Changeset 4221

Timestamp:

Apr 14, 2008, 2:40:57 PM (15 years ago)

Author:

Nicklas Nordborg

Message:

References #988: Add support for servlets in extensions

The main feature is now working.

Location:

trunk

Files:

• config/dist/web.xml (modified) (1 diff)
• doc/src/docbook/developerdoc/extensions.xml (modified) (2 diffs)
• src/clients/web/net/sf/basedb/clients/web/Base.java (modified) (12 diffs)
• src/clients/web/net/sf/basedb/clients/web/extensions/ExtensionsControl.java (modified) (7 diffs)
• src/clients/web/net/sf/basedb/clients/web/extensions/ExtensionsDirectory.java (modified) (4 diffs)
• src/clients/web/net/sf/basedb/clients/web/extensions/ExtensionsFile.java (modified) (5 diffs)
• src/clients/web/net/sf/basedb/clients/web/extensions/ServletLoader.java (added)
• src/clients/web/net/sf/basedb/clients/web/extensions/ServletWrapper.java (added)
• src/clients/web/net/sf/basedb/clients/web/servlet/ExtensionsServlet.java (modified) (4 diffs)
• src/core/net/sf/basedb/core/xsd/servlets.xsd (added)

trunk/config/dist/web.xml

@@ -167 +167 @@
     <load-on-startup>1</load-on-startup>
   </servlet>
-
+  <servlet-mapping>
+    <servlet-name>ExtensionsServlet</servlet-name>
+    <url-pattern>*.servlet</url-pattern>
+  </servlet-mapping>
+  
   <!-- The CompileAll servlet used to compile all JSP pages -->
   <!-- EXPERIMENTAL!! -->

trunk/doc/src/docbook/developerdoc/extensions.xml

@@ -709 +709 @@
     </para>
     
+    <note>
+      <para>
+      Unfortunately, the custom JSP page can't use classes that
+      are located in the extension's JAR file. The reason is that the
+      JAR file is not known to Tomcat and Tomcat will not look there to
+      try to find classes. The current workaround is to place classes need
+      by JSP pages in a separate JAR file that is then installed into
+      the <filename>WEB-INF/lib</filename> folder. This requires a restart
+      of Tomcat.
+      </para>
+    </note>
+    
     <sect2 id="extensions_developer.resources.scripts">
       <title>Javascript and stylesheets</title>
@@ -1107 +1119 @@
   </sect1>
   
