load and apply AspectJ in netty without spring

To load and apply an AspectJ aspect in a Netty application without using Spring, you need to follow these general steps:

1. Add the AspectJ runtime libraries to your project's classpath, including aspectjrt.jar, aspectjweaver.jar, and aspectjtools.jar. You can download these libraries from the official AspectJ website or include them as Maven dependencies in your project's POM file.

2. Define the aspect that implements the cross-cutting concern. For example, you can define an aspect called LoggingAspect that logs the entry and exit of a method as follows:

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;

@Aspect
public class LoggingAspect {

    @Before("execution(* com.example.MyService.*(..))")
    public void logEntry(JoinPoint joinPoint) {
        String methodName = joinPoint.getSignature().getName();
        System.out.println("Entering " + methodName);
    }

    @AfterReturning(value = "execution(* com.example.MyService.*(..))", returning = "result")
    public void logExit(JoinPoint joinPoint, Object result) {
        String methodName = joinPoint.getSignature().getName();
        System.out.println("Exiting " + methodName + " with result: " + result);
    }
}

This aspect intercepts the methods of a MyService class and logs their entry and exit.

3. Compile the aspect using the AspectJ compiler, either manually or using a build tool such as Maven or Gradle. For example, you can compile the aspect using the following command

ajc -cp  -inpath  -outjar  com/example/LoggingAspect.aj

This command compiles the LoggingAspect aspect and produces a JAR file that contains the aspect class and the required AspectJ runtime libraries.

4. Load the aspect and apply it to the target classes using the AspectJ load-time weaving (LTW) mechanism. LTW enables the aspect to be woven into the bytecode of the target classes at runtime, without modifying the source code or the class loader. You can configure LTW in various ways, depending on your application's runtime environment, such as using the -javaagent option, the META-INF/aop.xml file, or the ajc.xml file.

Here's an example of using the -javaagent option:

java -javaagent: -classpath  com.example.MyApplication

This command launches the MyApplication class and activates the AspectJ weaver, which loads the LoggingAspect aspect and applies it to the MyService class.

Note that the -javaagent option requires the AspectJ weaver JAR file (aspectjweaver.jar) to be specified as the agent in the command line. You also need to include the AspectJ runtime libraries and the compiled aspect JAR file in the classpath.

In summary, to load and apply an AspectJ aspect in a Netty application without using Spring, you need to define the aspect, compile it, and activate the AspectJ weaver using a runtime configuration mechanism such as the -javaagent option.