from the "java core pattern" book,i have learned that the service locator is a singleton,but when i downloaded the petstore1.3.1_01 and opened the source code,i find the web tier locator is a singleton,but the ejb tier locator is not a singleton,why?

the ejb tier locator as:




public class ServiceLocator {

private InitialContext ic;

private static ServiceLocator me;

public ServiceLocator() throws ServiceLocatorException {
try {
ic = new InitialContext();
} catch (NamingException ne) {
throw new ServiceLocatorException(ne);
} catch (Exception e) {
throw new ServiceLocatorException(e);
}
}

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the web tier locator as:


public class ServiceLocator {

private InitialContext ic;
private Map cache; //used to hold references to EJBHomes/JMS Resources for re-use

private static ServiceLocator me;

static {
try {
me = new ServiceLocator();
} catch(ServiceLocatorException se) {
System.err.println(se);
se.printStackTrace(System.err);
}
}

private ServiceLocator() throws ServiceLocatorException {
try {
ic = new InitialContext();
cache = Collections.synchronizedMap(new HashMap());
} catch (NamingException ne) {
throw new ServiceLocatorException(ne);
} catch (Exception e) {
throw new ServiceLocatorException(e);
}
}

static public ServiceLocator getInstance() {
return me;
}

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