Default Servlet Reference

Table of Contents

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_BASE/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>false</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 disabled and debugging is turned off.

What can I change?

The DefaultServlet allows the following initParamters:

Property Description
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. [0]
listings If no welcome file is present, can a directory listing be shown? value may be true or false [false]
Welcome files are part of the servlet api.
WARNING: Listings of directories containing many entries are expensive. Multiple requests for large directory listings can consume significant proportions of server resources.
gzip If a gzipped version of a file exists (a file with .gz appended to the file name located alongside the original file), Tomcat will serve the gzipped file if the user agent supports gzip and this option is enabled. [false]
The file with the .gz extension will be accessible if requested directly so if the original resource is protected with a security constraint, the gzipped version must be similarly protected.
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.
globalXsltFile If you wish to customize your directory listing, you can use an XSL transformation. This value is a relative file name (to either $CATALINA_BASE/conf/ or $CATALINA_HOME/conf/) which will be used for all directory listings. This can be overridden per context and/or per directory. See contextXsltFile and localXsltFile below. The format of the xml is shown below.
contextXsltFile You may also customize your directory listing by context by configuring contextXsltFile. This must be a context relative path (e.g.: /path/to/context.xslt) to a file with a .xsl or .xslt extension. 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.
localXsltFile You may also customize your directory listing by directory by configuring localXsltFile. This must be a file in the directory where the listing will take place to with a .xsl or .xslt extension. This overrides globalXsltFile and contextXsltFile. If this value is present but a file does not exist, then contextXsltFile will be used. If contextXsltFile 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]
fileEncoding File encoding to be used when reading static resources. [platform default]
sendfileSize If the connector used supports sendfile, this represents the minimal file size in KB for which sendfile will be used. Use a negative value to always disable sendfile. [48]
useAcceptRanges If true, the Accept-Ranges header will be set when appropriate for the response. [true]
showServerInfo Should server information be presented in the response sent to clients when directory listing is enabled. [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 understand what was just said, we will assume you 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" encoding="UTF-8"?>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  version="3.0">

  <xsl:output method="html" html-version="5.0"
    encoding="UTF-8" indent="no"
    doctype-system="about:legacy-compat"/>

  <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;}
        table td { padding: 5px; }
      </style>
    </head>
    <body>
      <h1>Sample Directory Listing For
            <xsl:value-of select="@directory"/>
      </h1>
      <hr style="height: 1px;" />
      <table style="width: 100%;">
        <tr>
          <th style="text-align: left;">Filename</th>
          <th style="text-align: center;">Size</th>
          <th style="text-align: right;">Last Modified</th>
        </tr>
        <xsl:apply-templates select="entries"/>
        </table>
      <xsl:apply-templates select="readme"/>
      <hr style="height: 1px;" />
      <h3>Apache Tomcat/<version-major-minor/></h3>
    </body>
   </html>
  </xsl:template>


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

  <xsl:template match="readme">
    <hr style="height: 1px;" />
    <pre><xsl:apply-templates/></pre>
  </xsl:template>

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

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