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SpEL docs: supported literals, null comparisons

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Issue: SPR-14361
Issue: SPR-14987
This commit is contained in:
Juergen Hoeller
2016-12-19 17:56:32 +01:00
parent 8c26717bdc
commit 6bdc5bfc08
1 changed files with 26 additions and 19 deletions
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45
src/reference/docbook/expressions.xml
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@@ -490,13 +490,12 @@ Boolean b = simple.booleanList.get(0);
<section xml:id="expressions-ref-literal">
<title>Literal expressions</title>
<para>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.</para>
<para>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.</para>
<programlisting language="java">ExpressionParser parser = new SpelExpressionParser();
@@ -626,8 +625,8 @@ int[][] numbers3 = (int[][]) parser.parseExpression("new int[4][5]").getValue(co
String c = parser.parseExpression("'abc'.substring(2, 3)").getValue(String.class);
// evaluates to true
boolean isMember = parser.parseExpression("isMember('Mihajlo Pupin')").getValue(societyContext,
Boolean.class);</programlisting>
boolean isMember = parser.parseExpression("isMember('Mihajlo Pupin')").getValue(societyContext, Boolean.class);
</programlisting>
</section>
<section xml:id="expressions-operators">
@@ -640,15 +639,24 @@ boolean isMember = parser.parseExpression("isMember('Mihajlo Pupin')").getValue(
or equal, greater than, and greater than or equal are supported using
standard operator notation.</para>
<para><programlisting language="java">// evaluates to true
<programlisting language="java">// evaluates to true
boolean trueValue = parser.parseExpression("2 == 2").getValue(Boolean.class);
// evaluates to false
boolean falseValue = parser.parseExpression("2 &lt; -5.0").getValue(Boolean.class);
// evaluates to true
boolean trueValue = parser.parseExpression("'black' &lt; 'block'").getValue(Boolean.class);</programlisting>
In addition to standard relational operators SpEL supports the
boolean trueValue = parser.parseExpression("'black' &lt; 'block'").getValue(Boolean.class);
</programlisting>
<para>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 &gt; null` is always `true`) and no other value
is ever less than nothing (`X &lt; 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 &gt; 0` or `X &lt; 0`).</para>
<para>In addition to standard relational operators SpEL supports the
'instanceof' and regular expression based 'matches' operator.</para>
<programlisting language="java">// evaluates to false
@@ -661,14 +669,13 @@ boolean trueValue =
//evaluates to false
boolean falseValue =
parser.parseExpression("'5.0067' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);
</programlisting>
</programlisting>
<para>Each symbolic operator can also be specified as a purely alphabetic equivalent. This avoids
problems where the symbols used have special meaning for the document type in which
the expression is embedded (eg. an XML document). The textual equivalents are shown
here: lt ('&lt;'), gt ('&gt;'), le ('&lt;='), ge ('&gt;='),
eq ('=='), ne ('!='), div ('/'), mod ('%'), not ('!').
These are case insensitive.</para>
<para>Each symbolic operator can also be specified as a purely alphabetic equivalent.
This avoids problems where the symbols used have special meaning for the document type
in which the expression is embedded (eg. an XML document). The textual equivalents are
shown here: lt ('&lt;'), gt ('&gt;'), le ('&lt;='), ge ('&gt;='), eq ('=='), ne ('!='),
div ('/'), mod ('%'), not ('!'). These are case insensitive.</para>
</section>
<section xml:id="expressions-operators-logical">