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Spring Framework example source code file (AbstractXsltView.java)

This example Spring Framework source code file (AbstractXsltView.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, exception, http, httpservletrequest, io, map, map, request, response, servlet, source, source, string, string, transformer, transformerconfigurationexception, transformerfactory, util, xslt, xslt

The Spring Framework AbstractXsltView.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.xslt;

import java.io.BufferedOutputStream;
import java.io.IOException;
import java.net.URL;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Map;
import java.util.Properties;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.transform.ErrorListener;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Templates;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.TransformerFactoryConfigurationError;
import javax.xml.transform.URIResolver;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

import org.w3c.dom.Node;

import org.springframework.context.ApplicationContextException;
import org.springframework.core.io.Resource;
import org.springframework.util.Assert;
import org.springframework.util.xml.SimpleTransformErrorListener;
import org.springframework.web.servlet.view.AbstractView;
import org.springframework.web.util.NestedServletException;

/**
 * Convenient superclass for views rendered using an XSLT stylesheet.
 * 
 * <p>Subclasses typically must provide the {@link Source} to transform
 * by overriding {@link #createXsltSource}. Subclasses do not need to
 * concern themselves with XSLT other than providing a valid stylesheet location.
 *
 * <p>Properties:
 * <ul>
 * <li>{@link #setStylesheetLocation(org.springframework.core.io.Resource) stylesheetLocation}:
 * a {@link Resource} pointing to the XSLT stylesheet
 * <li>{@link #setRoot(String) root}: the name of the root element; defaults to {@link #DEFAULT_ROOT "DocRoot"}
 * <li>{@link #setUriResolver(javax.xml.transform.URIResolver) uriResolver}:
 * the {@link URIResolver} to be used in the transform
 * <li>{@link #setErrorListener(javax.xml.transform.ErrorListener) errorListener} (optional):
 * the {@link ErrorListener} implementation instance for custom handling of warnings and errors during TransformerFactory operations
 * <li>{@link #setIndent(boolean) indent} (optional): whether additional whitespace
 * may be added when outputting the result; defaults to <code>true
 * <li>{@link #setCache(boolean) cache} (optional): are templates to be cached; debug setting only; defaults to true 
 * </ul>
 *
 * <p>Note that setting {@link #setCache(boolean) "cache"} to false
 * will cause the template objects to be reloaded for each rendering. This is
 * useful during development, but will seriously affect performance in production
 * and is not thread-safe.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Darren Davison
 */
public abstract class AbstractXsltView extends AbstractView {

	/** The default content type if no stylesheet specified */
	public static final String XML_CONTENT_TYPE = "text/xml;charset=ISO-8859-1";

	/** The default document root name */
	public static final String DEFAULT_ROOT = "DocRoot";


	private boolean customContentTypeSet = false;

	private Class transformerFactoryClass;

	private Resource stylesheetLocation;

	private String root = DEFAULT_ROOT;

	private boolean useSingleModelNameAsRoot = true;

	private URIResolver uriResolver;

	private ErrorListener errorListener = new SimpleTransformErrorListener(logger);

	private boolean indent = true;

	private Properties outputProperties;

	private boolean cache = true;

	private TransformerFactory transformerFactory;

	private volatile Templates cachedTemplates;


	/**
	 * This constructor sets the content type to "text/xml;charset=ISO-8859-1"
	 * by default. This will be switched to the standard web view default
	 * "text/html;charset=ISO-8859-1" if a stylesheet location has been specified.
	 * <p>A specific content type can be configured via the
	 * {@link #setContentType "contentType"} bean property.
	 */
	protected AbstractXsltView() {
		super.setContentType(XML_CONTENT_TYPE);
	}


	public void setContentType(String contentType) {
		super.setContentType(contentType);
		this.customContentTypeSet = true;
	}

	/**
	 * Specify the XSLT TransformerFactory class to use.
	 * <p>The default constructor of the specified class will be called
	 * to build the TransformerFactory for this view.
	 */
	public void setTransformerFactoryClass(Class transformerFactoryClass) {
		Assert.isAssignable(TransformerFactory.class, transformerFactoryClass);
		this.transformerFactoryClass = transformerFactoryClass;
	}

