Author: henrib
Date: Wed Dec 7 18:11:57 2011
New Revision: 1211579
URL: http://svn.apache.org/viewvc?rev=1211579&view=rev
Log:
JEXL-123:
Revamped package documentation
Modified:
commons/proper/jexl/trunk/src/main/java/org/apache/commons/jexl3/package.html
Modified:
commons/proper/jexl/trunk/src/main/java/org/apache/commons/jexl3/package.html
URL:
http://svn.apache.org/viewvc/commons/proper/jexl/trunk/src/main/java/org/apache/commons/jexl3/package.html?rev=1211579&r1=1211578&r2=1211579&view=diff
==============================================================================
---
commons/proper/jexl/trunk/src/main/java/org/apache/commons/jexl3/package.html
(original)
+++
commons/proper/jexl/trunk/src/main/java/org/apache/commons/jexl3/package.html
Wed Dec 7 18:11:57 2011
@@ -27,6 +27,7 @@
<li><a href="#usage">Using JEXL</a></li>
<li><a href="#configuration">Configuring JEXL</a></li>
<li><a href="#customization">Customizing JEXL</a></li>
+ <li><a href="#extension">Extending JEXL</a></li>
</ul>
<h2><a name="intro">Introduction</a></h2>
@@ -37,29 +38,29 @@
<h2><a name="example">A Brief Example</a></h2>
<p>
- When evaluating expressions, JEXL merges an
- {@link org.apache.commons.jexl3.Expression}
+ In its simplest form, JEXL merges an
+ {@link org.apache.commons.jexl3.JexlExpression}
with a
- {@link org.apache.commons.jexl3.JexlContext}.
+ {@link org.apache.commons.jexl3.JexlContext} when evaluating
expressions.
An Expression is created using
{@link
org.apache.commons.jexl3.JexlEngine#createExpression(java.lang.String)},
passing a String containing valid JEXL syntax. A simple
JexlContext can be created using
a {@link org.apache.commons.jexl3.MapContext} instance;
a map of variables that will be internally wrapped can be
optionally provided through its constructor.
- The following example, takes a variable named foo, and
- invokes the bar() method on the property innerFoo:
+ The following example, takes a variable named 'car', and
+ invokes the checkStatus() method on the property 'engine'
</p>
<pre>
// Create a JexlEngine (could reuse one instead)
JexlEngine jexl = new JexlEngine();
- // Create an expression object
- String jexlExp = "foo.innerFoo.bar()";
+ // Create an expression object equivalent to
'car.getEngine().checkStatus()':
+ String jexlExp = "car.engine.checkStatus()";
Expression e = jexl.createExpression( jexlExp );
-
+ // The car we have to handle coming as an argument...
+ Car car = theCarThatWeHandle;
// Create a context and add data
JexlContext jc = new MapContext();
- jc.set("foo", new Foo() );
-
+ jc.set("car", car );
// Now evaluate the expression, getting the result
Object o = e.evaluate(jc);
</pre>
@@ -74,14 +75,16 @@
</ul>
<h3><a name="usage_note">Important note</a></h3>
+ The public API classes start with 'Jexl*' or 'Jxl*'.
The only public packages you should use are:
<ul>
<li>org.apache.commons.jexl3</li>
<li>org.apache.commons.jexl3.introspection</li>
</ul>
- The following packages follow a "use at your own maintenance cost"
policy.
+ The following packages follow a "use at your own maintenance cost"
policy; these are only intended to be used
+ for extending JEXL.
Their classes and methods are not guaranteed to remain compatible in
subsequent versions.
- If you think you need to use some of their features, it might be a
good idea to check with
+ If you think you need to use directly some of their features or
methods, it might be a good idea to check with
the community through the mailing list first.
<ul>
<li>org.apache.commons.jexl3.parser</li>
@@ -143,9 +146,10 @@
The main methods are:
</p>
<ul>
- <li>{@link
org.apache.commons.jexl3.JexlEngine#createExpression}</li>
<li>{@link org.apache.commons.jexl3.JexlEngine#createScript}</li>
- <li>{@link org.apache.commons.jexl3.Expression#evaluate}</li>
+ <li>{@link org.apache.commons.jexl3.JexlScript#execute}</li>
+ <li>{@link
org.apache.commons.jexl3.JexlEngine#createExpression}</li>
+ <li>{@link org.apache.commons.jexl3.JexlExpression#evaluate}</li>
</ul>
The following example illustrates their usage:
<pre>
@@ -154,9 +158,9 @@
JexlContext jc = new MapContext();
jc.set("quuxClass", quux.class);
- Expression create = jexl.createExpression("quux = new(quuxClass,
'xuuq', 100)");
- Expression assign = jexl.createExpression("quux.froboz.value =
10");
- Expression check = jexl.createExpression("quux[\"froboz\"].value");
+ JexlExpression create = jexl.createExpression("quux =
new(quuxClass, 'xuuq', 100)");
+ JelxExpression assign = jexl.createExpression("quux.froboz.value =
10");
+ JexlExpression check =
jexl.createExpression("quux[\"froboz\"].value");
Quux quux = (Quux) create.evaluate(jc);
Object o = assign.evaluate(jc);
assertEquals("Result is not 10", new Integer(10), o);
@@ -164,87 +168,119 @@
assertEquals("Result is not 10", new Integer(10), o);
</pre>
- <h3><a name="usage_ujexl">UnifiedJEXL script expressions</a></h3>
+ <h3><a name="usage_ujexl">Unified Expressions and Templates</a></h3>
<p>
If you are looking for JSP-EL like and basic templating features,
you can
- use UnifiedJEXL.
+ use UnifiedExpression from a JxltEngine.
