unable to access context value.

[Vadiraj Jahagirdar]

Hi,

I have following code: 

1. Context context = Context.current().withValue(Constant.FOO_CONTEXT_KEY, "Test Value");

2. String valueStr = Constant.FOO_CONTEXT_KEY.get();
3. System.out.println(valueStr);  //Returns null
4. context.run(() -> {
5.         System.out.println("Context Data is:" + Constant.FOO_CONTEXT_KEY.get()); //Gives "Test Value"

6.}

I am not able to understand why is null returned at line no 3, where as proper value is returned at line no 5.

[Sergii Tkachenko]

On line 3, you're inspecting a value of a context key, Context.Key<T>. On its own, the key is not bound to any specific context. Many different Context can use the same Context key, and each can set its own value for this key.

Line 5 is executed within the specific context you created (created on line 1, executed on line 4). Let's call it context A. This specific context has the key Constant.FOO_CONTEXT_KEY is set to the specific value: "Test Value". So line 5 returns the value of key Constant.FOO_CONTEXT_KEY as set in context A.