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Spring Framework example source code file (VelocityView.java)

This example Spring Framework source code file (VelocityView.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

applicationcontextexception, context, context, exception, exception, http, httpservletrequest, httpservletrequest, httpservletresponse, locale, request, response, servlet, string, string, template, util, velocity, velocityconfig

The Spring Framework VelocityView.java source code

/*
 * Copyright 2002-2007 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.servlet.view.velocity;

import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Locale;
import java.util.Map;
import java.util.Properties;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.VelocityEngine;
import org.apache.velocity.app.tools.VelocityFormatter;
import org.apache.velocity.context.Context;
import org.apache.velocity.exception.MethodInvocationException;
import org.apache.velocity.exception.ResourceNotFoundException;
import org.apache.velocity.tools.generic.DateTool;
import org.apache.velocity.tools.generic.NumberTool;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.context.ApplicationContextException;
import org.springframework.util.ClassUtils;
import org.springframework.web.servlet.support.RequestContextUtils;
import org.springframework.web.servlet.view.AbstractTemplateView;
import org.springframework.web.util.NestedServletException;

/**
 * View using the Velocity template engine.
 *
 * <p>Exposes the following JavaBean properties:
 * <ul>
 * <li>url: the location of the Velocity template to be wrapped,
 * relative to the Velocity resource loader path (see VelocityConfigurer).
 * <li>encoding (optional, default is determined by Velocity configuration):
 * the encoding of the Velocity template file
 * <li>velocityFormatterAttribute (optional, default=null): the name of
 * the VelocityFormatter helper object to expose in the Velocity context of this
 * view, or <code>null if not needed. VelocityFormatter is part of standard Velocity.
 * <li>dateToolAttribute (optional, default=null): the name of the
 * DateTool helper object to expose in the Velocity context of this view,
 * or <code>null if not needed. DateTool is part of Velocity Tools 1.0.
 * <li>numberToolAttribute (optional, default=null): the name of the
 * NumberTool helper object to expose in the Velocity context of this view,
 * or <code>null if not needed. NumberTool is part of Velocity Tools 1.1.
 * <li>cacheTemplate (optional, default=false): whether or not the Velocity
 * template should be cached. It should normally be true in production, but setting
 * this to false enables us to modify Velocity templates without restarting the
 * application (similar to JSPs). Note that this is a minor optimization only,
 * as Velocity itself caches templates in a modification-aware fashion.
 * </ul>
 *
 * <p>Depends on a VelocityConfig object such as VelocityConfigurer being
 * accessible in the current web application context, with any bean name.
 * Alternatively, you can set the VelocityEngine object as bean property.
 *
 * <p>Note: Spring's VelocityView requires Velocity 1.3 or higher, and optionally
 * Velocity Tools 1.0 or higher (depending on the use of DateTool and/or NumberTool).
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see VelocityConfig
 * @see VelocityConfigurer
 * @see #setUrl
 * @see #setExposeSpringMacroHelpers
 * @see #setEncoding
 * @see #setVelocityEngine
 * @see VelocityConfig
 * @see VelocityConfigurer
 */
public class VelocityView extends AbstractTemplateView {

	private Map toolAttributes;

	private String velocityFormatterAttribute;

	private String dateToolAttribute;

	private String numberToolAttribute;

	private String encoding;

	private boolean cacheTemplate = false;

	private VelocityEngine velocityEngine;

	private Template template;


