Spring SPEL collection projection

Question

A simple question on SPEL collection selection.

Look at section 10.5.17 Collection Selection on this page https://docs.spring.io/spring/docs/4.3.10.RELEASE/spring-framework-reference/html/expressions.html

List<Inventor> list = (List<Inventor>) parser.parseExpression(
        "Members.?[Nationality == 'Serbian']").getValue(societyContext);

What i need is the selection 'Serbian' to come from outside and not be a fixed hard coded String.

Just for arguments sake consider that, we could get it as "selectedNationality" from the same society class from the same page in the link.

Modified class with selectedNationality

public class Society {
    private String name;
    public static String Advisors = "advisors";
    public static String President = "president";
    private List<Inventor> members = new ArrayList<Inventor>();
    private Map officers = new HashMap();
// new selector field
    private String selectedNationality;
......
 }

New Selection

The new selection SPEL would look like

List<Inventor> list = (List<Inventor>) parser.parseExpression(
        "Members.?[Nationality == selectedNationality]").getValue(societyContext);

When we try that the error is that "selectedNationality" is not a part of the Member object.

Does that mean that for collection selection in spring expression language we would need a hard coded String ? If yes does anyone know why ?

Why not simply "Members.?[Nationality == '" + selectedNationality + "']"? But why do you want to use SPEL for this in the first place? — dpr
Would that not just give me a string called selectedNationality, and not the value of selectedNationality ? The answer to Why is that just do not want to hard code anything in the el. — Suchak Jani

Suchak Jani Suchak Jani · Accepted Answer · 2020-08-05T11:44:20

Found out how to do it. So the way is to use variables see 10.5.11 Variables @ [https://docs.spring.io/spring/docs/4.3.10.RELEASE/spring-framework-reference/html/expressions.html][1]

Set Variable

So in our case we wold do this set variable :

Inventor tesla = new Inventor("Nikola Tesla", "Serbian");
StandardEvaluationContext context = new StandardEvaluationContext(tesla);
context.setVariable("selectedNationality ", "Serbian");

New Selection

The new selection SPEL would look like this with #selectedNationality

List<Inventor> list = (List<Inventor>) parser.parseExpression(
        "Members.?[Nationality == #selectedNationality]").getValue(societyContext);

Works like a charm !

Spring SPEL collection projection

1 Answers