Clean Code

Chapter 11: Systems
We defined an interface 
Bank
, which will be 
wrapped 
by the proxy, and a 
Plain-Old
Java Object
(POJO), 
BankImpl
, that implements the business logic. (We will revisit POJOs
shortly.)
The Proxy API requires an 
InvocationHandler
object that it calls to implement any
Bank
method calls made to the proxy. Our 
BankProxyHandler
uses the Java reflection
API to map the generic method invocations to the corresponding methods in 
BankImpl
,
and so on.
There is a 
lot
of code here and it is relatively complicated, even for this simple case.
10
Using one of the byte-manipulation libraries is similarly challenging. This code “volume”
// “InvocationHandler” required by the proxy API.
public class BankProxyHandler implements InvocationHandler {
private Bank bank;
public BankHandler (Bank bank) {
this.bank = bank;
}
// Method defined in InvocationHandler
public Object invoke(Object proxy, Method method, Object[] args) 
throws Throwable {
String methodName = method.getName();
if (methodName.equals("getAccounts")) {
bank.setAccounts(getAccountsFromDatabase());
return bank.getAccounts();
} else if (methodName.equals("setAccounts")) {
bank.setAccounts((Collection) args[0]);
setAccountsToDatabase(bank.getAccounts());
return null;
} else {
...
}
}
// Lots of details here:
protected Collection getAccountsFromDatabase() { ... }
protected void setAccountsToDatabase(Collection accounts) { ... }
}
// Somewhere else...
Bank bank = (Bank) Proxy.newProxyInstance(
Bank.class.getClassLoader(), 
new Class[] { Bank.class },
new BankProxyHandler(new BankImpl()));
10. For more detailed examples of the Proxy API and examples of its use, see, for example, [Goetz].