	/**
	 * Set the location of the XSLT stylesheet.
	 * <p>If the {@link TransformerFactory} used by this instance has already
	 * been initialized then invoking this setter will result in the
	 * {@link TransformerFactory#newTemplates(javax.xml.transform.Source) attendant templates}
	 * being re-cached.
	 * @param stylesheetLocation the location of the XSLT stylesheet
	 * @see org.springframework.context.ApplicationContext#getResource
	 */
	public void setStylesheetLocation(Resource stylesheetLocation) {
		this.stylesheetLocation = stylesheetLocation;
		// Re-cache templates if transformer factory already initialized.
		resetCachedTemplates();
	}

	/**
	 * Return the location of the XSLT stylesheet, if any.
	 */
	protected Resource getStylesheetLocation() {
		return this.stylesheetLocation;
	}

	/**
	 * The document root element name. Default is {@link #DEFAULT_ROOT "DocRoot"}.
	 * <p>Only used if we're not passed a single {@link Node} as the model.
	 * @param root the document root element name
	 * @see #DEFAULT_ROOT
	 */
	public void setRoot(String root) {
		this.root = root;
	}

	/**
	 * Set whether to use the name of a given single model object as the
	 * document root element name.
	 * <p>Default is true : If you pass in a model with a single object
	 * named "myElement", then the document root will be named "myElement"
	 * as well. Set this flag to <code>false if you want to pass in a single
	 * model object while still using the root element name configured
	 * through the {@link #setRoot(String) "root" property}.
	 * @param useSingleModelNameAsRoot <code>true if the name of a given single
	 * model object is to be used as the document root element name
	 * @see #setRoot
	 */
	public void setUseSingleModelNameAsRoot(boolean useSingleModelNameAsRoot) {
		this.useSingleModelNameAsRoot = useSingleModelNameAsRoot;
	}

	/**
	 * Set the URIResolver used in the transform.
	 * <p>The URIResolver handles calls to the XSLT document() function.
	 */
	public void setUriResolver(URIResolver uriResolver) {
		this.uriResolver = uriResolver;
	}

	/**
	 * Set an implementation of the {@link javax.xml.transform.ErrorListener}
	 * interface for custom handling of transformation errors and warnings.
	 * <p>If not set, a default
	 * {@link org.springframework.util.xml.SimpleTransformErrorListener} is
	 * used that simply logs warnings using the logger instance of the view class,
	 * and rethrows errors to discontinue the XML transformation.
	 * @see org.springframework.util.xml.SimpleTransformErrorListener
	 */
	public void setErrorListener(ErrorListener errorListener) {
		this.errorListener = errorListener;
	}

	/**
	 * Set whether the XSLT transformer may add additional whitespace when
	 * outputting the result tree.
	 * <p>Default is true (on); set this to false (off)
	 * to not specify an "indent" key, leaving the choice up to the stylesheet.
	 * @see javax.xml.transform.OutputKeys#INDENT
	 */
	public void setIndent(boolean indent) {
		this.indent = indent;
	}

	/**
	 * Set arbitrary transformer output properties to be applied to the stylesheet.
	 * <p>Any values specified here will override defaults that this view sets
	 * programmatically.
	 * @see javax.xml.transform.Transformer#setOutputProperty
	 */
	public void setOutputProperties(Properties outputProperties) {
		this.outputProperties = outputProperties;
	}

	/**
	 * Set whether to activate the template cache for this view.
	 * <p>Default is true. Turn this off to refresh
	 * the Templates object on every access, e.g. during development.
	 * @see #resetCachedTemplates()
	 */
	public void setCache(boolean cache) {
		this.cache = cache;
	}

	/**
	 * Reset the cached Templates object, if any.
	 * <p>The Templates object will subsequently be rebuilt on next
	 * {@link #getTemplates() access}, if caching is enabled.
	 * @see #setCache
	 */
	public final void resetCachedTemplates() {
		this.cachedTemplates = null;
	}