+  <sect1 id="extensions_developer.servlets">
+    <title>Custom servlets</title>
+    <para>
+      It is possible for an extension to include servlets without having
+      to register those servlets in Tomcat's <filename>WEB-INF/web.xml</filename>
+      file. The extension needs to be in a JAR file as usual. The servlet class
+      should be located in the JAR file following regular Java conventions.
+      Eg. The class <classname>my.domain.ServletClass</classname> should
+      be located at <filename>my/domain/ServletClass.class</filename>. You 
+      also need to create a second XML file that contains the servlet
+      definitions at <filename>META-INF/servlets.xml</filename>. The format for
+      defining servlets in this file is very similar to how servlets are
+      defined in the <filename>web.xml</filename> file. Here is an example:
+    </para>
+    
+    <programlisting language="xml">
+<![CDATA[
+<?xml version="1.0" encoding="UTF-8" ?>
+<servlets xmlns="http://base.thep.lu.se/servlets.xsd">
+   <servlet>
+      <servlet-name>HelloWorld</servlet-name>
+      <servlet-class>net.sf.basedb.examples.extensions.HelloWorldServlet</servlet-class>
+      <init-param>
+         <param-name>template</param-name>
+         <param-value>Hello {user}! Welcome to the Servlet world!</param-value>
+      </init-param>
+   </servlet>
+</servlets>
+]]>
+</programlisting>
+
+    <para>
+      The <sgmltag class="starttag">servlets</sgmltag> tag is the root tag and is 
+      needed to set up the namespace and schema validation. This may contain
+      any number of <sgmltag class="starttag">servlet</sgmltag> tags, each one
+      defining a single servlet.
+    </para>
+    
+    <para>
+      The <sgmltag class="starttag">servlet-name</sgmltag> tag contains the name
+      of the servlet. This is a required tag and must be unique among the servlets
+      defined by this extension. Other extensions may use the same name without any
+      problems.
+    </para>
+    
+    <para>
+      The <sgmltag class="starttag">servlet-class</sgmltag> tag contains the name
+      of implementing class. This is required and the class must implement
+      the <interfacename>Servlet</interfacename> interface and have a public,
+      no-argument constructor. We recommend that servlet implementations instead 
+      extends the <classname>HttpServlet</classname> class. This will make the 
+      servlet programming easier.
+    </para>
+    
+    <para>
+      A servlet may have any number <sgmltag class="starttag">init-param</sgmltag>
+      tags, containing initialisation parameters for the servlet. Here is the
+      code for the servlet references in the above example.
+    </para>
+
+    <programlisting language="java">
+<![CDATA[
+public class HelloWorldServlet 
+   extends HttpServlet 
+{
+   private String template;
+   public HelloWorldServlet()
+   {}
+
+   @Override
+   public void init()
+      throws ServletException
+   {
+      ServletConfig cfg = getServletConfig();
+      template = cfg.getInitParameter("template");
+      if (template == null) template = "Hello {user}.";
+   }
+
+   @Override
+   protected void doGet(HttpServletRequest request, HttpServletResponse response)
+      throws ServletException, IOException
+   {
+      final SessionControl sc = Base.getExistingSessionControl(request, true);
+      final DbControl dc = sc.newDbControl();
+      try
+      {
+         User current = User.getById(dc, sc.getLoggedInUserId());
+         PrintWriter out = response.getWriter();
+         out.print(template.replace("{user}", current.getName()));
+      }
+      finally
+      {
+         if (dc != null) dc.close();
+      }
+   }
+   @Override
+   protected void doPost(HttpServletRequest req, HttpServletResponse resp)
+      throws ServletException, IOException
+   {
+      doGet(req, resp);
+   }
+}
+]]>
+</programlisting>
+
+    <para>
+      Invoking the servlet is done with a URL that is constructed like:
+      <filename>$HOME$/[servlet-name].servlet</filename>, where <code>$HOME$</code>
+      is the home directory of the extension.
+    </para>
+
+    <programlisting language="xml">
+<![CDATA[
+<extension
+   id="net.sf.basedb.clients.web.menu.extensions.helloservletworld"
+   extends="net.sf.basedb.clients.web.menu.extensions"
+   >
+   <index>5</index>
+   <about>
+      <name>Hello Servlet world</name>
+      <description>
+         This example uses a custom Servlet page to display the
+         "Hello world" message instead of a javascript popup.
+      </description>
+   </about>
+   <action-factory>
+      <factory-class>
+         net.sf.basedb.clients.web.extensions.menu.FixedMenuItemFactory
+      </factory-class>
+      <parameters>
+         <title>Hello Servlet world!</title>
+         <tooltip>Opens a Servlet generated page with the message</tooltip>
+         <onClick>
+           Main.openPopup('$HOME$/HelloWorld.servlet?ID=' + getSessionId(), 'HelloServletWorld', 400, 300)
+         </onClick>
+         <icon>~/images/servlet.png</icon>
+      </parameters>
+   </action-factory>
+</extension>
+]]>
+</programlisting>
+    
+    <note>
+      <para>
+        To keep things as simple as possible, a new instance of the servlet 
+        class is created for each request. If the servlet needs complex or 
+        expensive initialisation, that should be externalised to other
+        classes that the servlet can use.
+      </para>
+    </note>
+    
+  </sect1>
+  
 </chapter>

