Master Java Proxy Patterns: From Static to Dynamic and MyBatis Integration

1. Static Proxy

During the autumn recruitment season, many developers face the need to record service response times; this scenario can be abstracted into the proxy pattern.

ISubject: abstract of the visited resource

SubjectImpl: concrete implementation of the visited resource (e.g., landlord)

SubjectProxy: proxy implementation of the visited resource (e.g., intermediary)

UML diagram:

Example: a boss asks to record the response time of a user service using a static proxy.

When the boss also wants to record product service response times, three more classes (IProductService, ProductServiceImpl, ProductServiceProxy) are needed, illustrating the duplication problem of static proxies.

2. Dynamic Proxy

Since JDK 1.3, Java introduced Dynamic Proxy, allowing runtime generation of proxy objects for specified interfaces, solving the duplication issue of static proxies.

Dynamic proxy relies on java.lang.reflect.Proxy and java.lang.reflect.InvocationHandler.

By implementing a single InvocationHandler, we can create proxies for both IUserService and IProductService to add the same cross‑cutting logic.

UML diagram of the dynamic proxy implementation:

3. MyBatis Core Design

MyBatis uses dynamic proxy to generate implementations of mapper interfaces at runtime. Role role = roleMapper.getRole(3L); The generated class is org.apache.ibatis.binding.MapperProxy, which corresponds to the SubjectProxy in the earlier UML.

Thus, MyBatis’s core idea is to map interface methods to SQL statements via a proxy, eliminating the need for manual implementation classes.