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## org.apache.velocity.servlet
Class VelocityServlet

    java.lang.Object
      |
      +--javax.servlet.GenericServlet
            |
            +--javax.servlet.http.HttpServlet
                  |
                  +--org.apache.velocity.servlet.VelocityServlet

All Implemented Interfaces:
  java.io.Serializable, javax.servlet.Servlet, javax.servlet.ServletConfig

public abstract class VelocityServlet
extends javax.servlet.http.HttpServlet

Base class which simplifies the use of Velocity with Servlets. Extend this class, implement the `handleRequest()` method, and add your data to the context. Then call `getTemplate("myTemplate.wm")`. This class puts some things into the context object that you should be aware of:

     "req" - The HttpServletRequest object
     "res" - The HttpServletResponse object

There are other methods you can override to access, alter or control any part of the request processing chain. Please see the javadocs for more information on :

- loadConfiguration() : for setting up the Velocity runtime
- createContext() : for creating and loading the Context
- setContentType() : for changing the content type on a request by request basis
- handleRequest() : you must implement this
- mergeTemplate() : the template rendering process
- requestCleanup() : post rendering resource or other cleanup
- error() : error handling

If you put a contentType object into the context within either your serlvet or within your template, then that will be used to override the default content type specified in the properties file. "contentType" - The value for the Content-Type: header

Author:
  Dave Bryson, Jon S. Stevens, Geir Magnusson Jr., Kent Johnson $Id: VelocityServlet.java,v 1.44 2002/02/06 23:42:01 dlr Exp $
See Also:
  Serialized Form

Field Summary
`static java.lang.String` | `CONTENT_TYPE` The HTTP content type context key.
`static java.lang.String` | `DEFAULT_CONTENT_TYPE` The default content type for the response
`static java.lang.String` | `DEFAULT_OUTPUT_ENCODING` Encoding for the output stream
`private static java.lang.String` | `defaultContentType` The default content type.
`private static java.lang.String` | `encoding` The encoding to use when generating outputing.
`protected static java.lang.String` | `INIT_PROPS_KEY` This is the string that is looked for when getInitParameter is called.
`static java.lang.String` | `REQUEST` The HTTP request object context key.
`static java.lang.String` | `RESPONSE` The HTTP response object context key.
`private static SimplePool` | `writerPool` Cache of writers

Fields inherited from class javax.servlet.http.HttpServlet
`HEADER_IFMODSINCE, HEADER_LASTMOD, LSTRING_FILE, lStrings, METHOD_DELETE, METHOD_GET, METHOD_HEAD, METHOD_OPTIONS, METHOD_POST, METHOD_PUT, METHOD_TRACE`

Fields inherited from class javax.servlet.GenericServlet
`config`

Constructor Summary
`VelocityServlet()`

Method Summary
`protected Context` | `createContext(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Returns a context suitable to pass to the handleRequest() method Default implementation will create a VelocityContext object, put the HttpServletRequest and HttpServletResponse into the context accessable via the keys VelocityServlet.REQUEST and VelocityServlet.RESPONSE, respectively.
`void` | `doGet(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Handles GET - calls doRequest()
`void` | `doPost(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Handle a POST request - calls doRequest()
`protected void` | `doRequest(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Handles all requests
`protected void` | `error(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, java.lang.Exception cause)` Invoked when there is an error thrown in any part of doRequest() processing.
`Template` | `getTemplate(java.lang.String name)` Retrieves the requested template.
`Template` | `getTemplate(java.lang.String name, java.lang.String encoding)` Retrieves the requested template with the specified character encoding.
`protected Template` | `handleRequest(Context ctx)` Deprecated. Use `handleRequest( HttpServletRequest request, HttpServletResponse response, Context ctx )`
`protected Template` | `handleRequest(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, Context ctx)` Implement this method to add your application data to the context, calling the `getTemplate()` method to produce your return value.
`void` | `init(javax.servlet.ServletConfig config)` Performs initialization of this servlet.
`protected void` | `initVelocity(javax.servlet.ServletConfig config)` Initializes the Velocity runtime, first calling loadConfiguration(ServletConvig) to get a java.util.Properties of configuration information and then calling Velocity.init().
`protected java.util.Properties` | `loadConfiguration(javax.servlet.ServletConfig config)` Loads the configuration information and returns that information as a Properties, which will be used to initialize the Velocity runtime.
`protected void` | `mergeTemplate(Template template, Context context, javax.servlet.http.HttpServletResponse response)` merges the template with the context.
`protected void` | `requestCleanup(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, Context context)` 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
`protected void` | `setContentType(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)` Sets the content type of the response.

