How can I get session from a common class in Spring Boot?

Question

I want to get session from a common class. Using @Autowired didn't work.

public class TMessageHandlerFactory implements MessageHandlerFactory {

    @Autowired
    private HttpSession session;

    @Override
    public void data(InputStream data) {
        int userId = (int)session.getAtrribute("key"); //session null
        ....        //do sth
    }
}

The constructor also didn't work

@Component
public class SMTPRunner implements ApplicationRunner {

    @Autowired
    private UserService userService;    // userService can access

    @Autowired
    private HttpSession session;        // session can't access

    @Override
    public void run(ApplicationArguments applicationArguments) throws Exception {
        TMessageHandlerFactory myFactory = new TMessageHandlerFactory(session);
        ....
    }
}

I also tried using SpringBeanFactory, it also didn't work.

@Component
public class SpringBeanFactoryUtil implements ApplicationContextAware {

    private static ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        if(SpringBeanFactoryUtil.applicationContext == null) {
            SpringBeanFactoryUtil.applicationContext = applicationContext;
        }
    }

    public static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    public static Object getBean(String name){
        return getApplicationContext().getBean(name);
    }

    public static <T> T getBean(Class<T> clazz){
        return getApplicationContext().getBean(clazz);
    }

    //通过name,以及Clazz返回指定的Bean
    public static <T> T getBean(String name,Class<T> clazz){
        return getApplicationContext().getBean(name, clazz);
    }
}

SpringBeanFactoryUtil only can get my custom bean, can't get HttpSession.
What should I do?

Answer 1

If I understand you right, you want to access something in the session scope from a component that a broader scope (singleton), as such the system can't know which one of the potential concurrent sessions in ther server you are interrested in an practically it would say at spring init time that the session scope isn't defined.

You can get arround that with the ObjectFactory pattern (1 of the possible solution)

@Autowired
ObjectFactory<HttpSession> httpSessionFactory;

And then when you need it, from a thread that is bound to the session:

HttpSession session = httpSessionFactory.getObject();

This way spring bind a receipe to get the object you need at the type you call the getObject() method rather than the actual object that is not yet available.

Please understand that if there no session bound to the current thread when you run the code, this will fail (return null) as no session is available. This mean either you call this code from a thread that you failed to forward the request thread local information of the request/session or you call this code from a context where it doesn't make sense.

Answer 2

Create session scope bean in pojo style. Inject it and use where you need set or get data from HttpSession. Spring will automatically set corresponding data into HttpSession. Eg:

@Component
@Scope(proxyMode= ScopedProxyMode.TARGET_CLASS, value=WebApplicationContext.SCOPE_SESSION)
public class SessionData {
    private Currency currency;

    public Currency getCurrency() {
        return currency;
    }

    public void setCurrency(Currency currency) {
        this.currency = currency;
    }
}


@Service
public class UserService {

   @Autowired
   private SessionData sessionData;

   public Currency getCurrentCurrency() {
       return sessionData.getCurrency();
   }

   public void setCurrentCurrency(Currency currency) {
       sessionData.setCurrency(currency);
   }
}

In such way getting/setting current currency using UserService will reflect in current HttpSession with corresponding attribute name of session bean property ('currency').