meljun_cortes_jedi slides web programming chapter10 advanced jsf

8/3/2019 MELJUN_CORTES_JEDI Slides Web Programming Chapter10 Advanced JSF

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Advanced JavaServerFacesTopics

Web Programming


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FacesContext

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In the previous chapter:

FacesContext was used to object in accessing a Map of the objectscurrently in the user session.

An instance of the FacesContext object can be obtained by callingthe FacesContext.getCurrentInstance() method.


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FacesContext and the

Component Tree

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For each views using JSF UI elements, there is acorresponding component tree that models it. The JSF

specification requires that all implementations of JSF storethis component tree inside the FacesContext object.


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Component Tree

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Allows developers access to all of the user interfacecomponents and their data.

Also allows developers to:

Programatically add components to the view. Change or add converters or validators dynamically.

Remove components.

Most often used to provide screen redirection within the

Faces framework.


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Component Tree

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Example:

...

String targetPage = "/newPage.jsp";

FacesContext context = FacesContext.getCurrentInstance();

context.getApplication().getViewHandler().createView(context, targetPage);

...

The createView method creates a copy of the component tree thatmakes up the targetPage and places it as the current viewcomponent tree.


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External Context

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The ExternalContext object accessible throughFacesContext gives us access to the environment the

framework is running on. For a web application, it gives us access to:

The HttpServletRequest object representing the current request.

A Map of the object stored in the user session.

The ServletContext object representing the context of the whole webapplication.


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External Context

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(Web application continued)

To retrieve the HttpServletRequest object:

FacesContext context = FacesContext.getCurrentInstance();HttpServletRequest request =(HttpServletRequest)context.getExternalContext()

.getRequest(); No way to have direct access to the actual HttpSession object

associated with our session, but the objects stored within it can beaccessed through a Map object:

Map sessionMap = context.getExternalContext().getSessionMap();


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External Context

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(Web application continued)

To retrieve the ServletContext representing our entire application:

ServletContext servletContext =(ServletContext)context.getExternalContext().getContext();


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JSF Standard Validators

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JSF provides us with a set of validators that we can use out-of-the-box for our application.

Three standard validators:

DoubleRangeValidator: Checks if the value in the input field isconvertible into double and that it is within the supplied minimumand maximum values.

JSP Tag: validateDoubleRange

Attributes: minimum, maximum

LengthValidator: Checks if the value in the input field is convertibleinto a String and that its length is within the supplied minimum andmaximum values.

JSP Tag: validateLength



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JSF Standard Validators

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(Standard validators continued)

LongRangeValidator: Checks if the value in the input field isconvertible into a long and that it is within the supplied minimum andmaximum values.

JSP Tag: validateLongRange


The JSP tags for the validators can all be found inside thecore tag library. To use them, we add the following line tothe top of the page:


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Using the Standard Validators

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Insert the JSP tag for the validator inside the body of theinput component to be validated.

Example:

...

...


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Using the Standard Validators

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(Example continued)

This is the JSP code for the login page we implemented in theprevious lesson using JSF, with some modifications:

The tag defining the password field () was changed such that the

tag no longer closed itself on the same line it was declared. It now makes use ofa matching tag to close itself.

The tag defining the validation to be performed () was insertedbetween the opening and closing tags.


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Customized Validation

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Three ways:

Extend the class of the UI component that accepts our input so thatwe could override its validate method.

Non-portable

Create an external validation method.

Create our own separate Validator implementations, register them inthe framework, then plug it into the UI component.


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External Validation Method

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Creating an external validation method

Similar to the one to create an application method that will handleaction events:

We also need to create a method adhering to a set of rules inside a JavaBean

managed by the framework and later bind that method to the appropriate UIcomponent.

The method that we create must conform to the following rules:

The method must be declared public, with a return type of void.

There is no limitation to the method name.

It must take the following parameters in this order: FacesContext ctxt, UIInputcomponent, Object value.

It must be declared to throw a ValidatorException.


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(Creating continued)

To create a custom validation method for our password field in theprevious example, one that would accept only alternating letters andnumbers:

public void validatePassword(FacesContext ctxt, UIInput component, Object value)throws ValidatorException

For the method implementation, we can make use of data providedthrough the parameters:

The FacesContext object provides us access to external resources such as theobjects in request and session scope, as well as other objects within the Faces

framework. The UIInput object is the instance of the input component that requires validation;

having an instance of this object gives us access to the component's state.