	/**
	 * Here we load our template, as we need the
	 * {@link org.springframework.context.ApplicationContext} to do it.
	 */
	protected final void initApplicationContext() throws ApplicationContextException {
		this.transformerFactory = newTransformerFactory(this.transformerFactoryClass);
		this.transformerFactory.setErrorListener(this.errorListener);
		if (this.uriResolver != null) {
			this.transformerFactory.setURIResolver(this.uriResolver);
		}
		if (getStylesheetLocation() != null && !this.customContentTypeSet) {
			// Use "text/html" as default (instead of "text/xml") if a stylesheet
			// has been configured but no custom content type has been set.
			super.setContentType(DEFAULT_CONTENT_TYPE);
		}
		try {
			getTemplates();
		}
		catch (TransformerConfigurationException ex) {
			throw new ApplicationContextException("Cannot load stylesheet for XSLT view '" + getBeanName() + "'", ex);
		}
	}

	/**
	 * Instantiate a new TransformerFactory for this view.
	 * <p>The default implementation simply calls
	 * {@link javax.xml.transform.TransformerFactory#newInstance()}.
	 * If a {@link #setTransformerFactoryClass "transformerFactoryClass"}
	 * has been specified explicitly, the default constructor of the
	 * specified class will be called instead.
	 * <p>Can be overridden in subclasses.
	 * @param transformerFactoryClass the specified factory class (if any)
	 * @return the new TransactionFactory instance
	 * @throws TransformerFactoryConfigurationError in case of instantiation failure
	 * @see #setTransformerFactoryClass
	 * @see #getTransformerFactory()
	 */
	protected TransformerFactory newTransformerFactory(Class transformerFactoryClass) {
		if (transformerFactoryClass != null) {
			try {
				return (TransformerFactory) transformerFactoryClass.newInstance();
			}
			catch (Exception ex) {
				throw new TransformerFactoryConfigurationError(ex, "Could not instantiate TransformerFactory");
			}
		}
		else {
			return TransformerFactory.newInstance();
		}
	}

	/**
	 * Return the TransformerFactory used by this view.
	 * Available once the View object has been fully initialized.
	 */
	protected final TransformerFactory getTransformerFactory() {
		return this.transformerFactory;
	}


	protected final void renderMergedOutputModel(
			Map model, HttpServletRequest request, HttpServletResponse response) throws Exception {

		response.setContentType(getContentType());

		Source source = null;
		String docRoot = null;
		// Value of a single element in the map, if there is one.
		Object singleModel = null;

		if (this.useSingleModelNameAsRoot && model.size() == 1) {
			docRoot = (String) model.keySet().iterator().next();
			if (logger.isDebugEnabled()) {
				logger.debug("Single model object received, key [" + docRoot + "] will be used as root tag");
			}
			singleModel = model.get(docRoot);
		}

		// Handle special case when we have a single node.
		if (singleModel instanceof Node || singleModel instanceof Source) {
			// Don't domify if the model is already an XML node/source.
			// We don't need to worry about model name, either:
			// we leave the Node alone.
			logger.debug("No need to domify: was passed an XML Node or Source");
			source = (singleModel instanceof Node ? new DOMSource((Node) singleModel) : (Source) singleModel);
		}
		else {
			// docRoot local variable takes precedence
			source = createXsltSource(model, (docRoot != null ? docRoot : this.root), request, response);
		}

		doTransform(model, source, request, response);
	}

	/**
	 * Return the XML {@link Source} to transform.
	 * @param model the model Map
	 * @param root name for root element. This can be supplied as a bean property
	 * to concrete subclasses within the view definition file, but will be overridden
	 * in the case of a single object in the model map to be the key for that object.
	 * If no root property is specified and multiple model objects exist, a default
	 * root tag name will be supplied.
	 * @param request HTTP request. Subclasses won't normally use this, as
	 * request processing should have been complete. However, we might want to
	 * create a RequestContext to expose as part of the model.
	 * @param response HTTP response. Subclasses won't normally use this,
	 * however there may sometimes be a need to set cookies.
	 * @return the XSLT Source to transform
	 * @throws Exception if an error occurs
	 */
	protected Source createXsltSource(
			Map model, String root, HttpServletRequest request, HttpServletResponse response)
			throws Exception {

