Apache xbean :: ASM Shaded (Repackaged) Application cases in the Java library
Apache Xbean is a Java class library for managing and processing Java and related resources.It provides a convenient way to scan and process the Java classes to achieve instance, injection and configuration of classes.
ASM Shaded is a module in Apache Xbean. It re -packages ASM (Analysis of Static Members) to avoid conflicts with other libraries using ASM.ASM is a very popular Java bytecode operating library for modification and enhancement of Java bytecode during compilation.
In the case of Apache Xbean, the ASM Shaded module is usually used to dynamically modify the Java class during runtime.The following is a simple example, showing how to use Apache Xbean's ASM Shaded module to achieve the Java class when runtime.
First of all, we need to introduce the dependencies of Apache Xbean in the project and the dependency item of the ASM Shaded module.You can use Maven to manage the dependencies, add the following dependencies to the pom.xml file of the project:
<dependency>
<groupId>org.apache.xbean</groupId>
<artifactId>xbean-asm-shaded</artifactId>
<version>4.14</version>
</dependency>
Next, we can create a Java class that uses APACHE XBEAN's ASM Shaded module to add a method to this type of dynamic at runtime.The example code is as follows:
import org.apache.xbean.asm.shaded.commons.Method;
import org.apache.xbean.asm.shaded.commons.ClassWriter;
import org.apache.xbean.asm.shaded.commons.ClassReader;
import org.apache.xbean.asm.shaded.commons.ClassVisitor;
import org.apache.xbean.asm.shaded.commons.ClassRemapper;
import org.apache.xbean.asm.shaded.commons.Remapper;
import org.apache.xbean.asm.shaded.commons.MethodVisitor;
import java.lang.reflect.Method;
public class DynamicMethodAdditionExample {
public static void main(String[] args) throws Exception {
String className = "com.example.MyClass";
// Read the original bytecode of the original class
ClassReader classReader = new ClassReader(className);
ClassWriter classWriter = new ClassWriter(classReader, 0);
// Create a ClassVisitor to modify the class definition
ClassVisitor classVisitor = new ClassVisitor(ASM7, classWriter) {
@Override
public void visitEnd() {
// Add a public static method
MethodVisitor methodVisitor = cv.visitMethod(ACC_PUBLIC + ACC_STATIC, "newMethod", "()V", null, null);
methodVisitor.visitCode();
methodVisitor.visitInsn(RETURN);
Methodvisitor.visitmaxs (0, 0); // State the stack of this method and the size of the local variable
methodVisitor.visitEnd();
cv.visitEnd();
}
};
// Create a ClassreMapper to pass the class definition to ClassVisitor
ClassRemapper classRemapper = new ClassRemapper(classVisitor, new Remapper() {
@Override
public String map(String internalName) {
return super.map(internalName);
}
});
// Modify the class definition
classReader.accept(classRemapper, 0);
// Get the modified bytecode
byte[] modifiedBytecode = classWriter.toByteArray();
// Use the custom class loader to load the modified class
ClassLoader classLoader = new ClassLoader() {};
Class<?> modifiedClass = classLoader.defineClass(className, modifiedBytecode, 0, modifiedBytecode.length);
// Use the method of dynamic adding to reflect calls
Method newMethod = modifiedClass.getMethod("newMethod");
newMethod.invoke(null);
}
}
In the above example, we first read a class code called "com.example.myclass", and then dynamically modified using the class provided by the ASM Shaded module, adding a public in itStatic method.Finally, we use a custom class loader to load the modified class and use reflexes to call the added method.
This is just a simple example, showing how to use Apache Xbean's ASM Shaded module to add a Java class when runtime.By using ASM's powerful features, Apache Xbean enables us to more flexibly modify and enhance the Java class, thereby achieving richer and powerful functions.
