There are two other aspects which are Choice_Roo_Plural and Choice_Roo_ToString.

"Choice" in Plural Form, "Choices"

Bind entity com.springsource.vote.domain.Choice on table choice

It is probably for the future use as a name of domain object in plural form may be frequently required when displaying the list of it.

Now, let’s look at the last aspect.

toString() method for Choice

privileged aspect Choice_Roo_ToString {

    public java.lang.String Choice.toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("id: ").append(getId()).append(", ");
        sb.append("version: ").append(getVersion()).append(", ");
        sb.append("namingChoice: ").append(getNamingChoice()).append(", ");
        sb.append("description: ").append(getDescription()).append(", ");
        return sb.toString();
    }    

}

It returns String containing the information about Choice which includes all the values of the variables from the aspects as well. This String is used to display the information about Choice object in the view, WEB-INF/jsp/vote/create.jsp.

All these mixins can be good Separation of Concerns (SoC). Each aspect has what should be a concern in a particular mixin only. For example, id and version of Choice are not really a concern of Choice itself as it does not have any meaning for Choice, yet it is very important for OR mapping. Thus it is separated from Choice and only occurs in Choice_Roo_Entity which plays the role of a persistent object.

It is not a completely new ways to write mixin using inter-type declarations in AspectJ (http://today.java.net/pub/a/today/2005/12/15/writing-mixins-with-aop.html). Nevertheless, Spring ROO is still so cool as I have never seen any automatically generated code by Java frameworks uses mixins written using inter-type declarations as a nice way of SoC. I may need to call ROO RSoC (Real Separation of Concerns).

OK, I am now running out of time so had better finish this post quickly.

I would just finally like to point out some minor issues I found.

1. An error in dojo JS toolkit.

dojo JS Toolkit Error

2. An error in roo.css file.

CSS Error

#wrap {
	margin:0 auto;
  	position:relative;
  	float:center;
  	top: 0px;
  	left:0px;
  	width:800px;
  	text-align:left;  	

}

center is not a float value.

3. Using a String’s equals() method to test for an empty String. This might be OK for a small application like the ROO example but it can bring about some performance issue for a big application with numerous simultaneous user requests.

Performance Issue - Test for Empty String

if (text == null || "".equals(text))

had better be

if (text == null || 0 == text.length())

I wrote more details about it here with performance tests.
http://blog.lckymn.com/2009/05/17/test-for-empty-string/

Finally, it’s my wish. I found that aspect code is not really supported by the Eclipse functions for Java such as Call Hierarchy and Open Declaration. It would be much better if aspects are fully supported by the Eclipse functions for Java. However, it may have something to do with AJDT not Spring ROO integration.

Phew, I have eventually written this. Even though I tried ROO approximately two weeks ago, I did not have time to write about it.

Now, let’s look at more interesting one that is the ROO generated source code!

As you can see, there are many AspectJ aspects in the com.springsource.vote.domain package. So I’ll firstly try to look at the Choice class which is not an aspect.

Domain object - Choice

So where are the others?

Check out the Choice_Roo_Entity aspect.

Persistent Object (Aspect)

    @javax.persistence.Id
    @javax.persistence.GeneratedValue(strategy = javax.persistence.GenerationType.AUTO)
    @javax.persistence.Column(name = "id")
    private java.lang.Long Choice.id;

This code above is declaring long type id variable to the type Choice to use as an identifier for OR mapping. Because it is declared as a private variable, it is impossible to access it inside the code of Choice but possible only inside this Choice_Roo_Entity aspect.

What about the Choice_Roo_JavaBean.

JavaBean (Aspect)

privileged aspect Choice_Roo_JavaBean {

    public java.lang.String Choice.getNamingChoice() {
        return this.namingChoice;
    }    

    public void Choice.setNamingChoice(java.lang.String namingChoice) {
        this.namingChoice = namingChoice;
    }    

    public java.lang.String Choice.getDescription() {
        return this.description;
    }    

    public void Choice.setDescription(java.lang.String description) {
        this.description = description;
    }    

}

So as shown above, Choice_Roo_JavaBean is a privileged aspect and therefore it can access namingChoice and description variables which are declared in Choice.

So what is it? It is a mixin. Mixin is a class which provides a functionality to a subclass yet mixin itself is not supposed to stand alone. So a class can collect its functionality by inheriting from one or more mixins through multiple inheritance. However, as we all know, Java does not support multiple inheritance. So to use mixins in Java world, inter-type declarations in AspectJ can be used.

privileged aspect Choice_Roo_Entity {

	(...)

    @javax.persistence.Id
    @javax.persistence.GeneratedValue(strategy = javax.persistence.GenerationType.AUTO)
    @javax.persistence.Column(name = "id")
    private java.lang.Long Choice.id;    

    (...)

    public java.lang.Long Choice.getId() {
        return this.id;
    }
}

As seen in the aspect code above, a long type variable is added to the type Choice and a getId() method which returns a long type value that is the value in the variable, id, just added by the aspect. So an instance of Choice type can have getId() method even though it does not exist in the Choice class. Therefore, as mentioned, Choice type can have characteristics of both persistent object and JavaBean.

AspectJ is also used to declare Choice type as a configurable type.

Make Choice @Configurable

privileged aspect Choice_Roo_Configurable {

    declare @type: Choice: @org.springframework.beans.factory.annotation.Configurable;    

}

Next:
http://blog.lckymn.com/2009/05/17/roo-so-cool-04/