Help!!! What training do you need?

My company, Intertech Inc., is conducting a survey on the training needs of the software development community. Whether you are a current customer or a potential future customer, your input is valuable! We want to understand what technology you and your organization are exploring and what training needs are at the top of your “want list.”

In addition to influencing our next course offerings, let me give you another reason to fill out the survey. If you complete the survey and provide Intertech with your email address at the end of the survey, Intertech will send you a coupon for $250 off your next Intertech class (valid for public classes held in 2010)! Its simple and takes about 10 minutes to complete. Just click on the survey link here - 2010 Intertech Course Planning Survey

Interest in Noop?

Have you heard of Noop yet? Noop (see project page here) is a new programming language developed by Google engineers (although not sponsored directly by Google) that is expected to run on the Java Virtual Machine. Why a new program language? According to the project Web site, the purpose of Noop is "encouraging what we believe to be good coding practices and discouraging the worst offenses."

Fans of Spring and the importance of testing (especially unit testing) will note the first two goals of the new language are to build dependency injection and testability right into the language versus having to use 3^rd party libraries to bring DI and testing into application environments. Not included in the language (supposedly to make things clearer, simpler, and easier to maintain), among other things are statics, primitive types, and subclassing (implementation inheritance).

To find out more about Noop join their mailing list at noop@googlegroups.com. Also, a short article on Noop can be found on Application Development Trends website here.

Hibernate’s Smart Automatic Dirty Check

I am one lucky guy. As an instructor, my job begins anew each week. Each week, I face a new group of people trying to learn a technology or skill. People have asked "don't you get bored teaching." How could I? Each week the topic changes and the needs of my students change. And when I am not teaching, I am working to understand new technologies and how/when to put it into courseware.

But perhaps what makes my job the most enjoyable is when I have a group of students that are really engaging and come up with questions that make me stop and think. In other words, they challenge me to improve my own skills/knowledge on a topic that I think I already know pretty well. This week, I was teaching Hibernate and had just one of those questions from one of my students, Josephine.

We were exploring Hibernate's automatic dirty checking. As those familiar with Hibernate have learned, Hibernate knows persistent objects and tracks state change to those objects. No explicit call to save (or update) a persistent object is necessary. Just committing the transaction causes the new state of a persistent object to be synchronized to the database. However, Josephine asked what would happen if the state of an object was changed and then changed back again to the original state in the same transaction? Would Hibernate know that no real change occurred and therefore avoid an SQL call to the database? What's your guess? In fact, the answer surprised me when I tested it out.

To describe the situation with a little more detail, explore the following persistent class and Hibernate mapping file. Nothing real complex about the Contact class or its mapping to a Contact table.

public class Contact {
 private Long id = 0L;
 private String firstName;
 private String lastName;
 private Date dateOfBirth;
 private boolean married = false;
 private int children;
 private int age;
 //getters and setters and constructors
}

<hibernate-mapping package="com.intertech.domain">
  <class name="Contact">
    <id name="id">
      <generator class="increment" />
    </id>
    <property name="firstName" column="first_name" not-null="true" />
    <property name="lastName" column="last_name" not-null="true" />
    <property name="dateOfBirth" column="date_of_birth" type="date" not-null="true" />
    <property name="married" />
    <property name="children" />
    <property name="age" formula="datediff('yy', date_of_birth, curdate())" access="field"/>
  </class>
</hibernate-mapping>

Now check out this little bit of test code. In this example, the Contact with an ID of 2 (2 long) has 4 children.

SessionFactory sf = new Configuration().configure().buildSessionFactory();
Session s = sf.openSession();
Transaction t = s.beginTransaction();
Contact c = (Contact) s.load(com.intertech.domain.Contact.class, 2L);
c.setChildren(32);
c.setChildren(4);
t.commit();
s.close();

So, what happens if code updates the number of children to another number (in this case 32) and then returning it to 4? Take a look at the log output (with hibernate.show_sql=true). The answer surprised me!

Hibernate:
     select
        contact0_.id as id0_0_,
        contact0_.first_name as first2_0_0_,
        contact0_.last_name as last3_0_0_,
        contact0_.date_of_birth as date4_0_0_,
        contact0_.married as married0_0_,
        contact0_.children as children0_0_,
        datediff('yy',contact0_.date_of_birth,curdate()) as formula0_0_     from
        Contact contact0_
     where
        contact0_.id=?