		return null;
	}

	/**
	 * Perform the actual transformation, writing to the HTTP response.
	 * <p>The default implementation delegates to the
	 * {@link #doTransform(javax.xml.transform.Source, java.util.Map, javax.xml.transform.Result, String)}
	 * method, building a StreamResult for the ServletResponse OutputStream
	 * or for the ServletResponse Writer (according to {@link #useWriter()}).
	 * @param model the model Map
	 * @param source the Source to transform
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @throws Exception if an error occurs
	 * @see javax.xml.transform.stream.StreamResult
	 * @see javax.servlet.ServletResponse#getOutputStream()
	 * @see javax.servlet.ServletResponse#getWriter()
	 * @see #useWriter()
	 */
	protected void doTransform(
			Map model, Source source, HttpServletRequest request, HttpServletResponse response)
			throws Exception {

		Map parameters = getParameters(model, request);
		Result result = (useWriter() ?
				new StreamResult(response.getWriter()) :
				new StreamResult(new BufferedOutputStream(response.getOutputStream())));
		String encoding = response.getCharacterEncoding();
		doTransform(source, parameters, result, encoding);
	}

	/**
	 * Return a Map of transformer parameters to be applied to the stylesheet.
	 * <p>Subclasses can override this method in order to apply one or more
	 * parameters to the transformation process.
	 * <p>The default implementation delegates to the
	 * {@link #getParameters(HttpServletRequest)} variant.
	 * @param model the model Map
	 * @param request current HTTP request
	 * @return a Map of parameters to apply to the transformation process
	 * @see #getParameters()
	 * @see javax.xml.transform.Transformer#setParameter
	 */
	protected Map getParameters(Map model, HttpServletRequest request) {
		return getParameters(request);
	}

	/**
	 * Return a Map of transformer parameters to be applied to the stylesheet.
	 * <p>Subclasses can override this method in order to apply one or more
	 * parameters to the transformation process.
	 * <p>The default implementation delegates to the simple
	 * {@link #getParameters()} variant.
	 * @param request current HTTP request
	 * @return a Map of parameters to apply to the transformation process
	 * @see #getParameters(Map, HttpServletRequest)
	 * @see javax.xml.transform.Transformer#setParameter
	 */
	protected Map getParameters(HttpServletRequest request) {
		return getParameters();
	}

	/**
	 * Return a Map of transformer parameters to be applied to the stylesheet.
	 * @return a Map of parameters to apply to the transformation process
	 * @deprecated as of Spring 2.0.4, in favor of the
	 * {@link #getParameters(HttpServletRequest)} variant
	 */
	protected Map getParameters() {
		return null;
	}

	/**
	 * Return whether to use a <code>java.io.Writer to write text content
	 * to the HTTP response. Else, a <code>java.io.OutputStream will be used,
	 * to write binary content to the response.
	 * <p>The default implementation returns false, indicating a
	 * a <code>java.io.OutputStream.
	 * @return whether to use a Writer (<code>true) or an OutputStream
	 * (<code>false)
	 * @see javax.servlet.ServletResponse#getWriter()
	 * @see javax.servlet.ServletResponse#getOutputStream()
	 */
	protected boolean useWriter() {
		return false;
	}


	/**
	 * Perform the actual transformation, writing to the given result.
	 * @param source the Source to transform
	 * @param parameters a Map of parameters to be applied to the stylesheet
	 * (as determined by {@link #getParameters(Map, HttpServletRequest)})
	 * @param result the result to write to
	 * @param encoding the preferred character encoding that the underlying Transformer should use
	 * @throws Exception if an error occurs
	 */
	protected void doTransform(Source source, Map parameters, Result result, String encoding)
			throws Exception {

		try {
			Transformer trans = buildTransformer(parameters);

			// Explicitly apply URIResolver to every created Transformer.
			if (this.uriResolver != null) {
				trans.setURIResolver(this.uriResolver);
			}

