Friday, December 25, 2009

Validating empty text field using JSF

JSF has a pretty comprehensive support for validations, but it is lack of a validation for an empty field. The built-in “required” property of JSF is not so usable, since it validates empty fields only. If a field has a space in it, JSF will accept it. In most scenarios, when inputting text in a form, a space (or several spaces) is considered to be an empty field. Since JSF doesn’t support “out of the box” validation for empty field, we will write our own Validator that will do the job.

Writing a JSF Validator mainly involves 3 things:

  1. Writing the Validator code by implementing a JSF Validator interface.
  2. Registering Validator in JSF faces-config.xml.
  3. Using the Validator in a JSF page.

In order to write the Validator we have to implement “validate” method of Validator interface. This method will be called automatically by JSF, when we use the Validator in some of our input fields. Our Validator class simply checks that the field value is not empty. If the field is empty a ValidationException is thrown from the Validator. JSF mechanism knows to treat this exception as a validation error, when it checks the form inputs for validation errors. Let’s have a look at the Validator code:

import javax.faces.application.FacesMessage;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.validator.Validator;
import javax.faces.validator.ValidatorException;
 * @author Bashan
public class RequiredValidator implements Validator {
  public void validate(FacesContext context, UIComponent component, Object value) throws ValidatorException {
    if (value == null || "".equals(value.toString().trim())) {
      FacesMessage message = new FacesMessage();
      String messageStr = (String)component.getAttributes().get("message");
      if (messageStr == null) {
        messageStr = "Please enter data";
      throw new ValidatorException(message);

Note, that the Validator tries to get an attribute named “message” from the component for which it is attached. The “message” attribute should contain a custom error message to show to the user. If “message” attribute is not used, a default error message: “Please enter data” is shown to the user.

Now, let’s register the Validator in JSF faces-config.xml file. This file should be located under the “WEB-INF” directory by default:

<?xml version="1.0" encoding="windows-1255"?>
<!DOCTYPE faces-config PUBLIC
  "-//Sun Microsystems, Inc.//DTD JavaServer Faces Config 1.1//EN"

You can see in this “faces-config.xml” file the validator id, which is used to call the validator from a JSF page, and the JSF class corresponds to this validator id.

Finally, let’s have a look how this validator is used in a JSF page:

<h:inputTextarea id="someText" value="#{support.message}" styleClass="textarea1" required="true" requiredMessage="Please write something">
  <f:attribute name="message" value="Please write something" />
  <f:validator validatorId="RequiredValidator" />             
  <h:message for="someText" styleClass="error"/>

This is only a fragment of a JSF page, showing a text area control and a message under it. Note, that the control can be any JSF input like <h:inputText />. Also note for the <f:attribue /> control used for sending a custom message to the Validator. Another important thing worth mentioning, it that the “required” attribute of the <h:inputTextArea /> control is also used with the same error message (using the “requiredMessage” property). One can say, using 2 validations is redundant, and that only the “RequiredValidator” could have been used. This was true, unless JSF mechanism had a problematic issue with empty fields: When field is empty (has no value and no spaces) validators and converters are not invoked. For this reason, both “required” and “RequiredValidtor” are needed to be used.

Monday, December 21, 2009

Tomcat Virtual Hosting

Tomcat is not only a servlet container. It supports many of the features of any HTTP web server and can be also used to serve static content as well. From my experience, it can handle heavy traffic quite decently. It doesn’t fall from it’s big brother: Apache Server, and frankly, there are times it seem to be functioning even better.

