Embedding ApacheDS as a Web Application

My initial aim was to demonstrate embedding ApacheDS in a very simple, but nevertheless impressive way. I thought about embedding the server in Apache Tomcat first. But then I got a better plan: Creating a standard web application which wraps ApacheDS and can be deployed on any compliant application server. ApacheDS in a war-archive!

Solution Outline

The solution is quite simple. A web application carries all the necessary jar files for ApacheDS within the lib-directory of the WEB-INF folder. When the web application is started by the servlet container, appropriate code has to be executed to start ApacheDS. And the server has to be stopped, if the web application goes down (for instance if the server shuts down). There are (at least) two standard compliant ways to acomplish this:

• A Servlet (automatically started with the web application, using the lifecycle methods init and destroy)
• A ServletContextListener

In the following we have choosen the second option.

A Servlet Context Listener to start and stop ApacheDS

A servler context listener receives notifications about changes to the servlet context of the web application it is part of. Documentation of the ServletContextListener interface can be found here. To receive notification events, the implementation class must be configured in the deployment descriptor for the web application. The two life cycle methods contextInitialized and contextDestroyed are suitable to start and stop ApacheDS.

A client within

After the server has been started from the Listener, it will be accessible from the outside via the network using LDAP. In order to demonstrate how to interact with the server from within the VM, a simple servlet is demonstrated. It allows you to communicate with the embedded server via web browser. This is so simple, because the server already lives within a web application, only a servlet has to added to act as an entry point. Our sample servlet will diplay the Root DSE of the server.

The following class diagram visualizes the complete example. The two gray elements use Servlet and ApacheDS API.

Step 1: The web component which starts and stops the server

The ApacheDS core is a JNDI provider that manages a local hierarchical store of Attributes objects, based on the LDAP namespace. JNDI is the access API used to hide internals, and it is also used to configure the core.

A helper class for configuration

In order to keep the source code of this example simple, the following class is used to provide the environment to the other classes. Standard JNDI keys are used to tell JNDI what the provider is etc.

package org.apache.directory.samples.embed.webapp;

import java.util.Hashtable;
import java.util.Properties;

import javax.naming.Context;

public class EnvHelper {

    public static Hashtable createEnv() {
        Hashtable env = new Properties();

        env.put(Context.PROVIDER_URL, "");
        env.put(Context.INITIAL_CONTEXT_FACTORY,
                "org.apache.directory.server.jndi.ServerContextFactory");

        env.put(Context.SECURITY_PRINCIPAL, "uid=admin,ou=system");
        env.put(Context.SECURITY_CREDENTIALS, "secret");
        env.put(Context.SECURITY_AUTHENTICATION, "simple");

        return env;
    }
}

The listener class

The class StartStopListener implements ServletContextListener and therefore contains the following two life cycle methods:

• contextInitialized() is executed if the web application is started by the servlet container, it starts ApacheDS embedded
• contextDestroyed() is executed if the web application is stopped by the servlet container, it stops the embedded server

First of all contextInitialized determines an appropriate working directory for the server. This directory is need to persist the partition data (entries). Our example uses a simple yet portable way for this task: the context attribute javax.servlet.context.tempdir.
Afterwards the method creates a configuration object which is suitable to start the server (class MutableServerStartupConfiguration). LDAP networking is enabled on port 10389, and the working directory is set. The configuration is combined with the environment from the helper class above. Invoking the constructor of InitialDirContext with these settings causes the ApacheDS core to start.

The method contextDestroyed is comparable. It uses a configuration suitable to shut down the server.

package org.apache.directory.samples.embed.webapp;

import java.io.File;
import java.util.Hashtable;

import javax.naming.NamingException;
import javax.naming.directory.InitialDirContext;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import org.apache.directory.server.configuration.MutableServerStartupConfiguration;
import org.apache.directory.server.core.configuration.ShutdownConfiguration;
import org.apache.directory.server.ldap.LdapConfiguration;

/**
 * A Servlet context listener to start and stop ApacheDS.
 * 
 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
 */
public class StartStopListener implements ServletContextListener {

    /**
     * Startup ApacheDS embedded.
     */
    public void contextInitialized(ServletContextEvent evt) {

        try {
            // Create a default configuration
            MutableServerStartupConfiguration cfg = new MutableServerStartupConfiguration();

            // Determine an appropriate working directory
            ServletContext servletContext = evt.getServletContext();
            File workingDir = (File) servletContext
                    .getAttribute("javax.servlet.context.tempdir");
            cfg.setWorkingDirectory(workingDir);