The SQL select is made to load to the Contact, but no update SQL is issued. Hibernate actually checks to see if the state has undergone real modification before issuing an SQL to synchronize the state with the database. Another case of the students teaching the instructor.

Come join me in learning Hibernate in Intertech's Complete Hibernate class. We offer both live and virtual training, and while I may not have all the answers, I'll work hard to find them for you! That's one of the best parts of my job!

HandlerInterceptors in Spring Web MVC Framework

Last week, I had a wonderful group of people in my class to learn the Spring Framework. In this group, one of my students – Eric - asked me about Spring Web MVC Interceptors. In particular, Eric had a great question about interceptors versus aspect-oriented programming (AOP) provided in Spring. Were they different? Could "normal" Spring AOP be used in place of interceptors and vice versa?

In general, Interceptors, or more precisely HandlerInterceptors, are used to provide cross cutting concerns to a Spring MVC Web application. Here is a quote from Rod Johnson et al's book Java Development with the Spring Framework: "HandlerInterceptors provide the capability to intercept incoming HTTP requests. Interceptors are useful to add additional crosscutting behavior to your web infrastructure, such as security, logging, auditing." Of course, you'll find "crosscutting behavior" the purpose of AOP as well. So indeed, HandlerInterceptors and AOP serve a similar purpose; that is they serve to collect cross cutting concern code usually sprinkled throughout the core concerns of an application. AOP provides a framework for providing cross-cutting concerns throughout all types of applications and application components. HandlerInterceptors are an extension point to a Spring MVC framework, and as such, are a means to provide cross-cutting concerns specific to Web applications. These special cross-cutting concern components also have access to the Web request, response and ModelAndView objects; something normal AOP aspects are not provided directly without some work. If you are unfamiliar with AOP, the Spring API documentation also indicates that HandlerInterceptors work like Servlet Filters.

While there is a rather large amount of documentation and tutorials on intertwining AOP into a Spring application, there is not as much on HandlerInterceptors. So let me use this blog entry to show you how HandlerInterceptors work both in Spring 2 and in Spring 2.5 where annotations (rather than XML) are used to specify the controller and request mapping.

HandlerInterceptors must implement the org.springframework.web.servlet.HandlerInterceptor interface. This interface defines three methods (preHandle, postHandle, and afterCompletion) that get called before a handler is executed (#1 in the diagram below), after a handler is executed but before the view is rendered (#2 below), and after completely handling a Web request and rendering the view(#3 below). These methods allow for all sorts of pre and post processing in the chain of execution associated to each and every Web request.

Here is a simple implementation of the HandlerInterceptor.

package com.intertech.controllers;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.HandlerInterceptor;
public class
TestInterceptor implements HandlerInterceptor {
  @Override
  public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    System.out.println("In pre-processing/n");
    return true;
  }
  @Override
  public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
    System.out.println("done with request/n");
  }
  @Override
  public void postHandle(HttpServletRequest request, HtpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
    System.out.println("In post-processing/n");
  }
}

Note that the preHandle method returns a boolean. If false is returned, the interceptor indicates the normal execution chain should be aborted. The result is to send an HTTP error or other custom response to the user. The postHandle method is provided a copy of the ModelAndView object. This allows the interceptor to modify the model information or view displayed as normally determined by the Spring MVC controller. Finally, the afterCompletion method serves as a kind of callback after processing the request and rendering the view. This method can and should clean up any resources used by the interceptor.

In Spring 2, interceptors are woven into the Web request execution chain through XML configuration of the handler mapping (note the interceptors property for the SimpleUrlHandlerMapping example below).

<bean id="testInterceptor" class="com.intertech.controllers.TestInterceptor" />
<bean class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
  <property name="interceptors">
    <list>
      <ref bean="testInterceptor"/>
    </list>
  </property>
  <property name="mappings">
    <props>
      <prop key="/addcontact.request">addContactController
      </prop>
      <prop key="/displayContacts.request">manageContactsController
      </prop>
      <prop key="/deleteContact.request">manageContactsController
      </prop>
    </props>
  </property>
</bean>

In Spring 2.5 and better, since handler mapping is handled via @RequestMapping annotations, the interceptor must be added to the DefaultAnnotationHandlerMapping. In Spring 2.5 and beyond, the DispatcherServlet enables the DefaultAnnotationHandlerMapping by default, which looks for @RequestMapping annotations on @Controllers. However, the DefaultAnnotationHandlerMapping can still be added to the Spring configuration file and the interceptors added to this handler mapping as shown below.

