...
Many
...
Actions
...
share
...
common
...
concerns.
...
Some
...
Actions
...
need
...
input
...
validated.
...
Other
...
Actions
...
may
...
need
...
a
...
file
...
upload
...
to
...
be
...
pre-processed.
...
Another
...
Action
...
might
...
need
...
protection
...
from
...
a
...
double
...
submit.
...
Many
...
Actions
...
need
...
drop-down
...
lists
...
and
...
other
...
controls
...
pre-populated
...
before
...
the
...
page
...
displays.
...
The
...
Struts
...
Action
...
Framework
...
makes
...
it
...
easy
...
to
...
share
...
solutions
...
to
...
these
...
concerns
...
using
...
an
...
"Interceptor"
...
strategy.
...
When
...
you
...
request
...
a
...
resource
...
that
...
maps
...
to
...
an
...
"action",
...
the
...
framework
...
invokes
...
the
...
Action
...
object.
...
But,
...
before
...
the
...
Action
...
is
...
executed,
...
the
...
invocation
...
can
...
be
...
intercepted
...
by
...
another
...
object.
...
After
...
the
...
Action
...
executes,
...
the
...
invocation
...
could
...
be
...
intercepted
...
again.
...
Unsurprisingly,
...
we
...
call
...
these
...
objects
...
"Interceptors."
...
Interceptors
...
can
...
execute
...
code
...
before
...
and
...
after
...
an
...
Action
...
is
...
invoked.
...
Most
...
of
...
the
...
framework's
...
core
...
functionality
...
is
...
implemented
...
as
...
Interceptors.
...
Features
...
like
...
double-submit
...
guards,
...
type
...
conversion,
...
object
...
population,
...
validation,
...
file
...
upload,
...
page
...
preparation,
...
and
...
more,
...
are
...
all
...
implemented
...
with
...
the
...
help
...
of
...
Interceptors.
...
Each
...
and
...
every
...
Interceptor
...
is
...
pluggable,
...
so
...
you
...
can
...
decide
...
exactly
...
which
...
features
...
an
...
Action
...
needs
...
to
...
support.
...
Interceptors
...
can
...
be
...
configured
...
on
...
a
...
per-action
...
basis.
...
Your
...
own
...
custom
...
Interceptors
...
can
...
be
...
mixed-and-matched
...
with
...
the
...
Interceptors
...
bundled
...
with
...
the
...
framework.
...
Interceptors
...
"set
...
the
...
stage"
...
for
...
the
...
Action
...
classes,
...
doing
...
much
...
of
...
the
...
"heavy
...
lifting"
...
before
...
the
...
Action
...
executes.
...
Action Lifecyle |
---|
|
In some cases, an Interceptor might keep an Action from firing, because of a double-submit or because validation failed. Interceptors can also change the state of an Action before it executes.
The Interceptors are defined in a stack that specifies the execution order. In some cases, the order of the Interceptors on the stack can be very important.
Configuring Interceptors
Code Block | ||||||
---|---|---|---|---|---|---|
| ||||||
Lifecyle || | !overview.png! | In some cases, an Interceptor might keep an Action from firing, because of a double-submit or because validation failed. Interceptors can also change the state of an Action before it executes. The Interceptors are defined in a stack that specifies the execution order. In some cases, the order of the Interceptors on the stack can be very important. h2. Configuring Interceptors {code:xml|title=action.xml} <package name="default" extends="action-default"> <interceptors> <interceptor name="timer" class=".."/> <interceptor name="logger" class=".."/> </interceptors> <action name="login" class="tutorial.Login"> <interceptor-ref name="timer"/> <interceptor-ref name="logger"/> <result name="input">login.jsp</result> <result name="success" type="redirect-action">/secure/home</result> </action> </package> {code} h2. Stacking Interceptors With most web applications, we find ourselves wanting to apply the same set of |
Stacking Interceptors
With most web applications, we find ourselves wanting to apply the same set of Interceptors over and over again. Rather than reiterate the same list of Interceptors, we can bundle these Interceptors together using an Interceptor Stack.