trunk/src/clients/web/net/sf/basedb/clients/web/Base.java

@@ -117 +117 @@
     throws BaseException
   {
+    return getSessionControl(pageContext.getRequest(), create);
+  }
+
+  /**
+    Get a new or existing <code>SessionControl</code> object
+    given a <code>ServletRequest</code> instance. This method will get
+    the <code>ID</code> parameter from the page URL and
+    try to retrieve the corresponding object from the
+    BASE {@link Application}. If no {@link SessionControl}
+    object exists, a new one will be created if the <code>create</code> 
+    parameter is TRUE.
+  
+    @param request The Servlet <code>request</code> variable
+    @param create If a new <code>SessionControl</code> should be created or not
+    @return A <code>SessionControl</code> object
+    @throws BaseException If there is an error
+    @since 2.7
+  */
+  public static final SessionControl getSessionControl(ServletRequest request, boolean create)
+  {
     SessionControl sc = null;
-    String id = pageContext.getRequest().getParameter("ID");
-    if (id == null && pageContext.getRequest().getAttribute("ID") instanceof String) 
-    {
-      id = (String)pageContext.getRequest().getAttribute("ID");
-    }
-    String remoteId = pageContext.getRequest().getRemoteAddr();
+    String id = request.getParameter("ID");
+    if (id == null && request.getAttribute("ID") instanceof String) 
+    {
+      id = (String)request.getAttribute("ID");
+    }
+    String remoteId = request.getRemoteAddr();
     try
     {
@@ -138 +158 @@
     return sc == null && create ? Application.newSessionControl("net.sf.basedb.clients.web", remoteId, id) : sc;
   }
-
+  
   /**
     Get an existing {@link SessionControl} object
@@ -157 +177 @@
     throws NotLoggedInException, BaseException
   {
-    SessionControl sc = getSessionControl(pageContext, false);
+    return getExistingSessionControl(pageContext.getRequest(), checkLoggedIn);
+  }
+
+  /**
+    Get an existing {@link SessionControl} object
+    given a <code>ServletRequest</code> object and optionally check that a user is logged in. 
+    This method will get the <code>ID</code> parameter from the page URL and
+    try to retrieve the corresponding object from the
+    {@link Application} and check that a user is logged in if
+    the <code>checkLoggedIn</code> parameter is TRUE.
+  
+    @param request The Servlet <code>request</code> variable
+    @param checkLoggedIn If the method should check if a user is logged in or not
+    @return A <code>SessionControl</code> object
+    @throws NotLoggedInException If a <code>SessionControl</code> object isn't found 
+      or no user is logged in
+    @throws BaseException If there is another error
+    @since 2.7
+  */
+  public static final SessionControl getExistingSessionControl(ServletRequest request, boolean checkLoggedIn)
+    throws NotLoggedInException, BaseException
+  {
+    SessionControl sc = getSessionControl(request, false);
     if (sc == null || (checkLoggedIn && !sc.isLoggedIn()))
     {
@@ -164 +206 @@
     return sc;
   }
-
+  
+  
   /**
     Get an existing {@link SessionControl} object given 
@@ -192 +235 @@
     throws PermissionDeniedException, NotLoggedInException, BaseException
   {
-    SessionControl sc = getExistingSessionControl(pageContext, true);
+    return getExistingSessionControl(pageContext.getRequest(), permission, itemType);
+  }
+
+  /**
+    Get an existing {@link SessionControl} object given 
+    a <code>ServletRequest</code> and check for generic (role-based)
+    permission to an item type. 
+  
+    This method will get the <code>ID</code> parameter from the page URL and
+    try to retrieve the corresponding object from the {@link Application}.
+    Then it checks that a user is logged in and that the logged in user has the 
+    specified permission for item type. If {@link Permission#DENIED} is specified, 
+    this method checks that the logged in user haven't been denied acces to
+    those items.
+  
+    @param request The Servlet <code>request</code> variable
+    @param permission The permission to check for, use one of the codes
+      defined by the {@link Permission} class
+    @param itemType The code for the item type to check for the permission,
+      use one of the values defined by the {@link Item} class
+    @return A <code>SessionControl</code> object
+    @throws PermissionDeniedException If the logged in user doesn't have the
+      requested permission
+    @throws NotLoggedInException If no user is logged in or a <code>SessionControl</code>
+      object not is found
+    @throws BaseException If there is another error
+    @since 2.7
+  */
+  public static final SessionControl getExistingSessionControl(ServletRequest request, 
+    Permission permission, Item itemType)
+    throws PermissionDeniedException, NotLoggedInException, BaseException
+  {
+    SessionControl sc = getExistingSessionControl(request, true);
     boolean hasPermission = sc.hasPermission(permission, itemType);
     boolean checkDenied = permission == Permission.DENIED;
@@ -200 +275 @@
     }
     return sc;
-  }
-
+  } 
+  
   /**
     Same as: <code>getAndSetCurrentContext(sc, itemType, "", pageContext, defaultContext, false)</code>.
     @see #getAndSetCurrentContext(SessionControl, Item, String, PageContext, ItemContext, boolean)
   */
-  public static ItemContext getAndSetCurrentContext(SessionControl sc, Item itemType, PageContext pageContext, ItemContext defaultContext)
+  public static ItemContext getAndSetCurrentContext(SessionControl sc, Item itemType, 
+      PageContext pageContext, ItemContext defaultContext)
   {
     return getAndSetCurrentContext(sc, itemType, "", pageContext, defaultContext, false);
@@ -215 +291 @@
     @see #getAndSetCurrentContext(SessionControl, Item, String, PageContext, ItemContext, boolean)
   */
-  public static ItemContext getAndSetCurrentContext(SessionControl sc, Item itemType, PageContext pageContext, ItemContext defaultContext, boolean resetTemporary)
+  public static ItemContext getAndSetCurrentContext(SessionControl sc, Item itemType, 
+      PageContext pageContext, ItemContext defaultContext, boolean resetTemporary)
   {
     return getAndSetCurrentContext(sc, itemType, "", pageContext, defaultContext, resetTemporary);
@@ -224 +301 @@
     @see #getAndSetCurrentContext(SessionControl, Item, String, PageContext, ItemContext, boolean)
   */
-  public static ItemContext getAndSetCurrentContext(SessionControl sc, Item itemType, String subContext, PageContext pageContext, ItemContext defaultContext)
-  {
-    return getAndSetCurrentContext(sc, itemType, subContext, pageContext, defaultContext, false);
+  public static ItemContext getAndSetCurrentContext(SessionControl sc, Item itemType, 
+      String subContext, PageContext pageContext, ItemContext defaultContext)
+  {
+    return getAndSetCurrentContext(sc, itemType, subContext, pageContext, 
+        defaultContext, false);
+  }
+  
+  /**
+    @see #getAndSetCurrentContext(SessionControl, Item, String, ServletRequest, ItemContext, boolean)
+  */
+  public static ItemContext getAndSetCurrentContext(SessionControl sc, Item itemType, 
+    String subContext, PageContext pageContext, ItemContext defaultContext, boolean resetTemporary)
+  {
+    ServletRequest request = pageContext == null ? null : pageContext.getRequest();
+    return getAndSetCurrentContext(sc, itemType, subContext, request, 
+        defaultContext, resetTemporary);
   }
   
