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One
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common
...
question
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about
...
JSF
...
is
...
how
...
to
...
manage
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messages
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of
...
various
...
types,
...
which
...
are
...
generated
...
by
...
JSF
...
components
...
and
...
backing
...
beans.
...
This
...
discussion
...
is
...
designed
...
as
...
an
...
introduction
...
to
...
the
...
topic
...
and
...
focused
...
on
...
entry
...
to
...
mid-level
...
JSF
...
users.
...
The
...
pattern
...
described
...
here
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is
...
just
...
one
...
approach
...
that
...
we
...
developed
...
which
...
meets
...
our
...
needs
...
for:
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- Providing
...
- a
...
- consistent
...
- and
...
- generic
...
- means
...
- for
...
- including
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- processing
...
- messages
...
- in
...
- all
...
- JSF
...
- pages.
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- Decorating
...
- the
...
- messages
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- with
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- images
...
- and
...
- styles
...
- to
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- differentiate
...
- severity
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- levels
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- to
...
- the
...
- user
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- which
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- is
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- browser
...
- safe.
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- Add
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- additional
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- messages
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- when
...
- appropriate.
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- Be
...
- localizable.
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- Not
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- affect
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- page
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- layouts
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- when
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- no
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- errors
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- are
...
- generated.
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Discussion
Our user-interface
...
requirements
...
dictate
...
that
...
(a)
...
as
...
far
...
as
...
the
...
user
...
is
...
concerned
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there
...
is
...
no
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such
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thing
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as
...
an
...
error,
...
(b)
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the
...
system
...
should
...
provide
...
as
...
little
...
information
...
as
...
necessary
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to
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draw
...
the
...
user's
...
attention
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to
...
any
...
issues
...
raised
...
during
...
processing
...
and
...
help
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them
...
correct
...
the
...
problem,
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(c)
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inform
...
on
...
all
...
operations
...
which
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change
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state
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in
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the
...
back-end
...
(success
...
as
...
well
...
as
...
failure),
...
and
...
(d)
...
provide
...
a
...
way
...
out
...
(i.e.
...
graceful
...
means
...
for
...
backing
...
out
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of
...
any
...
failed
...
operation).
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While
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(a)
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and
...
(d)
...
require
...
detailed
...
discussion
...
on
...
overall
...
system
...
design
...
which
...
is
...
out
...
of
...
scope
...
of
...
this
...
topic,
...
(b)
...
and
...
(c)
...
are
...
certainly
...
within
...
the
...
purview
...
of
...
this
...
JSF
...
discussion
...
and
...
are
...
our
...
points
...
of
...
focus.
...
JSF
...
message
...
components
...
The
...
basic
...
mechanism
...
for
...
managing
...
page-specific
...
messages
...
is
...
to
...
include
...
<h:message>
...
and
...
<h:messages>
...
tags
...
in
...
the
...
JSF
...
page.
...
<h:message>
...
is
...
component
...
specific
...
(i.e.
...
tied
...
to
...
a
...
particular
...
JSF
...
component
...
ID)
...
while
...
<h:messages>
...
can
...
provide
...
global
...
messaging
...
as
...
well
...
as
...
roll-up
...
all
...
component
...
specific
...
messages.
...
Our
...
experience
...
is
...
that
...
<h:message>
...
is
...
useful
...
for
...
components
...
which
...
have
...
validation
...
but
...
the
...
<h:messages>
...
tag
...
needs
...
to
...
be
...
better
...
managed
...
to
...
control
...
layout
...
and
...
information-provision.
...
For
...
example,
...
rather
...
than
...
displaying
...
a
...
list
...
of
...
validation
...
errors
...
that
...
have
...
been
...
generated
...
we
...
would
...
like
...
to
...
provide
...
a
...
new
...
message
...
such
...
as
...
'One
...
or
...
more
...
fields
...
have
...
missing
...
or
...
invalid
...
values.
...
Please
...
re-check
...
the
...
fields
...
indicated
...
below
...
and
...
re-submit
...
the
...
form.'
...
JSF
...
message
...
tags
...
display
...
messages
...
which
...
have
...
been
...
queued
...
as
...
the
...
request
...
is
...
processed.
...
Each
...
message
...
that
...
is
...
queued
...
has
...
a
...
message
...
priority
...
which
...
is
...
one
...
of
...
the
...
FacesMessage
...
priorities
...
defined
...
in
...
javax.faces.application.FacesMessage
...
and
...
are
...
defined
...
as
| Code Block | ||||
|---|---|---|---|---|
| ||||
{code:java} public static final FacesMessage.Severity SEVERITY_INFO = new Severity("Info", 1); public static final FacesMessage.Severity SEVERITY_WARN = new Severity("Warn", 2); public static final FacesMessage.Severity SEVERITY_ERROR = new Severity("Error", 3); public static final FacesMessage.Severity SEVERITY_FATAL = new Severity("Fatal", 4); {code} |
and
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can
...
be
...
either
...
associated
...
with
...
a
...
component
...
or
...
not.