	/**
	 * Set tool attributes to expose to the view, as attribute name / class name pairs.
	 * An instance of the given class will be added to the Velocity context for each
	 * rendering operation, under the given attribute name.
	 * <p>For example, an instance of MathTool, which is part of the generic package
	 * of Velocity Tools, can be bound under the attribute name "math", specifying the
	 * fully qualified class name "org.apache.velocity.tools.generic.MathTool" as value.
	 * <p>Note that VelocityView can only create simple generic tools or values, that is,
	 * classes with a public default constructor and no further initialization needs.
	 * This class does not do any further checks, to not introduce a required dependency
	 * on a specific tools package.
	 * <p>For tools that are part of the view package of Velocity Tools, a special
	 * Velocity context and a special init callback are needed. Use VelocityToolboxView
	 * in such a case, or override <code>createVelocityContext and
	 * <code>initTool accordingly.
	 * <p>For a simple VelocityFormatter instance or special locale-aware instances
	 * of DateTool/NumberTool, which are part of the generic package of Velocity Tools,
	 * specify the "velocityFormatterAttribute", "dateToolAttribute" or
	 * "numberToolAttribute" properties, respectively.
	 * @param toolAttributes attribute names as keys, and tool class names as values
	 * @see org.apache.velocity.tools.generic.MathTool
	 * @see VelocityToolboxView
	 * @see #createVelocityContext
	 * @see #initTool
	 * @see #setVelocityFormatterAttribute
	 * @see #setDateToolAttribute
	 * @see #setNumberToolAttribute
	 */
	public void setToolAttributes(Properties toolAttributes) {
		this.toolAttributes = new HashMap(toolAttributes.size());
		for (Enumeration attributeNames = toolAttributes.propertyNames(); attributeNames.hasMoreElements();) {
			String attributeName = (String) attributeNames.nextElement();
			String className = toolAttributes.getProperty(attributeName);
			Class toolClass = null;
			try {
				toolClass = ClassUtils.forName(className);
			}
			catch (ClassNotFoundException ex) {
				throw new IllegalArgumentException(
						"Invalid definition for tool '" + attributeName + "' - tool class not found: " + ex.getMessage());
			}
			this.toolAttributes.put(attributeName, toolClass);
		}
	}

	/**
	 * Set the name of the VelocityFormatter helper object to expose in the
	 * Velocity context of this view, or <code>null if not needed.
	 * <p>VelocityFormatter is part of the standard Velocity distribution.
	 * @see org.apache.velocity.app.tools.VelocityFormatter
	 */
	public void setVelocityFormatterAttribute(String velocityFormatterAttribute) {
		this.velocityFormatterAttribute = velocityFormatterAttribute;
	}

	/**
	 * Set the name of the DateTool helper object to expose in the Velocity context
	 * of this view, or <code>null if not needed. The exposed DateTool will be aware of
	 * the current locale, as determined by Spring's LocaleResolver.
	 * <p>DateTool is part of the generic package of Velocity Tools 1.0.
	 * Spring uses a special locale-aware subclass of DateTool.
	 * @see org.apache.velocity.tools.generic.DateTool
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getLocale
	 * @see org.springframework.web.servlet.LocaleResolver
	 */
	public void setDateToolAttribute(String dateToolAttribute) {
		this.dateToolAttribute = dateToolAttribute;
	}

	/**
	 * Set the name of the NumberTool helper object to expose in the Velocity context
	 * of this view, or <code>null if not needed. The exposed NumberTool will be aware of
	 * the current locale, as determined by Spring's LocaleResolver.
	 * <p>NumberTool is part of the generic package of Velocity Tools 1.1.
	 * Spring uses a special locale-aware subclass of NumberTool.
	 * @see org.apache.velocity.tools.generic.NumberTool
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getLocale
	 * @see org.springframework.web.servlet.LocaleResolver
	 */
	public void setNumberToolAttribute(String numberToolAttribute) {
		this.numberToolAttribute = numberToolAttribute;
	}

	/**
	 * Set the encoding of the Velocity template file. Default is determined
	 * by the VelocityEngine: "ISO-8859-1" if not specified otherwise.
	 * <p>Specify the encoding in the VelocityEngine rather than per template
	 * if all your templates share a common encoding.
	 */
	public void setEncoding(String encoding) {
		this.encoding = encoding;
	}

	/**
	 * Return the encoding for the Velocity template.
	 */
	protected String getEncoding() {
		return this.encoding;
	}

	/**
	 * Set whether the Velocity template should be cached. Default is "false".
	 * It should normally be true in production, but setting this to false enables us to
	 * modify Velocity templates without restarting the application (similar to JSPs).
	 * <p>Note that this is a minor optimization only, as Velocity itself caches
	 * templates in a modification-aware fashion.
	 */
	public void setCacheTemplate(boolean cacheTemplate) {
		this.cacheTemplate = cacheTemplate;
	}

	/**
	 * Return whether the Velocity template should be cached.
	 */
	protected boolean isCacheTemplate() {
		return this.cacheTemplate;
	}

	/**
	 * Set the VelocityEngine to be used by this view.
	 * If this is not set, the default lookup will occur: A single VelocityConfig
	 * is expected in the current web application context, with any bean name.
	 * @see VelocityConfig
	 */
	public void setVelocityEngine(VelocityEngine velocityEngine) {
		this.velocityEngine = velocityEngine;
	}

	/**
	 * Return the VelocityEngine used by this view.
	 */
	protected VelocityEngine getVelocityEngine() {
		return this.velocityEngine;
	}


