Apache HttpClient connection configuration

Issue

I am trying to setup a HttpClient through the HttpClientBuilder. I also had a look at the HttpClientConnectionManager and here the confusion started.

On the ConnectionManager or more exactly the PoolingHttpClientConnectionManager there are methods to:

• close expired connections
• close idle connections

When is a connection considered expired?
When is it idle?
What happens when a connection from the pool is closed? Is it ensured, that there are connections recreated when needed?

Solution

According to: https://hc.apache.org/httpcomponents-client-4.5.x/current/tutorial/html/connmgmt.html#d5e418

HttpClient tries to mitigate the problem by testing whether the connection is 'stale', that is no longer valid because it was closed on the server side, prior to using the connection for executing an HTTP request. The stale connection check is not 100% reliable. The only feasible solution that does not involve a one thread per socket model for idle connections is a dedicated monitor thread used to evict connections that are considered expired due to a long period of inactivity. The monitor thread can periodically call ClientConnectionManager#closeExpiredConnections() method to close all expired connections and evict closed connections from the pool. It can also optionally call ClientConnectionManager#closeIdleConnections() method to close all connections that have been idle over a given period of time.

The difference between expired and idle is that an expired connection has been closed on the server side, while the idle connection isn't necessarily closed on the server side, but it has been idle over a period of time. When a connection is closed, it becomes available again in the pool to be used.

Answered By - Sofo Gial