Code Block | ||||||
---|---|---|---|---|---|---|
| ||||||
Interceptors over and over again. Rather than reiterate the same list of Interceptors, we can bundle these Interceptors together using an Interceptor Stack. {code:xml|title=action.xml} <package name="default" extends="action-default"> <interceptors> <interceptor name="timer" class=".."/> <interceptor name="logger" class=".."/> <interceptor-stack name="myStack"> <interceptor-ref name="timer"/> <interceptor-ref name="logger"/> </interceptor-stack> </interceptors> <action name="login" class="tutuorial.Login"> <interceptor-ref name="myStack"/> <result name="input">login.jsp</result> <result name="success" type="redirect-action">/secure/home</result> </action> </package> {code} |
Looking
...
inside
...
action-default.xml
...
,
...
we
...
can
...
see
...
how
...
it's
...
done.
...
The
...
Default
...
Configuration
Code Block | |||||||
---|---|---|---|---|---|---|---|
|
| ||||||
} <!DOCTYPE xwork PUBLIC "-//OpenSymphony Group//XWork 1.0//EN" "http://www.opensymphony.com/xwork/xwork-1.1.dtd"> <!-- // START SNIPPET: webwork-default --> <xwork> <package name="action-default"> <result-types> <result-type name="chain" class="com.opensymphony.xwork.ActionChainResult"/> <result-type name="dispatcher" class="org.apache.struts.action2.dispatcher.ServletDispatcherResult" default="true"/> <result-type name="freemarker" class="org.apache.struts.action2.views.freemarker.FreemarkerResult"/> <result-type name="httpheader" class="org.apache.struts.action2.dispatcher.HttpHeaderResult"/> <result-type name="jasper" class="org.apache.struts.action2.views.jasperreports.JasperReportsResult"/> <result-type name="redirect" class="org.apache.struts.action2.dispatcher.ServletRedirectResult"/> <result-type name="redirect-action" class="org.apache.struts.action2.dispatcher.ServletActionRedirectResult"/> <result-type name="stream" class="org.apache.struts.action2.dispatcher.StreamResult"/> <result-type name="velocity" class="org.apache.struts.action2.dispatcher.VelocityResult"/> <result-type name="xslt" class="org.apache.struts.action2.views.xslt.XSLTResult"/> </result-types> <interceptors> <interceptor name="alias" class="com.opensymphony.xwork.interceptor.AliasInterceptor"/> <interceptor name="autowiring" class="com.opensymphony.xwork.spring.interceptor.ActionAutowiringInterceptor"/> <interceptor name="chain" class="com.opensymphony.xwork.interceptor.ChainingInterceptor"/> <interceptor name="component" class="com.opensymphony.xwork.interceptor.component.ComponentInterceptor"/> <interceptor name="conversionError" class="org.apache.struts.action2.interceptor.WebWorkConversionErrorInterceptor"/> <interceptor name="external-ref" class="com.opensymphony.xwork.interceptor.ExternalReferencesInterceptor"/> <interceptor name="execAndWait" class="corg.apache.struts.action2.interceptor.ExecuteAndWaitInterceptor"/> <interceptor name="exception" class="com.opensymphony.xwork.interceptor.ExceptionMappingInterceptor"/> <interceptor name="fileUpload" class="com.opensymphony.webwork.interceptor.FileUploadInterceptor"/> <interceptor name="i18n" class="com.opensymphony.xwork.interceptor.I18nInterceptor"/> <interceptor name="logger" class="com.opensymphony.xwork.interceptor.LoggingInterceptor"/> <interceptor name="model-driven" class="com.opensymphony.xwork.interceptor.ModelDrivenInterceptor"/> <interceptor name="params" class="com.opensymphony.xwork.interceptor.ParametersInterceptor"/> <interceptor name="prepare" class="com.opensymphony.xwork.interceptor.PrepareInterceptor"/> <interceptor name="static-params" class="com.opensymphony.xwork.interceptor.StaticParametersInterceptor"/> <interceptor name="servlet-config" class="org.apache.struts.action2.interceptor.ServletConfigInterceptor"/> <interceptor