1)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-of-use in the following ways:
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Makes it easy to construct a UI from a set of reusable UI components
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Simplifies migration of application data to and from the UI
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Helps manage UI state across server requests
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Provides a simple model for wiring client-generated events to server-side
application code
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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.
2)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");
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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.
3)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">
4)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();
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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).
5)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");
6)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']}"/>
7)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";
}
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The following code snippet allows to terminate the session from the jsp page:
<% session.invalidate(); %> <c:redirect url="loginPage.jsf" />
8)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}" value="Say Hello" />
</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">
9)How to reload the page after ValueChangeListener is
invoked?
At the end of the ValueChangeListener, call
FacesContext.getCurrentInstance().renderResponse()
10)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().getResponse();
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();
}
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This is a jsp file snippet:
<h:commandButton immediate="true" actionListener="#{backingBean.viewPdf}" value="Read PDF" />
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