EJB 最佳實踐：動態委派

級別：中級

package com.ibm.library;

import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;
import java.rmi.RemoteException;
import java.util.HashMap;
import java.util.Map;
import javax.ejb.CreateException;
import javax.naming.NamingException;

public class LibraryDelegate implements ILibrary {
  private ILibrary library;
  private Map availableMethods;

  public LibraryDelegate() {
    init();
  }

      public void init() {
        // Look up and obtain our session bean
        try {
          LibraryHome libraryHome =
            (LibraryHome)EJBHomeFactory.getInstance().lookup(
              "java:comp/env/ejb/LibraryHome", LibraryHome.class);
          library = libraryHome.create();

          // Get the methods available for use in proxying
          availableMethods = new HashMap();
          Method[] methods = ILibrary.class.getMethods();
          for (int i=0; i<methods.length; i++) {
            availableMethods.put(methods[i].getName(),
              methods[i]);
          }
        } catch (NamingException e) {
          throw new RuntimeException(e);
        } catch (CreateException e) {
          throw new RuntimeException(e);
        } catch (RemoteException e) {
          throw new RuntimeException(e);
        }
      }

      // All the hard-coded methods are removed
      public Object
        invoke(Object proxy, Method method, Object[] args)
        throws Throwable{

        try {
          // See if this is init() or destroy()
          if (method.getName().equals("init")) {
            init();
            return null;
          } else if (method.getName().equals("destroy")) {
            destroy();
            return null;
          } else {
            Method method =
              (Method)availableMethods.get(method.getName());

            // See if we found anything
            if (method != null) {
              return method.invoke(library, args);
            } else {
              throw new
                NoSuchMethodException("The Library does not " +
                "support the  " + method.getName() +" method.");
            }
          }
        } catch (InvocationTargetException e) {
          // We don't support throwing RuntimeExceptions from EJBs
          // directly
          if (e.getTargetException() instanceof RemoteException) {
            throw new RuntimeException(e);
            } else {
              throw e.getTargetException();
            }
          }
        }

        public void destroy() {
          // In this case, do nothing
        }
      }