name="sessionAutowiring" class="org.apache.struts.action2.spring.interceptor.SessionContextAutowiringInterceptor"/> <interceptor name="timer" class="com.opensymphony.xwork.interceptor.TimerInterceptor"/> <interceptor name="token" class="com.opensymphony.webwork.interceptor.TokenInterceptor"/> <interceptor name="token-session" class="com.opensymphony.webwork.interceptor.TokenSessionStoreInterceptor"/> <interceptor name="validation" class="com.opensymphony.xwork.validator.ValidationInterceptor"/> <interceptor name="workflow" class="com.opensymphony.xwork.interceptor.DefaultWorkflowInterceptor"/> <!-- Basic stack --> <interceptor-stack name="basicStack"> <interceptor-ref name="exception"/> <interceptor-ref name="servlet-config"/> <interceptor-ref name="prepare"/> <interceptor-ref name="static-params"/> <interceptor-ref name="params"/> <interceptor-ref name="conversionError"/> </interceptor-stack> <!-- Sample validation and workflow stack --> <interceptor-stack name="validationWorkflowStack"> <interceptor-ref name="basicStack"/> <interceptor-ref name="validation"/> <interceptor-ref name="workflow"/> </interceptor-stack> <!-- Sample file upload stack --> <interceptor-stack name="fileUploadStack"> <interceptor-ref name="fileUpload"/> <interceptor-ref name="basicStack"/> </interceptor-stack> <!-- Sample WebWork Inversion of Control stack Note: WebWork's IoC is deprecated - please look at alternatives such as Sprint --> <interceptor-stack name="componentStack"> <interceptor-ref name="component"/> <interceptor-ref name="basicStack"/> </interceptor-stack> <!-- Sample model-driven stack --> <interceptor-stack name="modelDrivenStack"> <interceptor-ref name="model-driven"/> <interceptor-ref name="basicStack"/> </interceptor-stack> <!-- Sample action chaining stack --> <interceptor-stack name="chainStack"> <interceptor-ref name="chain"/> <interceptor-ref name="basicStack"/> </interceptor-stack> <!-- Sample i18n stack --> <interceptor-stack name="chainStack"> <interceptor-ref name="i18n"/> <interceptor-ref name="basicStack"/> </interceptor-stack> <!-- Sample execute and wait stack. Note: execAndWait should always be the *last* interceptor. --> <interceptor-stack name="executeAndWaitStack"> <interceptor-ref name="basicStack"/> <interceptor-ref name="execAndWait"/> </interceptor-stack> <!-- A complete stack with all the common interceptors in place. Generally, this stack should be the one you use, though it may process additional stuff you don't need, which could lead to some performance problems. Also, the ordering can be switched around (ex: if you wish to have your components before prepare() is called, you'd need to move the component interceptor up --> <interceptor-stack name="defaultStack"> <interceptor-ref name="exception"/> <interceptor-ref name="alias"/> <interceptor-ref name="prepare"/> <interceptor-ref name="servlet-config"/> <interceptor-ref name="i18n"/> <interceptor-ref name="chain"/> <interceptor-ref name="model-driven"/> <interceptor-ref name="fileUpload"/> <interceptor-ref name="static-params"/> <interceptor-ref name="params"/> <interceptor-ref name="conversionError"/> <interceptor-ref name="validation"/> <interceptor-ref name="workflow"/> </interceptor-stack> <!-- The completeStack is here for backwards compatibility for applications that still refer to the defaultStack by the old name --> <interceptor-stack name="completeStack"> <interceptor-ref name="defaultStack"/> </interceptor-stack> </interceptors> <default-interceptor-ref name="defaultStack"/> </package> </xwork> <!-- // END SNIPPET: webwork-default --> {code} |
Since
...
we
...
included
...
action-default.xml
...
in
...
our
...
action.xml
...
,
...
all
...
the
...
predefined
...
interceptors
...
and
...
stacks
...
are
...
available
...
for
...
us
...
to
...
use
...
in
...
our
...
actions.
