Question

I don’t know the meaning of using proxy in spring. what is efficient?

Answer 1

The dynamic proxy is a feature of the JDK. It can be used to implement an interface using an invocation handler.

A dynamic proxy class (simply referred
to as a proxy class below) is a class
that implements a list of interfaces
specified at runtime when the class is
created, with behavior as described
below. A proxy interface is such an
interface that is implemented by a
proxy class. A proxy instance is an
instance of a proxy class. Each proxy
instance has an associated invocation
handler object, which implements the
interface InvocationHandler.

A dynamic proxy has some overhead. For most use cases the overhead won’t be significant, though. The real problem is that the (over)use of dynamic proxies makes an application harder to understand and debug. For example a dynamic proxy will show up with mulitple lines in a stacktrace.

Dynamic proxies are often used to implement decorators. One example of this is AOP in Spring. (I don’t want to go into the details of AOP and won’t use AOP terminology to keep things simple). Where certain concerns are implemented in one class and used in many places. The dynamic proxies (and invocation handlers) are only the glue code (provided by Spring) to intercept the method calls. (Actually, dynamic proxies are only an implementation detail of this capability. Generating classes on the fly is another possibility to implement it.)