<bean id="testInterceptor" class="com.intertech.controllers.TestInterceptor" />
<bean id="handlerMapping" class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping">
  <property name="interceptors">
    <list><ref bean="testInterceptor"/></list>
  </property>
</bean>

Spring already comes with several interceptor adapters (HandlerInterceptorAdapter, LocaleChangeInterceptor, ThemeChangeInterceptor, UserRoleAuthorizationInterceptor, WebContentInterceptor, WebRequestHandlerInterceptorAdapter) so that developers don't have to implement common Web application cross cutting concerns. For example, the UserRoleAuthorizationInterceptor checks the authorization of the current user against the Java EE security roles, as evaluated by HttpServletRequest's isUserInRole method.

To learn more about the Spring Framework or Spring Web MVC, please consider joining me for Intertech's Complete Spring Core or Complete Spring Web class. We offer training at our facility as well as virtually right to your desktop wherever you are.

Oracle-Sun Acquisition Near Approval

Oracle's acquisition of Sun was approved by the US Department of Justice August 20th (see details here ) and according to Bloomberg (see here) European regulators are expected to approve the deal Sept 3rd. European approval is the last hurdle before the acquisition can be finalized.

Simplifying the Hibernate Inverse Attribute on Associations

Hibernate is a framework to make storing and retrieving persistent objects and their association to one another simpler. While this is generally true, there are aspects of Hibernate configuration and mapping that can be challenging to learn and understand. Perhaps, one of the toughest to teach people is that of the inverse setting on a bi-directional relationship mapping in a one-to-many or many-to-many association. Without an understanding of the objects, the association, and SQL needed to save them, people new to Hibernate often struggle with this setting.

In fact, the inverse attribute on an association mapping can be easily understood with a simple example. So to start, assume there are two entities: BallPlayer and Team. As anyone who has played team sports knows, a team has many players, but a player can be on only one team at anytime. Therefore, the relationship between BallPlayer and Team is a one-to-many relationship, and in this example it is bi-directional. That is, a BallPlayer knows the team he plays for, and the Team knows the players on it. The UML showing the BallPlayer and Team attributes and the ERD diagrams for Player and Team are shown below.

The Hibernate mapping files for both BallPlayer and Team are straightforward.

<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.intertech.domain">
<class name="BallPlayer" table="Player" abstract="true">
<id name="id" access="field">
<generator class="sequence">
<param name="sequence">common_seq</param>
</generator>
</id>
<property name="name" />
<property name="dob" column="date_of_birth" />
<property name="uniformNumber" column="uniform_number" />
<many-to-one name="team" column="team_id" cascade="all"
class="com.intertech.domain.Team" not-null="true" />
</class>
</hibernate-mapping>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.intertech.domain">
<class name="Team">
<id name="id" access="field">
<generator class="sequence">
<param name="sequence">common_seq</param>
</generator>
</id>
<property name="nickname" />
<property name="founded" />
<set name="players" inverse="true" cascade="all">
<key column="team_id" />
<one-to-many class="com.intertech.domain.BallPlayer" />
</set>
</class>
</hibernate-mapping>

Note the inverse="true" on the <set> element in the Team mapping. When used, the inverse attribute must be set on the collection (in this case the <set> on Team) side of the association rather than the side containing the <many-to-one> element (the BallPlayer in this case). In a many-to-many relationship, the inverse attribute can be placed on the collection element on either side.

OK, but what is this inverse attribute all about? Well, to understand it, examine some test code that exercises the BallPlayer to Team relationship.

Calendar dob = Calendar.getInstance();

dob.set(1942, Calendar.DECEMBER, 13);
BallPlayer fergie = new BallPlayer();
fergie.setName("Ferguson Jenkins");
fergie.setDob(dob);
fergie.setUniformNumber((short) 31);

SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Team cubs = (Team) session.get(Team.class, 1L);
cubs.addPlayer(fergie);
fergie.setTeam(cubs);
transaction.commit();
session.close();

In this Hibernate code, a new BallPlayer (fergie) is created and associated to an already persistent Team (cubs) object. Once the BallPlayer and Team are associated to one another and since Team is already persistent, cascading persistence causes the BallPlayer (fergie) and relationship to the Team (cubs) to be saved.

The SQL issued to the database (shown with show_sql and use_sql_comments all set to true in the Hibernate configuration) when the test code above executes is shown below.

