Singletons - How to use it better?

Question

The web application has Actions <--> Services <--> Implementations. The user comes to the UI, changes some settings (pagination size, show/hide properties), and these settings are saved in an XML file. The XML file is read/written by a 'UIConfiguration' class and settings are stored as a bean. My singleton 'ConfigService' instantiates this UIConfiguration. The code is like this (how do I post code here?)
public class ConfigService {
private Configuration uiConfiguration;
private static ConfigService instance = null;
private Map<String, ConfigBean> uiConfig;
private ConfigService(){
init();
private void init(){
uiConfiguration = new UIConfiguration();
try {
uiConfig = uiConfiguration.getConfigurations();
} catch (Exception e) {
public String getServerUrl(){
return "http://"+ uiConfig.get("server.hostname").getValue()
+ ":" + uiConfig.get("server.port").getValue();
public String getUIProperty(String propertyName){
return uiConfig.get(propertyName).getValue();
public static ConfigService getInstance(){
if(instance == null)
instance = new ConfigService();
return instance;
public void updateUIConfig(Map<String, ConfigBean> configs){
uiConfig = configs;
public Map<String, ConfigBean> getAllUIProperties(){
return uiConfig;
**Things that I think that I am not doing right are:* *
1. I have ConfigService.getInstance() in the contextlistener.
2. Also, everywhere in the application I do ConfigService.getInstance() whereever I need a UI property.
3. I do ConfigService.getInstance().updateUIConfig(configurations) in my UIConfiguration class when I update the properties.
Is this a right way to do this? Is there any better/clean way of doing this. I also use Spring to inject services into my action classes. Can that help to better the behavior anyhow?
Please help me here.

Answer 1

user2893271 wrote:
2. Also, everywhere in the application I do ConfigService.getInstance() whereever I need a UI property.
3. I do ConfigService.getInstance().updateUIConfig(configurations) in my UIConfiguration class when I update the properties. There's nothing necessarily wrong with either of those.
On the other hand, if you have a lot of getInstance() calls in the same method or class, you might want to make a local or member variable and just assign it once, rather than repeatedly calling the method. This would be more for simplicity and clarity, but if you have a lot of activity there across many threads, it's possible that lock contention (if you go with lazy instantiation and a synchronized getInstance() method) could have a performance impact. (Do NOT assume that it will and then munge up your code just based on that. Only make performance-related changes if you have measured and found that to be a bottleneck.)
One other issue is whether you should even have a Singleton in the first place. There's been a lot of backlash against Singleton lately. It's true that it is overused and abused, but, IMHO, the backlash has been just as over the top and knee-jerky as the initial "let's use singleton everywhere" approach. There are cases where singletons are appropriate. Yours may be one, or it may not. I don't know enough of your design to comment on it one way or the other, and I'm not interested in pursuing that question. I just want to raise the issue to you as something to think about and possibly research further.