            // Set LDAP port to 10389
            LdapConfiguration ldapCfg = cfg.getLdapConfiguration();
            ldapCfg.setIpPort(10389);

            // Start the Server
            Hashtable env = EnvHelper.createEnv();
            env.putAll(cfg.toJndiEnvironment());
            new InitialDirContext(env);

        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Shutdown ApacheDS embedded.
     */
    public void contextDestroyed(ServletContextEvent evt) {
        try {
            Hashtable env = EnvHelper.createEnv();
            ShutdownConfiguration cfg = new ShutdownConfiguration();
            env.putAll(cfg.toJndiEnvironment());
            new InitialDirContext(env);
        } catch (NamingException e) {
            throw new RuntimeException(e);
        }
    }
}

Deployment descriptor

In order to execute the listener code, the class has to be defined in the deployment descriptor of a web application, as depicted below:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
  <display-name>ApacheDS embedded in a WebApp</display-name>
  <description>
    A simple yet portable way to run ApacheDS within a servlet
    container
  </description>

  <listener>
    <listener-class>
      org.apache.directory.samples.embed.webapp.StartStopListener
    </listener-class>
  </listener>
</web-app>

Packaging and Deploying the WebApp

A standard web archive (war-File) is needed in order to deploy the application to a servlet container. The Resources area at the end of this page provides a zip-File which contains the file structure. A build script for Apache Ant is included as well.

Directory layout for the sources, war file layout

The build script assumes that you have ApacheDS 1.5.1 and Tomcat 5.5.20 installed locally; it uses and (in the case of ApacheDS) copies the necessary your file from their lib directories to the lib directory of the web application. You will likely want to adjust the installation directories defined in the build.xml file.

After building the project, the classes folder will contain the compiled class files of the three Java classes above, and a properties file to configure the logging framework log4j. The lib folder will contain all jar-Files necessary, these are

• antlr-2.7.7.jar
• apacheds-bootstrap-extract-1.5.1.jar
• apacheds-bootstrap-partition-1.5.1.jar
• apacheds-btree-base-1.5.1.jar
• apacheds-core-1.5.1.jar
• apacheds-core-shared-1.5.1.jar
• apacheds-jdbm-store-1.5.1.jar
• apacheds-kerberos-shared-1.5.1.jar
• apacheds-protocol-changepw-1.5.1.jar
• apacheds-protocol-dns-1.5.1.jar
• apacheds-protocol-kerberos-1.5.1.jar
• apacheds-protocol-ldap-1.5.1.jar
• apacheds-protocol-ntp-1.5.1.jar
• apacheds-protocol-shared-1.5.1.jar
• apacheds-schema-bootstrap-1.5.1.jar
• apacheds-schema-extras-1.5.1.jar
• apacheds-schema-registries-1.5.1.jar
• apacheds-server-jndi-1.5.1.jar
• apacheds-utils-1.5.1.jar
• commons-collections-3.2.jar
• commons-lang-2.3.jar
• jdbm-1.0.jar
• log4j-1.2.14.jar
• mina-core-1.1.2.jar
• mina-filter-ssl-1.1.2.jar
• shared-asn1-0.9.7.jar
• shared-asn1-codec-0.9.7.jar
• shared-ldap-0.9.7.jar
• shared-ldap-constants-0.9.7.jar
• slf4j-api-1.4.3.jar
• slf4j-log4j12-1.4.3.jar

The webapp target in the build.xml file (which is the default target) packs the files for the web application together in a web archive called ApacheDS.war.

Deploying on Apache Tomcat

In order to run the application within Tomcat, simply put the ApacheDS.war file in the webapps directory of your Tomcat installation and start the server. If you have the manager application enabled (as described here), you can see and "manage" (start/stop) ApacheDS within its list view.

Connecting to ApacheDS from the outside

ApacheDS is up and running within the servlet container. Besides the administration tool listing, it seems to be invisible. But because we have configured network access via port 10389, you can easily access the server with an arbitrary LDAP client from outside.