@@ -241 +331 @@
       
     <li>The following settings are only updated if they are available in the
-      pageContext object's request parameters:
+      request parameters:
       
       <table>
@@ -343 +433 @@
     @param itemType The type of item to get the context for
     @param subContext The name of the subcontext
-    @param pageContext A <code>PageContext</code> object to get request
-      information from, or null if the curren context shouldn't be updated
+    @param request A <code>ServletRequest</code> object to get request
+      information from, or null if the current context shouldn't be updated
     @param defaultContext A default context to copy information from if a current context
       doesn't exist
@@ -350 +440 @@
       example the 'exclude' filter which is only used in popup windows
     @return an updated {@link net.sf.basedb.core.ItemContext} object.
+    @since 2.7
   */
   @SuppressWarnings("unchecked")
-  public static ItemContext getAndSetCurrentContext(SessionControl sc, Item itemType, String subContext, PageContext pageContext, ItemContext defaultContext, boolean resetTemporary)
+  public static ItemContext getAndSetCurrentContext(SessionControl sc, Item itemType, 
+    String subContext, ServletRequest request, ItemContext defaultContext, boolean resetTemporary)
   {
     ItemContext cc = sc.getCurrentContext(itemType, subContext, defaultContext);
@@ -395 +487 @@
       cc.setObject("defaultColumns", defaultContext.getObject("defaultColumns"));
     }
-    if (pageContext != null)
-    {
-      ServletRequest request = pageContext.getRequest();
+    if (request != null)
+    {
 
