What is Proxy Pattern in Java?
The Proxy Pattern is a structural design pattern that provides a surrogate or placeholder for another object to control access to it. In Java, this pattern is widely used to create a proxy object that acts as a stand-in for another object, often for the purpose of controlling access, adding additional functionality, or managing resources. The Proxy Pattern is part of the GoF (Gang of Four) design patterns, which are a set of design patterns that are widely recognized and used in software development.
The main idea behind the Proxy Pattern is to create a proxy object that acts as a stand-in for the real object. This proxy object can then provide additional functionality, such as lazy loading, caching, or security checks, before or after the real object is accessed. By using the Proxy Pattern, you can achieve the following benefits:
1. Control Access: The proxy can control access to the real object, ensuring that only authorized users or systems can access it. This can be useful for implementing security measures or access control lists (ACLs).
2. Add Additional Functionality: The proxy can add additional functionality to the real object, such as logging, caching, or lazy loading. This allows you to extend the behavior of the real object without modifying its code.
3. Resource Management: The proxy can manage resources associated with the real object, such as opening and closing connections, or releasing resources when the object is no longer needed.
4. Lazy Loading: The proxy can defer the creation of the real object until it is actually needed. This can improve performance by reducing the overhead of creating and managing objects that are not immediately required.
The Proxy Pattern in Java typically involves the following components:
– Subject: The subject is the interface for the real object and the proxy. It defines the methods that both the real object and the proxy implement.
– RealSubject: The real subject is the object that the proxy represents. It is the actual object that provides the real functionality.
– Proxy: The proxy is the class that implements the subject interface and acts as a stand-in for the real subject. It controls access to the real subject and can add additional functionality.
Here is a simple example of the Proxy Pattern in Java:
“`java
interface Image {
void display();
}
class RealImage implements Image {
private String fileName;
public RealImage(String fileName) {
this.fileName = fileName;
loadImageFromDisk();
}
private void loadImageFromDisk() {
System.out.println(“Loading ” + fileName);
}
@Override
public void display() {
System.out.println(“Displaying ” + fileName);
}
}
class ProxyImage implements Image {
private RealImage realImage;
private String fileName;
public ProxyImage(String fileName) {
this.fileName = fileName;
}
@Override
public void display() {
if (realImage == null) {
realImage = new RealImage(fileName);
}
realImage.display();
}
}
public class ProxyPatternDemo {
public static void main(String[] args) {
Image image = new ProxyImage(“test_image.jpg”);
// Image will be loaded from disk
image.display();
System.out.println(“”);
// Image will not be loaded from disk
image.display();
}
}
“`
In this example, the `RealImage` class represents the real image that needs to be loaded from disk. The `ProxyImage` class acts as a stand-in for the `RealImage` and only loads the image when it is actually displayed. This is a simple implementation of the Proxy Pattern that demonstrates how it can be used to control access to the real object and add additional functionality.
