THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
...
| Include Page | |||
|---|---|---|---|
|
|
...
| Wiki Markup |
|---|
{html}
<div class="content">
{html} |
...
Lifecycle
...
callbacks
...
It
...
is
...
often
...
necessary
...
to
...
create
...
a
...
POJO
...
object
...
as
...
soon
...
the
...
instance
...
becomes
...
valid
...
(i.e.
...
required
...
services
...
are
...
available).
...
It
...
is
...
also
...
often
...
needed
...
to
...
be
...
able
...
to
...
stop
...
it
...
nicely.
...
This
...
pages
...
presents
...
the
...
iPOJO
...
capabilities
...
to
...
achieve
...
such
...
actions.
...
iPOJO
...
allows
...
you
...
to
...
invoke
...
methods
...
(callbacks)
...
on
...
the
...
POJO
...
object
...
when
...
instance's
...
state
...
changed.
...
For
...
example,
...
it
...
allows
...
invoking
...
a
...
start
...
method
...
when
...
the
...
instance
...
becomes
...
valid
...
and
...
a
...
stop
...
method
...
when
...
the
...
instance
...
becomes
...
invalid.
...
It
...
allows
...
the
...
creation
...
of
...
immediate
...
component.
...
This
...
page
...
presents
...
how
...
to
...
use
...
this
...
handler.
| Wiki Markup |
|---|
_ {div:class=toc} {toc:maxLevel=4|minLevel=2} {div} h2. |
Instance
...
Lifecycle
...
iPOJO
...
instances
...
have
...
a
...
very
...
simple
...
lifecycle.
...
This
...
lifecycle
...
contains
...
two
...
states:
...
INVALID
...
and
...
VALID
...
.
...
Once
...
an
...
instance
...
is
...
created,
...
this
...
instance
...
can
...
only
...
be
...
valid
...
if
...
all
...
its
...
plugged
...
handlers
...
are
...
valid.
...
In
...
the
...
most
...
basic
...
case
...
it
...
means
...
all
...
required
...
services
...
are
...
available.
...
For
...
example,
...
an
...
instance
...
requiring
...
a
...
service
...
(and
...
so
...
using
...
the
...
dependency
...
handler)
...
cannot
...
be
...
valid
...
if
...
the
...
required
...
service
...
is
...
unavailable.
...
An
...
instance
...
starts
...
and
...
stops
...
in
...
the
...
invalid
...
state.
Lifecycle callback
This handler supports two kinds of callback. The INVALID=>VALID callback are invoked when the instance becomes valid (at starting or when an event allows the instance to become valid). The VALID=>INVALID callback are invoked when the instance becomes invalid (at stopping or when an event invalids the instance).
An example
Let's take an example. The following class requires a FooService and has two lifecycle callbacks: start and stop.
| Code Block |
|---|
!lifecycle.png|width=50%! h2. Lifecycle callback This handler supports two kinds of callback. The INVALID=>VALID callback are invoked when the instance becomes valid (at starting or when an event allows the instance to become valid). The VALID=>INVALID callback are invoked when the instance becomes invalid (at stopping or when an event invalids the instance). !callback.png! h2. An example Let's take an example. The following class requires a FooService and has two lifecycle callbacks: start and stop. {code} @Component @Instantiate public class Foo { @Requires FooService fs; @Validate private void start() { // Starting method //... fs.foo(); //... } @Invalidate protected void stop() { // Stopping method if(fs!=null) { fs.foo(); } } } {code} |
You
...
can
...
also
...
remove
...
the
...
annotations
...
to
...
use
...
the
...
XML
...
format:
| Code Block | ||||
|---|---|---|---|---|
| ||||
{code:xml} <component className="...Foo"> <requires field="fs"/> <callback transition="validate" method="start"/> <callback transition="invalidate" method="stop"/> </component> <instance component="...Foo"/> {code} |
When
...
an
...
instance
...
of
...
this
...
component
...
type
...
is
...
created,
...
the
...
start
...
method
...
is
...
called
...
as
...
soon
...
as
...
the
...
Foo
...
Service
...
(service
...
requirement)
...
becomes
...
available.
...
If
...
the
...
Foo
...
Service
...
is
...
no
...
more
...
available
...
or
...
when
...
the
...
instance
...
is
...
stopped,
...
the
...
stop
...
method
...
is
...
called.
...
The
...
invoked
...
methods
...
have
...
no
...
argument,
...
but
...
could
...
be
...
private,
...
protected
...
or
...
public.
