dynamic conditional code injection into a java file

Question

I have a java file which has a method that has been coded like this

public void testMethod() {
ClassA objA = new ClassA("objA");
objA.someMethod();
ClassA objB = new ClassA("objB");
objB.someMethod();
ClassA objC = new ClassA("objC");
objC.someMethod();
}

This file has been given to me and I have the liberty of a) changing this file manually and adding code to it b) changing this file automatically using a Java Parser. My aim here is to control the execution of someMethod(). For instance, I want to inject a Configuration object into the class, which will specify which object's someMethod() should be invoked. So, something like this:

Configuration config;

public void testMethod() {
ClassA objA = new ClassA("objA");
if(config.shouldExecuteFor(objA))
objA.someMethod();
ClassA objB = new ClassA("objB");
if(config.shouldExecuteFor(objB))
objB.someMethod();
ClassA objC = new ClassA("objC");
if(config.shouldExecuteFor(objC))
objC.someMethod();
}

The if conditions that are shown above, could be

a) manually added by editing the file or
b) could be auto inserted by parsing the java file using a java parser.
c) somehow control behavior at runtime?

I am inclined towards (b). I am not sure if I am solving this problem correctly or not, or if there is something that I can do to solve it in a simpler manner by leveraging annotations/aspects (as in 'c' above).

I would appreciate any input in solving this problem.

Lars Gendner · Accepted Answer

Here is an example using Spring AOP with AspectJ. I created a dummy configuration class MyConfiguration which simply returns an alternating boolean when calling its shouldExecuteFor() method to have some kind of test behavior. The ConfiguredCallAspect uses a call pointcut, which only works in Spring AOP when load time weaving is used. That is why I use XML configuration via applicationContext.xml and not annotations. The -Xreweavable option in aop.xml is also important for that, as well as the two -javaagent arguments passed to the JVM. This became rather complex but I think it does the job you were asking for.

src/experiments/stackoverflow/aspectj/ClassA.java

package experiments.stackoverflow.aspectj;

public class ClassA {

    private String name;

    public ClassA(String name) {
        this.name = name;
    }

    public void someMethod() {
        System.out.println("someMethod(\"" + name + "\") called on " + this);
    }

}

src/experiments/stackoverflow/aspectj/App.java

package experiments.stackoverflow.aspectj;

public class App {

    public void run() {
        ClassA object1 = new ClassA("obj1");
        object1.someMethod();
        ClassA object2 = new ClassA("obj2");
        object2.someMethod();
        ClassA object3 = new ClassA("obj3");
        object3.someMethod();
        ClassA object4 = new ClassA("obj4");
        object4.someMethod();
        ClassA object5 = new ClassA("obj5");
        object5.someMethod();
    }

}

src/experiments/stackoverflow/aspectj/ConfiguredCallAspect.java

package experiments.stackoverflow.aspectj;

import javax.inject.Inject;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.springframework.beans.factory.annotation.Configurable;

@Aspect
@Configurable
public class ConfiguredCallAspect {

    private MyConfiguration config;

    public MyConfiguration getConfig() {
        return config;
    }

    @Inject
    public void setConfig(MyConfiguration config) {
        this.config = config;
    }

    /**
     * Pointcut for all calls to ClassA.someMethod().
     */
    @Around("call(* ClassA.someMethod())")
    public void conditionalExecutionOfSomeMethod(ProceedingJoinPoint joinPoint) throws Throwable {
        System.out.println("Aspect start");
        if (config.shouldExecuteFor(joinPoint.getTarget())) {
            joinPoint.proceed();
        }
        System.out.println("Aspect end");
    }

}

src/experiments/stackoverflow/aspectj/Main.java

package experiments.stackoverflow.aspectj;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {

    public static void main(String[] args) {
        @SuppressWarnings("resource")
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        context.getBean(App.class).run();
    }

}

src/experiments/stackoverflow/aspectj/MyConfiguration.java

package experiments.stackoverflow.aspectj;

public class MyConfiguration {

    private boolean executionTrigger = false;

    public boolean shouldExecuteFor(Object anObject) {
        executionTrigger = !executionTrigger;
        System.out.println("should execute " + anObject + "? " + executionTrigger);
        return executionTrigger;
    }

}

src/META-INF/aop.xml

src/applicationContext.xml

pom.xml


    4.0.0
    experiments
    experiments
    0.0.1-SNAPSHOT
    
        4.2.1.RELEASE
        1.8.7
    
    
        
            javax.inject
            javax.inject
            1
        
        
            org.aspectj
            aspectjrt
            ${aspectj.version}
            runtime
        
        
            org.springframework
            spring-instrument
            ${org.springframework.version}
        
        
            org.aspectj
            aspectjtools
            ${aspectj.version}
        
        
            org.aspectj
            aspectjweaver
            ${aspectj.version}
        
        
            org.springframework
            spring-core
            ${org.springframework.version}
        
        
            org.springframework
            spring-beans
            ${org.springframework.version}
        
        
            org.springframework
            spring-context
            ${org.springframework.version}
        
    
    
        src
        
            
                maven-compiler-plugin
                3.3
                
                    1.8
                    1.8

Start the program using:

java -javaagent:/aspectjweaver-1.8.7.jar -javaagent:/spring-instrument-4.2.1.RELEASE.jar experiments.stackoverflow.aspectj.Main

Produced output:

Aspect start
should execute experiments.stackoverflow.aspectj.ClassA@a0bf272? true
someMethod("obj1") called on experiments.stackoverflow.aspectj.ClassA@a0bf272
Aspect end
Aspect start
should execute experiments.stackoverflow.aspectj.ClassA@4a89ef44? false
Aspect end
Aspect start
should execute experiments.stackoverflow.aspectj.ClassA@310a7859? true
someMethod("obj3") called on experiments.stackoverflow.aspectj.ClassA@310a7859
Aspect end
Aspect start
should execute experiments.stackoverflow.aspectj.ClassA@1cbc1dde? false
Aspect end
Aspect start
should execute experiments.stackoverflow.aspectj.ClassA@4971f459? true
someMethod("obj5") called on experiments.stackoverflow.aspectj.ClassA@4971f459
Aspect end

dynamic conditional code injection into a java file

Answers (1)

Related Questions