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Tools to be used in a servlet context.
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package org.apache.velocity.tools.view;
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.slf4j.Logger;
import org.apache.velocity.Template;
import org.apache.velocity.context.Context;
import org.apache.velocity.exception.MethodInvocationException;
import org.apache.velocity.exception.ResourceNotFoundException;
import org.apache.velocity.runtime.RuntimeConstants;
import org.apache.commons.lang3.StringEscapeUtils;
/**
* A servlet to process Velocity templates. This is comparable to the
* the JspServlet for JSP-based applications.
*
* The servlet provides the following features:
*
* - renders Velocity templates
* - provides support for an auto-loaded, configurable toolbox
* - provides transparent access to the servlet request attributes,
* servlet session attributes and servlet context attributes by
* auto-searching them
* - logs to the logging facility of the servlet API
*
*
* VelocityViewServlet supports the following configuration parameters
* in web.xml:
*
* - org.apache.velocity.tools
* - Path and name of the toolbox configuration file. The path must be
* relative to the web application root directory. If this parameter is
* not found, the servlet will check for a toolbox file at
* '/WEB-INF/tools.xml'.
* - org.apache.velocity.properties
* - Path and name of the Velocity configuration file. The path must be
* relative to the web application root directory. If this parameter
* is not present, Velocity will check for a properties file at
* '/WEB-INF/velocity.properties'. If no file is found there, then
* Velocity is initialized with the settings in the classpath at
* 'org.apache.velocity.tools.view.velocity.properties'.
* - org.apache.velocity.tools.shared.config
* - By default, this is {@code true}. If set to {@code false}, then
* the {@link VelocityView} used by this servlet will not be shared
* with {@link VelocityViewFilter}s, other VelocityViewServlets or
* org.apache.velocity.tools.view.jsp.VelocityViewTag's in the
* application.
* - org.apache.velocity.tools.loadDefaults
* - By default, this is {@code true}. If set to {@code false}, then
* the default toolbox configuration will not be added to your (if any)
* custom configuration.
* - org.apache.velocity.tools.cleanConfiguration
* - By default, this is {@code false}. If set to {@code true}, then
* then the final toolbox configuration (the combination of any custom
* one(s) provided by yourself and/or the default configuration(s))
* will have all invalid tools, properties, and/or data removed prior to
* configuring the ToolboxFactory for this servlet by a
* {@link org.apache.velocity.tools.config.ConfigurationCleaner}
* - org.apache.velocity.tools.bufferOutput
* - By default, the processed templates are merged directly into
* the {@link HttpServletResponse}'s writer. If this parameter is
* set to {@code true}, then the output of the merge process will be
* buffered before being fed to the response. This allows the {@link #error}
* method to be overridden to return a "500 Internal Server Error" or
* at least not return any of the failed request content. Essentially,
* setting this to {@code true} degrades performance in order to enable
* a more "correct" error response"
* - org.apache.velocity.tools.view.class
* - Allows to specify a custom class (inheriting from VelocityView) as
* the View class.
*
*
* @version $Id$
*/
public class VelocityViewServlet extends HttpServlet
{
public static final String BUFFER_OUTPUT_PARAM =
"org.apache.velocity.tools.bufferOutput";
private static final long serialVersionUID = -3329444102562079189L;
private transient VelocityView view;
private boolean bufferOutput = false;
/**
* Initializes servlet and VelocityView used to process requests.
* Called by the servlet container on loading.
*
* @param config servlet configuation
*/
public void init(ServletConfig config) throws ServletException
{
super.init(config);
// init the VelocityView (if it hasn't been already)
getVelocityView();
String buffer = findInitParameter(config, BUFFER_OUTPUT_PARAM);
if (buffer != null && buffer.equals("true"))
{
this.bufferOutput = true;
getLog().debug("VelocityViewServlet will buffer mergeTemplate output.");
}
}
/**
* Looks up an init parameter with the specified key in either the
* ServletConfig or, failing that, in the ServletContext.