...
Public
...
methods
...
can
...
be
...
in
...
parent
...
classes
...
too.
...
Moreover,
...
the
...
INVALID=>VALID
...
(validate)
...
method
...
can
...
use
...
service
...
dependencies
...
(the
...
instance
...
becomes
...
valid
...
means
...
that
...
all
...
required
...
services
...
are
...
available);
...
however,
...
in
...
the
...
stop
...
method
...
(invalidate)
...
it
...
is
...
possible
...
that
...
one
...
of
...
these
...
dependency
...
can
...
be
...
null
...
.
...
Indeed,
...
the
...
departure
...
of
...
a
...
service
...
can
...
be
...
the
...
cause
...
of
...
the
...
instance
...
invalidation.
...
Managing
...
threads
...
One
...
usage
...
of
...
lifecycle
...
callback
...
is
...
when
...
the
...
instance
...
needs
...
to
...
create
...
threads.
...
Indeed,
...
the
...
thread
...
can
...
be
...
created
...
in
...
the
...
validate
...
callback,
...
and
...
stopped
...
in
...
the
...
invalidate
...
method.
...
The
...
next
...
class
...
shows
...
an
...
example
...
of
...
a
...
class
...
handling
...
a
...
thread
...
by
...
using
...
lifecycle
...
callbacks.
| Code Block |
|---|
} @Component @Instantiate public class HelloRequesterImpl implements Runnable { final static int DELAY=10000; @Requires HelloService[] m_hello; // Service Dependency boolean end; public void run() { while (!end) { try { synchronized (this) { for(int i = 0; i < m_hello.length; i++) { System.out.println(m_hello[i].sayHello("Clement")); } } Thread.sleep(DELAY); } catch (InterruptedException ie) { /* will recheck quit */ } } } @Validate public void starting() { Thread T = new Thread(this); end = false; T.start(); } @Invalidate public void stopping() { end = true; } {code} h2. Invalidate callbacks and services The invalidate callback has to be developed defensively. Indeed, inside this callback, it might be possible that a service is no more there (the departure of this service has thrown the instance invalidation, which calls the callback). So, you must check that the service is not {{null}} before using it: {code} |
Invalidate callbacks and services
The invalidate callback has to be developed defensively. Indeed, inside this callback, it might be possible that a service is no more there (the departure of this service has thrown the instance invalidation, which calls the callback). So, you must check that the service is not null before using it:
| Code Block |
|---|
@Invalidate
public void stop() {
if (myservice != null) {
// you can use the service
}
// ...
}
{code}
|
Thanks
...
to
...
the
...
iPOJO
...
synchronization
...
model,
...
you
...
can
...
be
...
sure
...
that
...
if
...
the
...
service
...
is
...
available,
...
it
...
will
...
be
...
there
...
until
...
the
...
end
...
of
...
the
...
method.
...
Immediate
...
component
...
An
...
instance
...
of
...
an
...
immediate
...
component
...
type
...
is
...
instantiated
...
as
...
soon
...
it
...
becomes
...
valid.
...
It
...
means
...
that,
...
when
...
the
...
instance
...
becomes
...
valid,
...
the
...
constructor
...
of
...
the
...
implementation
...
class
...
is
...
called.
...
This
...
can
...
replace
...
the
...
validate
...
callback.
...
However,
...
it
...
stills
...
a
...
difference
...
between
...
the
...
immediate
...
and
...
the
...
validate
...
callback.
...
The
...
constructor
...
is
...
call
...
only
...
once
...
time.
...
The
...
validate
...
callback
...
is
...
re-called
...
each
...
time
...
the
...
instance
...
becomes
...
valid.
...
Components
...
that
...
do
...
not
...
provide
...
services
...
are
...
automatically
...
set
...
as
...
immediate.
To set a component as immediate you must add the immediate attribute to component:
| Code Block |
|---|
!constructor.png! To set a component as immediate you must add the {{immediate}} attribute to {{component}}: {code} @Component(immediate=true) @Instantiate public class MyComponent implements MyService { // ... } {code} |
However
...
as
...
there
...
is
...
no
...
'destructor'
...
in
...
Java,
...
the
...
invalidate
...
callback
...
is
...
necessary
...
if
...
some
...
actions
...
are
...
needed
...
when
...
stopping.
...
Callback on several objects
If you instance has created several objects (called the implementation class constructor several times), the callback is called on each object in the creation order.
| Include Page | ||||
|---|---|---|---|---|
|
...