[FIXED] What is the recommended way to pass state information to an HTTP interceptor?

Issue

I am trying to perform logging of all HTTP outbound requests from my application. However, I need the HTTP interceptor to have access to some meta-data of the HTTP calls. This data is set manually for each separate type of HTTP call in the app logic itself. Now, there are two apporaches I have found so far to pass this data on to the interceptor:

1. Include this metadata in a temporary HTTP header, log it when the call is intercepted, remove the header, make the call
2. Store the data in a static ThreadLocal variable, retrieve it in the interceptor and clear the ThreadLocal storage

Although both these methods work fine, there are some reservations I have regarding both methods. For the first method, it seems unwise to alter the HTTP request itself as, in case, the interceptor is not working/not being used, the metadata will be passed on to the remote server. For the second method, the use of ThreadLocal comes associated with problems of heap memory management as too many threads might eat up heap space.

Is there any other standard/recommended method to approach this problem? If not, which of the above mentioned methods would be better suited at addressing this problem statement?

Solution

An alternative method in Spring is to have a Bean with bean-scope set as "Request". Singleton scope beans are not thread-safe, however, with a Request scope, a Bean is established only within the context of a single HTTP-Request and as such. Such a Bean is instanitated at the start of an HTTP request and its state persists the entire duration of just that HTTP request. The syntax for this is:

@Bean
@Scope(value = WebApplicationContext.SCOPE_REQUEST, proxyMode = ScopedProxyMode.TARGET_CLASS)
public HelloMessageGenerator requestScopedBean() {
    return new HelloMessageGenerator();
}

or, alternatively, a shorter version of the same code:

@Bean
@RequestScope
public ScopedBeanClass requestScopedBean() {
    return new ScopedBeanClass();
}

The ScopedBeanClass may now be used to set and read values in a thread safe manner at any point during the lifetime of a single HTTP Request after which the Bean is cleared/reset in the next request (possibly from a concurrent Thread)

Request scope is one of 4 web-aware scopes that can be used. The other scopes are: Session Scope, Application Scope and WebSocket Scope More info on these scopes is present here

Answered By - Tabish Mir