AOP, namely aspect-oriented programming, is an important idea in Java programming. Compared with traditional object-oriented programming (OOP) based on classes and objects, AOP focuses more on runtime behavior and aspects. This article will introduce the idea of AOP programming in Java.
1. What is AOP?
AOP is a concept evolved from OOP (Object-Oriented Programming). It is a supplement to OOP. It improves the complexity and flexibility of the code by separating core concerns and horizontal concerns. sex. Simply put, AOP is a technology that enables code reuse across multiple objects and modules in Java.
2. How to implement AOP
In Java, AOP can be implemented in the following two ways:
In actual development, in order to achieve certain purposes (such as logging), we need to perform some additional operations before and after certain methods. At this time, we can manually write the proxy class and pass the target class into the proxy class. The proxy class will call the method in the target class and perform additional operations before and after the call. This proxy class is the aspect in AOP and realizes code reuse.
The schematic diagram of the static proxy is as follows:
(The picture comes from the Internet)
It can be seen that both the proxy object and the proxy object implement the same interface. A method of the proxied object is called, and additional operations are performed before and after the call.
Although static proxy can implement AOP, manually writing proxy classes will cause a lot of redundancy and duplication in our code, so we can use dynamic proxy Proxy to implement AOP and reduce code redundancy and duplication.
In Java, there are two ways to implement dynamic proxy: JDK dynamic proxy and CGLIB dynamic proxy.
JDK dynamic proxy requires the proxied class to implement one or more interfaces. JDK will generate a dynamic proxy class to implement this interface, and implement the enhanced logic of method calling in the dynamic proxy class. In the process of generating proxy classes, JDK uses reflection API, so the performance of proxy classes is relatively low.
CGLIB dynamic proxy can proxy classes that do not implement interfaces. The proxy class generated by CGLIB is a subclass of the target class, and the proxy logic is implemented by rewriting the methods in the target class. Compared with JDK dynamic proxy, CGLIB dynamic proxy has higher performance.
3. AOP application scenarios
When performing system operation and maintenance, recording system logs is an important operation. We can use AOP technology to record logs before and after each method is called to facilitate troubleshooting later.
When performing performance tuning, we need to monitor the methods in the system and count the number of method calls, time-consuming and other information. AOP technology can be used to extract public monitoring logic and implement method call monitoring.
When performing system security management, we need to control permissions on methods in the system. AOP technology can be used to achieve this purpose, deciding whether to allow access to a certain method based on the user's permissions.
When performing data operations, we need to ensure the consistency and integrity of the data. We can use AOP technology to start a transaction at the beginning of method execution. Commit or rollback the transaction at the end of method execution.
4. Summary
AOP is an important idea in Java programming. It improves the complexity and flexibility of the code by separating core concerns and horizontal concerns. In Java, AOP can be implemented in two ways: static proxy and dynamic proxy. The application scenarios of AOP technology include logging, performance monitoring, security control and transaction management, etc.
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