SpEL language - auto null reference initalization

Question

Please look at example code:

public static class MyTestClass {
    public List<Boolean> booleans = new ArrayList<>();
}

public static void main(String[] args) {
    SpelParserConfiguration config = new SpelParserConfiguration(true, true);

    MyTestClass myTestClass = new MyTestClass();

    SpelExpressionParser parser = new SpelExpressionParser(config);
    Object value = parser.parseExpression("booleans[1]").getValue(myTestClass); //exception

I try to initalize boolean list with default values. The problem is, Boolean class does not have default constructor so I got exception:

Caused by: java.lang.NoSuchMethodException: java.lang.Boolean.<init>()

It is possible to write how new objects should be initalized if they dont exists in list?

*"I try to initalize boolean list with default values"* Where do you try that? --- Did you try e.g. `public List booleans = Arrays.asList(true, false, false, true);` for a list of size 4? — Andreas, Jun 25 '19 at 17:21
@Andreas fixed 'simple' I try to intalize it automatically by SpEL expressions instead of manually while list creation — Thomas Banderas, Jun 25 '19 at 18:54
Since your question is about the initialization, it would be good to actually see *how* you're (trying) to do that initialization, don't you think? — Andreas, Jun 25 '19 at 18:59

Ken Chan · Answer 1 · 2019-06-26T05:11:33.880

I am sorry that the auto-grow collection features in SpEL only works if the item has the default constructor.

Unless you have a strong reason the need to initialise a list using SpEL , I suggest you use the normal java method call , it is much faster than SpEL and also type safely.

If you insist doing it in SpEL , the best you can do is :

List<Boolean> result =  parser.parseExpression( "{true,true,false,false,true}").getValue(List.class);
myTestClass.booleans = result;

SpEL language - auto null reference initalization

1 Answers1