HTTP Status

Hi,

I was reading as below

 100-199
 codes in the 100s are informational, indicating the client should respond with some other action.
  200-299
 values in the 200s signify that request was successful.
  300-399
 values in the 300s are used for files that have moved and usually include a Location header indicating the new address.
  400-499
 indicates error by client.
 500-599
 indicates error by server
200(Ok)
  A value of 200(SC_OK) means that everything is fine; the document follows for GET and POST request. This status is the default status for servlet.
302(Found)  
The value is similar to 301, except that in principal the URL given by Location header should be interpreted as temporary replacement not permanent one.
  404(Not Found)
  The infamous 404(SC_NOT_FOND) status tells the client that no resource should be found at that address. This value is the standard “no such page” response.
 

Are HTTP Status related to HTTP Resonse Header or HTTP Request Header?

When do we need to use HTTP Status.

Do i see it everytime i run a servlet or occasionally when the web contained failed to send the servlet response etc?


Please advise.

Any links resources ideas highly appreciated. Thanks in advance