One of Tomcat’s features, is Virtual Hosting. Virtual Hosting means that a single web server can server more than one website at the same time. The server knows which website to server according to the domain of the request. For example, if you have 2 domains: and and you direct both domains to the same IP, the server will get requests from 2 different domains. Then it should know to serve “one” website to requests coming from domain and “second” website to requests coming from domain

Configuring Tomcat to support Virtual Hosting is an easy task. The configuration takes place in Tomcat’s server.xml file, which is placed under the “conf” directory. Inside the “Engine” xml tag, “Host” element should be added for every domain you would like to serve. For example, if we have a web application named “one” and a domain named:, The “Host” element should look like:

<Host name="" appBase="webapps/one">
  <Context path="" docBase="" debug="0"/>

Note that “one” is places under “webapps” which is Tomcat’s natural directory for web applications. Therefore, a relative path is used. In addition, take a look at the alias: That will allow the server to acept traffic from both: and
Let’s have a look at a full server.xml example file, which defines 2 virtual hosts for 2 web applications: “one” and “two”:
<?xml version='1.0' encoding='utf-8'?>
  Licensed to the Apache Software Foundation (ASF) under one or more
  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
  the License.  You may obtain a copy of the License at
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  See the License for the specific language governing permissions and
  limitations under the License.
<!-- Note:  A "Server" is not itself a "Container", so you may not
     define subcomponents such as "Valves" at this level.
     Documentation at /docs/config/server.html
<Server port="8005" shutdown="SHUTDOWN">
  <!--APR library loader. Documentation at /docs/apr.html -->
  <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />
  <!--Initialize Jasper prior to webapps are loaded. Documentation at /docs/jasper-howto.html -->
  <Listener className="org.apache.catalina.core.JasperListener" />
  <!-- JMX Support for the Tomcat server. Documentation at /docs/non-existent.html -->
  <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" />
  <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
  <!-- Global JNDI resources
       Documentation at /docs/jndi-resources-howto.html
    <!-- Editable user database that can also be used by
         UserDatabaseRealm to authenticate users
    <Resource name="UserDatabase" auth="Container"
              description="User database that can be updated and saved"
              pathname="conf/tomcat-users.xml" />
  <!-- A "Service" is a collection of one or more "Connectors" that share
       a single "Container" Note:  A "Service" is not itself a "Container",
       so you may not define subcomponents such as "Valves" at this level.
       Documentation at /docs/config/service.html
  <Service name="Catalina">

    <!--The connectors can use a shared executor, you can define one or more named thread pools-->
    <Executor name="tomcatThreadPool" namePrefix="catalina-exec-"
        maxThreads="150" minSpareThreads="4"/>
    <!-- A "Connector" represents an endpoint by which requests are received
         and responses are returned. Documentation at :
         Java HTTP Connector: /docs/config/http.html (blocking & non-blocking)
         Java AJP  Connector: /docs/config/ajp.html
         APR (HTTP/AJP) Connector: /docs/apr.html
         Define a non-SSL HTTP/1.1 Connector on port 8080
    <Connector port="80" protocol="HTTP/1.1"
               redirectPort="8443" URIEncoding="UTF-8" disableUploadTimeout="true" compression="on" compressableMimeType="text/html,text/xml,text/plain,application/xml"/>
    <!-- A "Connector" using the shared thread pool-->
    <Connector executor="tomcatThreadPool"
               port="8080" protocol="HTTP/1.1"
               redirectPort="8443" />
    <!-- Define a SSL HTTP/1.1 Connector on port 8443
         This connector uses the JSSE configuration, when using APR, the
         connector should be using the OpenSSL style configuration
         described in the APR documentation -->
    <Connector port="8443" protocol="HTTP/1.1" SSLEnabled="true"
               maxThreads="150" scheme="https" secure="true"
               clientAuth="false" sslProtocol="TLS" />
    <!-- Define an AJP 1.3 Connector on port 8009 -->
    <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />
    <!-- An Engine represents the entry point (within Catalina) that processes
         every request.  The Engine implementation for Tomcat stand alone
         analyzes the HTTP headers included with the request, and passes them
         on to the appropriate Host (virtual host).
         Documentation at /docs/config/engine.html -->
    <!-- You should set jvmRoute to support load-balancing via AJP ie :
    <Engine name="Standalone" defaultHost="localhost" jvmRoute="jvm1">      
    <Engine name="Catalina" defaultHost="localhost">
      <!--For clustering, please take a look at documentation at:
          /docs/cluster-howto.html  (simple how to)
          /docs/config/cluster.html (reference documentation) -->
      <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"/>
      <!-- The request dumper valve dumps useful debugging information about
           the request and response data received and sent by Tomcat.
           Documentation at: /docs/config/valve.html -->
      <Valve className="org.apache.catalina.valves.RequestDumperValve"/>
      <!-- This Realm uses the UserDatabase configured in the global JNDI
           resources under the key "UserDatabase".  Any edits
           that are performed against this UserDatabase are immediately
           available for use by the Realm.  -->
      <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
      <!-- Define the default virtual host
           Note: XML Schema validation will not work with Xerces 2.2.
      <!--Host name="localhost"  appBase="webapps"
            unpackWARs="true" autoDeploy="true"
            xmlValidation="false" xmlNamespaceAware="false"-->
        <!-- SingleSignOn valve, share authentication between web applications
             Documentation at: /docs/config/valve.html -->
        <Valve className="org.apache.catalina.authenticator.SingleSignOn" />
        <!-- Access log processes all example.
             Documentation at: /docs/config/valve.html -->
        <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
               prefix="localhost_access_log." suffix=".txt" pattern="common" resolveHosts="false"/>
  <Host name="" appBase="webapps/one">
   <Context path="" docBase="" debug="0"/>
  <Host name="" appBase="webapps/two">
     <Context path="" docBase="" debug="0"/>

