businessobjectvalidationservice.java

动态代理实例源代码

package com.lakeviewtech;

/**
 * Static utility class for validating method calls.  In this very simple
 * implementation, we only check to see that all parameters are non-null
 * values - in a real application, this class could delegate validation to
 * a real validation engine, providing configurable rules for acceptable
 * parameters.
 */
public class BusinessObjectValidationService {

    private BusinessObjectValidationService() {
    }

    /**
     * Validates the parameters for the given method call on the given target.
     * @param target the target of the operation.  Typically, this is the
     * business object implementation.
     * @param methodName the name of the method that was called.
     * @param parameters the parameters on the method call.
     * @throws ValidationException indicates that validation failed.  The
     * exception will contain information as to what went wrong.
     */
    public static void validate(Object target, String methodName, 
                                Object[] parameters) 
    throws ValidationException {

        /* The following is an extremely simplified validation check to make
           sure none of the parameters are null.  If a null parameter is found,
           then a validation exception is thrown.
           
           This is typically where we would call out to a validation engine
           which could find validation rule matches on the given target/method/
           parameter list, and run those validations.  
           
           Another interesting alternative for property changes might be to
           use the vetoable change support provided by the JavaBeans
           architecture to notify interested listeners that a property change
           is about to happen - allowing them to approve/veto the property
           change.
        */

        if (parameters != null) {
            for (int i = 0; i < parameters.length; i++) {
                if (parameters[i] == null) {
                    /* found a null parameter, construct a ValidationException
                       with the correct id, and a useful text message.
                    */
                    throw new ValidationException("null.parameter", 
                                                  "A null parameter was passed to the " +
                                                  methodName + "() method");
                }
            }
        }
    }
}