	/**
 	 * Invoked on startup. Looks for a single VelocityConfig bean to
 	 * find the relevant VelocityEngine for this factory.
 	 */
	protected void initApplicationContext() throws BeansException {
		super.initApplicationContext();

		if (getVelocityEngine() == null) {
			// No explicit VelocityEngine: try to autodetect one.
			setVelocityEngine(autodetectVelocityEngine());
		}

		checkTemplate();
	}

	/**
	 * Autodetect a VelocityEngine via the ApplicationContext.
	 * Called if no explicit VelocityEngine has been specified.
	 * @return the VelocityEngine to use for VelocityViews
	 * @throws BeansException if no VelocityEngine could be found
	 * @see #getApplicationContext
	 * @see #setVelocityEngine
	 */
	protected VelocityEngine autodetectVelocityEngine() throws BeansException {
		try {
			VelocityConfig velocityConfig = (VelocityConfig)
					BeanFactoryUtils.beanOfTypeIncludingAncestors(
							getApplicationContext(), VelocityConfig.class, true, false);
			return velocityConfig.getVelocityEngine();
		}
		catch (NoSuchBeanDefinitionException ex) {
			throw new ApplicationContextException(
					"Must define a single VelocityConfig bean in this web application context " +
					"(may be inherited): VelocityConfigurer is the usual implementation. " +
					"This bean may be given any name.", ex);
		}
	}

	/**
	 * Check that the Velocity template used for this view exists and is valid.
	 * <p>Can be overridden to customize the behavior, for example in case of
	 * multiple templates to be rendered into a single view.
	 * @throws ApplicationContextException if the template cannot be found or is invalid
	 */
	protected void checkTemplate() throws ApplicationContextException {
		try {
			// Check that we can get the template, even if we might subsequently get it again.
			this.template = getTemplate();
		}
		catch (ResourceNotFoundException ex) {
			throw new ApplicationContextException("Cannot find Velocity template for URL [" + getUrl() +
				"]: Did you specify the correct resource loader path?", ex);
		}
		catch (Exception ex) {
			throw new ApplicationContextException(
					"Could not load Velocity template for URL [" + getUrl() + "]", ex);
		}
	}


	/**
	 * Process the model map by merging it with the Velocity template.
	 * Output is directed to the servlet response.
	 * <p>This method can be overridden if custom behavior is needed.
	 */
	protected void renderMergedTemplateModel(
			Map model, HttpServletRequest request, HttpServletResponse response) throws Exception {

		exposeHelpers(model, request);

		Context velocityContext = createVelocityContext(model, request, response);
		exposeHelpers(velocityContext, request, response);
		exposeToolAttributes(velocityContext, request);

		doRender(velocityContext, response);
	}

	/**
	 * Expose helpers unique to each rendering operation. This is necessary so that
	 * different rendering operations can't overwrite each other's formats etc.
	 * <p>Called by renderMergedTemplateModel. The default implementation
	 * is empty. This method can be overridden to add custom helpers to the model.
	 * @param model the model that will be passed to the template for merging
	 * @param request current HTTP request
	 * @throws Exception if there's a fatal error while we're adding model attributes
	 * @see #renderMergedTemplateModel
	 */
	protected void exposeHelpers(Map model, HttpServletRequest request) throws Exception {
	}

	/**
	 * Create a Velocity Context instance for the given model,
	 * to be passed to the template for merging.
	 * <p>The default implementation delegates to {@link #createVelocityContext(Map)}.
	 * Can be overridden for a special context class, for example ChainedContext which
	 * is part of the view package of Velocity Tools. ChainedContext is needed for
	 * initialization of ViewTool instances.
	 * <p>Have a look at {@link VelocityToolboxView}, which pre-implements
	 * ChainedContext support. This is not part of the standard VelocityView class
	 * in order to avoid a required dependency on the view package of Velocity Tools.
	 * @param model the model Map, containing the model attributes to be exposed to the view
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @return the Velocity Context
	 * @throws Exception if there's a fatal error while creating the context
	 * @see #createVelocityContext(Map)
	 * @see #initTool
	 * @see org.apache.velocity.tools.view.context.ChainedContext
	 * @see VelocityToolboxView
	 */
	protected Context createVelocityContext(
			Map model, HttpServletRequest request, HttpServletResponse response) throws Exception {

		return createVelocityContext(model);
	}

	/**
	 * Create a Velocity Context instance for the given model,
	 * to be passed to the template for merging.
	 * <p>Default implementation creates an instance of Velocity's
	 * VelocityContext implementation class.
	 * @param model the model Map, containing the model attributes
	 * to be exposed to the view
	 * @return the Velocity Context
	 * @throws Exception if there's a fatal error while creating the context
	 * @see org.apache.velocity.VelocityContext
	 */
	protected Context createVelocityContext(Map model) throws Exception {
		return new VelocityContext(model);
	}

