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Spring Framework example source code file (SpringBindingActionForm.java)

This example Spring Framework source code file (SpringBindingActionForm.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Spring Framework tags/keywords

actionmessages, actionmessages, convertutilsbean, fielderror, http, messageresources, messagesourceresolvable, nosuchmethodexception, nosuchmethodexception, object, object, objecterror, reflection, request, response, servlet, springbindingactionform, string, string, util

The Spring Framework SpringBindingActionForm.java source code

/*
 * Copyright 2002-2006 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.struts;

import java.lang.reflect.InvocationTargetException;
import java.util.Iterator;
import java.util.Locale;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.beanutils.BeanUtilsBean;
import org.apache.commons.beanutils.ConvertUtilsBean;
import org.apache.commons.beanutils.PropertyUtilsBean;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.struts.Globals;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionMessage;
import org.apache.struts.action.ActionMessages;
import org.apache.struts.util.MessageResources;

import org.springframework.context.MessageSourceResolvable;
import org.springframework.validation.Errors;
import org.springframework.validation.FieldError;
import org.springframework.validation.ObjectError;

/**
 * A thin Struts ActionForm adapter that delegates to Spring's more complete
 * and advanced data binder and Errors object underneath the covers to bind
 * to POJOs and manage rejected values.
 *
 * <p>Exposes Spring-managed errors to the standard Struts view tags, through
 * exposing a corresponding Struts ActionMessages object as request attribute.
 * Also exposes current field values in a Struts-compliant fashion, including
 * rejected values (which Spring's binding keeps even for non-String fields).
 *
 * <p>Consequently, Struts views can be written in a completely traditional
 * fashion (with standard <code>html:form, html:errors, etc),
 * seamlessly accessing a Spring-bound POJO form object underneath.
 *
 * <p>Note this ActionForm is designed explicitly for use in request scope.
 * It expects to receive an <code>expose call from the Action, passing
 * in the Errors object to expose plus the current HttpServletRequest.
 *
 * <p>Example definition in struts-config.xml:
 *
 * <pre>
 * <form-beans>
 *   <form-bean name="actionForm" type="org.springframework.web.struts.SpringBindingActionForm"/>
 * </form-beans></pre>
 * 
 * Example code in a custom Struts <code>Action:
 *
 * <pre>
 * public ActionForward execute(ActionMapping actionMapping, ActionForm actionForm, HttpServletRequest request, HttpServletResponse response) throws Exception {
 *   SpringBindingActionForm form = (SpringBindingActionForm) actionForm;
 *   MyPojoBean bean = ...;
 *   ServletRequestDataBinder binder = new ServletRequestDataBinder(bean, "myPojo");
 *   binder.bind(request);
 *   form.expose(binder.getBindingResult(), request);
 *   return actionMapping.findForward("success");
 * }</pre>
 *
 * This class is compatible with both Struts 1.2.x and Struts 1.1.
 * On Struts 1.2, default messages registered with Spring binding errors
 * are exposed when none of the error codes could be resolved.
 * On Struts 1.1, this is not possible due to a limitation in the Struts
 * message facility; hence, we expose the plain default error code there.
 *
 * @author Keith Donald
 * @author Juergen Hoeller
 * @since 1.2.2
 * @see #expose(org.springframework.validation.Errors, javax.servlet.http.HttpServletRequest)
 */
public class SpringBindingActionForm extends ActionForm {

	private static final Log logger = LogFactory.getLog(SpringBindingActionForm.class);

	private static boolean defaultActionMessageAvailable = true;


	static {
		// Register special PropertyUtilsBean subclass that knows how to
		// extract field values from a SpringBindingActionForm.
		// As a consequence of the static nature of Commons BeanUtils,
		// we have to resort to this initialization hack here.
		ConvertUtilsBean convUtils = new ConvertUtilsBean();
		PropertyUtilsBean propUtils = new SpringBindingAwarePropertyUtilsBean();
		BeanUtilsBean beanUtils = new BeanUtilsBean(convUtils, propUtils);
		BeanUtilsBean.setInstance(beanUtils);

		// Determine whether the Struts 1.2 support for default messages
		// is available on ActionMessage: ActionMessage(String, boolean)
		// with "false" to be passed into the boolean flag.
		try {
			ActionMessage.class.getConstructor(new Class[] {String.class, boolean.class});
		}
		catch (NoSuchMethodException ex) {
			defaultActionMessageAvailable = false;
		}
	}


	private Errors errors;

	private Locale locale;

	private MessageResources messageResources;


	/**
	 * Set the Errors object that this SpringBindingActionForm is supposed
	 * to wrap. The contained field values and errors will be exposed
	 * to the view, accessible through Struts standard tags.
	 * @param errors the Spring Errors object to wrap, usually taken from
	 * a DataBinder that has been used for populating a POJO form object
	 * @param request the HttpServletRequest to retrieve the attributes from
	 * @see org.springframework.validation.DataBinder#getBindingResult()
	 */
	public void expose(Errors errors, HttpServletRequest request) {
		this.errors = errors;

		// Obtain the locale from Struts well-known location.
		this.locale = (Locale) request.getSession().getAttribute(Globals.LOCALE_KEY);