       // If the filter has changed we must return to the first page

trunk/src/clients/web/net/sf/basedb/clients/web/extensions/ExtensionsControl.java

@@ -25 +25 @@
 import java.io.File;
 import java.util.Collections;
+import java.util.EnumSet;
 import java.util.Iterator;
 import java.util.Set;
 import java.util.TimerTask;
 
+import javax.servlet.ServletContext;
 import javax.servlet.jsp.PageContext;
 
@@ -90 +92 @@
   private static Settings settings;
   
+  // The Servlet Context provided by the web server
+  private static ServletContext servletContext;
+  
   // Automatic check for new/updated/deleted extensions
   private static TimerTask autoInstallTask;
@@ -103 +108 @@
     {@link ExtensionsServlet} when the web server starts up.
   */
-  public static synchronized void init(ExtensionsDirectory directory)
+  public static synchronized void init(ExtensionsDirectory directory, 
+    ServletContext servletContext)
   {
     if (initialised) return;
@@ -118 +124 @@
     
     // Install extensions
-    lastScanResults = extensionsDir.installAndUpdateExtensions(registry, false, false);
+    lastScanResults = extensionsDir.installAndUpdateExtensions(registry, 
+      servletContext, false, false);
     initAutoInstaller();
     initialised = true;
@@ -161 +168 @@
     web client application is needed.
     
-    @param dc The DbControl to use for database access and permission checks
+    @param dc The DbControl to use for database access and 
+      permission checks, or null to only get read permission
     @return An extensions control instance
   */
   public static ExtensionsControl get(DbControl dc)
   {
-    SessionControl sc = dc.getSessionControl();
-    Client c = Client.getById(dc, sc.getClientId());
-    return new ExtensionsControl(c.getPermissions());
+    Set<Permission> permissions = null;
+    if (dc != null)
+    {
+      SessionControl sc = dc.getSessionControl();
+      Client c = Client.getById(dc, sc.getClientId());
+      permissions = c.getPermissions();
+    }
+    else
+    {
+      permissions = EnumSet.of(Permission.READ);
+    }
+    return new ExtensionsControl(permissions);
   }
   
@@ -259 +276 @@
     checkPermission(Permission.WRITE, "extensions");
     lastScanResults = 
-      extensionsDir.installAndUpdateExtensions(registry, true, forceUpdate);
+      extensionsDir.installAndUpdateExtensions(registry, servletContext, true, forceUpdate);
     return lastScanResults;
   }
@@ -508 +525 @@
       log.debug("Checking for new/updated/deleted extensions");
       int autoInstall = settings.getAutoInstall();
-      lastScanResults = extensionsDir.installAndUpdateExtensions(registry, false, false);
+      lastScanResults = extensionsDir.installAndUpdateExtensions(registry, 
+          servletContext, false, false);
       nextAutoScan = autoInstall > 0 ? 
         System.currentTimeMillis() + autoInstall * 1000L : 0;

trunk/src/clients/web/net/sf/basedb/clients/web/extensions/ExtensionsDirectory.java