	/**
	 * Expose helpers unique to each rendering operation. This is necessary so that
	 * different rendering operations can't overwrite each other's formats etc.
	 * <p>Called by renderMergedTemplateModel. Default implementation
	 * delegates to <code>exposeHelpers(velocityContext, request). This method
	 * can be overridden to add special tools to the context, needing the servlet response
	 * to initialize (see Velocity Tools, for example LinkTool and ViewTool/ChainedContext).
	 * @param velocityContext Velocity context that will be passed to the template
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @throws Exception if there's a fatal error while we're adding model attributes
	 * @see #exposeHelpers(org.apache.velocity.context.Context, HttpServletRequest)
	 */
	protected void exposeHelpers(
			Context velocityContext, HttpServletRequest request, HttpServletResponse response) throws Exception {

		exposeHelpers(velocityContext, request);
	}

	/**
	 * Expose helpers unique to each rendering operation. This is necessary so that
	 * different rendering operations can't overwrite each other's formats etc.
	 * <p>Default implementation is empty. This method can be overridden to add
	 * custom helpers to the Velocity context.
	 * @param velocityContext Velocity context that will be passed to the template
	 * @param request current HTTP request
	 * @throws Exception if there's a fatal error while we're adding model attributes
	 * @see #exposeHelpers(Map, HttpServletRequest)
	 */
	protected void exposeHelpers(Context velocityContext, HttpServletRequest request) throws Exception {
	}

	/**
	 * Expose the tool attributes, according to corresponding bean property settings.
	 * <p>Do not override this method unless for further tools driven by bean properties.
	 * Override one of the <code>exposeHelpers methods to add custom helpers.
	 * @param velocityContext Velocity context that will be passed to the template
	 * @param request current HTTP request
	 * @throws Exception if there's a fatal error while we're adding model attributes
	 * @see #setVelocityFormatterAttribute
	 * @see #setDateToolAttribute
	 * @see #setNumberToolAttribute
	 * @see #exposeHelpers(Map, HttpServletRequest)
	 * @see #exposeHelpers(org.apache.velocity.context.Context, HttpServletRequest, HttpServletResponse)
	 */
	protected void exposeToolAttributes(Context velocityContext, HttpServletRequest request) throws Exception {
		// Expose generic attributes.
		if (this.toolAttributes != null) {
			for (Iterator it = this.toolAttributes.entrySet().iterator(); it.hasNext();) {
				Map.Entry entry = (Map.Entry) it.next();
				String attributeName = (String) entry.getKey();
				Class toolClass = (Class) entry.getValue();
				try {
					Object tool = toolClass.newInstance();
					initTool(tool, velocityContext);
					velocityContext.put(attributeName, tool);
				}
				catch (Exception ex) {
					throw new NestedServletException("Could not instantiate Velocity tool '" + attributeName + "'", ex);
				}
			}
		}

		// Expose VelocityFormatter attribute.
		if (this.velocityFormatterAttribute != null) {
			velocityContext.put(this.velocityFormatterAttribute, new VelocityFormatter(velocityContext));
		}

		// Expose locale-aware DateTool/NumberTool attributes.
		if (this.dateToolAttribute != null || this.numberToolAttribute != null) {
			Locale locale = RequestContextUtils.getLocale(request);
			if (this.dateToolAttribute != null) {
				velocityContext.put(this.dateToolAttribute, new LocaleAwareDateTool(locale));
			}
			if (this.numberToolAttribute != null) {
				velocityContext.put(this.numberToolAttribute, new LocaleAwareNumberTool(locale));
			}
		}
	}

	/**
	 * Initialize the given tool instance. The default implementation is empty.
	 * <p>Can be overridden to check for special callback interfaces, for example
	 * the ViewContext interface which is part of the view package of Velocity Tools.
	 * In the particular case of ViewContext, you'll usually also need a special
	 * Velocity context, like ChainedContext which is part of Velocity Tools too.
	 * <p>Have a look at {@link VelocityToolboxView}, which pre-implements such a
	 * ViewTool check. This is not part of the standard VelocityView class in order
	 * to avoid a required dependency on the view package of Velocity Tools.
	 * @param tool the tool instance to initialize
	 * @param velocityContext the Velocity context
	 * @throws Exception if initializion of the tool failed
	 * @see #createVelocityContext
	 * @see org.apache.velocity.tools.view.context.ViewContext
	 * @see org.apache.velocity.tools.view.context.ChainedContext
	 * @see VelocityToolboxView
	 */
	protected void initTool(Object tool, Context velocityContext) throws Exception {
	}


