The principle of CGLIB and applications in Java development
The principle of CGLIB and applications in Java development
CGLIB is a bytecode -based generating library that is specifically used to expand the Java class during runtime.It uses ASM (a universal Java bytecode operation and analysis framework) to generate the underlying byte code and provide an easy -to -use API to generate and modify the Java class.The principle of CGLIB is to expand the target class by dynamically generating subclasses, that is, inherit the target class, and then cover and enhance the method in the target class.
The application of CGLIB is very wide, mainly including the following aspects:
1. Agent: CGLIB can generate a subclass of the target class as the proxy class, so that its function can be expanded without modifying the original class.Compared with the dynamic proxy of JDK, CGLIB is more suitable for class proxy because it does not require the target class to implement any interface.Below is a simple example code that demonstrates how to use CGLIB to generate proxy categories:
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import java.lang.reflect.Method;
public class ProxyDemo {
public static void main(String[] args) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(HelloService.class);
enhancer.setCallback(new MethodInterceptor() {
@Override
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
System.out.println("Before method: " + method.getName());
Object result = proxy.invokeSuper(obj, args);
System.out.println("After method: " + method.getName());
return result;
}
});
HelloService proxy = (HelloService) enhancer.create();
proxy.sayHello();
}
}
public class HelloService {
public void sayHello() {
System.out.println("Hello, world!");
}
}
In the above code, we use the Enhancer class to generate the proxy object of the target class HelloService.The target class is specified by the setsuperClass () method as HelloService, and the setcallback () method specifies the proxy logic.In the proxy logic, we conducted some operations before and after the implementation of the method.
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import java.lang.reflect.Method;
public class LogInterceptor implements MethodInterceptor {
@Override
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
System.out.println("Before method: " + method.getName());
Object result = proxy.invokeSuper(obj, args);
System.out.println("After method: " + method.getName());
return result;
}
}
In the above code, the LoginterCepptor implements CGLIB's MethodInterCepTor interface, which defines Intercept () that intercepts the method of intercepting the target method.In the intercept () method, we have printed some log information before and after the implementation of the goal method.By configured in the AOP framework of Spring, the interceptor can be used to achieve cutting programming.
3. Single mode: CGLIB can also be used to create a singles object.Compared with the traditional singles model, CGLIB can achieve higher performance in the mode of creating instances during business use.The following is an example of creating a single example using CGLIB:
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import java.lang.reflect.Method;
public class Singleton {
private static Singleton instance;
private Singleton() {
// Private structure function
}
public static Singleton getInstance() {
if (instance == null) {
synchronized (Singleton.class) {
if (instance == null) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(Singleton.class);
enhancer.setCallback(new MethodInterceptor() {
@Override
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
return proxy.invokeSuper(obj, args);
}
});
instance = (Singleton) enhancer.create();
}
}
}
return instance;
}
public void doSomething() {
System.out.println("Singleton instance is created!");
}
}
public class SingletonDemo {
public static void main(String[] args) {
Singleton singleton1 = Singleton.getInstance();
Singleton singleton2 = Singleton.getInstance();
System.out.println(singleton1 == singleton2); // Output: true
singleton1.doSomething();
}
}
In the above example code, first obtain the Singleton instance through the getInstance () method. If the instance is NULL, use Enhancer to create a proxy object and return it.In the method call of the proxy object, the method of calling the target class through the INVOKESUPER () method.In this way, the GetInstance () method is called each time the same instance is obtained.
Summarize:
CGLIB is a powerful byte code generation library, which is widely used in Java development.Through CGLIB, we can realize dynamic proxy, cutting programming, and creating single -case objects, thereby improving the flexibility and performance of the program.Whether it is an independent library or integrated with other frameworks (such as Spring), CGLIB is one of the indispensable tools in Java development.