...
When
...
a
...
message
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is
...
generated
...
during
...
processing,
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the
...
component,
...
validator
...
or
...
backing
...
generating
...
the
...
message
...
palces
...
the
...
message
...
into
...
one
...
of
...
the
...
message
...
queues
...
where
...
it
...
can
...
be
...
accessed
...
by
...
the
...
JSF
...
during
...
the
...
rendering
...
phase.
...
Generating
...
Messages
...
Messages
...
(error/info/warn/fatal)
...
can
...
be
...
enqueued
...
by
...
calling
...
the
...
FacesContext.getCurrentInstance().addMessage()
...
method.
...
Our
...
requirements
...
state
...
that
...
messages
...
are
...
displayed
...
on
...
all
...
change
...
in
...
state
...
as
...
well
...
as
...
processing
...
errors
...
such
...
as
...
bad
...
databases
...
retrievals
...
etc.
...
which
...
means
...
that
...
the
...
majority
...
of
...
our
...
pages
...
need
...
to
...
be
...
able
...
to
...
generate
...
messages.
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To
...
this
...
end,
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we
...
found
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it
...
is
...
convienient
...
to
...
put
...
quick-access
...
methods
...
in
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a
...
base
...
class
...
and
...
sub-class
...
all
...
backing
...
beans
...
from
...
it.
...
This
...
is
...
similar
...
to
...
how
...
Sun
...
Creator's
...
1.0
...
manages
...
backing
...
beans
...
and
...
our
...
methods
...
are
...
adopted
...
from
...
this.
...
For
...
severity
...
our
...
base
...
class
...
has
...
two
...
methods
...
as
...
below
...
for
...
INFO.
| Code Block | ||||
|---|---|---|---|---|
| ||||
{code:java} protected void setInfoMessage(String summary) { getFacesContext().addMessage(null, new FacesMessage(FacesMessage.SEVERITY_INFO, summary, null)); } protected void setInfoMessage(UIComponent component, String summary) { getFacesContext().addMessage(component.getClientId(getFacesContext()), new FacesMessage(FacesMessage.SEVERITY_INFO, summary, null)); } {code} |
The
...
first
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method
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enqueues
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a
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global
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message
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with
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INFO
...
severity
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while
...
the
...
second
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method
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associates
...
the
...
INFO
...
message
...
with
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a
...
component
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(most
...
probably
...
from
...
a
...
custom
...
(page-specific)
...
validation.
...
We
...
also
...
have
...
a
...
base
...
class
...
for
...
all
...
our
...
validators
...
(which
...
perform
...
page-specific
...
validation
...
when
...
necessary)
...
which
...
uses
...
the
...
following
...
protected
...
method
...
for
...
raising
...
messages
| Code Block | ||||
|---|---|---|---|---|
| ||||
{code:java} protected static void invalidateInput(UIInput uii, String message) { uii.setValid(false); FacesMessage facesMessage = new FacesMessage(FacesMessage.SEVERITY_WARN, message, null); throw new ValidatorException(facesMessage); } {code} |
Note
...
that
...
we
...
only
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raise
...
messages
...
with
...
WARN
...
severity
...
as
...
our
...
requirements
...
preclude
...
displaying
...
anything
...
which
...
looks
...
or
...
smells
...
like
...
an
...
error
...
to
...
our
...
users.
...
As
...
all
...
our
...
backing
...
beans
...
have
...
these
...
methods
...
accesible
...
to
...
them,
...
we
...
can
...
simply
...
add
...
appropriate
...
calls
...
to
...
enqueue
...
messages
...
in
...
our
...
business
...
logic
...
such
...
as
| Code Block | ||||
|---|---|---|---|---|
| ||||
{code:java} setInfoMessage(Messages.getString("MANIFEST_SAVED")); or setWarnMessage(Messages.getString("UPDATE_DATABASE_ERROR")); or setInfoMessage(Messages.getString("STORAGE_TRANSFER_ONE", new Integer(count), fromUnit.getName(), toUnit.getName())); {code} |
where
...
the
...
Messages
...
class
...
provides
...
access
...
to
...
a
...
messages
...
properties
...
file
...
and
...
performs
...
standard
...
parameter
...
replacement
...
using
...
Apache's
...
Common
...
Lang
...
StringUtils.
...
Displaying
...
Messages
...
Rasing
...
messages
...
is
...
one
...
topic,
...
displaying
...
them
...
another.
...
As
...
we
...
need
...
a
...
consistent
...
look
...
and
...
feel
...
for
...
all
...
messages
...
we
...
choose
...
to
...
include
...
a
...
JSP
...
in
...
each
...
page
...
which
...
handles
...
all
...
messages
...
which
...
are
...
not
...
component
...
specific.
...
Our
...
