Sometimes JPA entity classes get hijacked.

Say for instance you have a need to pass entity classes to another system, via JAXB.  Its possible to use DTO objects for the transfer or you could just annotate the the entity classes.  In the example below, I wanted to fetch something from a database via JPA and write it into gigaspaces.  It soon gets messy your Entity classes start to become a hub in the middle of your application with things dipping into some of the classes and annotating them and throwing them here and there.

Lets look at a simple one from my example system.  This one is only used by gigaspaces and hibernate, it could get much messier than this if I chose to add one or two more technologies.  I am deliberately leaving the imports in the examples so you can see where it all came from.

import com.gigaspaces.annotation.pojo.SpaceClass;
import com.gigaspaces.annotation.pojo.SpaceId;
import com.gigaspaces.annotation.pojo.SpaceRouting;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.persistence.Transient;

@Entity
@Table(name = "HOUSE")
@SpaceClass
public class MessyHouse {

    private String id;
    private String name;
    private String address;
    private String pageId;

    public MessyHouse() {
    }  

    @SpaceRouting
    @Transient
    public String getPageId() {
    return pageId;
    }

    public void setPageId(String pageId) {
    this.pageId = pageId;
    }

    @Id
    @GeneratedValue
    @Column(name = "HOUSE_ID")
    @SpaceId(autoGenerate = false)
    public String getId() {
    return id;
    }

    public void setId(String id) {
    this.id = id;
    }

    public String getAddress() {
    return address;
    }

    public void setAddress(String address) {
    this.address = address;
    }

    public String getName() {
    return name;
    }

    public void setName(String name) {
    this.name = name;
    }
}

Some things I dislike about what I have done here

• See the block I have marked below SpaceRouting.  In this class I wanted to change the Gigaspace routing strategy, so I have a method that has nothing to do with the persistence.  Does adding annotations break the “A class should have only one responsibility” design goal?  No perhaps not, but adding a whole method that is a Gigaspace concern does.
• As you add more and more annotations from different technologies things get messy very quickly.
• I have a JPA based DAO that uses this class.  I also have a set of gigaspace processing units that use this class.  Both systems are impinging their own design requirements on the class.  At the moment they are deceptively similar.  Gigaspace insists upon a default constructor, and getters and setters for all fields you wish to persist.  Hibernate is not quite as strict.  What if Gigaspaces relaxes that rule later and allows you to annotate the fields instead?  Or perhaps added some other design restriction.  Its unclear by looking at the class what things are there for hibernates soft contract and what gigaspace is insisting upon.
• If my gigaspace experiment gets big (not that likely!).  I might want to split off the gigaspace into its own project and use it as a component.  Ah! so what about the MessyHouse class then?  Where should that live?  Indeed its going to be in the wrong project wherever I decide to keep it.

This is one solution that I put to you.  Create a class for the gigaspace fields, and compose a House class into it.  With composition we can neatly separate the concerns.  Well almost.  Gigaspace may store these objects and need to restore them at some point.  I believe to do that it creates House, and populates it.  Then it creates GsHouseWrapper and injects House into it.  To do that you need a setter for the house but at least we have a class with Gigaspace design constraints and another with Hibernate peculiarities.  Check out the classes below and let me know what you make of the design.  Are there alternatives?

Also, currently there is a problem with the design below. The delegation methods fail with an exception. i.e house.setId(id); fails when writing the object to the space. I need to submit a ticket with the Gigaspace crew to figure out why.

The refactored classes.

package javapuzzlers.compose;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "HOUSE")
public class House {

    private String id;
    private String name;
    private String address;

    public House() {
    }

    @Id
    @GeneratedValue
    @Column(name = "HOUSE_ID")
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

package javapuzzlers.compose;

import com.gigaspaces.annotation.pojo.SpaceClass;
import com.gigaspaces.annotation.pojo.SpaceId;
import com.gigaspaces.annotation.pojo.SpaceRouting;

@SpaceClass
public class GsHouseWrapper {

    private House house;
    private String pageId;

    public GsHouseWrapper() {
    }

    public GsHouseWrapper(House house) {
      this.house = house;
    }

    @SpaceId(autoGenerate = false)
    public String getId() {
        return house.getId();
    }

    public void setId(String id) {
        house.setId(id);
    }

    @SpaceRouting
    public String getPageId() {
        return pageId;
    }

    public void setPageId(String pageId) {
        this.pageId = pageId;
    }

    public GsHouseWrapper(House house) {
        this.house = house;
    }

    public String getName() {
        return house.getName();
    }

    public String getAddress() {
        return house.getAddress();
    }
}

                          

1. 21:45 Open Eclipse.
2. 21:49 Updates downloaded and maven re-indexed.
3. 21:53 Start tutorial, lots of downloads from maven after project creation.
4. 21:55 Restart eclipse to enable the runtime weaving, STS does not return…restarted it from the prompt, deleted the project and started again as it looked incomplete.
5. 22:00 Bumbling through the tutorial.  This is very easy, love the CTRL^space completion.  I have done quite a bit of Linux work, and this shell is very easy to use.
6. 22:14 Running the tests using roo> perform test. This runs maven, which fails because it cant find the integration test class, RsvpIntegrationTest.  Investigation from the bash prompt reveals that all tests pass under maven, so its not an issue with the project roo has created.  More download and fiddling about.  The test runs from eclipse too, so I move on.
7. 22:38 Website up! Selenium tests all pass.  Investigation of the functionality shows that its working!  Done in 53 mins not bad I think!

Roo Up and Running!

Conclusion

Yea easy, a quick look over the project shows its very neat and tidy. Most of the time was spent in download and the false start. The configuration easy to follow and the generated code would be easy to use. So yes, might have a proper look at Roo at some point!

                          

I used Spring STS for a few months before starting at Lab49, and found it to be a good distribution over the standard Eclipse build. It has lots of extra productivity features for Spring based development some of which are not available by downloading Spring plugins and adding them to a normal distribution.
The things I like best are:

• The edit, navigation and search systems now support the spring annotations. So now you can navigate and search for beans declared via annotations.
• Ability to include new XML domains in the spring configuration from a popup list.
• The enhanced XML editing support now has inline error checking.
• This XML editor also supports completion and checking of class and bean names.
• Roo shell looks interesting too.

Roo and Roo Shell
The Roo system looks great. Its a system to generate and support a JEE system. The roo shell can be used to configure JEE components. You can have a basic website up in seconds. Like Groovy and Grails you get spring standards built in, and your not dependent on the Roo system once your finished.

I am going to take a proper look at it at some point.