Start the Roo shell from the C:\roo-cookbook\ch01-recipe directory, which contains the flight-app project.

Roo provides field commands, which you can use to add different types of fields in your Java class, shown as follows:

The given output for each of these commands shows that when an attribute is added to the Passenger class for the first time, the Passenger_Roo_JavaBean.aj and Passenger_Roo_ToString.aj files are created. You may notice that every time you add an attribute, the Passenger_Roo_JavaBean.aj and Passenger_Roo_ToString.aj AspectJ ITD files are also updated.

Spring Roo provides multiple field commands for adding different types of attributes to the Java class. For instance, field string is for adding a String type field, field date is for adding a java.util.Date or java.util.Calendar type field, field other is for adding a field of custom Java type, and so on.

The field string, field other, and field number commands accept the name argument, which identifies the name of the attribute to be added to the Java class. The field other and field number also require the type of the attribute.

The following code shows Passenger_Roo_JavaBean.aj AspectJ ITD, which was modified by Spring Roo when we added fields to the Passenger class:

privileged aspect Passenger_Roo_JavaBean
{
   public String Passenger.getFirstName()
   {
      return this.firstName;
   }
   public void Passenger.setFirstName(String firstName)
   {
      this.firstName = firstName;
   }
...
}

The given code shows that Passenger_Roo_JavaBean.aj was updated by Spring Roo to introduce getter and setter methods for each of the fields added to Passenger class. This was possible because of the presence of @RooJavaBean annotation in the Passenger class.

The following code shows Passenger_Roo_ToString.aj AspectJ ITD, which was also modified by Spring Roo when fields were added to the Passenger class:

privileged aspect Passenger_Roo_ToString
{
   public String Passenger.toString()
   {
      StringBuilder sb = new StringBuilder();
      sb.append("FirstName:").append(getFirstName()).append(",");
      sb.append("LastName: ").append(getLastName()).append(", ");
      sb.append("Age: ").append(getAge()).append(", ");
      sb.append("Address: ").append(getAddress());
      return sb.toString();
   }
}

As the given code suggests, it introduces a toString method to the Passenger class, which returns a concatenated String containing the value of each of its attribute. This was possible because the Passenger class was annotated with the @RooToString annotation.

The following figure shows how Spring Roo manages AspectJ ITD files:

The given figure shows that when you start the Spring Roo shell from a directory, it actively monitors the Java classes in the file system that are annotated with Roo annotations (for example @RooToString, @RooJavaBean, and so on). When any of these Java classes are modified using an IDE or any other editor, Spring Roo checks if the AspectJ ITD files (which follow the naming convention *_Roo_*.aj, as explained earlier) corresponding to the Java classes are in sync with the Java classes. If they are not, it updates the AspectJ ITD files accordingly. Spring Roo makes use of add-ons to make modifications to the AspectJ ITD files.

This recipe showed that if you want Roo to automatically generate a toString method and getter and setter methods for all the attributes, then annotate your class with @RooToString and @RooJavaBean annotations.

Spring Roo doesn't provide commands to remove or modify an attribute. So, if you want to remove or modify an existing attribute of a Java class, you can do so using your IDE. Spring Roo will take care of removing or modifying the attribute in corresponding AspectJ ITD files.