PageMessages.jspf
...
is
...
as
...
follows:
| Code Block | ||||
|---|---|---|---|---|
| ||||
{code:xml} <%@ taglib uri="http://java.sun.com/jsf/html" prefix="h"%> <%@ taglib uri="http://java.sun.com/jsf/core" prefix="f"%> <%@ taglib uri="http://myfaces.apache.org/tomahawk" prefix="t"%> <h:panelGrid styleClass="group" columns="2" cellpadding="2" cellspacing="0" width="100%" columnClasses="buttonCol, leftAlignCol" rowClasses="vertAlignTop" rendered="#{! empty facesContext.maximumSeverity}" > <h:graphicImage value="#{PageMessages.messageImage}" style="float: left; vertical-align: top;" /> <h:panelGrid columns="1" cellpadding="2" cellspacing="2" columnClasses="leftAlignCol" rowClasses="vertAlignTop" width="100%"> <h:outputText value="#{PageMessages.messageHeader}" escape="false" rendered="#{PageMessages.renderMessage}"/> <h:messages errorClass="errorMessage" infoClass="infoMessage" layout="table" globalOnly="true" showDetail="false" showSummary="true"/> </h:panelGrid> </h:panelGrid> {code} The messages are only displayed only if one or more messages are enqueued by conditionally rendering the table using {{ |
The messages are only displayed only if one or more messages are enqueued by conditionally rendering the table using rendered="#{!
...
empty
...
facesContext.maximumSeverity
...
}
...
" which
...
uses
...
EL
...
to
...
check
...
if
...
the
...
queues
...
are
...
empty
...
or
...
not.
...
Depending
...
on
...
the
...
level
...
of
...
severity
...
we
...
display
...
an
...
themed
...
image
...
followed
...
by
...
an
...
optional
...
pre-amble
...
to
...
the
...
messages
...
and
...
then
...
the
...
global
...
messages
...
themselves.
...
The
...
global
...
messages
...
are
...
displayed
...
in
...
table
...
format.
...
You
...
will
...
notice
...
that
...
we
...
use
...
a
...
backing
...
bean
...
(PageMessages.java)
...
in
...
request
...
scope
...
to
...
control
...
the
...
JSPF.
...
The
...
code
...
for
...
this
...
is
...
as
...
follows:
| Code Block | ||||
|---|---|---|---|---|
| =
| |||
} import Messages; import org.apache.commons.lang.StringUtils; import javax.faces.application.FacesMessage; import javax.faces.application.FacesMessage.Severity; public class PageMessages extends AbstractUIBean { private static final long serialVersionUID = -6479897299239746841L; private static final String BEAN_NAME = PageMessages.class.getName(); private String messageHeader; private String messageImage; private Severity severityLevel; public PageMessages() { messageHeader = null; // See if there are messages queued for the page severityLevel = getFacesContext().getMaximumSeverity(); if (null != severityLevel) { getLogger().debug("Severity Level Trapped: level = '" + severityLevel.toString() + "'"); if (severityLevel.equals(FacesMessage.SEVERITY_ERROR)) { messageHeader = Messages.getString("PAGE_MESSAGE_ERROR"); messageImage = "resources/warning.gif"; } else if (severityLevel.equals(FacesMessage.SEVERITY_INFO)) { messageHeader = null; messageImage = "resources/information.gif"; } else if (severityLevel.equals(FacesMessage.SEVERITY_WARN)) { messageHeader = null; messageImage = "resources/warning.gif"; } else if (severityLevel.equals(FacesMessage.SEVERITY_FATAL)) { messageHeader = Messages.getString("PAGE_FATAL_ERROR"); messageImage = "resources/stop.gif"; } } else { getLogger().debug("Severity Level Trapped: level = 'null'"); } } public Boolean getRenderMessage() { return new Boolean(StringUtils.isNotBlank(getMessageHeader())); } public String getBeanName() { return BEAN_NAME; } public String getMessageHeader() { return messageHeader; } public String getMessageImage() { return messageImage; } } {code} |
Our
...
backing
...
bean
...
extends
...
our
...
basic
...
UI
...
base
...
classes
...
which
...
provides
...
access
...
to
...
central
...
logging
...
etc.
...
You
...
can
...
see
...
that
...
if
...
a
...
component
...
has
...
enqueued
...
a
...
message
...
of
...
ERROR
...
we
...
add
...
a
...
localized
...
message
...
at
...
the
...
top
...
of
...
the
...
page
...
which
...
(we
...
hope)
...
gracefully
...
moderates
...
the
...
user-impact
...
of
...
seeing
...
the
...
same
...
form
...
again
...
with
...
a
...
bunch
...
of
...
annotations!
...
The
...
PageMessages.jspf
...
is
...
included
...
into
...
each
...
JSP
...
using
...
the
...
following
...
code:
| Code Block | ||||
|---|---|---|---|---|
| ||||
{code:xml} <f:subview id="messages"> <jsp:directive.include file="PageMessages.jspf" /> </f:subview> {code} |
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