One option is a command line tool like ldapsearch (see ApacheDS Basic User's Guide for details on how to connect to ApacheDS with such tools in general). Here is an example how to connect as administrator (simple bind) and fetch the Root DSE of our embedded ApacheDS instance:

$ ldapsearch -h localhost -p 10389 -D "uid=admin,ou=system" -w secret \\
    -b "" -s base "(objectClass=*)" * +
version: 1
dn:
supportedLDAPVersion: 3
objectClass: extensibleObject
objectClass: top
subschemaSubentry: cn=schema
supportedFeatures: 1.3.6.1.4.1.4203.1.5.1
vendorName: Apache Software Foundation
supportedExtension: 1.3.6.1.4.1.1466.20036
namingContexts: ou=system
namingContexts: ou=schema
supportedSASLMechanisms: GSSAPI
supportedSASLMechanisms: DIGEST-MD5
supportedSASLMechanisms: CRAM-MD5
supportedControl: 2.16.840.1.113730.3.4.3
supportedControl: 2.16.840.1.113730.3.4.7
supportedControl: 1.3.6.1.4.1.4203.1.10.1
supportedControl: 2.16.840.1.113730.3.4.2
supportedControl: 1.3.6.1.4.1.18060.0.0.1
vendorVersion: 1.5.1
$

Another choice are graphical LDAP clients (see ApacheDS Basic User's Guide for details on how to connect to ApacheDS with such tools in general).

With our popular Eclipse RCP application Directory studio for instance, connecting goes like this:
In the Connections view, select "New connection ...". Within a wizard dialog, you provide the connection data (host name, port, bind DN and password).

After successfully connecting to the embedded ApacheDS, you can browse the tree, add and manipulate entries and so on. If you check the connection properties, you can study the Root DSE as well.

Other Web Application Servers

The web application described here has been successfully deployed on

• Apache Tomcat 5.5.20 and 6.0.9-beta (Homepage)
• IBM WebSphere Application Server 6.1 (Homepage)
• Jetty 6.1.0 (Homepage)

Here is a screen shot of the web based administration console of WebSphere Application Server 6 with the ApacheDS.war deployed and running, no changes in the deployment archive were needed.

Step 2: Adding functionality: A servlet which displays the Root DSE

To finish with, here is a simple example on how to access the server internally.

The following servlet, which will be deployed together with the other two classes in the web archive, connects to ApacheDS directly, i.e. via the internal JNDI provider. No network access is needed. In the doGet method it performs a search operation against the Root DSE of the server, as the examples above do.

package org.apache.directory.samples.embed.webapp;

import java.io.IOException;
import java.io.PrintWriter;

import javax.naming.NamingEnumeration;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;
import javax.naming.directory.SearchControls;
import javax.naming.directory.SearchResult;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class RootDseServlet extends HttpServlet {

    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {

        try {
            resp.setContentType("text/plain");
            PrintWriter out = resp.getWriter();

            out.println("*** ApacheDS RootDSE ***\n");

            DirContext ctx = new InitialDirContext(EnvHelper.createEnv());

            SearchControls ctls = new SearchControls();
            ctls.setReturningAttributes(new String[] { "*", "+" });
            ctls.setSearchScope(SearchControls.OBJECT_SCOPE);

            NamingEnumeration result = ctx.search("", "(objectClass=*)", ctls);
            if (result.hasMore()) {
                SearchResult entry = (SearchResult) result.next();
                Attributes as = entry.getAttributes();

                NamingEnumeration ids = as.getIDs();
                while (ids.hasMore()) {
                    String id = (String) ids.next();
                    Attribute attr = as.get(id);
                    for (int i = 0; i < attr.size(); ++i) {
                        out.println(id + ": " + attr.get(i));
                    }
                }
            }
            ctx.close();

            out.flush();
        } catch (Exception e) {
            throw new ServletException(e);
        }
    }
}

In order to make the servlet available to clients, it has to be declared in the deployment descriptor web.xml, here are the additions (a servlet named RootDseServlet for the class above, and a URL mapping)

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>

  ...
  <servlet>
    <servlet-name>RootDseServlet</servlet-name>
    <servlet-class>
      org.apache.directory.samples.embed.webapp.RootDseServlet
    </servlet-class>
  </servlet>

   <servlet-mapping>
     <servlet-name>RootDseServlet</servlet-name>
     <url-pattern>/RootDse</url-pattern>
   </servlet-mapping>
</web-app>

Redeploy the web application. If you point to your tomcat server with the appropriate URL (http://localhost:8080/ApacheDS/RootDse), you'll see the content of the Root DSE as depicted below:

Download the source code

EnvHelper.java
StartStopListener.java
RootDseServlet.java
web.xml
ApacheDSWebApp.zip all sources including a build script for Apache Ant (build.xml)