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<title>Tracing the call through container</title><link rel="stylesheet" href="styles.css" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/styles.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets Vimages/callouts/"><link rel="home" href="index.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/index.html" title="JBoss 3.0 Documentation"><link rel="up" href="ch12.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12.html" title="Chapter 12. Container architecture - design notes"><link rel="previous" href="ch12s68.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12s68.html" title="Security"><link rel="next" href="ch13.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch13.html" title="Chapter 13. HOWTO"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><table border="0" cellpadding="0" cellspacing="0" height="65"><tr height="65"><td rowspan="2"><img src="jboss.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/jboss.gif" border="0"></td><td rowspan="2" background="gbar.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/gbar.gif" width="100%" align="right" valign="top"><a href="index.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/index.html"><img src="doc.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/doc.gif" border="0"></a><a href="ch12.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12.html"><img src="toc.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/toc.gif" border="0"></a><a href="ch12s68.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12s68.html"><img src="prev.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/prev.gif" border="0"></a><a href="ch13.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch13.html"><img src="next.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/next.gif" border="0"></a></td></tr><tr></tr></table><div class="section"><a name="d0e8749"></a><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="d0e8749"></a>Tracing the call through container</h2></div></div><p>The preceding sections discussed specific pieces of call handling
at length. Now it is time to put all the pieces together to see how a
complete method invocation is handled. In particular, let's look at the
handling of method calls on an Entity Bean.</p><p>The call is first logged. Then the TxInterceptor decides how to manage
transactions for this call. The information needed for this decision
comes from the standard XML descriptor. Then, the SecurityInterceptor
checks if the caller is allowed to perform this call, again by using
information from the XML descriptor. Up until this point no instance
has been acquired. After all interceptors have been passed the container
will invoke the business method on the EJB instance, so now we
acquire this instance.</p><p>The interceptor calls the InstanceCache with
the given primary key to perform this. Since the cache does not yet
have an instance associated with the given primary key, it first gets
a free instance from the instance pool, which it associates with the
primary key. It then calls the persistence manager which will activate
the instance. This usually only involves calling ejbActivate.</p><p>After instance acquisition the next interceptor deals with how this
instance is
synchronized with the database. There are a number of options (load on
transaction start, load on each call, load on activate, etc.) and the
interceptor has been configured to perform one of these options. In
this example it will load on activate, so it calls the persistence
manager to perform this. This will cause an ejbLoad call to be made
on the instance.</p><p>Next, the last interceptor is invoked, which is the
container itself. The container always adds itself as the last interceptor
at the end of the chain. The call is now delegated to the EJB instance.
The instance performs some work, and returns a result. The interceptor
chain is now followed in reverse by having each interceptor return from
the invoke-operation. The instance synchronization interceptor chooses
to store the current state into the database and hence calls storeEntity
on the persistence manager. Another valid option would be to wait until
transaction commit.</p><p>Next, the instance is returned to the cache. If the
transaction does not end with this call, it will first lock the instance
to this transaction so that no other transaction may use it for the
duration of this current transaction. This is the same as pessimistic
locking. The transaction interceptor handles the method return according
to the transaction settings, possibly commiting or rollbacking the current
transaction. Finally, the container invoker returns the result to the
client. This completes the call.</p><p>As you can see, all implementation decisions are performed by various
plugins.
These decisions are fairly loosely coupled, which allows the deployer of
the EJB-application to tweak the behaviour of the container to a great
degree. This also allows for a number of independent plugins to co-exist,
each one allowing for slightly, or radically, different behaviour.</p><p>For example, some persistence managers could use an XML-file as the
backing
store instead of an RDBMS, and some security interceptor could use ACL's
from a database instead of the XML descriptor to perform security checks.
Or multiple security checks could be done by configuring the container
to have several security interceptors of different types. All of these
options are available by this componentized container architecture.</p></div><table border="0" cellpadding="0" cellspacing="0" height="65"><tr height="65"><td rowspan="2"><img src="gbar.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/gbar.gif" width="432" height="79"></td><td rowspan="2" background="gbar.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/gbar.gif" width="100%" align="right" valign="top"><a href="index.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/index.html"><img src="doc.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/doc.gif" border="0"></a><a href="ch12.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12.html"><img src="toc.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/toc.gif" border="0"></a><a href="ch12s68.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12s68.html"><img src="prev.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/prev.gif" border="0"></a><a href="ch13.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch13.html"><img src="next.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/next.gif" border="0"></a></td></tr><tr></tr></table></body></html>⌨️ 快捷键说明
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