[Java] Class TemplateServlet

  • groovy.servlet.TemplateServlet 
public class TemplateServlet
extends AbstractHttpServlet

A generic servlet for serving (mostly HTML) templates.

It delegates work to a groovy.text.TemplateEngine implementation processing HTTP requests.

Usage

helloworld.html is a headless HTML-like template 


  <html>
    <body>
      <% 3.times { %>
        Hello World!
      <% } %>
      <br>
    </body>
  </html>

Minimal web.xml example serving HTML-like templates 


 <web-app>
   <servlet>
     <servlet-name>template</servlet-name>
     <servlet-class>groovy.servlet.TemplateServlet</servlet-class>
   </servlet>
   <servlet-mapping>
     <servlet-name>template</servlet-name>
     <url-pattern>*.html</url-pattern>
   </servlet-mapping>
 </web-app>

Template engine configuration

By default, the TemplateServer uses the SimpleTemplateEngine which interprets JSP-like templates. The init parameter template.engine defines the fully qualified class name of the template to use: 

   template.engine = [empty] - equals groovy.text.SimpleTemplateEngine
   template.engine = groovy.text.SimpleTemplateEngine
   template.engine = groovy.text.GStringTemplateEngine
   template.engine = groovy.text.XmlTemplateEngine

Servlet Init Parameters

Logging and extra-output options

This implementation provides a verbosity flag switching log statements. The servlet init parameter name is: 

   generated.by = true(default) | false

Groovy Source Encoding Parameter

The following servlet init parameter name can be used to specify the encoding TemplateServlet will use to read the template groovy source files: 

   groovy.source.encoding
See Also:
TemplateServlet.setVariables
Inherited fields
Fields inherited from class Fields
class AbstractHttpServlet CONTENT_TYPE_TEXT_HTML, INC_PATH_INFO, INC_REQUEST_URI, INC_SERVLET_PATH, INIT_PARAM_RESOURCE_NAME_REGEX, INIT_PARAM_RESOURCE_NAME_REGEX_FLAGS, encoding, namePrefix, reflection, resourceNamePattern, resourceNameReplaceAll, resourceNameReplacement, servletContext, verbose

Constructor Summary

Constructors
Constructor and description
TemplateServlet ()
Create new TemplateServlet.

Methods Summary

Methods
Type Params Return Type Name and description
protected Template getTemplate(File file)
Gets the template created by the underlying engine parsing the request.
protected Template getTemplate(URL url)
Gets the template created by the underlying engine parsing the request.
public void init(ServletConfig config)
Initializes the servlet from hints the container passes.
protected TemplateEngine initTemplateEngine(ServletConfig config)
Creates the template engine.
public void service(HttpServletRequest request, HttpServletResponse response)
Services the request with a response.

Inherited Methods Summary

Inherited Methods
Methods inherited from class Name
class AbstractHttpServlet applyResourceNameMatcher, generateNamePrefixOnce, getResourceConnection, getScriptUri, getScriptUriAsFile, init, removeNamePrefix, setVariables

Constructor Detail

public TemplateServlet()

Create new TemplateServlet.

Method Detail

protected Template getTemplate(File file)

Gets the template created by the underlying engine parsing the request.

This method looks up a simple (weak) hash map for an existing template object that matches the source file. If the source file didn't change in length and its last modified stamp hasn't changed compared to a precompiled template object, this template is used. Otherwise, there is no or an invalid template object cache entry, a new one is created by the underlying template engine. This new instance is put to the cache for consecutive calls.

throws:
ServletException If the request specified an invalid template source file
Returns:
The template that will produce the response text.
Parameters:
file - The file containing the template source.

protected Template getTemplate(URL url)

Gets the template created by the underlying engine parsing the request.

This method looks up a simple (weak) hash map for an existing template object that matches the source URL. If there is no cache entry, a new one is created by the underlying template engine. This new instance is put to the cache for consecutive calls.

throws:
ServletException If the request specified an invalid template source URL
Returns:
The template that will produce the response text.
Parameters:
url - The URL containing the template source..

public void init(ServletConfig config)

Initializes the servlet from hints the container passes.

Delegates to sub-init methods and parses the following parameters:

  • "generatedBy" : boolean, appends "Generated by ..." to the HTML response text generated by this servlet.
throws:
ServletException if this method encountered difficulties
Parameters:
config - Passed by the servlet container.
See Also:
TemplateServlet.initTemplateEngine

protected TemplateEngine initTemplateEngine(ServletConfig config)

Creates the template engine.

Called by TemplateServlet.init and returns just new groovy.text.SimpleTemplateEngine() if the init parameter template.engine is not set by the container configuration.

Parameters:
config - Current servlet configuration passed by the container.
Returns:
The underlying template engine or null on error.

public void service(HttpServletRequest request, HttpServletResponse response)

Services the request with a response.

First the request is parsed for the source file uri. If the specified file could not be found or can not be read an error message is sent as response.

throws:
IOException if an input or output error occurs while the servlet is handling the HTTP request
throws:
ServletException if the HTTP request cannot be handled
Parameters:
request - The http request.
response - The http response.

© 2003-2020 The Apache Software Foundation
Licensed under the Apache license.
https://docs.groovy-lang.org/3.0.7/html/gapi/groovy/servlet/TemplateServlet.html