	/**
	 * Render the Velocity view to the given response, using the given Velocity
	 * context which contains the complete template model to use.
	 * <p>The default implementation renders the template specified by the "url"
	 * bean property, retrieved via <code>getTemplate. It delegates to the
	 * <code>mergeTemplate method to merge the template instance with the
	 * given Velocity context.
	 * <p>Can be overridden to customize the behavior, for example to render
	 * multiple templates into a single view.
	 * @param context the Velocity context to use for rendering
	 * @param response servlet response (use this to get the OutputStream or Writer)
	 * @throws Exception if thrown by Velocity
	 * @see #setUrl
	 * @see #getTemplate()
	 * @see #mergeTemplate
	 */
	protected void doRender(Context context, HttpServletResponse response) throws Exception {
		if (logger.isDebugEnabled()) {
			logger.debug("Rendering Velocity template [" + getUrl() + "] in VelocityView '" + getBeanName() + "'");
		}
		mergeTemplate(getTemplate(), context, response);
	}

	/**
	 * Retrieve the Velocity template to be rendered by this view.
	 * <p>By default, the template specified by the "url" bean property will be
	 * retrieved: either returning a cached template instance or loading a fresh
	 * instance (according to the "cacheTemplate" bean property)
	 * @return the Velocity template to render
	 * @throws Exception if thrown by Velocity
	 * @see #setUrl
	 * @see #setCacheTemplate
	 * @see #getTemplate(String)
	 */
	protected Template getTemplate() throws Exception {
		// We already hold a reference to the template, but we might want to load it
		// if not caching. Velocity itself caches templates, so our ability to
		// cache templates in this class is a minor optimization only.
		if (isCacheTemplate() && this.template != null) {
			return this.template;
		}
		else {
			return getTemplate(getUrl());
		}
	}

	/**
	 * Retrieve the Velocity template specified by the given name,
	 * using the encoding specified by the "encoding" bean property.
	 * <p>Can be called by subclasses to retrieve a specific template,
	 * for example to render multiple templates into a single view.
	 * @param name the file name of the desired template
	 * @return the Velocity template
	 * @throws Exception if thrown by Velocity
	 * @see org.apache.velocity.app.VelocityEngine#getTemplate
	 */
	protected Template getTemplate(String name) throws Exception {
		return (getEncoding() != null ?
				getVelocityEngine().getTemplate(name, getEncoding()) :
				getVelocityEngine().getTemplate(name));
	}

	/**
	 * Merge the template with the context.
	 * Can be overridden to customize the behavior.
	 * @param template the template to merge
	 * @param context the Velocity context to use for rendering
	 * @param response servlet response (use this to get the OutputStream or Writer)
	 * @throws Exception if thrown by Velocity
	 * @see org.apache.velocity.Template#merge
	 */
	protected void mergeTemplate(
			Template template, Context context, HttpServletResponse response) throws Exception {

		try {
			template.merge(context, response.getWriter());
		}
		catch (MethodInvocationException ex) {
			throw new NestedServletException(
					"Method invocation failed during rendering of Velocity view with name '" +
					getBeanName() + "': " + ex.getMessage() + "; reference [" + ex.getReferenceName() +
					"], method '" + ex.getMethodName() + "'",
					ex.getWrappedThrowable());
		}
	}


	/**
	 * Subclass of DateTool from Velocity Tools, using a passed-in Locale
	 * (usually the RequestContext Locale) instead of the default Locale.N
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getLocale
	 */
	private static class LocaleAwareDateTool extends DateTool {

		private final Locale locale;

		private LocaleAwareDateTool(Locale locale) {
			this.locale = locale;
		}

		public Locale getLocale() {
			return this.locale;
		}
	}


	/**
	 * Subclass of NumberTool from Velocity Tools, using a passed-in Locale
	 * (usually the RequestContext Locale) instead of the default Locale.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getLocale
	 */
	private static class LocaleAwareNumberTool extends NumberTool {

		private final Locale locale;

		private LocaleAwareNumberTool(Locale locale) {
			this.locale = locale;
		}

		public Locale getLocale() {
			return this.locale;
		}
	}

}

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