CODEWITHSUNDEEP
javaspringnaming-conventions
gus.jz
gus.jz

Reputation: 53

How to access a singleton and name it in java?

I want to create a singleton in Java that requires reading from a file configuration to instanciate, amongst other logic (so it's not just a new MySingletonObject()).

What's the proper way to achieve that in Spring ? I was wondering if I should do the following:

public interface MySingletonObjectAccessor {
  MySingletonObject getInstance();
}

@Service
public class MySingletonObjectAccessorImpl implements MySingletonObjectAccessor {
  private MySingletonObject mySingletonObject;
  @Override
  public MySingletonObject getInstance() {
    return mySingletonObject;
  }

  MySingletonObjectAccessorImpl() {
    this.MySingletonObject = // complex logic here, that includes reading from a config file

  }
}

the usage would then be:

@Autowired
MySingletonObjectAccessor msoa;

MySingletonObject mso = msoa.getInstance();

Am I on the right track ? If so, what would be the correct naming convention for the MySingletonObjectAccessor service ?

Upvotes: 0

Views: 776

Answers (3)

Madhu Potana
Madhu Potana

Reputation: 91

If you are using singleton as config then use @Component and use @Scope(value = ConfigurableBeanFactory.SCOPE_SINGLETON) for singleton.

If it is configuring a file the use FileConfig as class name, as per java standards class name must specify the what it have and what it can do. Ex:- FileReadConfig, FileUploadConfig, DBConnectConfig, EagerInitializedSingleton, StaticBlockSingleton, EnumSingleton ....,

Example:-

@Configuration
public class MySingletonObject {
   private MySingletonObject mySingletonObject;
   public static final String FILENAME = "/Users/xxx/Projects/xxx/config.xml";
   private XMLObject config = null;

    private boolean loadConfig(String fileName) {
        BufferedReader reader;
        String line;
        String content = "";

        try {
            reader = new BufferedReader(new FileReader(fileName));

            while ((line = reader.readLine()) != null) {
                content += line;
            }
        } catch (IOException ex) {
            LOGGER.log(Level.SEVERE, null, ex);
            return false;
        }

        /**
         * IF there is no content, the file must not be valid
         */
        if (content.length() <= 0) {
            return false;
        }
        this.config = new XMLObject(content);

        return true;
    }
    private Configuration() {
        boolean result = this.loadConfig(FILENAME);

        if (!result) {
            if (!this.createConfig(FILENAME)) {
                System.exit(0); //Catastrophic
            }
        }else{
            mySingletonObject = new MySingletonObject ();
        }
    }

   @Bean("mySingletonObject")
   @Scope(value = ConfigurableBeanFactory.SCOPE_SINGLETON)
   public MySingletonObject getMySingletonObject () {
      return mySingletonObject;
   }
}

Now 

@Autowired
MySingletonObject msoa;

Upvotes: 0

Shafiul
Shafiul

Reputation: 1512

You can define a Bean and add a scope to make it singleton.

    @Configuration
    class MySingletonBeanConfiguration {

      //default is singleton scope
      @Bean
      public MySingletonBean mySingletonBean() {
        return new MySingletonBean();
      }
    }

Upvotes: 2

kumesana
kumesana

Reputation: 2490

You could have a public Configuration class like this in your Spring-scanned packages:

@Configuration
public class MySingletonProvider {

  @Bean
  public MySingleton nameTheMethodExactlyLikeTheBeanNameYouWant(@Value("${singleton.xml.file}") String xmlConfigFile) {
    Library lib = new Library(xmlConfigFile);
    return new MySingleton(lib);
  }
}

Upvotes: 0

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