* @param config servlet config
* @param key parameter key
* @return parameter value or null
*/
protected String findInitParameter(ServletConfig config, String key)
{
// check the servlet config
String param = config.getInitParameter(key);
if (param == null || param.length() == 0)
{
// check the servlet context
ServletContext servletContext = config.getServletContext();
param = servletContext.getInitParameter(key);
}
return param;
}
protected VelocityView getVelocityView()
{
if (this.view == null)
{
setVelocityView(ServletUtils.getVelocityView(getServletConfig()));
assert (this.view != null);
}
return this.view;
}
protected void setVelocityView(VelocityView view)
{
this.view = view;
}
protected String getVelocityProperty(String name, String alternate)
{
return getVelocityView().getProperty(name, alternate);
}
protected Logger getLog()
{
return getVelocityView().getLog();
}
/**
* Handles GET - calls doRequest()
* @param request servlet request
* @param response servlet response
* @throws ServletException from underlying call
* @throws IOException from underlying call
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
doRequest(request, response);
}
/**
* Handle a POST request - calls doRequest()
* @param request servlet request
* @param response servlet response
* @throws ServletException from underlying call
* @throws IOException from underlying call
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
doRequest(request, response);
}
/**
* Handles with both GET and POST requests
*
* @param request HttpServletRequest object containing client request
* @param response HttpServletResponse object for the response
* @throws IOException from underlying processing
*/
protected void doRequest(HttpServletRequest request, HttpServletResponse response)
throws IOException
{
Context context = null;
try
{
// prepare needed request and response attributes and properties
initRequest(request, response);
// then get a context
context = createContext(request, response);
// call standard extension point
fillContext(context, request);
setContentType(request, response);
// get the template
Template template = handleRequest(request, response, context);
// merge the template and context into the response
mergeTemplate(template, context, request, response);
} catch (IOException e) {
error(request, response, e);
throw e;
}
catch (ResourceNotFoundException e)
{
manageResourceNotFound(request, response, e);
}
catch (RuntimeException e)
{
error(request, response, e);
throw e;
}
finally
{
requestCleanup(request, response, context);
}
}
/**
*
* Request and response initialization. Default version does
* only one thing: set request POST parameters encoding to
* Velocity input encoding.
*
*
* @param request HttpServletRequest object containing client request
* @param response HttpServletResponse object for the response
* @throws IOException if thrown by underlying handling
*/
protected void initRequest(HttpServletRequest request, HttpServletResponse response) throws IOException
{
// adjust HTTP encoding: use value provided for input.encoding
// (this affects POST parameters only;
// to adjust GET URI and parameters encoding, please refer to your
// J2EE container documentation (for instance, under tomcat,
// use )
try
{
request.setCharacterEncoding(getVelocityProperty(RuntimeConstants.INPUT_ENCODING, RuntimeConstants.ENCODING_DEFAULT));
}
catch (UnsupportedEncodingException uee)
{
error(request, response, uee);
throw uee;
}
}
/**
* This was a common extension point, but now it is usually
* simpler to override {@link #fillContext} to add custom things
* to the {@link Context} or override a {@link #getTemplate}
* method to change how {@link Template}s are retrieved.
* This is only recommended for more complicated use-cases.
*
* @param request client request
* @param response client response
* @param ctx VelocityContext to fill
* @return Velocity Template object or null
*/
protected Template handleRequest(HttpServletRequest request,
HttpServletResponse response,
Context ctx)
{
return getTemplate(request, response);
}
/**
* Get a configured Velocity context for the current request and response
* @param request client request
* @param response client response
* @return configured context
*/
protected Context createContext(HttpServletRequest request,
HttpServletResponse response)
{
return getVelocityView().createContext(request, response);
}
/**
* Standard extension point to populate the context with additional entries
* @param context target context
* @param request client request
*/
protected void fillContext(Context context, HttpServletRequest request)
{
// this implementation does nothing
}
/**
* Sets the content type of the response. This is available to be overriden
* by a derived class.
*
* The default implementation is :
*
* response.setContentType(getVelocityView().getDefaultContentType());
*
* where defaultContentType is set to the value of the default.contentType
* property, or "text/html" if that was not set for the {@link VelocityView}.
*
*
* @param request servlet request from client
* @param response servlet reponse to client
*/
protected void setContentType(HttpServletRequest request,
HttpServletResponse response)
{
response.setContentType(getVelocityView().getDefaultContentType());
}
/**
* Get a template by client request and response
* @param request client request
* @param response client response
* @return found template
*/
protected Template getTemplate(HttpServletRequest request,
HttpServletResponse response)
{
return getVelocityView().getTemplate(request);
}
/**
* Get a template by name
* @param name template name
* @return found template
*/
protected Template getTemplate(String name)
{
return getVelocityView().getTemplate(name);
}
/**
* Merge template
* @param template input template
* @param context Velocity context
* @param request client request
* @param response client response
* @throws IOException
*/
protected void mergeTemplate(Template template, Context context, HttpServletRequest request, HttpServletResponse response)
throws IOException
{
Writer writer = getOutputWriter(request, response);
getVelocityView().merge(template, context, writer);
Boolean buffered = request == null ? Boolean.FALSE : (Boolean)request.getAttribute(BUFFER_OUTPUT_PARAM);
if (buffered != null && buffered)
{
response.getWriter().write(writer.toString());
}
}
/**
* Get the output stream writer to use. If the writer is to be written afterwards to the response writer
* (as when org.apache.velocity.tools.bufferOutput is true), this method must set the
* org.apache.velocity.tools.bufferOutput request attribute to true.
