jsf interview questions and answers

Java Server Pages FAQ-->2

Q11. What is JavaServer Faces?

JavaServer Faces (JSF) is a user interface (UI) framework for Java web applications. It is designed to significantly ease the burden of writing and maintaining applications that run on a Java application server and render their UIs back to a target client. JSF provides ease-ofuse in the following ways:

• Makes it easy to construct a UI from a set of reusable UI components
• Simplifies migration of application data to and from the UI
• Helps manage UI state across server requests
• Provides a simple model for wiring client-generated events to server-side application code
• Allows custom UI components to be easily built and re-used

Most importantly, JSF establishes standards which are designed to be leveraged by tools to provide a developer experience which is accessible to a wide variety of developer types, ranging from corporate developers to systems programmers. A "corporate developer" is characterized as an individual who is proficient in writing procedural code and business logic, but is not necessarily skilled in object-oriented programming. A "systems programmer" understands object-oriented fundamentals, including abstraction and designing for re-use. A corporate developer typically relies on tools for development, while a system programmer may define his or her tool as a text editor for writing code. Therefore, JSF is designed to be tooled, but also exposes the framework and programming model as APIs so that it can be used outside of tools, as is sometimes required by systems programmers.

Q12. How to pass a parameter to the JSF application using the URL string?

if you have the following URL: http://your_server/your_app/product.jsf?id=777, you access the passing parameter id with the following lines of java code:

FacesContext fc = FacesContext.getCurrentInstance();
String id = (String) fc.getExternalContext().getRequestParameterMap().get("id");
From the page, you can access the same parameter using the predefined variable with name param. For example,

<h:outputText value="#{param['id']}" />
Note: You have to call the jsf page directly and using the servlet mapping.

Q13. How to add context path to URL for outputLink?

Current JSF implementation does not add the context path for outputLink if the defined path starts with '/'. To correct this problem use
#{facesContext.externalContext.requestContextPath} prefix at the beginning of the
outputLink value attribute.
For example:
<h:outputLink value="#{facesContext.externalContext.requestContextPath}/myPage.faces">

Q14 How to get current page URL from backing bean?

You can get a reference to the HTTP request object via FacesContext like this:
FacesContext fc = FacesContext.getCurrentInstance();
HttpServletRequest request = (HttpServletRequest) fc.getExternalContext().getRequest();
and then use the normal request methods to obtain path information. Alternatively,
context.getViewRoot().getViewId();
will return you the name of the current JSP (JSF view IDs are basically just JSP path
names).

Q15. How to access web.xml init parameters from java code?

You can get it using externalContext getInitParameter method. For example, if you have:

<context-param>
<param-name>connectionString</param-name>
<param-value>jdbc:oracle:thin:scott/tiger@cartman:1521:O901DB</param-value>
</context-param>
You can access this connection string with:
FacesContext fc = FacesContext.getCurrentInstance();
String connection = fc.getExternalContext().getInitParameter("connectionString");

Q16. How to access web.xml init parameters from jsp page?

You can get it using initParam pre-defined JSF EL valiable.
For example, if you have:
<context-param>
<param-name>productId</param-name>
<param-value>2004Q4</param-value>
</context-param>
You can access this parameter with #{initParam['productId']} . For example:
Product Id: <h:outputText value="#{initParam['productId']}"/>

Q17. How to terminate the session?

In order to terminate the session you can use session invalidate method.
This is an example how to terminate the session from the action method of a backing bean:
public String logout() {
FacesContext fc = FacesContext.getCurrentInstance();
HttpSession session = (HttpSession) fc.getExternalContext().getSession(false);
session.invalidate();
return "login_page";
}
The following code snippet allows to terminate the session from the jsp page:
<% session.invalidate(); %> <c:redirect url="loginPage.jsf" />

Q18. How to implement "Please, Wait..." page?

The client-side solution might be very simple. You can wrap the jsp page (or part of it you want to hide) into the DIV, then you can add one more DIV that appears when user clicks the submit button. This DIV can contain the animated gif you speak about or any other content.
Scenario: when user clicks the button, the JavaScript function is called. This function hides the page and shows the "Wait" DIV. You can customize the look-n-fill with CSS if you like.

