Source Code : Spring Aspect Introduction Example

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Spring Aspect Introduction Example

/*
Pro Spring
By Rob Harrop
Jan Machacek
ISBN: 1-59059-461-4
Publisher: Apress
*/



///////////////////////////////////////////////////////////////////////////////////////

public interface IsModified {

    public boolean isModified();
}


///////////////////////////////////////////////////////////////////////////////////////

import org.springframework.aop.support.DefaultIntroductionAdvisor;

public class IsModifiedAdvisor extends DefaultIntroductionAdvisor {

    public IsModifiedAdvisor() {
        super(new IsModifiedMixin());
    }
}


///////////////////////////////////////////////////////////////////////////////////////

public class TargetBean {

    private String name;
    
    public void setName(String name) {
        this.name = name;
    }
    
    public String getName() {
        return name;
    }
}


///////////////////////////////////////////////////////////////////////////////////////

import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

import org.aopalliance.intercept.MethodInvocation;
import org.springframework.aop.support.DelegatingIntroductionInterceptor;

public class IsModifiedMixin extends DelegatingIntroductionInterceptor
        implements IsModified {

    private boolean isModified = false;

    private Map methodCache = new HashMap();

    public boolean isModified() {
        return isModified;
    }

    public Object invoke(MethodInvocation invocation) throws Throwable {

        if (!isModified) {
            if ((invocation.getMethod().getName().startsWith("set"))
                    && (invocation.getArguments().length == 1)) {

                // invoke the corresponding get method to see
                // if the value has actually changed
                Method getter = getGetter(invocation.getMethod());

                if (getter != null) {
                    // modification check is unimportant
                    // for write only methods
                    Object newVal = invocation.getArguments()[0];
                    Object oldVal = getter.invoke(invocation.getThis(), null);
                    
                    if((newVal == null) && (oldVal == null)) {
                        isModified = false;
                    } else if((newVal == null) && (oldVal != null)) {
                        isModified = true;
                    } else if((newVal != null) && (oldVal == null)) {
                        isModified = true;
                    } else {
                        isModified = (!newVal.equals(oldVal));
                    }
                }

            }
        }

        return super.invoke(invocation);
    }

    private Method getGetter(Method setter) {
        Method getter = null;

        // attempt cache retrieval.
        getter = (Method) methodCache.get(setter);

        if (getter != null) {
            return getter;
        }

        String getterName = setter.getName().replaceFirst("set", "get");
        try {
            getter = setter.getDeclaringClass().getMethod(getterName, null);

            // cache getter
            synchronized (methodCache) {
                methodCache.put(setter, getter);
            }

            return getter;
        } catch (NoSuchMethodException ex) {
            // must be write only
            return null;
        }
    }
}

///////////////////////////////////////////////////////////////////////////////////////
import org.springframework.aop.IntroductionAdvisor;
import org.springframework.aop.framework.ProxyFactory;

public class IntroductionExample {

    public static void main(String[] args) {
        // create the target
        TargetBean target = new TargetBean();
        target.setName("Name");

        // create the advisor
        IntroductionAdvisor advisor = new IsModifiedAdvisor();

        // create the proxy
        ProxyFactory pf = new ProxyFactory();
        pf.setTarget(target);
        pf.addAdvisor(advisor);
        pf.setOptimize(true);
        
        TargetBean proxy = (TargetBean)pf.getProxy();
        IsModified proxyInterface = (IsModified)proxy;
        
        // test interfaces
        System.out.println("Is TargetBean?: " + (proxy instanceof TargetBean));
        System.out.println("Is IsModified?: " + (proxy instanceof IsModified));
        
        // test is modified implementation
        System.out.println("Has been modified?: " + proxyInterface.isModified());
        proxy.setName("Rob Harrop");
        System.out.println("Has been modified?: " + proxyInterface.isModified());
        proxy.setName("Joe Schmoe");
        System.out.println("Has been modified?: " + proxyInterface.isModified());
     
    }
}

           
       

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