and add the following element:

[…]
<GlobalNamingResources>
  <!-- Add this -->
  <Resource name="ldap/name" type="net.sf.michaelo.dirctxsrc.DirContextSource"
    factory="net.sf.michaelo.dirctxsrc.DirContextSourceFactory"
    urls="ldap://domain-name"
    additionalProperties="net.sf.michaelo.activedirectory.site=debln-01;dns.com.sun.jndi.dns.timeout.initial=200;dns.com.sun.jndi.dns.timeout.retries=2" />
</GlobalNamingResources>
[…]

This resource still needs to be linked to your application. Open or create your app's context.xml and add:

<Context>
[…]
  <!-- Add this -->
  <ResourceLink global="ldap/name" name="ldap/localName"
    type="net.sf.michaelo.dirctxsrc.DirContextSource" />
[…]
</Context>

Now you have successfully linked a global resource to your webapp. It is now ready to use.