What is a canonical way to check if the String is null or empty using SpEL?
I would like to achieve the same result as Strings.isNullOrEmpty(myString) from Guava does.
My candidates:
"#myString.?length=0"
"#myString = ''"
Not sure if any is canonical, and the documentation is pretty vague (https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#expressions-operators)
This is how it's done according to latest documentation:
not null or empty #myString > ''
null or empty #myString <= ''
not null or blank #myString?.trim() > ''
null or blank #myString?.trim() <= ''
You can call any Java method on an object, e.g. #myString.length(), #myString.isEmpty() or #myString.isBlank(). I'd say, that would be the canonical way to check whether a string is empty or blank.
For null or empty: #myString == null || #myString.isEmpty()
For null or blank: #myString == null || #myString.isBlank()
You can test this with:
System.out.println(new SpelExpressionParser().parseExpression("#root?.isEmpty()").getValue("x")); // false
System.out.println(new SpelExpressionParser().parseExpression("#root?.isEmpty()").getValue("")); // true
System.out.println(new SpelExpressionParser().parseExpression("#root?.isEmpty()").getValue((Object) null)); // null
System.out.println(new SpelExpressionParser().parseExpression("#root == null || #root.isEmpty()").getValue("x")); // false
System.out.println(new SpelExpressionParser().parseExpression("#root == null || #root.isEmpty()").getValue("")); // true
System.out.println(new SpelExpressionParser().parseExpression("#root == null || #root.isEmpty()").getValue((Object) null)); // true
/*
list=['a','b']
list=[]
list=""
*/
${empty list}//false
${empty list1}//true
${empty list2}//true