@@ -36 +36 @@
 import java.util.TreeMap;
 import java.util.regex.Pattern;
+
+import javax.servlet.ServletContext;
 
 import net.sf.basedb.util.RegexpFileFilter;
@@ -239 +241 @@
     @return The result of the scan
   */
-  public synchronized ScanResults installAndUpdateExtensions(Registry registry, 
-    boolean manualScan, boolean forceUpdate)
+  synchronized ScanResults installAndUpdateExtensions(Registry registry, 
+    ServletContext servletContext, boolean manualScan, boolean forceUpdate)
   {
     log.info("Begin scan for new/updated/deleted extensions");
@@ -276 +278 @@
         extractResources(forceUpdate, results);
         
-        // 5. Register new and updated extensions with the registry
+        // 5. Load servlets
+        loadServlets(servletContext, forceUpdate, results);
+        
+        // 6. Register new and updated extensions with the registry
         registerExtensions(registry, forceUpdate, results);
       }
@@ -538 +543 @@
   
   /**
+    Load servlet definitions from JAR files. Servlets should be
+    defined in META-INF/servlets.xml. 
+  */
+  private void loadServlets(ServletContext servletContext, boolean forceUpdate, ScanResults results)
+  {
+    for (ExtensionsFile extFile : installedFiles.values())
+    {
+      // Do not load servlets from files with an error
+      if (extFile.hasError()) continue;
+      
+      try
+      {
+        if (forceUpdate || extFile.isModified())
+        {
+          int numServlets = extFile.loadServlets(servletContext);
+          if (numServlets > 0)
+          {
+            results.addMessage(extFile, 
+                numServlets + " servlets defined successfully.");
+          }
+        }
+      }
+      catch (Throwable ex)
+      {
+        extFile.setError(true);
+        results.addErrorMessage(extFile, "Could not load servlets: " + ex.getMessage());
+        log.error("Could not load servlets from " + extFile.getName(), ex);
+      }
+    }
+  }
+
+  
+  /**
     Register extensions with the registry. Unless forceUpdate is TRUE only
     new and modified extensions are registered. Extensions files that has

trunk/src/clients/web/net/sf/basedb/clients/web/extensions/ExtensionsFile.java

@@ -32 +32 @@
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Map;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -39 +41 @@
 import java.util.zip.ZipFile;
 import java.util.zip.ZipInputStream;
+
+import javax.servlet.ServletContext;
 
 import net.sf.basedb.core.plugin.About;
@@ -77 +81 @@
   private About about;
   private boolean hasError;
+  
+  private Map<String, ServletWrapper> servlets;
   
   /**
@@ -423 +429 @@
     return about;
   }
+  
+  
+    
+  /**
+    Load servlet definitions from a JAR file.
+  */
+  int loadServlets(ServletContext context)
+  {
+    if (!isJar) return 0;
+    log.info("Loading servlets from JAR file: " + file.getName());
+    InputStream in = null;
+    ZipFile zipFile = null;
+    int numServlets = 0;
+    try
+    {
+      zipFile = new ZipFile(file);
+      ZipEntry zipEntry = zipFile.getEntry("META-INF/servlets.xml");
+      if (zipEntry == null)
+      {
+        log.info("META-INF/servlets.xml not found in file: " + file.getName());
+        return 0;
+      }
+      
+      if (servlets == null) servlets = new HashMap<String, ServletWrapper>();
+      servlets.clear();
+      in = zipFile.getInputStream(zipEntry);
+      
+      ClassLoader jarLoader = JarClassLoader.getInstance(file.getAbsolutePath(), true);
+      
+      ServletLoader servletLoader = new ServletLoader();
+      servletLoader.loadXmlFile(in, file.getName(), jarLoader, true);
+      for (ServletWrapper wrapper : servletLoader.getServlets())
+      {
+        wrapper.setServletContext(context);
+        servlets.put(wrapper.getServletName(), wrapper);
+        numServlets++;
+      }
+    }
+    catch (Exception ex)
+    {
+      log.error("Error loading servlets from JAR file: " + file, ex);
+      throw new RuntimeException("Error loading servlets from '" + file + "': " + 
+        ex.getMessage(), ex);
+    }
+    finally
+    {
+      try
+      {
+        if (in != null) in.close();
+        if (zipFile != null) zipFile.close();
+      }
+      catch (IOException ex)
+      {}
+    }
+    log.info(numServlets + " servlets loaded from JAR file: " + file.getName());
+    return numServlets;
+  }
+  
   
