Domain Lookup
Here is some code to do domain lookup in java (nslookup style):
Hashtable env = new Hashtable();
env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
DirContext ictx = new InitialDirContext(env);
Attributes attrs = ictx.getAttributes("gmail.com", new String[]{"MX"});
Attribute attr = attrs.get("MX");
JBoss Seam
So I took up the task of learning to use the JBoss Application server and while the server itself is really nice the real power seems to be in a concept called the Seam.
There are 2 Terms to consider when trying to figure out exactly what a seam is:
Bijection :
allows objects to be in-jected or out-jected to/from assigned variables using the @In and @Out annotations
Contexts :
Stateless context
Event (or request) context
Page context
Conversation context
Session context
Business process context
Application context
Most of these contexts are similar to other technologies but the 2 new ones are: conversation context, and business process context.
The documentation says they are:
3.1.6. Business process context
The business process context holds state associated with the long running business process. This state is managed and made persistent by the BPM engine (JBoss jBPM). The business process spans multiple interactions with multiple users, so this state is shared between multiple users, but in a well-defined manner. The current task determines the current business process instance, and the lifecycle of the business process is defined externally using a process definition language, so there are no special annotations for business process demarcation.
3.1.4. Conversation context
The conversation context is a truly central concept in Seam. A conversation is a unit of work from the point of view of the user. It might span several interactions with the user, several requests, and several database transactions. But to the user, a conversation solves a single problem. For example, "book hotel", "approve contract", "create order" are all conversations. You might like to think of a conversation implementing a single "use case" or "user story", but the relationship is not necessarily quite exact.
A conversation holds state associated with "what the user is doing now, in this window". A single user may have multiple conversations in progress at any point in time, usually in multiple windows. The conversation context allows us to ensure that state from the different conversations does not collide and cause bugs.
It might take you some time to get used to thinking of applications in terms of conversations. But once you get used to it, we think you'll love the notion, and never be able to not think in terms of conversations again!
Some conversations last for just a single request. Conversations that span multiple requests must be demarcated using annotations provided by Seam.
Some conversations are also tasks. A task is a conversation that is significant in terms of a long-running business process, and has the potential to trigger a business process state transition when it is successfully completed. Seam provides a special set of annotations for task demarcation.
Conversations may be nested, with one conversation taking place "inside" a wider conversation. This is an advanced feature.
Usually, conversation state is actually held by Seam in the servlet session between requests. Seam implements configurable conversation timeout, automatically destroying inactive conversations, and thus ensuring that the state held by a single user login session does not grow without bound if the user abandons conversations.
Seam serializes processing of concurrent requests that take place in the same long-running conversation context, in the same process.
Alternatively, Seam may be configured to keep conversational state in the client browser.
Struts 2 validator types
<validator name="required" class="com.opensymphony.xwork2.validator.validators.RequiredFieldValidator"/> <validator name="requiredstring" class="com.opensymphony.xwork2.validator.validators.RequiredStringValidator"/> <validator name="int" class="com.opensymphony.xwork2.validator.validators.IntRangeFieldValidator"/> <validator name="long" class="com.opensymphony.xwork2.validator.validators.LongRangeFieldValidator"/> <validator name="short" class="com.opensymphony.xwork2.validator.validators.ShortRangeFieldValidator"/> <validator name="double" class="com.opensymphony.xwork2.validator.validators.DoubleRangeFieldValidator"/> <validator name="date" class="com.opensymphony.xwork2.validator.validators.DateRangeFieldValidator"/> <validator name="expression" class="com.opensymphony.xwork2.validator.validators.ExpressionValidator"/> <validator name="fieldexpression" class="com.opensymphony.xwork2.validator.validators.FieldExpressionValidator"/> <validator name="email" class="com.opensymphony.xwork2.validator.validators.EmailValidator"/> <validator name="url" class="com.opensymphony.xwork2.validator.validators.URLValidator"/> <validator name="visitor" class="com.opensymphony.xwork2.validator.validators.VisitorFieldValidator"/> <validator name="conversion" class="com.opensymphony.xwork2.validator.validators.ConversionErrorFieldValidator"/> <validator name="stringlength" class="com.opensymphony.xwork2.validator.validators.StringLengthFieldValidator"/> <validator name="regex" class="com.opensymphony.xwork2.validator.validators.RegexFieldValidator"/> <validator name="conditionalvisitor" class="com.opensymphony.xwork2.validator.validators.ConditionalVisitorFieldValidator"/> Link to Ref
Struts 2 Zip Code Validator
<field name="ah.address.zip">
<field-validator type="required">
<param name="trim">true</param>
<message>Zip Code is required</message>
</field-validator>
<field-validator type="regex">
<param name="expression"><![CDATA[^\d{5}$]]></param>
<message>Zip Code must be 5 characters</message>
</field-validator>
</field>