This is a working example:
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<f:loadBundle basename="demo.bundle.Messages" var="Message"/>
<html>
<head>
<title>Input Name Page</title>
<script>
function gowait() {
document.getElementById("main").style.visibility="hidden";
document.getElementById("wait").style.visibility="visible";
}
</script>
</head>
<body bgcolor="white">
<f:view>
<div id="main">
<h1><h:outputText value="#{Message.inputname_header}"/></h1>
<h:messages style="color: red"/>
<h:form id="helloForm">
<h:outputText value="#{Message.prompt}"/>
<h:inputText id="userName" value="#{GetNameBean.userName}" required="true">
<f:validateLength minimum="2" maximum="20"/>
</h:inputText>
<h:commandButton onclick="gowait()" id="submit" action="#{GetNameBean.action}" </h:form>
</div>
<div id="wait" style="visibility:hidden; position: absolute; top: 0; left: 0">
<table width="100%" height ="300px">
<tr>
<td align="center" valign="middle">
<h2>Please, wait...</h2>
</td>
</tr>
</table>
</div>
</f:view>
</body>
</html>

If you want to have an animated gif of the "Wait" Page, the gif should be reloaded after the form is just submitted. So, assign the id for your image and then add reload code that will be called after some short delay. For the example above, it might be:

<script>
function gowait() {
document.getElementById("main").style.visibility="hidden";
document.getElementById("wait").style.visibility="visible";
window.setTimeout('showProgress()', 500);
}
function showProgress(){
var wg = document.getElementById("waitgif");
wg.src=wg.src;
}
</script>
....
....
....
<img id="waitgif" src="animated.gif">

Q19. How to reload the page after ValueChangeListener is invoked?

At the end of the ValueChangeListener, call FacesContext.getCurrentInstance().renderResponse()

Q20. How to download PDF file with JSF?

This is an code example how it can be done with action listener of the backing bean.
Add the following method to the backing bean:

public void viewPdf(ActionEvent event) {
String filename = "filename.pdf";
// use your own method that reads file to the byte array
byte[] pdf = getTheContentOfTheFile(filename);
FacesContext faces = FacesContext.getCurrentInstance();
HttpServletResponse response = (HttpServletResponse) faces.getExternalContext().response.setContentType("application/pdf");
response.setContentLength(pdf.length);
response.setHeader( "Content-disposition", "inline; filename=\""+fileName+"\"");
try {
ServletOutputStream out;
out = response.getOutputStream();
out.write(pdf);
} catch (IOException e) {
e.printStackTrace();
}
faces.responseComplete();
}
This is a jsp file snippet:
<h:commandButton immediate="true" actionListener="#{backingBean.viewPdf}" value="Read

Q21. How to show Confirmation Dialog when user Click the Command Link?

h:commandLink assign the onclick attribute for internal use. So, you cannot use it to write your own code. This problem will fixed in the JSF 1.2. For the current JSF version you can use onmousedown event that occurs before onclick.

<script language="javascript">
function ConfirmDelete(link) { var delete = confirm('Do you want to Delete?'); if (delete ==
true) { link.onclick(); } } </script> . . . . <h:commandLink action="delete"
onmousedown="return ConfirmDelete(this);"> <h:outputText value="delete it"/>
</h:commandLink>

Q22. What is the different between getRequestParameterMap() and getRequestParameterValuesMap()?

getRequestParameterValuesMap() similar to getRequestParameterMap(), but contains multiple values for for the parameters with the same name. It is important if you one of the components such as <h:selectMany>.

Q23. Is it possible to have more than one Faces Configuration file?

Yes. You can define the list of the configuration files in the web.xml.
This is an example:
<context-param>
<param-name>javax.faces.CONFIG_FILES</param-name>
<param-value>/WEB-INF/faces-config-navigation.xml,/WEB-INF/faces-beans.xml</param-</context-param>

Note: Do not register /WEB-INF/faces-config.xml file in the web.xml . Otherwise, the JSF implementation will process it twice.

Hi there, I guess the Note: column should have been meant or intended for "facesconfig.xml" file as thats the default configuration file for JSF (which is similar to strutsconfig.xml for Struts!!). faces-context.xml file sounds like the user defined config file similar to the aforementioned two xml files.

