src/main/java/org/apache/velocity/tools/view/VelocityLayoutServlet.java - velocity-tools - Git at Google

 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.StringWriter;
 import javax.servlet.ServletConfig;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import org.apache.velocity.Template;
 import org.apache.velocity.context.Context;
 import org.apache.velocity.exception.MethodInvocationException;

 /**
  * Extension of the VelocityViewServlet to perform "two-pass"
  * layout rendering and allow for a customized error screen.
  *
  * @author Nathan Bubna
  * @version $Id$
  */
 public class VelocityLayoutServlet extends VelocityViewServlet
 {

     /** serial version id */
     private static final long serialVersionUID = -4521817395157483487L;

     /**
      * The velocity.properties key for specifying the
      * servlet's error template.
      */
     public static final String PROPERTY_ERROR_TEMPLATE =
         "tools.view.servlet.error.template";

     /**
      * The velocity.properties key for specifying the
      * relative directory holding layout templates.
      */
     public static final String PROPERTY_LAYOUT_DIR =
         "tools.view.servlet.layout.directory";

     /**
      * The velocity.properties key for specifying the
      * servlet's default layout template's filename.
      */
     public static final String PROPERTY_DEFAULT_LAYOUT =
         "tools.view.servlet.layout.default.template";


     /**
      * The default error template's filename.
      */
     public static final String DEFAULT_ERROR_TEMPLATE = "Error.vm";

     /**
      * The default layout directory
      */
     public static final String DEFAULT_LAYOUT_DIR = "layout/";

     /**
      * The default filename for the servlet's default layout
      */
     public static final String DEFAULT_DEFAULT_LAYOUT = "Default.vm";


     /**
      * The context key that will hold the content of the screen.
      *
      * This key ($screen_content) must be present in the layout
      * template for the current screen to be rendered.
      */
     public static final String KEY_SCREEN_CONTENT = "screen_content";

     /**
      * The context/parameter key used to specify an alternate
      * layout to be used for a request instead of the default layout.
      */
     public static final String KEY_LAYOUT = "layout";


     /**
      * The context key that holds the {@link Throwable} that
      * broke the rendering of the requested screen.
      */
     public static final String KEY_ERROR_CAUSE = "error_cause";

     /**
      * The context key that holds the stack trace of the error that
      * broke the rendering of the requested screen.
      */
     public static final String KEY_ERROR_STACKTRACE = "stack_trace";

     /**
      * The context key that holds the {@link MethodInvocationException}
      * that broke the rendering of the requested screen.
      *
      * If this value is placed in the context, then $error_cause
      * will hold the error that this invocation exception is wrapping.
      */
     public static final String KEY_ERROR_INVOCATION_EXCEPTION = "invocation_exception";


     protected String errorTemplate;
     protected String layoutDir;
     protected String defaultLayout;

     /**
      * Initializes Velocity, the view servlet and checks for changes to
      * the initial layout configuration.
      *
      * @param config servlet configuration parameters
      */
     public void init(ServletConfig config) throws ServletException
     {
         // first do VVS' init()
         super.init(config);

         // check for default template path overrides
         errorTemplate =
             getVelocityProperty(PROPERTY_ERROR_TEMPLATE, DEFAULT_ERROR_TEMPLATE);
         layoutDir =
             getVelocityProperty(PROPERTY_LAYOUT_DIR, DEFAULT_LAYOUT_DIR);
         defaultLayout =
             getVelocityProperty(PROPERTY_DEFAULT_LAYOUT, DEFAULT_DEFAULT_LAYOUT);

         // preventive error checking! directory must end in /
         if (!layoutDir.endsWith("/"))
         {
             layoutDir += '/';
         }

         // log the current settings
         getLog().info("VelocityLayoutServlet: Error screen is '"+errorTemplate+"'");
         getLog().info("VelocityLayoutServlet: Layout directory is '"+layoutDir+"'");
         getLog().info("VelocityLayoutServlet: Default layout template is '"+defaultLayout+"'");

         // for efficiency's sake, make defaultLayout a full path now
         defaultLayout = layoutDir + defaultLayout;
     }


     /**
      * Overrides VelocityViewServlet to check the request for
      * an alternate layout
      *
      * @param ctx context for this request
      * @param request client request
      */
     protected void fillContext(Context ctx, HttpServletRequest request)
     {
         String layout = findLayout(request);
         if (layout != null)
         {
             // let the template know what its new layout is
             ctx.put(KEY_LAYOUT, layout);
         }
     }

     /**
      * Searches for a non-default layout to be used for this request.
      * This implementation checks the request parameters and attributes.
      */
     protected String findLayout(HttpServletRequest request)
     {
         // check if an alternate layout has been specified
         // by way of the request parameters
         String layout = request.getParameter(KEY_LAYOUT);
         // also look in the request attributes
         if (layout == null)
         {
             layout = (String)request.getAttribute(KEY_LAYOUT);
         }
         return layout;
     }

