Evaluating Expressions with groovy.util.Eval

A few days ago I faced a problem of evaluating dynamic expressions on domain objects. The scenario was that, depending upon the user input, I needed to sort a list of objects on some properties, which were nested deep in the object, e.g.,

[java]
student.course?.college?.name // if a user chose to sort students by college name
student.course.teacher.name // if a user chose to sort students by teacher name.
[/java]

Using if, else could not have been an elegant solution, considering that there were many more fields to be sorted upon. This is when groovy.util.Eval class came to my notice. I found a useful function there:
[java]Eval.x(java.lang.Object x, java.lang.String expression)[/java]

Its usage is like this:

[java]assert 10 == Eval.x(2, ‘ x * 4 + 2’)[/java]

and I wrote:

[java]
students.sort {Eval.x(it, "x.${sortField}")} // sortField could be student.course?.college?.name
[/java]

In addition to this, groovy.util.Eval has some more useful methods like:

[java]

assert 10 == Eval.me(‘ 2 * 4 + 2’)
assert 10 == Eval.xyz(2, 4, 2, ‘ x * y + z’)
assert 10 == Eval.xy(2, 4, ‘ x * y + 2’)
[/java]

Hope this helps.
Imran Mir
imran[@]intelligrape.com