Note, that I remarked Tomcat’s default “Host” element:

<!--Host name="localhost"  appBase="webapps"
            unpackWARs="true" autoDeploy="true"
            xmlValidation="false" xmlNamespaceAware="false"-->

Remarking the default “Host” element is necessary. Otherwise Tomcat will simply load each web application twice: one for the default host definition and the second for the virtual host definition.

Installing Tomcat 6 on Windows 2008 server 64bit

Tomcat installation is actually composed of 2 parts:
  1. Installing Java Runtime Environment.
  2. Installing Tomcat.
In order to install Tomcat 6 on Windows 2008 server, you first have to download and install Java JRE for 64bit. The latest JRE can be easily downloaded from Sun’s website.
As it is for now, Tomcat doesn’t have 64bits version. In order to be able to run Tomcat 6 on Windows 2008 server 64bit, you will first have to download and install Tomcat 6 for 32bit and then download tomcat6.exe and tomcat6w.exe supporting 64bits from Apache svn repository. Replace the files located under Tomcat’s “bin” directory with these 2 files. These are actually the only 2 native files Tomcat is using to run as a Service. Running Tomcat as a service is necessary to be able to start the server, even if there is no user logged to the system.

Monday, December 7, 2009

Automatically focus first input field using JQuery

jQuery is a well know JavaScript framework. It has core libraries which contains many useful out of the box functions, that makes JavaScript code writing much better, easier, cleaner and cross browser. On top of jQuery there are many ready to use widgets and components that can be integrated into your web application in relatively short time. jQuery core js can be downloaded from jQuery main site, but it is much easier calling Google CDN (content delivery network) for getting jQuery. For example, if you want to use jQuery version 1.3.2 you can simply request this link:

or, as a JavaScript tag:

<script type="text/javascript" src=""></script>

Google has wide range of jQuery versions for your selection. It also offers additional frameworks and libraries as well (like MooTools, Yahoo UI and more). You can find more material about it in Google AJAX Libraries API.

Automatically focusing the first input field in web page that contains a form is a small but important feature in terms of user experience. Doing it in jQuery is an easy task:

<script type="text/javascript">

Of course, this code should be put after your form fields to function properly.

Note that the code is generic and doesn’t relate to any specific element id on the page.