   /**
@@ -637 +701 @@
   }
   
+  /**
+    Get a servlet that has been defined in this JAR file.
+    @param servletName The name of the servlet, specified by the
+      &lt;servlet-name&gt; tag in the XML file.
+    @return A wrapper that can be used to invoke the servlet,
+      or null if not servlet with the given name exists
+  */
+  public ServletWrapper getServlet(String servletName)
+  {
+    return servlets == null ? null : servlets.get(servletName);
+  }
   
 }

trunk/src/clients/web/net/sf/basedb/clients/web/servlet/ExtensionsServlet.java

@@ -24 +24 @@
 
 import java.io.File;
+import java.io.IOException;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import javax.servlet.ServletConfig;
@@ -29 +32 @@
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
 
 import net.sf.basedb.clients.web.extensions.ExtensionsControl;
 import net.sf.basedb.clients.web.extensions.ExtensionsDirectory;
+import net.sf.basedb.clients.web.extensions.ExtensionsFile;
+import net.sf.basedb.clients.web.extensions.ServletWrapper;
 
 /**
@@ -38 +45 @@
   <code>&lt;load-on-startup&gt;1&lt;/load-on-startup&gt;</code>
   option in the web.xml file. When the servlet is loaded it will initialise the
-  {@link ExtensionsControl} class. This servlet is not used to handle
-  any requests.
+  {@link ExtensionsControl} class.
+  <p>
+  
+  This servlet is also acting as a proxy for requests to extension defined
+  servlets. Such servlets are defined in <code>META-INF/servlets.xml</code>
+  in the extension JAR file. A request to a servlet must have the following
+  URL pattern:
+  <code>/extensions/[jar-name]/[servlet-name].servlet</code>
   
   @author nicklas
@@ -66 +79 @@
     ExtensionsDirectory extensions = new ExtensionsDirectory(
         extensionsDir, resourcesDir, rootUrl, rootUrl + ExtensionsControl.RESOURCES_URL);
-    ExtensionsControl.init(extensions);
+    ExtensionsControl.init(extensions, context);
   }
 
+  /**
+    Path to servlet must match: /extensions/[jar-file-name]/[servlet-name].servlet
+    group(1) = JAR name, group(2) = Servlet name
+  */
+  private static final Pattern PATH_MATCH = 
+    Pattern.compile(ExtensionsControl.RESOURCES_URL + "/([^/]+)/(.+)\\.servlet");
+  
+  @Override
+  protected void doGet(HttpServletRequest request, HttpServletResponse response)
+    throws ServletException, IOException
+  {
+    
+    String servletPath = request.getServletPath();
+    Matcher m = PATH_MATCH.matcher(servletPath);
+    if (!m.matches())
+    {
+      response.sendError(HttpServletResponse.SC_NOT_FOUND, servletPath);
+      return;
+    }
+    
+    String jarName = m.group(1);
+    String servletName = m.group(2);
+    ExtensionsControl ec = ExtensionsControl.get(null);
+    ExtensionsFile file = ec.getFile(jarName);
+    if (file == null)
+    {
+      response.sendError(HttpServletResponse.SC_NOT_FOUND, servletPath);
+      return;
+    }
+    else if (!file.isJar())
+    {
+      response.sendError(HttpServletResponse.SC_BAD_REQUEST, servletPath + " is not a JAR file.");
+      return;
+    }
+  
+    ServletWrapper wrapper = file.getServlet(servletName);
+    if (wrapper == null)
+    {
+      response.sendError(HttpServletResponse.SC_NOT_FOUND, servletPath);
+      return;
+    }
+    wrapper.service(request, response);
+  }
+
+  @Override
+  protected void doPost(HttpServletRequest req, HttpServletResponse resp)
+    throws ServletException, IOException
+  {
+    doGet(req, resp);
+  }
+  
 }