		// Obtain the MessageResources from Struts' well-known location.
		this.messageResources = (MessageResources) request.getAttribute(Globals.MESSAGES_KEY);

		if (errors != null && errors.hasErrors()) {
			// Add global ActionError instances from the Spring Errors object.
			ActionMessages actionMessages = (ActionMessages) request.getAttribute(Globals.ERROR_KEY);
			if (actionMessages == null) {
				request.setAttribute(Globals.ERROR_KEY, getActionMessages());
			}
			else {
				actionMessages.add(getActionMessages());
			}
		}
	}


	/**
	 * Return an ActionMessages representation of this SpringBindingActionForm,
	 * exposing all errors contained in the underlying Spring Errors object.
	 * @see org.springframework.validation.Errors#getAllErrors()
	 */
	private ActionMessages getActionMessages() {
		ActionMessages actionMessages = new ActionMessages();
		Iterator it = this.errors.getAllErrors().iterator();
		while (it.hasNext()) {
			ObjectError objectError = (ObjectError) it.next();
			String effectiveMessageKey = findEffectiveMessageKey(objectError);
			if (effectiveMessageKey == null && !defaultActionMessageAvailable) {
				// Need to specify default code despite it not being resolvable:
				// Struts 1.1 ActionMessage doesn't support default messages.
				effectiveMessageKey = objectError.getCode();
			}
			ActionMessage message = (effectiveMessageKey != null) ?
					new ActionMessage(effectiveMessageKey, resolveArguments(objectError.getArguments())) :
					new ActionMessage(objectError.getDefaultMessage(), false);
			if (objectError instanceof FieldError) {
				FieldError fieldError = (FieldError) objectError;
				actionMessages.add(fieldError.getField(), message);
			}
			else {
				actionMessages.add(ActionMessages.GLOBAL_MESSAGE, message);
			}
		}
		if (logger.isDebugEnabled()) {
			logger.debug("Final ActionMessages used for binding: " + actionMessages);
		}
		return actionMessages;
	}

	private Object[] resolveArguments(Object[] arguments) {
		if (arguments == null || arguments.length == 0) {
			return arguments;
		}
		for (int i = 0; i < arguments.length; i++) {
			Object arg = arguments[i];
			if (arg instanceof MessageSourceResolvable) {
				MessageSourceResolvable resolvable = (MessageSourceResolvable)arg;
				String[] codes = resolvable.getCodes();
				boolean resolved = false;
				if (this.messageResources != null) {
					for (int j = 0; j < codes.length; j++) {
						String code = codes[j];
						if (this.messageResources.isPresent(this.locale, code)) {
							arguments[i] = this.messageResources.getMessage(
									this.locale, code, resolveArguments(resolvable.getArguments()));
							resolved = true;
							break;
						}
					}
				}
				if (!resolved) {
					arguments[i] = resolvable.getDefaultMessage();
				}
			}
		}
		return arguments;
	}

	/**
	 * Find the most specific message key for the given error.
	 * @param error the ObjectError to find a message key for
	 * @return the most specific message key found
	 */
	private String findEffectiveMessageKey(ObjectError error) {
		if (this.messageResources != null) {
			String[] possibleMatches = error.getCodes();
			for (int i = 0; i < possibleMatches.length; i++) {
				if (logger.isDebugEnabled()) {
					logger.debug("Looking for error code '" + possibleMatches[i] + "'");
				}
				if (this.messageResources.isPresent(this.locale, possibleMatches[i])) {
					if (logger.isDebugEnabled()) {
						logger.debug("Found error code '" + possibleMatches[i] + "' in resource bundle");
					}
					return possibleMatches[i];
				}
			}
		}
		if (logger.isDebugEnabled()) {
			logger.debug("Could not find a suitable message error code, returning default message");
		}
		return null;
	}


	/**
	 * Get the formatted value for the property at the provided path.
	 * The formatted value is a string value for display, converted
	 * via a registered property editor.
	 * @param propertyPath the property path
	 * @return the formatted property value
	 * @throws NoSuchMethodException if called during Struts binding
	 * (without Spring Errors object being exposed), to indicate no
	 * available property to Struts
	 */
	private Object getFieldValue(String propertyPath) throws NoSuchMethodException {
		if (this.errors == null) {
			throw new NoSuchMethodException(
					"No bean properties exposed to Struts binding - performing Spring binding later on");
		}
		return this.errors.getFieldValue(propertyPath);
	}


	/**
	 * Special subclass of PropertyUtilsBean that it is aware of SpringBindingActionForm
	 * and uses it for retrieving field values. The field values will be taken from
	 * the underlying POJO form object that the Spring Errors object was created for.
	 */
	private static class SpringBindingAwarePropertyUtilsBean extends PropertyUtilsBean {

		public Object getNestedProperty(Object bean, String propertyPath)
				throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {

			// Extract Spring-managed field value in case of SpringBindingActionForm.
			if (bean instanceof SpringBindingActionForm) {
				SpringBindingActionForm form = (SpringBindingActionForm) bean;
				return form.getFieldValue(propertyPath);
			}

			// Else fall back to default PropertyUtils behavior.
			return super.getNestedProperty(bean, propertyPath);
		}
	}

}

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