import java.beans.*;
import java.lang.reflect.*;
import java.util.*;

/**
 * DynamicBeanProxy is a version of BeanProxy that is implemented as a JDK 1.3
 * dynamic proxy class.
 *
 * @author Thornton Rose
 */
public class DynamicBeanProxy {

   // Static factory methods --------------------------------------------------

   // newProxyInstance(Class):
   /**
    * Create a new proxy instance for objects of the given class.
    */
   public static IBeanProxy newProxyInstance(Class theBeanClass) 
         throws Exception {
      return (IBeanProxy) Proxy.newProxyInstance(
         theBeanClass.getClassLoader(), 
         new Class[] { IBeanProxy.class }, 
         new BeanProxy(theBeanClass));
   }

   // newProxyInstance(Object):
   /**
    * Create a new proxy instance for objects of the class of the given 
    * object and set the target object to the given object.
    */
   public static IBeanProxy newProxyInstance(Object theBean) 
         throws Exception {
      IBeanProxy proxy = newProxyInstance(theBean.getClass());
      proxy.setBean(theBean);
      return proxy;
   }
   
   // BeanProxy ---------------------------------------------------------------

   /**
    * BeanProxy is the actual bean proxy.
    */
   private static class BeanProxy implements InvocationHandler, IBeanProxy {
      private Object    bean;
      private Class     beanClass;
      private Hashtable pdsByName = new Hashtable();
      
      // Constructors ---------------------------------------------------------

      // BeanProxy(Class):
      /**
       * Construct a proxy for the given class.
       *
       * @param theBeanClass The target bean class.
       */
      protected BeanProxy(Class theBeanClass) throws IntrospectionException {
         BeanInfo             bi;
         PropertyDescriptor[] pds;
         String               name;
         Method               m;
   
         // Save reference to bean class.
         
         beanClass = theBeanClass;
   
         // Build hashtable for bean property descriptors.
   
         bi = Introspector.getBeanInfo(beanClass);
         pds = bi.getPropertyDescriptors();
   
         for (int i = 0; i < pds.length; i ++) {
            name = pds[i].getName();
            pdsByName.put(name, pds[i]);
         }
      }

      // BeanProxy(Object):
      /**
       * Construct a proxy for the given bean.
       *
       * @param theBean The target bean.
       */
      protected BeanProxy(Object theBean) throws IntrospectionException {
         this(theBean.getClass());
         bean = theBean;
      }
      
      // InvocationHandler ----------------------------------------------------

      // invoke(Object, Method, Object[]):
      /**
       * Handle invocation of the given method for the given proxy.
       */
      public Object invoke(Object proxy, Method method, Object[] args) 
            throws Throwable {
         return method.invoke(this, args);
      }
      
      // IBeanProxy --------------------------------------------------------------

      // getBean();
      /**
       * Return the target bean.
       */
      public Object getBean() {
         return bean;
      }
   
      // setBean(Object);
      /**
       * Set the target bean to the given object.
       */
      public void setBean(Object newBean) {
         bean = newBean;
      }

      // get(String):      
      /**
       * Get bean property.
       *
       * @param name Bean property name.
       *
       * @return Bean property value as Object.
       */
      public Object get(String name) throws Exception {
         PropertyDescriptor pd;
         Method             getter;
   
         pd = (PropertyDescriptor) pdsByName.get(name);
   
         if (pd == null) {
            throw new NoSuchFieldException("Unknown property: " + name);
         }
   
         getter = pd.getReadMethod();
   
         if (getter == null) {
            throw new NoSuchMethodException("No read method for: " + name);
         }
   
         return getter.invoke(bean, new Object[] {});
      }
   
      // set(String, Object):
      /**
       * Set bean property.
       *
       * @param name   Bean property name.
       * @param value  Bean property value.
       */
      public Object set(String name, Object value) throws Exception {
         PropertyDescriptor pd;
         Method             setter;
   
         pd = (PropertyDescriptor) pdsByName.get(name);
   
         if (pd == null) {
            throw new NoSuchFieldException("Unknown property: " + name);
         }
   
         setter = pd.getWriteMethod();
   
         if (setter == null) {
            throw new NoSuchMethodException("No write method for: " + name);
         }
   
         return setter.invoke(bean, new Object[] { value } );
      }

      // invoke(String, Class[], Object[]):
      /**
       * Invoke named method on target bean.
       *
       * @param name       Method name.
       * @param types      Parameter types.
       * @param parameters List of parameters passed to method.
       *
       * @return Return value from method (may be null).
       *
       * @throws Throwable When any exception occurs.
       */
      public Object invoke(String name, Class[] types, Object[] parameters) 
            throws Exception {
         return beanClass.getMethod(name, types).invoke(bean, parameters);
      }
   }
}