Package groovy.servlet

Class TemplateServlet

java.lang.Object
javax.servlet.GenericServlet
javax.servlet.http.HttpServlet
groovy.servlet.AbstractHttpServlet
groovy.servlet.TemplateServlet
All Implemented Interfaces:
ResourceConnector, Serializable, Servlet, ServletConfig
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:
AbstractHttpServlet.setVariables(ServletBinding), Serialized Form

  • Constructor Details

    • TemplateServlet

      public TemplateServlet()
      Create new TemplateServlet.

  • Method Details

    • getTemplate

      protected Template getTemplate​(File file) throws ServletException
      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.

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

    • getTemplate

      protected Template getTemplate​(URL url) throws ServletException
      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.

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

    • init

      public void init​(ServletConfig config) throws ServletException
      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.
      Specified by:
      init in interface Servlet
      Overrides:
      init in class AbstractHttpServlet
      Parameters:
      config - Passed by the servlet container.
      Throws:
      ServletException - if this method encountered difficulties
      See Also:
      initTemplateEngine(ServletConfig)

    • initTemplateEngine

      protected TemplateEngine initTemplateEngine​(ServletConfig config)
      Creates the template engine.

      Called by init(ServletConfig) 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.

    • service

      public void service​(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
      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.

      Overrides:
      service in class HttpServlet
      Parameters:
      request - The http request.
      response - The http response.
      Throws:
      IOException - if an input or output error occurs while the servlet is handling the HTTP request
      ServletException - if the HTTP request cannot be handled