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SpEL docs: supported literals, null comparisons 

Issue: SPR-14361
Issue: SPR-14987
This commit is contained in:
Juergen Hoeller 2016-12-08 18:16:48 +01:00
parent 6517c53768
commit 05579fd1b9
1 changed files with 19 additions and 6 deletions
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25
src/asciidoc/core-expressions.adoc
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@ -220,6 +220,7 @@ example for Spring bean or Spring Web Flow definitions. In this case, the parser
evaluation context, root object and any predefined variables are all set up implicitly,
requiring the user to specify nothing other than the expressions.
====
As a final introductory example, the use of a boolean operator is shown using the
Inventor object in the previous example.
@ -583,12 +584,13 @@ Autowired methods and constructors can also use the `@Value` annotation.
[[expressions-ref-literal]]
=== Literal expressions
The types of literal expressions supported are strings, dates, numeric values (int,
real, and hex), boolean and null. Strings are delimited by single quotes. To put a
single quote itself in a string use two single quote characters. The following listing
shows simple usage of literals. Typically they would not be used in isolation like this,
but as part of a more complex expression, for example using a literal on one side of a
logical comparison operator.
The types of literal expressions supported are strings, numeric values (int, real, hex),
boolean and null. Strings are delimited by single quotes. To put a single quote itself
in a string, use two single quote characters.
The following listing shows simple usage of literals. Typically they would not be used
in isolation like this but rather as part of a more complex expression, for example
using a literal on one side of a logical comparison operator.
[source,java,indent=0]
[subs="verbatim,quotes"]
@ -777,6 +779,17 @@ and greater than or equal are supported using standard operator notation.
boolean trueValue = parser.parseExpression("'black' < 'block'").getValue(Boolean.class);
----
[NOTE]
====
Greater/less-than comparisons against `null` follow a simple rule: `null` is treated as
nothing here (i.e. NOT as zero). As a consequence, any other value is always greater
than `null` (`X > null` is always `true`) and no other value is ever less than nothing
(`X < null` is always `false`).
If you prefer numeric comparisons instead, please avoid number-based `null` comparisons
in favor of comparisons against zero (e.g. `X > 0` or `X < 0`).
====
In addition to standard relational operators SpEL supports the `instanceof` and regular
expression based `matches` operator.