How to use the CGLIB FULL framework to realize the custom ClassLoader loaded the Java class library
How to use the CGLIB FULL framework to realize the custom ClassLoader loaded the Java class library
introduction:
CGLIB (Code Generation Library) is a byte code generating library based on ASM (Java bytecode operation and analysis framework). It provides rich APIs and tools that can dynamically generate and modify the bytecode of the Java class by runtime.EssenceThe CGLIB FULL framework is an extension of CGLIB, which allows us to customize the ClassLoader to achieve a more flexible class library load when loading the Java class.This article will introduce how to load the Java class library with the CGLIB FULL framework and provide the corresponding Java code example.
1. Introduce CGLIB FULL framework dependencies
To use the CGLIB FULL framework, you need to introduce the corresponding dependencies in the project.You can add the following dependencies in the construction file of the project (such as pom.xml):
<dependencies>
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.4.1</version>
</dependency>
</dependencies>
By introducing this dependencies, we can use the function of the CGLIB FULL framework.
2. Create custom classloader
In order to realize the ClassLoader loaded the Java class library, we need to derive a subclass from the ClassLoader class.In the subclass, we can rewrite some methods of ClassLoader to achieve customized libraries loading logic.The following is a customized ClassLoader code of an example:
public class MyClassLoader extends ClassLoader {
@Override
protected Class<?> findClass(String name) throws ClassNotFoundException {
// Implement the Library loading logic, for example
byte[] bytes = loadClassBytes(name);
return defineClass(name, bytes, 0, bytes.length);
}
private byte[] loadClassBytes(String className) {
// Implement the logic of loading of bytecode code
// For example
// Return a byte array, indicating the byte code of the loaded class
}
}
In the above code, we rewritten the FindClass method of ClassLoader to achieve customized library loading logic.In the FindClass method, we first load the byte code of class by loading the class by the LoadClassBytes method, and then use the defineClass method to define this class.
3. Use the CGLIB FULL framework to generate proxy classes
To use the CGLIB FULL framework to generate an agent class, we need to use the CGLIB's enhancer class.The following is an example of an example of an example:
public class ProxyGenerator {
public static Object createProxy(Class<?> targetClass, MethodInterceptor interceptor) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(targetClass);
enhancer.setCallback(interceptor);
enhancer.setClassLoader (new myclassloader ()); // Set custom classloader
return enhancer.create();
}
}
In the above code, we use the Enhancer class to create a proxy object.We specify the target class to be agent through the setsuperClass method, and set the method logic of the agent logic through the Setcallback method, that is, the interceptor object.We also set custom classloaders through the SetClassLoader method.
4. Use custom ClassLoader to load the Java class library
To use custom ClassLoader to load the Java class library, we can call MyClassLoader's FindClass method.The following is an example code:
public class Main {
public static void main(String[] args) throws ClassNotFoundException {
MyClassLoader classLoader = new MyClassLoader();
Class <?> loadedClass = classloader.findClass ("com.example.myClass"); // Load the class in the class library
Object instance = loadedclass.newinstance (); // Create instances
// Use the method of calling the target class with the proxy class
MyInterface proxy = (MyInterface) ProxyGenerator.createProxy(loadedClass, new MyInterceptor());
proxy.doSomething();
}
}
In the above code, we created a MyClassLoader instance and called its FindClass method to load the class in the class library.We then created an instance of a class through the Newinstance method.Finally, we created a proxy object through the CreateProxy method of ProxyGenerator and used the proxy object to call the target class.
in conclusion:
Using the CGLIB FULL framework can flexibly realize custom ClassLoader to load the Java class library and modify the byte code of the Java class by dynamically generating and modifying the Java class.This article introduces how to load the Java class library with the CGLIB FULL framework and gives a detailed code example.By using custom ClassLoader, we can achieve more flexible and customized libraries loading logic.
