11. Exercise: Dynamic Proxy

Exercise: Dynamic Proxy

Hey, remember that UdacisearchClient class you used in some previous exercises? Yeah, that one. Don't worry — this will be the last time you'll be adding to it.

Your team is testing out a trendy, schemaless NoSQL database for storing client records. To look client info up from this database, you give it a numeric (long) ID, and it gives you back a Map<String, Object> of properties: the keys in the map are the String names of client properties, and the values in the map could be any Object, depending on what the property is.

You would like to create a prototype data access object for this database, and a Dynamic Proxy is the perfect tool for the job. What's so "dynamic" about this proxy, you might ask? Well, the proxy itself is implemented at runtime. This means you can create a dynamic proxy for any interface, and the proxy implements that interface dynamically — as methods get called on the proxy object, the proxy is able to examine the method calls and arguments as they come in, and decide on-the-fly how to handle them. In this case, your dynamic proxy will be handling method calls by looking up properties from the property map (a Map<String, Object>) discussed earlier.

Notice that this time, UdacisearchClient is an interface and not a class. That's because Java's dynamic proxy (java.lang.reflect.Proxy) only works on interfaces, not classes.

The starter code already takes care of some boilerplate for you. All you have to do is fill in the UdacisearchClientFactory.Handler static inner class. In the invoke() method:

1. Call Method#getName() to get the name of the method that is being called on the proxy.
2. Convert the method name to a camelCase property name. For example, a method name of "getBillingAddress" should result in a property name of "billingAddress". You can use the provided static getPropertyName() method to take care of this for you.
3. Look in the properties map for the value corresponding to that named property, and return the value.

Running the solution

Main.java has already been filled in for you! Try it out:

javac Main.java
java Main

If everything worked, you should see the client information printed to standard output:

{quarterlyBudget=8000, numEmployees=5, name=CatFacts LLC, timeZone=America/Los_Angeles, id=17, billingAddress=555 Meowmers Ln, Riverside, CA 92501, contractStart=2020-10-11T23:03:39.374133Z, contractLength=PT4320H}
UdacisearchClient{name='CatFacts LLC', id=17, quarterlyBudget=8000, numEmployees=5, contractStart=2020-10-11T23:03:39.374133Z, contractLength=PT4320H, timeZone=America/Los_Angeles, billingAddress='555 Meowmers Ln, Riverside, CA 92501'}