MyBatis Simple implementation principle of interface

Used MyBatis3 Why do you think MyBatis Of Mapper Interface has no implementation class , But it can be used directly ?

That's because MyBatis use Java Interface implemented by dynamic agent .

Here is just a simple example to illustrate the principle , Not exactly MyBatis Of , This kind of thinking can also be applied in other places .

Define an interface
public interface MethodInterface { String helloWorld(); }
Implement dynamic agent interface
public class MethodProxy<T> implements InvocationHandler { private Class<T>
methodInterface;public MethodProxy(Class<T> methodInterface) { this
.methodInterface = methodInterface; }@Override public Object invoke(Object
proxy, Method method, Object[] args)throws Throwable { System.out.println(
"========================="); System.out.println(" Method name :" + method.getName());
// Different operations for different methods return null; } }
This is for invoke The method is simple MyBatis Implementation principle of , In this method , We passed Method Ability to get interface and method names , The full name of the interface is equivalent to MyBatis XML In
namespace, The method name is equivalent to the id. That is to say, after dynamic proxy , Through SqlSession To pass namespace.id
Method to call the corresponding method . Easier to use interface , But it's an indirect way .

Dynamic agent factory class
public class MethodProxyFactory { public static <T> T newInstance(Class<T>
methodInterface) {final MethodProxy<T> methodProxy = new
MethodProxy<T>(methodInterface);return (T) Proxy.newProxyInstance(
Thread.currentThread().getContextClassLoader(),new Class[]{methodInterface},
methodProxy); } }
Through this factory class, you can generate a dynamic proxy class of any interface .

test
MethodInterface method =
MethodProxyFactory.newInstance(MethodInterface.class); method.helloWorld();
You can see MethodInterface Can execute without implementation class .

summary

When it comes to dynamic agents, we usually deal with transactions , Application of log or record method in execution efficiency . It is a special treatment of the pre or post implementation of class methods .

Through this article , In fact, we can see another application direction , That is, there is no need to implement classes , Implement interface methods directly through dynamic agents ,MyBatis In this way, it is convenient for us to call methods , With this idea, we may be able to make some better designs in other aspects .

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