EJB 3.1 Singleton example

Simplest Possible EJB 3.1 Singleton - Injected Into Servlet 3.0, WAR Deployment
http://www.adam-bien.com/roller/abien/entry/simplest_possible_ejb_3_14

Java EE6 Tutorial : A Singleton Session Bean Example: counter
http://download.oracle.com/javaee/6/tutorial/doc/gipvi.html

A singleton session bean is instantiated once per application and exists for the lifecycle of the application. Singleton session beans are designed for circumstances in which a single enterprise bean instance is shared across and concurrently accessed by clients.

Singleton bean - implements cache

package testservice;

import java.util.HashMap;
import java.util.Map;

import javax.annotation.PostConstruct;


/**
 * Session Bean implementation class MasterDataCache
 */
@javax.ejb.Singleton
public class MasterDataCache implements MasterDataCacheLocal {

    private Map cache;

    @PostConstruct
    public void initCache() {
        System.out.println("MasterDataCache.initCache");
        this.cache = new HashMap();
    }

    public Object get(String key) {
        System.out.println("MasterDataCache.get " + key);
        return this.cache.get(key);
    }

    public void store(String key, Object value) {
        System.out.println("MasterDataCache.store " + key);
        this.cache.put(key, value);
    }

}

TestService Session Bean

package testservice;

import javax.annotation.Resource;
import javax.ejb.EJB;
import javax.ejb.EJBContext;
import javax.ejb.SessionContext;
import javax.ejb.Stateless;

import testejb.BackendBeanLocal;

/**
 * Session Bean implementation class TestService
 */
@Stateless
public class TestService implements TestServiceRemote, TestServiceLocal {

    @EJB
    MasterDataCacheLocal masterDataCache;
    
    @EJB
    BackendBeanLocal service;
    
    @Resource SessionContext sessionContext;
    
    public void callService(){
        
        System.out.println("principal=" + sessionContext.getCallerPrincipal());
        
        if(masterDataCache.get("dave") == null){
            System.out.println("TestService: masterDataCache.store" );
            masterDataCache.store("dave","dave");
        } else {
            System.out.println("TestService: masterDataCache get" );
        }
        
        System.out.println("TestService: callService" );
        service.runService();
        
    }

}