Shulou(Shulou.com)05/31 Report--

In this article, the editor introduces in detail "how to apply the java agent mode". The content is detailed, the steps are clear, and the details are handled properly. I hope this article "how to apply the java agent mode" can help you solve your doubts.

I. introduction of agency mode

In fact, the agency mode is to find a stand-in, to do a thing, do not go, find someone to replace you, this is the agent mode. In the program, it provides a stand-in for the object and controls the stand-in to access the target object. The advantage of this is that in addition to the functions that the target object can provide, it also allows the avatar to do more work, that is, it can expand the function of the target object. The proxies can be remote objects, objects that are expensive to create, or objects that require security control.

Agent models are mainly divided into the following three types:

Static agents dynamic agents (also known as JDK agents, interface agents) cglib agents (also belong to the category of dynamic agents) II. Static agents

"1. Static agent introduction:"

When using a static proxy, you need to define an interface or parent class, and the proxied object and the proxy object need to implement the same interface or inherit the same parent class together.

"2. Application example:"

Define an interface: TeacherDao defines the proxied object: TeacherDaoImpl, need to implement TeacherDao define proxy object: TeacherDaoProxy, also need to implement TeacherDao to call the TeacherDaoImpl method, you need to create a TeacherDaoProxy object, then create a TeacherDaoImpl object, give the TeacherDaoImpl object to the TeacherDaoProxy object, and then call the relevant method code to implement: TeacherDao.java:public interface TeacherDao {

Void teach ()

}

TeacherDaoImpl.java:public class TeacherDaoImpl implements TeacherDao {

@ Override

Public void teach () {

System.out.println ("Today is another day without girls")

}

}

TeacherDaoProxy.java:public class TeacherDaoProxy implements TeacherDao {

Private TeacherDao target; / / the object being proxied

Public TeacherDaoProxy (TeacherDao target) {

This.target = target

}

@ Override

Public void teach () {

System.out.println ("Agent start")

/ / some additional logic can be written here to achieve the purpose of extending the proxied object, which is equivalent to the advance notification of spring

Target.teach ()

/ / you can also write some additional logic here to extend the proxied object, which is equivalent to the post notification of spring

System.out.println ("Agent end")

}

}

Client.java: call the proxy object public class Client {

Public static void main (String [] args) {

/ / create the proxied object

TeacherDao target = new TeacherDaoImpl ()

/ / create a proxy object

TeacherDaoProxy proxy = new TeacherDaoProxy (target)

/ / call the method through the proxy object

Proxy.teach ()

}

}

"3. Advantages and disadvantages of static agents:"

Advantages: you can extend the proxied object without modifying the proxied object, and do some enhancements and disadvantages: you need to implement the same interface or inherit the same parent class, so there will be many proxy classes, and if the interface or parent class changes, both the proxy object and the proxied object need to maintain a dynamic proxy (JDK proxy).

"1. Introduction to dynamic agents:"

Proxy objects do not implement interfaces, but proxied objects still need to implement interfaces. The generation of dynamic proxy object uses the API of JDK and the Proxy class under the reflection package to build the proxy object in memory dynamically.

2. Java.lang.reflect.Proxy:

This class has a newProxyInstance method that takes three parameters, as follows:

Static Object newProxyInstance (ClassLoader loader, Class [] interfaces, InvocationHandler h)

"3. Application examples:"

Define an interface: TeacherDao defines the proxied object: TeacherDaoImpl, needs to implement TeacherDao to define a proxy factory ProxyFactory, has a getProxyInstance method, needs to pass in the proxied object, and then returns the proxy object instance, which is implemented by calling the method code of the proxied object through the proxy object: TeacherDao.java:public interface TeacherDao {

Void teach ()

}

TeacherDaoImpl.java:public class TeacherDaoImpl implements TeacherDao {

@ Override

Public void teach () {

System.out.println ("Today is another day without girls")

}

}

ProxyFactory.javapublic class ProxyFactory {

Private Object target; / / the object being proxied

Public ProxyFactory (Object target) {

This.target = target

}

/ / generate a proxy object for the proxied object

Public Object getProxyInstance () {

/ / Parameter 1: specifies the class loader of the proxied object

/ / Parameter 2: the type of interface implemented by the proxy object

/ / Parameter 3: event handling, the method of executing the proxied object

Return Proxy.newProxyInstance (target.getClass (). GetClassLoader (), target.getClass (). GetInterfaces (), new InvocationHandler () {

@ Override

Public Object invoke (Object proxy, Method method, Object [] args) throws Throwable {

System.out.println ("JDK Agent start")

/ / call method, the parameter of the method of args

Object returnValue = method.invoke (target, args)

System.out.println ("JDK Agent end")

/ / the resulting return will be executed

Return returnValue

}

});

}

}

Client.java: call the method public class Client {through the proxy

Public static void main (String [] args) {

/ / create the proxied object

TeacherDao target = new TeacherDaoImpl ()

/ / create a proxy object

TeacherDao proxy = TeacherDao) new ProxyFactory (target) .getProxyInstance ()

/ / call the method of the proxied object through the proxy object

Proxy.teach ()

}

} IV. Cglib agent

"1. Cglib Agent introduction:"

Static and dynamic proxies, proxied objects, all need to implement interfaces. If a class does not implement any interfaces, use cglib proxies. Cglib agent, also known as subclass proxy, builds a subclass object in memory to extend the proxied object. The underlying layer of the cglib proxy implements the proxy through a bytecode processing framework called ASM to convert bytecode and generate new classes. The class being proxied cannot be final, otherwise an error will be reported. If the method of the proxied object is final/static, it will not be intercepted, that is, the additional business methods of the proxied object will not be executed.

"2. Application example:"

The first step is to add cglib related dependencies:

Cglib

Cglib

3.3.0

TeacherDaoImpl.java:public class TeacherDaoImpl implements TeacherDao {

@ Override

Public void teach () {

System.out.println ("Today is another day without girls")

}

}

CglibProxyFactory.java:// needs to implement MethodInterceptor and rewrite its methods

Public class CglibProxyFactory implements MethodInterceptor {

Private Object target

Public CglibProxyFactory (Object target) {

This.target = target

}

/ * *

* return the proxy object of target

* @ return

, /

Public Object getProxyInstance () {

/ / 1. Create a tool class

Enhancer enhancer = new Enhancer ()

/ / 2. Set parent class

Enhancer.setSuperclass (target.getClass ())

/ / 3. Set callback function

Enhancer.setCallback (this)

/ / 4. Create a subclass object, that is, a proxy object

Return enhancer.create ()

}

@ Override

Public Object intercept (Object o, Method method, Object [] args, MethodProxy methodProxy) throws Throwable {

System.out.println ("CGLIB Agent start")

Object returnValue = method.invoke (target, args)

System.out.println ("CGLIB Agent end")

Return returnValue

}

}

Client.java: call the method public class Client {through the proxy

Public static void main (String [] args) {

/ / create the proxied object

TeacherDaoImpl target = new TeacherDaoImpl ()

/ / get the proxy object and pass the proxy object to the proxy object

TeacherDaoImpl proxy = TeacherDaoImpl) new CglibProxyFactory (target) .getProxyInstance ()

/ / execute the method, which triggers the intecept method, thus implementing the method of executing the proxied object

Proxy.teach ()

}

}

After reading this, the article "how to apply java Agent Mode" has been introduced. If you want to master the knowledge points of this article, you still need to practice and use it yourself to understand it. If you want to know more about related articles, welcome to follow the industry information channel.

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