Methods inherited from class javax.servlet.http.HttpServlet
`, doDelete, doHead, doOptions, doPut, doTrace, getAllDeclaredMethods, getLastModified, maybeSetLastModified, service, service`

Methods inherited from class javax.servlet.GenericServlet
`destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, log, log`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, registerNatives, toString, wait, wait, wait`

Field Detail

### REQUEST

    public static final java.lang.String REQUEST

  The HTTP request object context key.

### RESPONSE

    public static final java.lang.String RESPONSE

  The HTTP response object context key.

### CONTENT_TYPE

    public static final java.lang.String CONTENT_TYPE

  The HTTP content type context key.

### DEFAULT_CONTENT_TYPE

    public static final java.lang.String DEFAULT_CONTENT_TYPE

  The default content type for the response

### DEFAULT_OUTPUT_ENCODING

    public static final java.lang.String DEFAULT_OUTPUT_ENCODING

  Encoding for the output stream

### encoding

    private static java.lang.String encoding

  The encoding to use when generating outputing.

### defaultContentType

    private static java.lang.String defaultContentType

  The default content type.

### INIT_PROPS_KEY

    protected static final java.lang.String INIT_PROPS_KEY

  This is the string that is looked for when getInitParameter is called.

### writerPool

    private static SimplePool writerPool

  Cache of writers

Constructor Detail

### VelocityServlet

    public VelocityServlet()

Method Detail

### init

    public void init(javax.servlet.ServletConfig config)
              throws javax.servlet.ServletException

  Performs initialization of this servlet. Called by the servlet container on loading.
  Overrides:
    `init` in class `javax.servlet.GenericServlet`
  Parameters:
    `config` - The servlet configuration to apply.
  Throws:
    `javax.servlet.ServletException` -

### initVelocity

    protected void initVelocity(javax.servlet.ServletConfig config)
                         throws javax.servlet.ServletException

  Initializes the Velocity runtime, first calling loadConfiguration(ServletConvig) to get a java.util.Properties of configuration information and then calling Velocity.init(). Override this to do anything to the environment before the initialization of the singelton takes place, or to initialize the singleton in other ways.

### loadConfiguration

    protected java.util.Properties loadConfiguration(javax.servlet.ServletConfig config)
                                              throws java.io.IOException,
                                                     java.io.FileNotFoundException

  Loads the configuration information and returns that information as a Properties, which will be used to initialize the Velocity runtime.
  Currently, this method gets the initialization parameter VelocityServlet.INIT_PROPS_KEY, which should be a file containing the configuration information.
  To configure your Servlet Spec 2.2 compliant servlet runner to pass this to you, put the following in your WEB-INF/web.xml file

          <servlet>
            <servlet-name> YourServlet </servlet-name>
            <servlet-class> your.package.YourServlet </servlet-class>
            <init-param>
               <param-name> properties </param-name>
               <param-value> velocity.properties </param-value>
            </init-param>
          </servlet>

  Alternately, if you wish to configure an entire context in this fashion, you may use the following:

          <context-param>
             <param-name> properties </param-name>
             <param-value> velocity.properties </param-value>
             <description> Path to Velocity configuration </description>
          </context-param>

  Derived classes may do the same, or take advantage of this code to do the loading for them via :

            Properties p = super.loadConfiguration( config );

  and then add or modify the configuration values from the file.
  Parameters:
    `config` - ServletConfig passed to the servlets init() function Can be used to access the real path via ServletContext (hint)
  Returns:
    java.util.Properties loaded with configuration values to be used to initialize the Velocity runtime.
  Throws:
    `java.io.FileNotFoundException` - if a specified file is not found.
    `java.io.IOException` - I/O problem accessing the specified file, if specified.

### doGet

    public void doGet(javax.servlet.http.HttpServletRequest request,
                      javax.servlet.http.HttpServletResponse response)
               throws javax.servlet.ServletException,
                      java.io.IOException

  Handles GET - calls doRequest()
  Overrides:
    `doGet` in class `javax.servlet.http.HttpServlet`

### doPost

    public void doPost(javax.servlet.http.HttpServletRequest request,
                       javax.servlet.http.HttpServletResponse response)
                throws javax.servlet.ServletException,
                       java.io.IOException

  Handle a POST request - calls doRequest()
  Overrides:
    `doPost` in class `javax.servlet.http.HttpServlet`

### doRequest

    protected void doRequest(javax.servlet.http.HttpServletRequest request,
                             javax.servlet.http.HttpServletResponse response)
                      throws javax.servlet.ServletException,
                             java.io.IOException

  Handles all requests
  Parameters:
    `request` - HttpServletRequest object containing client request
    `response` - HttpServletResponse object for the response