			// Specify default output properties.
			trans.setOutputProperty(OutputKeys.ENCODING, encoding);
			if (this.indent) {
				TransformerUtils.enableIndenting(trans);
			}

			// Apply any arbitrary output properties, if specified.
			if (this.outputProperties != null) {
				Enumeration propsEnum = this.outputProperties.propertyNames();
				while (propsEnum.hasMoreElements()) {
					String propName = (String) propsEnum.nextElement();
					trans.setOutputProperty(propName, this.outputProperties.getProperty(propName));
				}
			}

			// Perform the actual XSLT transformation.
			trans.transform(source, result);
		}
		catch (TransformerConfigurationException ex) {
			throw new NestedServletException(
					"Couldn't create XSLT transformer in XSLT view with name [" + getBeanName() + "]", ex);
		}
		catch (TransformerException ex) {
			throw new NestedServletException(
					"Couldn't perform transform in XSLT view with name [" + getBeanName() + "]", ex);
		}
	}

	/**
	 * Build a Transformer object for immediate use, based on the
	 * given parameters.
	 * @param parameters a Map of parameters to be applied to the stylesheet
	 * (as determined by {@link #getParameters(Map, HttpServletRequest)})
	 * @return the Transformer object (never <code>null)
	 * @throws TransformerConfigurationException if the Transformer object
	 * could not be built
	 */
	protected Transformer buildTransformer(Map parameters) throws TransformerConfigurationException {
		Templates templates = getTemplates();
		Transformer transformer =
				(templates != null ? templates.newTransformer() : getTransformerFactory().newTransformer());
		applyTransformerParameters(parameters, transformer);
		return transformer;
	}

	/**
	 * Obtain the Templates object to use, based on the configured
	 * stylesheet, either a cached one or a freshly built one.
	 * <p>Subclasses may override this method e.g. in order to refresh
	 * the Templates instance, calling {@link #resetCachedTemplates()}
	 * before delegating to this <code>getTemplates() implementation.
	 * @return the Templates object (or <code>null if there is
	 * no stylesheet specified)
	 * @throws TransformerConfigurationException if the Templates object
	 * could not be built
	 * @see #setStylesheetLocation
	 * @see #setCache
	 * @see #resetCachedTemplates
	 */
	protected Templates getTemplates() throws TransformerConfigurationException {
		if (this.cachedTemplates != null) {
			return this.cachedTemplates;
		}
		Resource location = getStylesheetLocation();
		if (location != null) {
			Templates templates = getTransformerFactory().newTemplates(getStylesheetSource(location));
			if (this.cache) {
				this.cachedTemplates = templates;
			}
			return templates;
		}
		return null;
	}

	/**
	 * Apply the specified parameters to the given Transformer.
	 * @param parameters the transformer parameters
	 * (as determined by {@link #getParameters(Map, HttpServletRequest)})
	 * @param transformer the Transformer to aply the parameters
	 */
	protected void applyTransformerParameters(Map parameters, Transformer transformer) {
		if (parameters != null) {
			for (Iterator it = parameters.entrySet().iterator(); it.hasNext();) {
				Map.Entry entry = (Map.Entry) it.next();
				transformer.setParameter(entry.getKey().toString(), entry.getValue());
			}
		}
	}

	/**
	 * Load the stylesheet from the specified location.
	 * @param stylesheetLocation the stylesheet resource to be loaded
	 * @return the stylesheet source
	 * @throws ApplicationContextException if the stylesheet resource could not be loaded
	 */
	protected Source getStylesheetSource(Resource stylesheetLocation) throws ApplicationContextException {
		if (logger.isDebugEnabled()) {
			logger.debug("Loading XSLT stylesheet from " + stylesheetLocation);
		}
		try {
			URL url = stylesheetLocation.getURL();
			String urlPath = url.toString();
			String systemId = urlPath.substring(0, urlPath.lastIndexOf('/') + 1);
			return new StreamSource(url.openStream(), systemId);
		}
		catch (IOException ex) {
			throw new ApplicationContextException("Can't load XSLT stylesheet from " + stylesheetLocation, ex);
		}
	}

}

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