* @param request
* @param response
* @return
* @throws IOException
*/
protected Writer getOutputWriter(HttpServletRequest request, HttpServletResponse response)
throws IOException
{
Writer writer;
if (this.bufferOutput)
{
writer = new StringWriter();
request.setAttribute(BUFFER_OUTPUT_PARAM, true);
}
else
{
writer = response.getWriter();
}
return writer;
}
/**
* Merge template
* @param template target template
* @param context client request
* @param response client response
* @throws IOException
* @deprecated see {{@link #mergeTemplate(Template, Context, HttpServletRequest, HttpServletResponse)}}
*/
@Deprecated
protected void mergeTemplate(Template template, Context context, HttpServletResponse response)
throws IOException
{
mergeTemplate(template, context, null, response);
}
/**
* Invoked when there is an error thrown in any part of doRequest() processing.
*
* Default will send a simple HTML response indicating there was a problem.
*
* @param request original HttpServletRequest from servlet container.
* @param response HttpServletResponse object from servlet container.
* @param e Exception that was thrown by some other part of process.
*/
protected void error(HttpServletRequest request,
HttpServletResponse response,
Throwable e)
{
String path = ServletUtils.getPath(request);
if (response.isCommitted())
{
getLog().error("An error occured but the response headers have already been sent.");
getLog().error("Error processing a template for path '{}'", path, e);
return;
}
try
{
getLog().error("Error processing a template for path '{}'", path, e);
StringBuilder html = new StringBuilder();
html.append("\n");
html.append("Error \n");
html.append("\n");
html.append("VelocityView : Error processing a template for path '");
html.append(StringEscapeUtils.escapeHtml4(path));
html.append("'
\n");
Throwable cause = e;
String why = cause.getMessage();
if (why != null && why.length() > 0)
{
html.append(StringEscapeUtils.escapeHtml4(why));
html.append("\n
\n");
}
//TODO: add line/column/template info for parse errors et al
// if it's an MIE, i want the real stack trace!
if (cause instanceof MethodInvocationException)
{
// get the real cause
cause = cause.getCause();
}
StringWriter sw = new StringWriter();
cause.printStackTrace(new PrintWriter(sw));
html.append("\n");
html.append(StringEscapeUtils.escapeHtml4(sw.toString()));
html.append("\n");
html.append("\n");
html.append("");
response.getWriter().write(html.toString());
}
catch (Exception e2)
{
// clearly something is quite wrong.
// let's log the new exception then give up and
// throw a runtime exception that wraps the first one
String msg = "Exception while printing error screen";
getLog().error(msg, e2);
throw new RuntimeException(msg, e);
}
}
/**
* Manages the {@link ResourceNotFoundException} to send an HTTP 404 result
* when needed.
*
* @param request The request object.
* @param response The response object.
* @param e The exception to check.
* @throws IOException If something goes wrong when sending the HTTP error.
*/
protected void manageResourceNotFound(HttpServletRequest request,
HttpServletResponse response, ResourceNotFoundException e)
throws IOException
{
String path = ServletUtils.getPath(request);
getLog().debug("Resource not found for path '{}'", path, e);
String message = e.getMessage();
if (!response.isCommitted() && path != null &&
message != null && message.contains("'" + path + "'"))
{
response.sendError(HttpServletResponse.SC_NOT_FOUND, path);
}
else
{
error(request, response, e);
throw e;
}
}
/**
* Cleanup routine called at the end of the request processing sequence
* allows a derived class to do resource cleanup or other end of
* process cycle tasks. This default implementation does nothing.
*
* @param request servlet request from client
* @param response servlet response
* @param context Context that was merged with the requested template
*/
protected void requestCleanup(HttpServletRequest request,
HttpServletResponse response,
Context context)
{
}
}
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