### requestCleanup

    protected void requestCleanup(javax.servlet.http.HttpServletRequest request,
                                  javax.servlet.http.HttpServletResponse response,
                                  Context context)

  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
  Parameters:
    `request` - servlet request from client
    `response` - servlet reponse
    `context` - context created by the createContext() method

### mergeTemplate

    protected void mergeTemplate(Template template,
                                 Context context,
                                 javax.servlet.http.HttpServletResponse response)
                          throws ResourceNotFoundException,
                                 ParseErrorException,
                                 MethodInvocationException,
                                 java.io.IOException,
                                 java.io.UnsupportedEncodingException,
                                 java.lang.Exception

  merges the template with the context. Only override this if you really, really really need to. (And don't call us with questions if it breaks :)
  Parameters:
    `template` - template object returned by the handleRequest() method
    `context` - context created by the createContext() method
    `response` - servlet reponse (use this to get the output stream or Writer

### setContentType

    protected void setContentType(javax.servlet.http.HttpServletRequest request,
                                  javax.servlet.http.HttpServletResponse response)

  Sets the content type of the response. This is available to be overriden by a derived class. The default implementation is : response.setContentType( defaultContentType ); where defaultContentType is set to the value of the default.contentType property, or "text/html" if that is not set.
  Parameters:
    `request` - servlet request from client
    `response` - servlet reponse to client

### createContext

    protected Context createContext(javax.servlet.http.HttpServletRequest request,
                                    javax.servlet.http.HttpServletResponse response)

  Returns a context suitable to pass to the handleRequest() method
  Default implementation will create a VelocityContext object, put the HttpServletRequest and HttpServletResponse into the context accessable via the keys VelocityServlet.REQUEST and VelocityServlet.RESPONSE, respectively.
  Parameters:
    `request` - servlet request from client
    `response` - servlet reponse to client
  Returns:
    context

### getTemplate

    public Template getTemplate(java.lang.String name)
                         throws ResourceNotFoundException,
                                ParseErrorException,
                                java.lang.Exception

  Retrieves the requested template.
  Parameters:
    `name` - The file name of the template to retrieve relative to the template root.
  Returns:
    The requested template.
  Throws:
    `ResourceNotFoundException` - if template not found from any available source.
    `ParseErrorException` - if template cannot be parsed due to syntax (or other) error.
    `java.lang.Exception` - if an error occurs in template initialization

### getTemplate

    public Template getTemplate(java.lang.String name,
                                java.lang.String encoding)
                         throws ResourceNotFoundException,
                                ParseErrorException,
                                java.lang.Exception

  Retrieves the requested template with the specified character encoding.
  Parameters:
    `name` - The file name of the template to retrieve relative to the template root.
    `encoding` - the character encoding of the template
  Returns:
    The requested template.
  Throws:
    `ResourceNotFoundException` - if template not found from any available source.
    `ParseErrorException` - if template cannot be parsed due to syntax (or other) error.
    `java.lang.Exception` - if an error occurs in template initialization
  Since:
    Velocity v1.1

### handleRequest

    protected Template handleRequest(javax.servlet.http.HttpServletRequest request,
                                     javax.servlet.http.HttpServletResponse response,
                                     Context ctx)
                              throws java.lang.Exception

  Implement this method to add your application data to the context, calling the `getTemplate()` method to produce your return value.
  In the event of a problem, you may handle the request directly and return `null` or throw a more meaningful exception for the error handler to catch.
  Parameters:
    `request` - servlet request from client
    `response` - servlet reponse
    `ctx` - The context to add your data to.
  Returns:
    The template to merge with your context or null, indicating that you handled the processing.
  Since:
    Velocity v1.1

### handleRequest

    protected Template handleRequest(Context ctx)
                              throws java.lang.Exception

  Deprecated. Use `handleRequest( HttpServletRequest request, HttpServletResponse response, Context ctx )`

  Implement this method to add your application data to the context, calling the `getTemplate()` method to produce your return value.
  In the event of a problem, you may simple return `null` or throw a more meaningful exception.
  Parameters:
    `ctx` - The context to add your data to.
  Returns:
    The template to merge with your context.

### error

    protected void error(javax.servlet.http.HttpServletRequest request,
                         javax.servlet.http.HttpServletResponse response,
                         java.lang.Exception cause)
                  throws javax.servlet.ServletException,
                         java.io.IOException

  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.
  Parameters:
    `request` - original HttpServletRequest from servlet container.
    `response` - HttpServletResponse object from servlet container.
    `cause` - Exception that was thrown by some other part of process.

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Copyright © 2003 Apache Software Foundation. All Rights Reserved.