Sleepless in Salt Lake City: An Example of Caching with REST using Jersey JAX-RS

Sleepless in Salt Lake City: An Example of Caching with REST using Jersey JAX-RS

Using the "Expires" header the server can tell the client to cache the data till a particular date or provide a time duration to cache. The former can be a problem if the client and server clocks are not in sync. For example, the server tells the client to cache a piece of data till Dec 20th, 2012. However, the Client clock is 10 mins behind the server. So although the data on the client has not expired, the server data has. For this reason, setting a duration for expiration via a time duration such as 10 mins will allow both Client/Server to be in sync regarding expiration of the cache.

What about a case when caching is recommended on the client but there is a certain amount of volatility involved with the data. For example, lets say we have an OrderClient that GETs order information about a particular order from the server. The Order information could potentially be updated by a user subsequently, for example, adding a new line item to the Order. In such a case one could avail the Conditional GET features of HTTP to obtain new payload only if the data cached by the Client is stale. The server determines whether the data has changed between the last time the client requested the payload and either provides the entire data or responds back with a HTTP status of 304, indicating UN-Modified payload. The client in turn can in turn as a result of a 304 returned from the server, respond the consumer with the data it has previously cached. This reduces the amount of data transferred between client and server and thus alleviates network bandwidth utilization. Conditional HTTP GET can be availed using either Etags or Last-Modified header attributes.

As an example of the above, let us look at a Jersey, JAX-RS example. In the example, we have two clients, a ProductClient that obtains information about Products and an OrderClient used to manage the life cycle of an Order. The Product Client will cache the Products until the time has come to re-fetch the products due to expiration while the OrderClient will cache the payload obtained an issue a Conditional GET to only obtain the payload if the data has changed on the server since its last request.

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