     /**
      * Overrides VelocityViewServlet.mergeTemplate to do a two-pass
      * render for handling layouts
      */
     protected void mergeTemplate(Template template, Context context,
                                  HttpServletResponse response)
         throws IOException
     {
         //
         // this section is based on Tim Colson's "two pass render"
         //
         // Render the screen content
         StringWriter sw = new StringWriter();
         template.merge(context, sw);
         // Add the resulting content to the context
         context.put(KEY_SCREEN_CONTENT, sw.toString());

         // Check for an alternate layout
         //
         // we check after merging the screen template so the screen
         // can overrule any layout set in the request parameters
         // by doing #set( $layout = "MyLayout.vm" )
         Object obj = context.get(KEY_LAYOUT);
         String layout = (obj == null) ? null : obj.toString();
         if (layout == null)
         {
             // no alternate, use default
             layout = defaultLayout;
         }
         else
         {
             // make it a full(er) path
             layout = layoutDir + layout;
         }

         try
         {
             //load the layout template
             template = getTemplate(layout);
         }
         catch (Exception e)
         {
             getLog().error("Can't load layout \"" + layout + "\"", e);

             // if it was an alternate layout we couldn't get...
             if (!layout.equals(defaultLayout))
             {
                 // try to get the default layout
                 // if this also fails, let the exception go
                 template = getTemplate(defaultLayout);
             }
         }

         // Render the layout template into the response
         super.mergeTemplate(template, context, response);
     }


     /**
      * Overrides VelocityViewServlet to display user's custom error template
      */
     protected void error(HttpServletRequest request,
                          HttpServletResponse response,
                          Throwable e)
     {
         try
         {
             // get a velocity context
             Context ctx = createContext(request, response);

             Throwable cause = e;

             // if it's an MIE, i want the real cause and stack trace!
             if (cause instanceof MethodInvocationException)
             {
                 // put the invocation exception in the context
                 ctx.put(KEY_ERROR_INVOCATION_EXCEPTION, e);
                 // get the real cause
                 cause = ((MethodInvocationException)e).getWrappedThrowable();
             }

             // add the cause to the context
             ctx.put(KEY_ERROR_CAUSE, cause);

             // grab the cause's stack trace and put it in the context
             StringWriter sw = new StringWriter();
             cause.printStackTrace(new java.io.PrintWriter(sw));
             ctx.put(KEY_ERROR_STACKTRACE, sw.toString());

             // retrieve and render the error template
             Template et = getTemplate(errorTemplate);
             mergeTemplate(et, ctx, response);

         }
         catch (Exception e2)
         {
             // d'oh! log this
             getLog().error("Error during error template rendering", e2);
             // then punt the original to a higher authority
             super.error(request, response, e);
         }
     }


 }
	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.StringWriter;
	import javax.servlet.ServletConfig;
	import javax.servlet.ServletException;
	import javax.servlet.http.HttpServletRequest;
	import javax.servlet.http.HttpServletResponse;
	import org.apache.velocity.Template;
	import org.apache.velocity.context.Context;
	import org.apache.velocity.exception.MethodInvocationException;

	/**
	* Extension of the VelocityViewServlet to perform "two-pass"
	* layout rendering and allow for a customized error screen.
	*
	* @author Nathan Bubna
	* @version $Id$
	*/
	public class VelocityLayoutServlet extends VelocityViewServlet
	{

	/** serial version id */
	private static final long serialVersionUID = -4521817395157483487L;

	/**
	* The velocity.properties key for specifying the
	* servlet's error template.
	*/
	public static final String PROPERTY_ERROR_TEMPLATE =
	"tools.view.servlet.error.template";

	/**
	* The velocity.properties key for specifying the
	* relative directory holding layout templates.
	*/
	public static final String PROPERTY_LAYOUT_DIR =
	"tools.view.servlet.layout.directory";

	/**
	* The velocity.properties key for specifying the
	* servlet's default layout template's filename.
	*/
	public static final String PROPERTY_DEFAULT_LAYOUT =
	"tools.view.servlet.layout.default.template";


	/**
	* The default error template's filename.
	*/
	public static final String DEFAULT_ERROR_TEMPLATE = "Error.vm";

	/**
	* The default layout directory
	*/
	public static final String DEFAULT_LAYOUT_DIR = "layout/";

	/**
	* The default filename for the servlet's default layout
	*/
	public static final String DEFAULT_DEFAULT_LAYOUT = "Default.vm";


	/**
	* The context key that will hold the content of the screen.
	*
	* This key ($screen_content) must be present in the layout
	* template for the current screen to be rendered.
	*/
	public static final String KEY_SCREEN_CONTENT = "screen_content";

	/**
	* The context/parameter key used to specify an alternate
	* layout to be used for a request instead of the default layout.
	*/
	public static final String KEY_LAYOUT = "layout";


	/**
	* The context key that holds the {@link Throwable} that
	* broke the rendering of the requested screen.
	*/
	public static final String KEY_ERROR_CAUSE = "error_cause";

	/**
	* The context key that holds the stack trace of the error that
	* broke the rendering of the requested screen.
	*/
	public static final String KEY_ERROR_STACKTRACE = "stack_trace";

