CODEWITHSUNDEEP
javaspringspring-el
Abhay
Abhay

Reputation: 130

How to extract list of single property of objects in list using SpEL?

I want just list of id from the Tester object list using SpEL

List<Tester> tests = new ArrayList<Tester>();
tests.add(new Tester(1)); ...
ExpressionParser parser = new SpelExpressionParser();
StandardEvaluationContext context = new StandardEvaluationContext();
context.setVariable("tests",tests);
System.out.println(tests.stream().map(Tester::getId).collect(Collectors.toList())); // LIKE THIS
System.out.println(parser.parseExpression("#tests what to write here").getValue(context));

Desired Result : [1, 2, 3, 4]

Tester is 

public class Tester {
        private Integer id;
    }

Upvotes: 8

Views: 6187

Answers (2)

Abhay
Abhay

Reputation: 130

This is a dirty way to do so:

public class ParseCheck {
    public static void main(String[] args) throws NoSuchMethodException, SecurityException {
        List<Tester> tests = Arrays.asList(new Tester(1),new Tester(2),new Tester(3),new Tester(4),new Tester(1));

        ExpressionParser parser = new SpelExpressionParser();
        StandardEvaluationContext context = new StandardEvaluationContext();
        context.registerFunction("stream", ParseCheck.class.getMethod("stream", String.class));

        context.setVariable("tests",tests);
        System.out.println(tests.stream().map(Tester::getId).distinct().collect(Collectors.toList()));

        System.out.println(parser.parseExpression("#tests.stream().map(#stream('id')).distinct().collect(T(java.util.stream.Collectors).toList())").getValue(context));
    }

    public static Function<Object, Object> stream(String property) {
        ExpressionParser parser = new SpelExpressionParser();
        return s -> parser.parseExpression(property).getValue(s);
    }
}

Here a function is registered in the context which will return a stream of the property required to be extracted. The property is extracted using SpEL too.

Upvotes: 0

Grzegorz Oledzki
Grzegorz Oledzki

Reputation: 24271

You can use (what they call) Collection Projection (also known as map in functional programming world):

tests.![id]

Look at the Spring docs for SpEL for reference.

Upvotes: 15

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