<Final MethodArgValidationInterceptor>
package jbriscoe.article.spring.validation.interceptor;

import java.beans.PropertyDescriptor;
import java.util.*;
import jbriscoe.article.spring.validation.exception.ValidationException;
import org.aopalliance.intercept.*;
import org.apache.commons.beanutils.PropertyUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.validation.*;

public class MethodArgValidationInterceptor implements MethodInterceptor {

  private List<Validator> validators = new ArrayList<Validator>();
  private Log log = LogFactory.getLog(getClass());

  public Object invoke(final MethodInvocation methodInvocation) throws Throwable {
    final List<Errors> errors = new ArrayList<Errors>();
    allMethodArgsLoop: 
    for (int i = 0; i < methodInvocation.getArguments().length; i++) {
	final Object arg = methodInvocation.getArguments()[i];
	// Inspect fields... of this arg.
      inspectObject(errors, arg);
    }
    if (errors.size() > 0) {
	log.warn("Validation error(s) found, throwing ValidationException.");
      throw new ValidationException(errors);
    }
    return methodInvocation.proceed();
  }
  public List<Validator> getValidators() {
    return validators;
  }
  public void setValidators(List<Validator> validators) {
    this.validators = validators;
  }
  private void inspectObjectProperties(final Object arg,
    final List<Errors> errors) throws Exception {
    // Inspect supported properties.
    final PropertyDescriptor[] propertyDescriptors = PropertyUtils
      .getPropertyDescriptors(arg.getClass());
    for (final PropertyDescriptor propertyDescriptor : propertyDescriptors) {
      final Object propertyValue = propertyDescriptor.getReadMethod().invoke(arg);
	if (propertyValue != null
	  && isArrayOrCollection(propertyValue.getClass())) {
	  if (propertyValue.getClass().isArray()) {
	    for (final Object propertyElementValue : ((Object[]) propertyValue)) {
		for (final Validator validator : getValidators()) {
		  if (validator.supports(propertyElementValue.getClass())) {
		    log.debug("Validator supported: "						           
		    + propertyElementValue.getClass());
		    validateAndAddErrors(propertyElementValue, validator, errors);		          
		    inspectObjectProperties(propertyElementValue, errors);
		  }
		}
	    }
	  } else {
	    for (final Object propertyElementValue : ((Collection) propertyValue)) {
		for (final Validator validator : getValidators()) {
		  if (validator.supports(propertyElementValue.getClass())) {
		    log.debug("Validator supported: " + 			            
		    propertyElementValue.getClass());					          
		    validateAndAddErrors(propertyElementValue, validator, errors);
		    inspectObjectProperties(propertyElementValue, errors);
		  }
		}
	    }
	  }
	} else if (propertyValue != null) {
	  // Non-Scalar property
	  for (final Validator validator : getValidators()) {
	    if (validator.supports(propertyValue.getClass())) {
		log.debug("Validator supported: " + propertyValue.getClass());
		validateAndAddErrors(propertyValue, validator, errors);
		inspectObjectProperties(propertyValue, errors);
	    }
	  }
	}
    }
  }
  private Errors validateAndAddErrors(final Object arg,
    final Validator validator, final List<Errors> errors) {
    final BindException objErrors = new BindException(arg, arg.getClass()
      .getName());
    validator.validate(arg, objErrors);
    if (objErrors.hasErrors()) {
      errors.add(objErrors);
    }
  return objErrors;
  }
  private void inspectObject(final List<Errors> errors, final Object arg)
    throws Exception {
    allValidatorLoop: for (final Validator validator : getValidators()) {
      if (validator.supports(arg.getClass())) {
	  log.debug("Validator supported: " + arg.getClass());
	  validateAndAddErrors(arg, validator, errors);
	  inspectObjectProperties(arg, errors);
      }
    }
  }
  private boolean isArrayOrCollection(final Class clazz) {
    return (clazz.isArray() || clazz.isAssignableFrom(List.class)
				|| clazz.isAssignableFrom(ArrayList.class)
				|| clazz.isAssignableFrom(Set.class)
				|| clazz.isAssignableFrom(SortedSet.class)
				|| clazz.isAssignableFrom(AbstractCollection.class)
				|| clazz.isAssignableFrom(AbstractList.class)
				|| clazz.isAssignableFrom(AbstractSet.class)
				|| clazz.isAssignableFrom(HashSet.class)
				|| clazz.isAssignableFrom(LinkedHashSet.class)
				|| clazz.isAssignableFrom(LinkedList.class)
				|| clazz.isAssignableFrom(TreeSet.class) || clazz
				.isAssignableFrom(Vector.class));
  }
}

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