Q24. How to mask actual URL to the JSF page?

You'll need to implement your own version of javax.faces.ViewHandler which does what you need. Then, you register your own view handler in faces-config.xml.
Here's a simple abstract ViewHandler you can extend and then implement the 3 abstract methods for. The abstract methods you override here are where you'll do your conversions to/from URI to physical paths on the file system. This information is just passed right along to the default ViewHandler for JSF to deal with in the usual way. For example, you could override these methods to add and remove the file extension of an incoming view id (like in your example), for extension-less view URIs.

import java.io.IOException;
import java.util.Locale;
import javax.faces.FacesException;
import javax.faces.application.ViewHandler;
import javax.faces.component.UIViewRoot;
import javax.faces.context.FacesContext;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
* A facade view handler which maps URIs into actual physical views that the 
* underlying implementation can deal with regularly.
* Therefore, all internal references to view ids, for example in faces-config,
* will use the path to the physical files. Everything publicized, however, will
* see a "converted" / facade url.
*/
public abstract class SimpleConverterViewHandler extends ViewHandler {
private static final Log LOG = LogFactory.getLog(SimpleConverterViewHandler.class);
private final ViewHandler base;
public SimpleConverterViewHandler(ViewHandler base) {
this.base = base;
}

/**
* Distinguishes a URI from a physical file view.
* Tests if a view id is in the expected format -- the format corresponding
* to the physical file views, as opposed to the URIs.
* This test is necessary because JSF takes the view ID from the
* faces-config navigation, and calls renderView() on it, etc.
*/
public abstract boolean isViewFormat(FacesContext context, String viewId);
/**
* Convert a private file path (view id) into a public URI.
*/
public abstract String convertViewToURI(FacesContext context, String viewId);
/**
* Convert a public URI into a private file path (view id)
* note: uri always starts with "/";
*/
public abstract String convertURIToView(FacesContext context, String uri);
public String getActionURL(FacesContext context, String viewId) {
// NOTE: this is used for FORM actions.
String newViewId = convertViewToURI(context, viewId);
LOG.debug("getViewIdPath: " + viewId + "->" + newViewId);
return base.getActionURL(context, newViewId);
}
private String doConvertURIToView(FacesContext context, String requestURI) {
if (isViewFormat(context, requestURI)) {
return requestURI;
} else {
return convertURIToView(context, requestURI);
}
}
public void renderView(FacesContext context, UIViewRoot viewToRender)
throws IOException, FacesException {
if (null == context || null == viewToRender)
throw new NullPointerException("null context or view");
String requestURI = viewToRender.getViewId();
String newViewId = doConvertURIToView(context, requestURI);
LOG.debug("renderView: " + requestURI + "->" + newViewId);
viewToRender.setViewId(newViewId);
base.renderView(context, viewToRender);
}
public UIViewRoot restoreView(FacesContext context, String viewId) {
String newViewId = doConvertURIToView(context, viewId);
LOG.debug("restoreView: " + viewId + "->" + newViewId);
return base.restoreView(context, newViewId);
}
public Locale calculateLocale(FacesContext arg0) {
return base.calculateLocale(arg0);
}
public String calculateRenderKitId(FacesContext arg0) {
return base.calculateRenderKitId(arg0);
}
public UIViewRoot createView(FacesContext arg0, String arg1) {
return base.createView(arg0, arg1);
}
public String getResourceURL(FacesContext arg0, String arg1) {
return base.getResourceURL(arg0, arg1);
}
public void writeState(FacesContext arg0) throws IOException {
base.writeState(arg0);
}
}

Q25. How to print out html markup with h:outputText?

The h:outputText has attribute escape that allows to escape the html markup. By default, it equals to "true". It means all the special symbols will be replaced with '&' codes. If you set it to "false", the text will be printed out without ecsaping.

For example, <h:outputText value="<b>This is a text</b>"/>
will be printed out like:
<b>This is a text</b>
In case of <h:outputText escape="false" value="<b>This is a text</b>"/>
you will get:
This is a text

Q26. h:inputSecret field becomes empty when page is reloaded. How to fix this?

Set redisplay=true, it is false by default.