Several Jelly ExamplesIntroduction
In Jelly a lot is possible. The functionality used most by the user is
the use of variables. It is possible to use variables as text, where XML
is not interpreted, but it is also possible to interpret the XML and even
to select only a part of the XML with an XPath expression.
More information about Jelly can be found in .
Note that the Jelly expression $${..} will be executed
even from a CDATA tag or a <!-- --> comment
section. The way to escape it is to use an extra dollar as in
$$$${..}.
Note that variables inside a JEXL expression may not contain
-. It is allowed to use _ and to use
dotted variables like
my.dotted.variable.
Some variables are automatically set and allow access to various
information. It is possible to overwrite these locally, but this is not
recommended. The variables are:
$formdata
For a submitted form this consists of a tag variables,
containing the submitted form data.
$instance
This contains internal information and should not be needed.
First an example will be given with text and then another with XML code.
Note that the namespaces used are xmlns:c="jelly:core" and
xmlns:x="jelly:xml".
Some Examples
An example with text set and read using <code>jelly:core</code>.
4.2
The version is or $${version}.
]]>
This is an example where the text 4.2 is put in a
variable named version. The trim
attribute eith value true indicates that any whitespace at the
beginning or the end should be removed. The result is displayed
below:
4.2
The version is or ${version}.
An example with XML set and read using <code>jelly:xml</code>.
21
The formula is . The part of the
formula right of the equals-sign is
.
]]>
This is an example where an Openmath function definition is put in a
variable called formula. With x:copyOf it
is possible to select the whole object or to select a part of it. The
output is displayed below.
21
The formula is . The part of the
formula right of the equals-sign is
.
An example with <tag>core:if</tag>
Jelly has both core:if and xml:if tags. The
contents will only be processed if the value of the test
attribute evaluates to true.
In the following code a counter is either set to
1 or increased if it already exists.
The counter is now $${counter}. Increasing the counter.
The counter is now $${counter}.
]]>
When run this will output the following:
Initialising the counter.
The counter is now ${counter}. Increasing the counter.
The counter is now ${counter}.
The tag xml:if is like core:if, but uses XPath
and XML variables.
An example with <tag>core:choose</tag> and <tag>core:when</tag>.
Instead of using several core:if statements it is possible
to use a core:choose. A core:choose consists at
least one core:when tags and might contain an
core:otherwise tag. The first core:when tag for
which the test evaluates to true will be processed. If no
core:when tags have a test that evaluates to true and a
core:otherwise is present then the core:otherwise
tag will be processed.
The following code converts the counter from the
previous example to text.
The counter is now $${counter}.
The text is now $${countertext}.
]]>
Ininitialise or increase the counter.
The counter is now ${counter}.
The text is now ${countertext}.
Note that the expressions now need to be written as a jelly expression:
$${..}.
Furthermore note that there is no xml:choose tag, so it is
impossible to use XML variables or XPath in a choose.
More information
The main Jelly page is the Apache Jelly page.
On that site is also more about the jelly:core
tags (c:-tags), more about the other
tags (one of which is xml)
and more about JEXL, the
Java Expression Language.