The Object value is the value inside the component that requires validation.


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Implementation of our method:

public void validatePassword(FacesContext ctxt, UIInput component, Object value)throws ValidatorException {

if (null == value)return;

if ( ! (isPasswordValid(value.toString() ) ) {FacesMessage message = new FacesMessage(Input error, Password is not

valid);throw new ValidatorException(message);

}

}

protected boolean isPasswordValid(String password) {... FacesMessage: Models a message within the Faces framework. The first

parameter passed into its constructor is a summary, the second the details ofthe actual message.


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To be able to actually display the generated error message,developers should add an or tag in theJSP page.

...

... : Displays messages only for a specific component, indicated by

the value in the for attribute. An tag will display all themessages available for all the components in the page


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Separate Validator

Implementation

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Create a separate class that implements the Validatorinterface.

Defines one method: a validate method Public

Returns void

Parameters are instances of the FacesContext, UIInput, and Object classes

No difference with that of an external validation method in terms ofinternal method implementation.


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External vs. Separate

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Difference: how they are used.

An external validation method is used more for validation codespecific to a particular component.

A separate Validator implementation is used to contain general-

purpose validation code that will be reused extensively within yourapplication(s).


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Separate Validator

Implementation

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Registering a Validator component

To use a custom Validator component, we must first register it sothat it can be recognized by the JSF Framework.

This is done by placing a configuration entry in the faces-config.xmlfile.

Example:

A validator for checking the password

fieldAlternatingValidatorjedi.sample.jsf.validator.AlternatingValidator


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Separate Validator

Implementation

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Using a validator component

To use the Validator component that we just registered, we makeuse of the tag and supply in its validatorId attribute ourvalidator's id.

Example:

...

...


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Separate Validator

Implementation

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Adding attributes to our validator

Add a property within our class for each of the attributes it wouldsupport and implement get and set methods for each of them.

Include an entry for each of the attributes within our configurationentry for the validator.


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package jedi.sample.jsf.validator;

public class AlternatingValidator implements Validator {private Integer interval;

public Integer getInterval() {return interval;

}

public void setInterval(Integer interval) {this.interval = interval;

}

public void validate(FacesContext ctxt, UIInput component, Object value)throws ValidatorException {

if (null == value || interval == null)return;

if ( ! (isPasswordValid(value.toString() ) ) {FacesMessage message = new FacesMessage(Input error, Password is not valid);

throw new ValidatorException(message);}

}

protected boolean isPasswordValid(String password) {...


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A validator for checking the password fieldAlternatingValidatorjedi.sample.jsf.validator.AlternatingValidator

intervaljava.lang.Integer

___________________________________________________________________________

...

...


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Converters

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Convert the values given by the user from their native stringrepresentation into the appropriate format or type usedinternally by the server.

Bi-directional: They can also be used to change how internal

data is displayed to the user.

Define a getAsString() and getAsObject() method that canbe called by the framework at the appropriate time.

getAsString: Called to provide a String representation to the data.

getAsObject: Used to convert the String into the type required.


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Converters

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Associated to input types by making use of the converterattribute built-in into some of the input components providedby Faces.

Components that support the converter attribute:

inputText

inputSecret

inputHidden

OutputText

Example:

To modify an inputText tag so that it naturally allows for Integerconversion:


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Converters

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Converters

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Of this set of converters:

Most of the converter sets are non-configurable.

DateTimeConverter and NumberConverter, however, can make useof special tags, which may allow a developer to customize their

behavior.


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DateTimeConverter

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Can be used to convert user input into instances ofjava.util.Date.

Provides a number of attributes with which the developercan specify the format used in the conversion.

Format specified is enforced when the user supplies his input. Ifviolated, a conversion error will occur, and the framework will haltfurther processing of data.


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DateTimeConverter

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Attributes made available using tag:

dateStyle: One of the date styles defined in java.text.DateFormat.Possible values are: default, short, long, medium, or full.

parseLocale: Locale to use during conversion.

pattern: Formatting pattern to be used in conversion. If a value forthis attribute is specified, the system will ignore any values fordateStyle, timeStyle, and type.

timeStyle: One of the time styles defined in java.text.DateFormat.Possible values are: default, short, medium, long, or full.

timeZone: Time zone to use.

type: A String that defines whether the output will be a data or timeinstance, or both. The possible values are: date, time, and both.Default value is date.


