Understanding Java and Proxy-Related Knowledge
For every Java developer, the term “proxy” is not unfamiliar. You may have heard of proxy modes, dynamic proxy, reverse proxy, and more. But what exactly is a proxy, and what are the differences between them? In this article, we will delve into the world of proxy technology and explore its various aspects.
Agent Technology: A Brief Overview
Agent technology is not exclusive to the Java language; it has been around since the early days of the Internet. At the computer network level, common proxy technologies include forward proxy, transparent proxy, and reverse proxy. The most commonly used are forward proxy and reverse proxy.
Forward Proxy
A forward proxy is a server located between the client and the destination server. It acts as an intermediary, obtaining the target content from the server on behalf of the client. The client sends a request to the proxy server, which then forwards the request to the target server and retrieves the response, returning it to the client. The client must be configured to use a forward proxy, and this technology is commonly used in various scenarios, such as accessing foreign websites or breaking through IP access restrictions.
Reverse Proxy
A reverse proxy, on the other hand, is a server that accepts connection requests from the Internet and forwards them to a server on the internal network. The reverse proxy server then returns the results to the requesting client. This technology is commonly used in web development, particularly in server load balancing, where the client sends a request to the load balancing server, which then forwards the request to a real server to perform, and returns the results to the client.
Proxy Modes in Java
In the context of Java, proxy modes refer to a mechanism that allows an object to provide an agent, controlling access to the original object. This is achieved through the use of a proxy class, which can be either static or dynamic.
Static Proxy
A static proxy is a proxy class that is created by a programmer or generated automatically through a specific tool. The proxy class is compiled before the program is run, and its .class file already exists. A static proxy class is typically used when the proxy class method is known in advance.
Dynamic Proxy
A dynamic proxy, on the other hand, is a proxy class that is generated dynamically at runtime. This type of proxy class is useful when the proxy class method is not known in advance or when the proxy class needs to implement multiple interfaces.
Java Static Proxy
A Java static proxy is a proxy class that is created by a programmer. It is determined at compile time and is typically used when the proxy class method is known in advance. Here is an example of a Java static proxy:
public interface HelloService {
public void say();
}
public class HelloServiceImpl implements HelloService {
@Override
public void say() {
System.out.println("hello world");
}
}
public class HelloServiceProxy implements HelloService {
private HelloService target;
public HelloServiceProxy(HelloService target) {
this.target = target;
}
@Override
public void say() {
System.out.println("log");
target.say();
System.out.println("Cleanup Data");
}
}
Real Object Access Control
A static proxy can be used to control access to a real object. For example, a proxy object can be used to control usage rights for a real object.
Avoid Creating Large Objects
A static proxy can also be used to avoid creating large objects. For example, a proxy object can be used to represent a real big object by using a small object, reducing the consumption of system resources.
Enhanced Real Object Function
A static proxy can also be used to enhance the function of a real object. For example, a proxy object can be used to add additional functionality around method calls to the real object.
Dynamic Proxies in Java
Dynamic proxies are useful when the proxy class method is not known in advance or when the proxy class needs to implement multiple interfaces. There are two types of dynamic proxies in Java: JDK dynamic proxy and Cglib dynamic proxy.
JDK Dynamic Proxy
A JDK dynamic proxy is a proxy class that is generated dynamically at runtime using the Proxy class and the InvocationHandler interface.
Cglib Dynamic Proxy
A Cglib dynamic proxy is a proxy class that is generated dynamically at runtime using the Cglib library. Cglib is a powerful code generation library that can extend Java classes and implement Java interfaces at runtime.
Difference between JDK Dynamic Proxy and Cglib Dynamic Proxy
The main difference between JDK dynamic proxy and Cglib dynamic proxy is that the JDK dynamic proxy requires the proxy class to implement one or more interfaces, while the Cglib dynamic proxy does not require the proxy class to implement an interface.
The Use of Dynamic Proxies
Dynamic proxies are widely used in various frameworks, such as Spring AOP and Struts2 interceptor. They are used to implement aspects, filters, interceptors, and other functionality.
Conclusion
In conclusion, this article has introduced you to the world of proxy technology and explored its various aspects, including forward proxy, reverse proxy, static proxy, and dynamic proxy. We have also discussed the use of dynamic proxies in Java and the differences between JDK dynamic proxy and Cglib dynamic proxy. We hope that this article has provided you with a better understanding of proxy technology and its applications.