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Clarify behavior of the Elvis SpEL operator in documentation #30352

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merged 2 commits into from
May 5, 2023
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Clarify behavior of the Elvis SpEL operator in documentation #30352

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671e5a5
Clarify behavior of the Elvis SpEL operator in documentation
simonbasle Apr 18, 2023
af35aa2
Applying wording suggestion from code review
simonbasle Apr 19, 2023
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8 changes: 6 additions & 2 deletions ...ework-docs/modules/ROOT/pages/core/expressions/language-ref/operator-elvis.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,10 @@ Kotlin::
----
======

NOTE: The SpEL Elvis operator also checks for _empty_ Strings in addition to `null` objects.
The original snippet is thus only close to emulating the semantics of the operator (it would need an
additional `!name.isEmpty()` check).

The following listing shows a more complex example:

[tabs]
Expand All @@ -53,7 +57,7 @@ Java::
String name = parser.parseExpression("name?:'Elvis Presley'").getValue(context, tesla, String.class);
System.out.println(name); // Nikola Tesla

tesla.setName(null);
tesla.setName("");
name = parser.parseExpression("name?:'Elvis Presley'").getValue(context, tesla, String.class);
System.out.println(name); // Elvis Presley
----
Expand All @@ -69,7 +73,7 @@ Kotlin::
var name = parser.parseExpression("name?:'Elvis Presley'").getValue(context, tesla, String::class.java)
println(name) // Nikola Tesla

tesla.setName(null)
tesla.setName("")
name = parser.parseExpression("name?:'Elvis Presley'").getValue(context, tesla, String::class.java)
println(name) // Elvis Presley
----
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10 changes: 5 additions & 5 deletions spring-expression/src/main/java/org/springframework/expression/spel/ast/Elvis.java
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Expand Up @@ -26,9 +26,9 @@
import org.springframework.util.ObjectUtils;

/**
* Represents the elvis operator <code>?:</code>. For an expression <code>a?:b</code> if <code>a</code> is not null,
* the value of the expression is <code>a</code>, if <code>a</code> is null then the value of the expression is
* <code>b</code>.
* Represents the Elvis operator <code>?:</code>. For an expression <code>a?:b</code> if <code>a</code> is neither null
* nor an empty String, the value of the expression is <code>a</code>.
* If <code>a</code> is null or the empty String, then the value of the expression is <code>b</code>.
*
* @author Andy Clement
* @author Juergen Hoeller
Expand All @@ -43,8 +43,8 @@ public Elvis(int startPos, int endPos, SpelNodeImpl... args) {


/**
* Evaluate the condition and if not null, return it.
* If it is null, return the other value.
* Evaluate the condition and if neither null nor an empty String, return it.
* If it is null or an empty String, return the other value.
* @param state the expression state
* @throws EvaluationException if the condition does not evaluate correctly
* to a boolean or there is a problem executing the chosen alternative
Expand Down