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DateTimeConverter

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Example: usage of the DateTimeConverter:

Create a blank web application ready for JSF.

Create a simple bean that will hold the date we will input later.

import java.util.Date;

public class DateBean {private Date date;

public Date getDate() {return date;

}

public void setDate(Date date) {this.date = date;

}}


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DateTimeConverter

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(Example continued)

Add its configuration entry in the faces-config.xml.

This bean serves as the backing model for our date conversion exampledateBeanjedi.sample.DateBeanrequest

date


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DateTimeConverter

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(Example continued)

Create the JSP file that will generate the view.

Date :


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DateTimeConverter

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(Example continued)

Notes for the sample JSP page:

For our DateTimeConverter, we have specified a pattern of M/d/yy. Since theconverter enforces this pattern on the user, the user will have to input somethinglike 1/13/06 as a date before he can continue.

We have added a required attribute with a true value for our input field. Thisensures that the user cannot post blank inputs.

We have made use of an tag associated with our dateField input.This makes sure that any messages generated by the input field (like thosegenerated by conversion errors) are displayed.

The action attribute for the commandButton has deliberately been left blank, so

we can focus solely on the messages generated by the converter.


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DateTimeConverter

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(Example continued)

Loading the web application into a compatible server and accessingthe page:


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DateTimeConverter

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(Example continued)

Trying out an input of January 13, 2006 would result in the following:


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DateTimeConverter

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(Example continued)

Entering a date in the proper format would result in no change to ourpage, which indicates that the data was successfully converted andstored in our bean.


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DateTimeConverter

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(Example continued)

What if we did not use the converter?

Date :


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DateTimeConverter

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(Example continued)

Now, entering a date of any format will cause an error:

This is because the property associated with our input field is a Date object. Theframework cannot automatically change the String representation of the inputinto a date, so it looks for a Converter object that will handle it. Since nonewere found, it threw a null error.


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NumberConverter

40Web Programming

Used to convert number inputs and enforce specialformatting on them.

Attributes:

currencyCode: An ISO 4217 currency code to be applied when

formatting currency.

currencySymbol: The currency symbol to use when formattingcurrency.

groupingUsed: Indicates whether a grouping symbol will be used.

integerOnly: Indicates whether the integer part only of the numberwill be displayed or stored.

locale: Locale used.

maxIntegerDigits: The maximum number of digits shown or usedwhen handling the integer part of the number.


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NumberConverter

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(Attributes continued)

maxFractionDigits: The maximum number of digits that will beshown or used when handling the decimal part of the number.

minFractionDigits: The minimum number of digits that will be shown

or used when handling the decimal part of the number. minIntegerDigits: The minimum number of digits that will be shown

or used when handling the integer part of the number.

pattern: The pattern to be used when formatting or displaying thenumber.

type: Indicates whether the number to be converted is treated as acurrency, percent, or number. Possible values are currency, percent,and number.


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NumberConverter

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(Attributes continued)

Any patterns or symbols indicated in the attributes are enforced asrules on the user, and if violated, a conversion error will occur andfurther processing of the data will halt.


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Custom Converters

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Can be created by creating a class which implements theConverter interface. This interface defines two methods:

public Object getAsObject(FacesContext ctxt, UIComponentcomponent, String input)

public Object getAsString(FacesContext ctxt, UIComponentcomponent, Object source)


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Custom Converters

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Web Programming

Sample scenario:

We have a form page that requires the user to input a monetaryamount.

We would like to store this input as a Double object so as to facilitate

easier processing later on. The input field must be flexible enough to handle straight number

inputs (ex. 2000), or inputs that include grouping symbols (2,000).Since the page will revert control back to itself, the data should beredisplayed as having grouping symbols.


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getAsObject

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Web Programming

Called by the framework on the associated converter when itneeds to convert the user's input from its string representationinto another object type.

Concept: Perform processing operations on the provided

String parameter and return the Object that will represent it onthe server side.