...
timer | clocks how long the action (including nested interceptors and view) takes to execute |
logger | logs the action being executed |
chain | makes the previous action's properties available to the current action. Used to make action chaining (reference: Result Types) |
static-params | sets the parameters defined in |
params | sets the request (POST and GET) parameters onto the action class. We have seen an example of this in TODO |
model-driven | if the action implements |
component | enables and makes registered components available to the actions. (reference: IoC & Components) |
token | checks for valid token presence in action, prevents duplicate form submission |
token-session | same as above, but storing the submitted data in session when handed an invalid token; |
validation | performs validation using the validators defined in { |
workflow | calls the validate method in your action class. If action errors created then it returns the |
servlet-config | give access to |
prepare | allows you to programmatic access to your Action class before the parameters are set on it. |
conversionError | Adds field errors if any type-conversion errors occurred\ |
execAndWait | Spawns a separate thread to execute the action |
fileUpload | Sets uploaded files as action files (File objects) |
In addition to the prepackaged Interceptors, action-default.xml
includes prepackaged combinations in named Interceptor Stacks.
Building Your Own Interceptor
If the stock Interceptors aren't enough, you can implement custom Interceptors to solve a new problem or and old problem differently.
Suppose several pages in an application would like to to display a greeting that changes according to the time of day. A good way to solve this use case is to use an Interceptor to place the greeting in the session on each request. As soon as the time of day changes, so would the greeting. As an Interceptor, the greeting can be created automatically, so that the Actions need not be bothered.
Implementing a Greeting Interceptor
- Create an Interceptor class by implementing the
com.opensymphony.xwork.interceptor.Interceptor
...
- interface
...
- (bundled
...
- in
...
- the
...
xwork-1.1.jar
...
- provided
...
- with
...
- the
...
- framework
...
- distribution).
...
- Declare
...
- the
...
- class
...
- in
...
- your
...
- XML
...
- configuration
...
- file
...
- (
...
action.xml
...
- )
...
- using
...
- the
...
- element
...
<interceptor
...
/>
...
- nested
...
- within
...
<interceptors
...
/>
...
- .
...
- Create
...
- stacks
...
- of
...
- Interceptors,
...
- using
...
- the
...
<interceptor-stack
...
/>
...
- element
...
- (
...
- optional
...
- ).
...
- Determine
...
- which
...
- Interceptors
...
- are
...
- used
...
- by
...
- which
...
- mapping,
...
- using
...
<interceptor-ref
...
/>
...
- or
...
<default-interceptor-ref
...
/>
...
- .
...
- The
...
<interceptor-ref>
...
- defines
...
- the
...
- interceptors
...
- to
...
- be
...
- used
...
- in
...
- a
...
- specific
...
- action.
...
- The
...
<default-interceptor-ref
...
/>
...
- determines
...
- the
...
- default
...
- interceptor
...
- stack
...
- to
...
- be
...
- used
...
- by
...
- all
...
- actions
...
- that
...
- do
...
- not
...
- specify
...
- their
...
- own
...
<interceptor-ref
...
/>
.
Coding the Interceptor class
Code Block | ||||||
---|---|---|---|---|---|---|
| ||||||
}}. h3. Coding the Interceptor class {code:java|title= package tutorial; import java.util.Calendar; import com.opensymphony.xwork.interceptor.Interceptor; import com.opensymphony.xwork.ActionInvocation; public class GreetingInterceptor implements Interceptor { public void init() { } public void destroy() { } public String intercept(ActionInvocation invocation) throws Exception { Calendar calendar = Calendar.getInstance(); int hour = calendar.get(Calendar.HOUR_OF_DAY); String greeting = (hour < 6) ? "Good evening" : ((hour < 12) ? "Good morning": ((hour < 18) ? "Good afternoon": "Good evening")); invocation.getInvocationContext().getSession().put("greeting", greeting); String result = invocation.invoke(); return result; } } {null} h3. Coding the configuration {code:xml|title= |
Coding the configuration
Code Block | ||||||
---|---|---|---|---|---|---|
| ||||||
<!DOCTYPE xwork PUBLIC "-//OpenSymphony Group//XWork 1.0//EN" "http://www.opensymphony.com/xwork/xwork-1.0.dtd"> <xwork> <include file="action-default.xml" /> <!-- Configuration for the default package. --> <package name="default" extends="action-default"> <interceptors> <interceptors> <interceptor name="greeting" class="tutorial.GreetingInterceptor" /> </interceptors> <action name="greeting" class="tutorial.GreetingAction"> <interceptor-ref name="greeting" /> <result name="success" type="velocity">greeting.vm</result> </action> </action> <!-- other action mappings --> </package> </xwork> |
Coding the Action class
Code Block | ||||||
---|---|---|---|---|---|---|
| ||||||
package tutorial{null} h3. Coding the Action class {code:java|title= package lesson05; import com.opensymphony.xwork.ActionSupport; public class GreetingAction extends ActionSupport { public String execute() throws Exception { return SUCCESS; } } |
Coding the result page
Code Block | ||||||
---|---|---|---|---|---|---|
| ||||||
<html> <head> {null} h3. Coding the result page {code:html|title= <html> <head> <title>Understanding Interceptors</title> </head> <body> #set ($ses = $req.getSession()) <p><b>${ses.getAttribute('greeting')}!</b></p> </body> </html> {null} h3. How the code works |
How the code works
Let's
...