Hibernate: /* load com.intertech.domain.Team */ select team0_.id as id1_0_, team0_.nickname as nickname1_0_, team0_.founded as founded1_0_ from Team team0_ where team0_.id=?

Hibernate: /* load one-to-many com.intertech.domain.Team.players */ select players0_.team_id as team5_1_, players0_.id as id1_, players0_.id as id0_0_, players0_.name as name0_0_, players0_.date_of_birth as date3_0_0_, players0_.uniform_number as uniform4_0_0_, players0_.team_id as team5_0_0_ from Player players0_ where players0_.team_id=?

Hibernate: call next value for common_seq

Hibernate: /* insert com.intertech.domain.BallPlayer */ insert into Player (name, date_of_birth, uniform_number, team_id, id) values (?, ?, ?, ?, ?)

However, when the inverse="true" is removed from the Team mapping file, look how the SQL changes.

Hibernate: /* load com.intertech.domain.Team */ select team0_.id as id1_0_, team0_.nickname as nickname1_0_, team0_.founded as founded1_0_ from Team team0_ where team0_.id=?

Hibernate: /* load one-to-many com.intertech.domain.Team.players */ select players0_.team_id as team5_1_, players0_.id as id1_, players0_.id as id0_0_, players0_.name as name0_0_, players0_.date_of_birth as date3_0_0_, players0_.uniform_number as uniform4_0_0_, players0_.team_id as team5_0_0_ from Player players0_ where players0_.team_id=?

Hibernate: call next value for common_seq

Hibernate: /* insert com.intertech.domain.BallPlayer */ insert into Player (name, date_of_birth, uniform_number, team_id, id) values (?, ?, ?, ?, ?)

Hibernate: /* create one-to-many row com.intertech.domain.Team.players */ update Player set team_id=? where id=?

It might be hard to see at first, but one extra SQL statement got executed. Notice the extra SQL update statement that is called (the last line in italics)? What gives? Why the extra SQL? This is a result of the absences of the inverse attribute on the relationship mapping.

From a database perspective, since only the Player table holds the reference (foreign key) to the Team, only one insert is needed for the relationship to be persisted – an insert into the Player table. However, Hibernate does not detect this fact by default. In the persistence context, all Hibernate knows is that both persistent objects (the BallPlayer called fergie and the Team called cubs) have been created or modified and need to be persisted. Therefore, at the next point of synchronization (transaction commit in this case) with the database, Hibernate attempts to persist both. If inverse attribute is not set to true, Hibernate looks at Team and notices the new BallPlayer.

It inserts the new BallPlayer, and association from cubs-to-fergie. However, it then looks at the new BallPlayer and sees the relationship fergie-to-cubs. Not told that the relationship is the inverse of one it has already taken care of, it thinks an update might be necessary to save this new relationship. Thus the extra "update Player set team_id=? where id=?" SQL is issued.

So, the inverse=true attribute informs Hibernate of the existence of a bidirectional relationship which allows it to ignore the relationship from the Team to BallPlayer direction.

This raises an important issue in your management of Java objects and their association to each other. With inverse="true", Hibernate essentially ignores the association of Team to BallPlayer. Therefore, if you add a BallPlayer to Team, but do not handle the reverse association in your coding, the association is ignored!

// - forget to do this - aPlayer.setTeam(aTeam);
aTeam.addPlayer(aPlayer);
session.save(aTeam);
session.save(aPlayer);

Hibernate manages the persistence of Java objects and their associations to each other into the database, but only if they are physically there! For this reason, good Hibernate developers write methods to update both sides of an entity relationship when either side is updated.

public void addPlayer(BallPlayer aPlayer){
players.add(aPlayer);
aPlayer.setTeam(this);
}

If you still find the invert attribute and associations confusing, I encourage you to download the code for this blog post here and see if it makes more sense after you play with the setting in this simple example.

To learn more about Hibernate, consider taking Intertech's Complete Hibernate class.

Free Learning Event - Globalizing your Java App

My fellow Java Intertech instructor , Jason Shapiro, is providing a talk on Globalizing your Java Application September 11th (one at 9am central time, the other - virtual classroom - at 1pm central time). In this free 2 hour talk, Jason discusses the basic considerations and processes one must follow to create a globalized application; that is how to move text and images into resource bundles, dealing with numbers, dates, and currency, character encoding issues, and localization/internationalization patterns and best practices. Jason is a phenomenal classroom presenter. This talk is well worth your time. Sign up on Intertech's web site for either the in-person or virtual class here.