	/**
	* The context key that holds the {@link MethodInvocationException}
	* that broke the rendering of the requested screen.
	*
	* If this value is placed in the context, then $error_cause
	* will hold the error that this invocation exception is wrapping.
	*/
	public static final String KEY_ERROR_INVOCATION_EXCEPTION = "invocation_exception";


	protected String errorTemplate;
	protected String layoutDir;
	protected String defaultLayout;

	/**
	* Initializes Velocity, the view servlet and checks for changes to
	* the initial layout configuration.
	*
	* @param config servlet configuration parameters
	*/
	public void init(ServletConfig config) throws ServletException
	{
	// first do VVS' init()
	super.init(config);

	// check for default template path overrides
	errorTemplate =
	getVelocityProperty(PROPERTY_ERROR_TEMPLATE, DEFAULT_ERROR_TEMPLATE);
	layoutDir =
	getVelocityProperty(PROPERTY_LAYOUT_DIR, DEFAULT_LAYOUT_DIR);
	defaultLayout =
	getVelocityProperty(PROPERTY_DEFAULT_LAYOUT, DEFAULT_DEFAULT_LAYOUT);

	// preventive error checking! directory must end in /
	if (!layoutDir.endsWith("/"))
	{
	layoutDir += '/';
	}

	// log the current settings
	getLog().info("VelocityLayoutServlet: Error screen is '"+errorTemplate+"'");
	getLog().info("VelocityLayoutServlet: Layout directory is '"+layoutDir+"'");
	getLog().info("VelocityLayoutServlet: Default layout template is '"+defaultLayout+"'");

	// for efficiency's sake, make defaultLayout a full path now
	defaultLayout = layoutDir + defaultLayout;
	}


	/**
	* Overrides VelocityViewServlet to check the request for
	* an alternate layout
	*
	* @param ctx context for this request
	* @param request client request
	*/
	protected void fillContext(Context ctx, HttpServletRequest request)
	{
	String layout = findLayout(request);
	if (layout != null)
	{
	// let the template know what its new layout is
	ctx.put(KEY_LAYOUT, layout);
	}
	}

	/**
	* Searches for a non-default layout to be used for this request.
	* This implementation checks the request parameters and attributes.
	*/
	protected String findLayout(HttpServletRequest request)
	{
	// check if an alternate layout has been specified
	// by way of the request parameters
	String layout = request.getParameter(KEY_LAYOUT);
	// also look in the request attributes
	if (layout == null)
	{
	layout = (String)request.getAttribute(KEY_LAYOUT);
	}
	return layout;
	}

	/**
	* Overrides VelocityViewServlet.mergeTemplate to do a two-pass
	* render for handling layouts
	*/
	protected void mergeTemplate(Template template, Context context,
	HttpServletResponse response)
	throws IOException
	{
	//
	// this section is based on Tim Colson's "two pass render"
	//
	// Render the screen content
	StringWriter sw = new StringWriter();
	template.merge(context, sw);
	// Add the resulting content to the context
	context.put(KEY_SCREEN_CONTENT, sw.toString());

	// Check for an alternate layout
	//
	// we check after merging the screen template so the screen
	// can overrule any layout set in the request parameters
	// by doing #set( $layout = "MyLayout.vm" )
	Object obj = context.get(KEY_LAYOUT);
	String layout = (obj == null) ? null : obj.toString();
	if (layout == null)
	{
	// no alternate, use default
	layout = defaultLayout;
	}
	else
	{
	// make it a full(er) path
	layout = layoutDir + layout;
	}

	try
	{
	//load the layout template
	template = getTemplate(layout);
	}
	catch (Exception e)
	{
	getLog().error("Can't load layout \"" + layout + "\"", e);

	// if it was an alternate layout we couldn't get...
	if (!layout.equals(defaultLayout))
	{
	// try to get the default layout
	// if this also fails, let the exception go
	template = getTemplate(defaultLayout);
	}
	}

	// Render the layout template into the response
	super.mergeTemplate(template, context, response);
	}


	/**
	* Overrides VelocityViewServlet to display user's custom error template
	*/
	protected void error(HttpServletRequest request,
	HttpServletResponse response,
	Throwable e)
	{
	try
	{
	// get a velocity context
	Context ctx = createContext(request, response);

	Throwable cause = e;

	// if it's an MIE, i want the real cause and stack trace!
	if (cause instanceof MethodInvocationException)
	{
	// put the invocation exception in the context
	ctx.put(KEY_ERROR_INVOCATION_EXCEPTION, e);
	// get the real cause
	cause = ((MethodInvocationException)e).getWrappedThrowable();
	}

	// add the cause to the context
	ctx.put(KEY_ERROR_CAUSE, cause);

	// grab the cause's stack trace and put it in the context
	StringWriter sw = new StringWriter();
	cause.printStackTrace(new java.io.PrintWriter(sw));
	ctx.put(KEY_ERROR_STACKTRACE, sw.toString());

	// retrieve and render the error template
	Template et = getTemplate(errorTemplate);
	mergeTemplate(et, ctx, response);

	}
	catch (Exception e2)
	{
	// d'oh! log this
	getLog().error("Error during error template rendering", e2);
	// then punt the original to a higher authority
	super.error(request, response, e);
	}
	}


	}