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Web Programming

public Object getAsObject(FacesContext facesContext, UIComponent uIComponent,String str) {

Double doubleObject = null;try {

doubleObject = Double.valueOf(str);} catch (NumberFormatException nfe) {

//if exception occurs, one probable cause is existence of grouping symbol

//retrieve an instance of a NumberFormat object//and make it recognize grouping symbols

NumberFormat formatter = NumberFormat.getNumberInstance();

formatter.setGroupingUsed(true);

// use the NumberFormat object to retrieve the numerical value of the inputtry {

Number number = formatter.parse(str);if (number.doubleValue()


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Web Programming

} catch (ParseException pe) {// if code reaches this point, none of the supported formats were followed.// create an error message and display it to the user through the exception object

FacesMessage message = new FacesMessage("Unsupported format","This field supports only numbers (5000), or numbers with commas (5,000)");

throw new ConverterException(message);}

}

return doubleObject;

}


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getAsString

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Web Programming

Makes Converters bi-directional: It dictates the Stringrepresentation of the relevant internal data.

Concept: Display the amount stored within the Double objectas a number with grouping symbols.

Simpler because we know with certainty the exact format ofour input.


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Web Programming

public String getAsString(FacesContext context, UIComponent component, Objectsource) {

Double doubleValue = (Double)obj;

NumberFormat formatter = NumberFormat.getNumberInstance();

formatter.setGroupingUsed(true);

return formatter.format(doubleValue);

}


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Using the Custom Converter

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Web Programming

After we have created our custom converter:

Configure the framework so that it can recognize its existence. Adda configuration entry in the faces-config.xml.

Configuration entries for converters come after all entries for validators, butbefore any entries for managed beans.

Custom converter for accepting monetary inputmyConverterjedi.sample.MyCustomConverter

Specify its converter id within an tag:


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Value Binding

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Web Programming

(Example continued)

The JSF page is able to associate the loginPage identifier to aninstance of a LoginPageBean due to our entry in the faces-config.xml. The relevant entry is presented below:

This bean serves as the backing model for our login formloginPagejedi.sample.LoginPageBeanrequest...

Since the LoginPageBean is declared to be a managed bean in the framework,an instance of LoginPageBean will be created and placed in the configuredscope (if one doesn't already exist) when the JSF page is evaluated. On pagesubmission, the values that the user has entered would be automatically placedwithin the bean's properties.

Registering Action Handlers


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Registering Action Handlersto View Components

52Web Programming

JSF introduces the concept of event-based programminginto the web environment.

Some of the UI components that JSF provides will, given theappropriate user action or input, generate events that can beprocessed by action handlers.

Registering Action Handlers


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Registering Action Handlersto View Components

53Web Programming

Example:

To "register" a handler for a commandButton component:

...

...

The # notation binds a method named performLogin found in a bean referencedwith the name loginPage to our button. This time, instead of storing the value forthe component, the bound method acts as the action handler for the button click.


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Page Navigation

54Web Programming

JSF determines the next screen that will be displayed to theuser upon form submission using the return value of themethod that serves as the action handler for the submitbutton.

The String value is looked up against navigation rules defined withinthe configuration file.


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Page Navigation

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Example:/login.jsfAny failure result should bring the user to an error page

failure/error.jspSuccessful login should bring user to welcome pagesuccess/welcome.jsp

So, if the performLogin method were to return a value or outcome of"failure", the user will be redirected to error.jsp.

P N i i


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Page Navigation

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(Example continued)

As an alternative to using an action handler, it is also possible tostatically provide the navigation rule to be called:

...

...

Oth JSF C t T


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Other JSF Component Tags

57Web Programming

Acts in a way similar to that of the tag in the Strutsframework.

Exposes messages from the application into the output text.

Displays an HTML element.

Takes in an array (or collection of objects) and iterates over them,automatically creating the necessary and elements.

Defines a child tag named . Content placed inside the body of a tag form the template for the

column definition for each row in the table.

Oth JSF C t T


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( continued)

Example:


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( continued)

HTML equivalent

Ewan

Coba

DevonShire

California

San Diego

Oth JSF C t T


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( continued)

Attributes include (but are not limited to):

value: Defines the collection or array to be iterated over. This could either be aproperty inside a managed bean or a method in a bean that will return thenecessary content.

var: Defines the name of the variable which will expose the contents of thecollection or array being iterated over. This variable is visible only within the tag.

border, cellspacing: Standard HTML table attributes.

rowClasses: A comma-delimited list of CSS styles that will alternately be appliedto each of the rows in the table.

Oth JSF C t T


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Container tags like only allow JSF tags within theirbody. This means that custom tags or even JSTL tags will not workinside of them. This can be circumvented with the use of the tag

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