CODEWITHSUNDEEP
javaspringspring-boot
Lucas
Lucas

Reputation: 3

Using an autowired singleton bean in a non spring managed java class

Alright, this might seem pretty stupid to all the veterans out there, but bear with me here, as I'm only finding my way around Spring & Spring Boot.

I've got a Controller class here,

@RestController
public class Controller {

    private static final Logger logger = LogManager.getLogger(Controller.class);

    private static Controller controller = null;

    @Autowired
    private ApplicationParameters applicationParameters;

    public static Controller getInstance() {
        if (controller == null) {
            synchronized (Controller.class) {
                if (controller == null) {
                    controller = new Controller();
                }
            }
        }
        return controller;
    }

    public Controller() {}

    public ApplicationParameters getApplicationParameters() {
        return applicationParameters;
    }

    @RequestMapping("/")
    public void init() {
        try {
            for (Entry<String, String> prop : applicationParameters.getProperties().entrySet())
                logger.info("Loaded System Property: " + prop.getKey() + " -> " + prop.getValue());

                Utils.concatenate("key1", "key2");
        } catch (Exception e) {
            logger.error(e.getMessage(), e);
        }
    }
}

which autowires the ApplicationParameters bean with properties from a Property file.

Utils Class

public class Utils {

protected static final Logger logger = LogManager.getLogger(Utils.class);

    //Need to get the value of the property keys propKey1 & propKey2 and concat them.
    public static String concatenate(String propKey1, String propKey2) throws Exception {
        if(StringUtils.isNoneEmpty(propKey2) && StringUtils.isNoneEmpty(propKey1)) {
            return Controller.getInstance().getApplicationParameters().getProperties().get(propKey1) + Controller.getInstance().getApplicationParameters().getProperties().get(propKey2)
        } else {
            logger.error("System Property is undefined." );
            return null;
        }
    }

So, I'd like use this autowired ApplicationParameters bean as a singleton instance throughout the lifecycle of my project.

For instance, I'd like to use it in the Utils class. Clearly Utils class is not spring managed, its just a regular old java class.

So I'd like to know how to use fully initialized applicationParameters in my Utils class.

This is what I've tried so far:

  1. Autowiring the ApplicationParameters again in the Utils class, like this,

    public class Utils {

@Autowired
private ApplicationParameters applicationParameters;

protected static final Logger logger = LogManager.getLogger(Utils.class);

But applicationParameters will be null here as, I'm presuming, this is because, Utils is not a spring managed bean.

  1. Make Controller class singleton. (Not sure how to go about doing this as init() needs to get invoked when web server starts, then where to call getInstance()?)

Hence, would someone be so kind as to assist a novice here.

P.S. The Utils class is shown only as a sample to bring home the fact that, a spring managed autowired bean has to be used in a regular java class.

Upvotes: 0

Views: 845

Answers (2)

M. Deinum
M. Deinum

Reputation: 124441

As a first rule, don't. A second don't either. Only if you really must, as there is no garantuee that this will work reliable as there is no way that everything has been properly initialized when this method is called. Instead try re-working your util to be a spring managed class as well.

If you really want, ditch most of your code as you are trying to be too smart in your code. Use this hack (yes it is a hack imho and should be avoided if necessary!). 

public class SpringUtil {

  private static final ApplicationContext ctx;

  SpringUtil(ApplicationContext ctx) {
    SpringUtil.ctx=ctx;
  }

  public static Controller getController() {
    return this.ctx.getBean(Controller.class);
  }

  public static ApplicationParameters getApplicationParameters() {
    return ctx.getBean(ApplicationParameters.class);
  }
}

Then cleanup your controller 

@RestController
public class Controller {

    private static final Logger logger = LogManager.getLogger(Controller.class);

    @Autowired
    private ApplicationParameters applicationParameters;

    @GetMapping("/")
    public void init() {
        try {
            for (Entry<String, String> prop : applicationParameters.getProperties().entrySet())
                logger.info("Loaded System Property: " + prop.getKey() + " -> " + prop.getValue());

                Utils.concatenate("key1", "key2");
        } catch (Exception e) {
            logger.error(e.getMessage(), e);
        }
    }
}

THen use the SpringUtil to obtain the ApplicationParameters instead of the controller

public class Utils {

protected static final Logger logger = LogManager.getLogger(Utils.class);

    //Need to get the value of the property keys propKey1 & propKey2 and concat them.
    public static String concatenate(String propKey1, String propKey2) throws Exception {
        if(StringUtils.isNoneEmpty(propKey2) && StringUtils.isNoneEmpty(propKey1)) {
            return SpringUtils.getApplicationParameters().getProperties().get(propKey1) + SpringUtils.getApplicationParameters().getProperties().get(propKey2)
        } else {
            logger.error("System Property is undefined." );
            return null;
        }
    }

However this is quite a hack and might work in 90% of the cases. Also there is quite a design flaw/smell as you are doing a lot of getter chaining in your class. So all in all you are probably better of refactoring the Utils to make use of regular method calls and proper design techniques.

Upvotes: -1

D-rk
D-rk

Reputation: 5919

You could make the spring context accessible from outside with a helper class like this one:

public class SpringContextUtil implements ApplicationContextAware {
   static ApplicationContext applicationContext;     

   public void setApplicationContext(ApplicationContext context) throws BeansException {
     applicationContext = context;
   }

   public static ApplicationContext getApplicationContext() {
     return applicationContext;
   }
}

Then, you could do something like this: SpringContextUtil.getApplicationContext.getBean("applicationParameters")

Upvotes: 3

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