adam bien's blog

Simplest Possible EJB 3.1 Singleton - Injected Into Servlet 3.0, WAR Deployment 📎


@Singleton
public class MasterDataCache {

    private Map cache;

    @PostConstruct
    public void initCache(){
        this.cache = new HashMap();
    }

    public Object get(String key){
        return this.cache.get(key);
    }
    
    public void store(String key,Object value){
        this.cache.put(key, value);
    }
}

How to compile:

You will need the the EJB 3.1 API in the classpath, or at least the @Singleton annotation.

How to deploy:

Just JAR the class and put the JAR into e.g: [glassfishv3]\glassfish\domains\domain1\autodeploy

How to use:


@WebServlet(name="SingletonTester", urlPatterns={"/SingletonTester"})
public class SingletonTester extends HttpServlet {

    @EJB
    MasterDataCache masterDataCache;

    @Override
    public void init(){
     masterDataCache.store("startup", new Date());
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        try {
            out.println("Startup time: " + masterDataCache.get("startup") );
        } finally { 
            out.close();
        }
    } 
}

And: there is no XML, strange configuration, libraries, additional frameworks or jars needed...

The whole WAR-project (Singleton) was checked in into: http://kenai.com/projects/javaee-patterns/. It was developed with Netbeans 6.8 and tested with Glassfish v3. The deployment took: INFO: Deployment of Singleton done is 272 ms.

[See also "Real World Java EE Patterns - Rethinking Best Practices", ServiceStarter page 207 and especially Singleton 211]