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One
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common
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question
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about
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JSF
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is
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how
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to
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manage
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messages
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of
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various
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types,
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which
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are
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generated
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by
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JSF
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components
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and
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backing
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beans.
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This
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discussion
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is
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designed
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as
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an
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introduction
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to
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the
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topic
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and
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focused
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on
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entry
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to
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mid-level
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JSF
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users.
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The
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pattern
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described
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here
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is
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just
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one
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approach
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that
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we
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developed
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which
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meets
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our
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needs
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for:
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- Providing
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- a
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- consistent
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- and
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- generic
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- means
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- for
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- including
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- processing
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- messages
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- in
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- all
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- JSF
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- pages.
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- Decorating
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- the
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- messages
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- with
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- images
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- and
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- styles
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- to
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- differentiate
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- severity
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- levels
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- to
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- the
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- user
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- which
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- is
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- browser
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- safe.
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- Add
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- additional
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- messages
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- when
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- appropriate.
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- Be
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- 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
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- generated.
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Discussion
Our user-interface
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requirements
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dictate
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that
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(a)
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as
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far
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as
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the
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user
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is
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concerned
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there
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is
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no
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such
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thing
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as
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an
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error,
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(b)
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the
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system
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should
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provide
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as
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little
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information
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as
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necessary
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to
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draw
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the
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user's
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attention
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to
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any
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issues
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raised
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during
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processing
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and
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help
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them
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correct
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the
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problem,
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(c)
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inform
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on
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all
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operations
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which
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change
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state
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in
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the
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back-end
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(success
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as
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well
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as
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failure),
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and
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(d)
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provide
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a
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way
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out
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(i.e.
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graceful
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means
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for
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backing
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out
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of
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any
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failed
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operation).
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While
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(a)
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and
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(d)
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require
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detailed
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discussion
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on
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overall
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system
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design
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which
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is
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out
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of
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scope
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of
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this
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topic,
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(b)
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and
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(c)
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are
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certainly
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within
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the
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purview
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of
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this
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JSF
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discussion
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and
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are
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our
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points
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of
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focus.
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JSF
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message
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components
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The
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basic
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mechanism
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for
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managing
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page-specific
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messages
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is
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to
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include
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<h:message>
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and
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<h:messages>
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tags
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in
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the
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JSF
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page.
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<h:message>
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is
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component
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specific
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(i.e.
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tied
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to
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a
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particular
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JSF
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component
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ID)
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while
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<h:messages>
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can
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provide
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global
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messaging
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as
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well
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as
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roll-up
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all
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component
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specific
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messages.
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Our
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experience
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is
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that
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<h:message>
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is
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useful
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for
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components
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which
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have
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validation
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but
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the
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<h:messages>
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tag
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needs
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to
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be
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better
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managed
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to
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control
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layout
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and
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information-provision.
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For
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example,
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rather
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than
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displaying
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a
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list
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of
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validation
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errors
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that
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have
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been
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generated
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we
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would
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like
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to
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provide
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a
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new
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message
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such
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as
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'One
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or
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more
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fields
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have
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missing
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or
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invalid
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values.
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Please
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re-check
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the
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fields
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indicated
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below
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and
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re-submit
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the
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form.'
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JSF
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message
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tags
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display
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messages
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which
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have
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been
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queued
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as
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the
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request
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is
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processed.
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Each
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message
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that
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is
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queued
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has
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a
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message
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priority
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which
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is
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one
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of
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the
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FacesMessage
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priorities
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defined
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in
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javax.faces.application.FacesMessage
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and
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are
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defined
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as
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and
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can
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be
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either
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associated
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with
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a
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component
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or
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not.
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When
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a
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message
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is
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generated
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during
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processing,
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the
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component,
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validator
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or
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backing
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generating
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the
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message
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palces
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the
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message
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into
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one
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of
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the
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message
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queues
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where
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it
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can
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be
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accessed
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by
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the
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JSF
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during
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the
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rendering
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phase.
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Generating
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Messages
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Messages
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(error/info/warn/fatal)
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can
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be
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enqueued
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by
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calling
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the
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FacesContext.getCurrentInstance().addMessage()
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method.
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Our
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requirements
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state
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that
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messages
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are
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displayed
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on
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all
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change
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in
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state
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as
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well
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as
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processing
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errors
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such
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as
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bad
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databases
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retrievals
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etc.
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which
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means
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that
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the
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majority
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of
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our
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pages
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need
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to
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be
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able
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to
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generate
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messages.
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To
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this
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end,
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we
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found
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it
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is
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convienient
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to
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put
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quick-access
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methods
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in
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a
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base
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class
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and
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sub-class
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all
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backing
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beans
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from
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it.
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This
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is
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similar
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to
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how
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Sun
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Creator's
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1.0
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manages
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backing
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beans
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and
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our
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methods
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are
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adopted
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from
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this.
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For
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severity
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our
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base
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class
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has
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two
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methods
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as
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below
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for
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INFO.
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The first method enqueues a global message with INFO severity while the second method associates the INFO message with a component (most probably from a custom (page-specific)
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validation.
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We
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also
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have
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a
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base
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class
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for
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all
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our
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validators
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(which
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perform
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page-specific
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validation
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when
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necessary)
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which
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uses
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the
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following
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protected
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method
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for
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raising
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messages
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Note that we only 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
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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:
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The messages are only displayed only if one or more messages are enqueued by conditionally rendering the table using rendered="#{!
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empty
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facesContext.maximumSeverity}"
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which
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uses
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EL
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to
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check
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if
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the
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queues
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are
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empty
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or
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not.
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Depending
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on
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the
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level
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of
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severity
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we
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display
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an
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themed
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image
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followed
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by
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an
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optional
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pre-amble
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to
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the
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messages
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and
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then
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the
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global
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messages
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themselves.
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The
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global
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messages
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are
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displayed
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in
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table
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format.
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You
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will
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notice
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that
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we
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use
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a
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backing
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bean
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(PageMessages.java)
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in
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request
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scope
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to
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control
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the
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JSPF.
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The
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code
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for
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this
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is
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as
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follows:
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Our
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backing
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bean
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extends
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our
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basic
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UI
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base
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classes
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which
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provides
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access
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to
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central
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logging
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etc.
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You
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can
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see
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that
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if
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a
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component
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has
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enqueued
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a
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message
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of
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ERROR
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we
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add
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a
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localized
...
message
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at
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the
...
top
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of
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the
...
page
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which
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(we
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hope)
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gracefully
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moderates
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the
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user-impact
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of
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seeing
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the
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same
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form
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again
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with
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a
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bunch
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of
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annotations!
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The
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PageMessages.jspf
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is
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included
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into
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each
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JSP
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using
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the
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following
...
code:
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