Default Servlet Reference

 

 

Introduction

 This discusses different ways to manipulate the default servlet. Topics are

 

What is the DefaultServlet

 The default servlet is the servlet which serves static resources as well as serves the directory listings (if directory listings are enabled).

 

Where is it declared?

 It is declared globally in $CATALINA_HOME/conf/web.xml. By default here is it's declaration: 
    <servlet>
        <servlet-name>default</servlet-name>
        <servlet-class>
          org.apache.catalina.servlets.DefaultServlet
        </servlet-class>
        <init-param>
            <param-name>debug</param-name>
            <param-value>0</param-value>
        </init-param>
        <init-param>
            <param-name>listings</param-name>
            <param-value>true</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

...

    <servlet-mapping>
        <servlet-name>default</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
So by default, the default servlet is loaded at webapp startup and directory listings are enabled and debugging is turned off.

 

What can I change?

 The DefaultServlet allows the following initParamters:

debug Debugging level. It is not very useful unless you are a tomcat developer. As of this writing, useful values are 0, 1, 11, 1000.
listings If no welcome file is present, can a directory listing be shown? value may be true or false
Welcome files are part of the servlet api.
readmeFile If a directory listing is presented, a readme file may also be presented with the listing. This file is inserted as is so it may contain HTML. default value is null
globalXsltFile If you wish to customize your directory listing, you can use an XSL transformation. This value is an absolute file name which be used for all direcotory listings. This can be disabled by per webapp by also declaring the default servlet in your local webapp's web.xml. The format of the xml is shown below.
localXsltFile You may also customize your directory listing by directory by configuring localXsltFile. This should be a relative file name in the directory where the listing will take place. This overrides globalXsltFile. If this value is present but a file does not exist, then globalXsltFile will be used. If globalXsltFile does not exist, then the default directory listing will be shown.
input Input buffer size (in bytes) when reading resources to be served. [2048]
output Output buffer size (in bytes) when writing resources to be served. [2048]
readonly Is this context "read only", so HTTP commands like PUT and DELETE are rejected? [true]

 

How do I customize directory listings?

You can override DefaultServlet with you own implementation and use that in your web.xml declaration. If you can undertand what was just said, we will assume yo can read the code to DefaultServlet servlet and make the appropriate adjustments. (If not, then that method isn't for you)

You can use either localXsltFile or globalXsltFile and DefaultServlet will create an xml document and run it through an xsl transformation based on the values provided in localXsltFile and globalXsltFile. localXsltFile is first checked, followed by globalXsltFile, then default behaviors takes place.

Format: 

    <listing>
     <entries>
      <entry type='file|dir' urlPath='aPath' size='###' date='gmt date'>
        fileName1
      </entry>
      <entry type='file|dir' urlPath='aPath' size='###' date='gmt date'>
        fileName2
      </entry>
      ...
     </entries>
     <readme></readme>
    </listing>
  • size will be missing if type='dir'
  • Readme is a CDATA entry
The following is a sample xsl file which mimics the default tomcat behavior: 
<?xml version="1.0"?>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  version="1.0">

  <xsl:output method="xhtml" encoding="iso-8859-1" indent="no"/>

  <xsl:template match="listing">
   <html>
    <head>
      <title>
        Sample Directory Listing For
        <xsl:value-of select="@directory"/>
      </title>
      <style>
        h1{color : white;background-color : #0086b2;}
        h3{color : white;background-color : #0086b2;}
        body{font-family : sans-serif,Arial,Tahoma;
             color : black;background-color : white;}
        b{color : white;background-color : #0086b2;}
        a{color : black;} HR{color : #0086b2;}
      </style>
    </head>
    <body>
      <h1>Sample Directory Listing For
            <xsl:value-of select="@directory"/>
      </h1>
      <hr size="1" />
      <table cellspacing="0"
                  
            cellpadding="5"
                  align="center">
        <tr>
          <th align="left">Filename</th>
          <th align="center">Size</th>
          <th align="right">Last Modified</th>
        </tr>
        <xsl:apply-templates select="entries"/>
        </table>
      <xsl:apply-templates select="readme"/>
      <hr size="1" />
      <h3>Apache Tomcat/5.0</h3>
    </body>
   </html>
  </xsl:template>


  <xsl:template match="entries">
    <xsl:apply-templates select="entry"/>
  </xsl:template>

  <xsl:template match="readme">
    <hr size="1" />
    <pre><xsl:apply-templates/></pre>
  </xsl:template>

  <xsl:template match="entry">
    <tr>
      <td align="left">
        <xsl:variable name="urlPath" select="@urlPath"/>
        <a href="{$urlPath}">
          <tt><xsl:apply-templates/></tt>
        </a>
      </td>
      <td align="right">
        <tt><xsl:value-of select="@size"/></tt>
      </td>
      <td align="right">
        <tt><xsl:value-of select="@date"/></tt>
      </td>
    </tr>
  </xsl:template>

</xsl:stylesheet>

 

How do I secure directory listings?

 Use web.xml in each individual webapp. See the security section of the Servlet specification.