take
...
a
...
look
...
at
...
our
...
Interceptor
...
class
...
first.
...
An
...
Interceptor
...
must
...
implement
...
com.opensymphony.xwork.interceptor.Interceptor
...
which
...
expects
...
three
...
methods.
...
init()
...
- is
...
- called
...
- during
...
- interceptor
...
- initialization,
...
destroy()
...
- is
...
- called
...
- during
...
- destruction,
...
- and
...
- most
...
- importantly,
...
intercept(ActionInvocation
...
invocation)
...
- is
...
- where
...
- we
...
- place
...
- the
...
- code
...
- that
...
- does
...
- the
...
- work.
...
The
...
Greeting
...
Interceptor
...
returns
...
the
...
result
...
from
...
invocation.invoke
...
.
...
The
...
invoke
...
method
...
executes
...
the
...
next
...
Interceptor
...
in
...
the
...
stack
...
or,
...
if
...
this
...
is
...
the
...
last
...
Interceptor,
...
the
...
appropriate
...
method
...
of
...
the
...
Action
...
class.
...
The
...
invoke
...
method
...
grants
...
the
...
Interceptor
...
the
...
power
...
to
...
short-circuiting
...
the
...
Action
...
Invocation.
...
Instead
...
of
...
calling
...
invoke
...
,
...
the
...
Interceptor
...
can
...
return
...
a
...
result
...
String
...
and
...
bypass
...
any
...
remaining
...
Interceptors
...
on
...
the
...
stack
...
and
...
the
...
Action's
...
execute
...
method.
...
An
...
Interceptor
...
can
...
also
...
execute
...
code
...
after
...
the
...
Action
...
method
...
executes.
...
Just
...
place
...
more
...
code
...
after
...
the
...
invocation.invoke
...
call.
...
Control
...
returns
...
to
...
each
...
Interceptor
...
on
...
the
...
stack
...
in
...
reverse
...
order.
...
When
...
the
...
call
...
to invoke
returns,
...
you
...
can
...
continue
...
processing.
...
Many
...
Interceptors
...
execute
...
code
...
only
...
before
...
or
...
after
...
the
...
Action,
...
but
...
some
...
do
...
execute
...
code
...
in
...
both
...
places.
...
To
...
make
...
coding
...
Interceptors
...
a
...
little
...
easier,
...
the
...
framework
...
provides
...
an
...
abstract
...
class
...
that
...
implements
...
the
...
"before
...
and
...
after"
...
behaviour.
...
Instead
...
of
...
calling
...
invoke}
...
]
...
itself,
...
an
...
Interceptor
...
can
...
extend
...
{{com.opensymphony.xwork.interceptor.AroundInterceptor
...
and
...
implement
...
the
...
methods
...
before(ActionInvocation
...
invocation)
...
and
...
after(ActionInvocation
...
dispatcher,
...
String
...
result)
.
Summary
The Interceptor strategy promotes reusability and simplicity. Interceptors make it easier to separate concerns, so that we can solve one problem at a time. The best part is that each application, and each Action, controls exactly what Interceptors are used in what order.
Next | Onward to Understanding Validation |
---|---|
Prev | Return to Understanding Results |