</p>
The main methods are:
<ul>
- <li>{@link org.apache.commons.jexl3.UnifiedJEXL#parse}</li>
- <li>{@link
org.apache.commons.jexl3.UnifiedJEXL.Expression#evaluate}</li>
- <li>{@link
org.apache.commons.jexl3.UnifiedJEXL.Expression#prepare}</li>
+ <li>{@link
org.apache.commons.jexl3.JxltEngine#createExpression}</li>
+ <li>{@link
org.apache.commons.jexl3.JxltEngine.UnifiedExpression#prepare}</li>
+ <li>{@link
org.apache.commons.jexl3.JxltEngine.UnifiedExpression#evaluate}</li>
+ <li>{@link org.apache.commons.jexl3.JxltEngine#createTemplate}</li>
+ <li>{@link
org.apache.commons.jexl3.JxltEngine.Template#prepare}</li>
+ <li>{@link
org.apache.commons.jexl3.JxltEngine.Template#evaluate}</li>
</ul>
The following example illustrates their usage:
<pre>
JexlEngine jexl = new JexlEngine();
- UnifiedJEXL ujexl = new UnifiedJEXL(jexl);
- UnifiedJEXL.Expression expr = ujexl.parse("Hello ${user}");
- String hello = expr.evaluate(context, expr).toString();
+ JxltEngine jxlt = jexl.jxlt();
+ JxltEngine.UnifiedExpression expr = jxlt.createExpression("Hello
${user}");
+ String hello = jxlt.evaluate(context, jxlt).toString();
</pre>
- <h3>Expressions Script and UnifiedJEXL.Expression: differences</h3>
- <h4>Expression</h4>
+ <h3>JexlExpression, JexlScript, UnifiedExpression and Template:
differences</h3>
+ <h4>JexlExpression </h4>
<p>
- This only allows for a single command to be executed and the result
from
- that is returned. If you try to use multiple commands it ignores
+ These are the most basic form of JexlEngine expressions and only
allows for a single command
+ to be executed and its result returned. If you try to use multiple
commands it ignores
everything after the first semi-colon and just returns the result from
the first command.
</p>
- <h4>Script</h4>
+ <h4>JexlScript</h4>
<p>
This allows you to put multiple commands in the expression and you can
- use variable assignments, loops, calculations, etc. The result from
the
- last command is returned from the script.
+ use variable assignments, loops, calculations, etc. More or less what
can be achieved in Shell or
+ JavaScript at its basic level. The result from the last command is
returned from the script.
</p>
- <h4>UnifiedJEXL.Expression</h4>
+ <h4>JxltEngine.UnifiedExpression</h4>
<p>
- This is ideal to produce text. To get a calculation you use the
EL-like syntax
+ These are ideal to produce "one-liner" text, like a 'toString()' on
steroids.
+ To get a calculation you use the EL-like syntax
as in ${someVariable}. The expression that goes between the brackets
- behaves like a script, not an expression. You can use semi-colons to
+ behaves like a JexlScript, not an expression. You can use semi-colons
to
execute multiple commands and the result from the last command is
returned from the script. You also have the ability to use a 2-pass
evaluation using
the #{someScript} syntax.
</p>
+ <h4>JxltEngine.Template</h4>
+ <p>
+ These produce text documents. Each line beginning with '$$' (as a
default) is
+ considered JEXL code and all others considered as
JxltEngine.UnifiedExpression.
+ Think of those as simple Velocity templates. A rewritten MudStore
initial Velocity sample looks like this:
+ </p>
+ <pre><code>
+ <html>
+<body>
+Hello ${customer.name}!
+<table>
+$$for(var mud : mudsOnSpecial ) {
+$$ if (customer.hasPurchased(mud) ) {
+ <tr>
+ <td>
+ ${flogger.getPromo( mud )}
+ </td>
+ </tr>
+$$ }
+$$}
+</table>
+</body>
+</html>
+ </code></pre>
<h2><a name="configuration">JEXL Configuration</a></h2>
<p>
The JexlEngine can be configured through a few parameters that
will drive how it reacts
- in case of errors. These configuration methods are best called at
JEXL engine initialization time; it
- is recommended to derive from JexlEngine to call those in a
constructor.
+ in case of errors.
+ These configuration methods are embedded through a {@link
org.apache.commons.jexl3.JexlBuilder}.
+ <p>
+ Most configuration options can be overriden during evaluation by
using a {@link org.apache.commons.jexl3.JexlEvalContext}
+ which merges both a {@link org.apache.commons.jexl3.JexlContext}
to expose variables and a
+{@link org.apache.commons.jexl3.JexlEngine$Options} to carry evaluation
options.
</p>
<p>
- {@link org.apache.commons.jexl3.JexlEngine#setLenient} configures
when JEXL considers 'null' as an error or not in various situations;
+ {@link org.apache.commons.jexl3.JexlBuilder#strict} configures
when JEXL considers 'null' as an error or not in various situations;
when facing an unreferenceable variable, using null as an argument
to an arithmetic operator or failing to call
a method or constructor. The lenient mode is close to JEXL-1.1
behavior.
</p>
<p>
- {@link org.apache.commons.jexl3.JexlEngine#setSilent} configures
how JEXL reacts to errors; if silent, the engine will not throw exceptions
+ {@link org.apache.commons.jexl3.JexlBuilder#silent} configures how
JEXL reacts to errors; if silent, the engine will not throw exceptions
but will warn through loggers and return null in case of errors.
Note that when non-silent, JEXL throws
JexlException which are unchecked exception.
</p>
<p>
- {@link org.apache.commons.jexl3.JexlEngine#setDebug} makes
stacktraces carried by JExlException more meaningfull; in particular, these
+ {@link org.apache.commons.jexl3.JexlBuilder#debug} makes
stacktraces carried by JExlException more meaningfull; in particular, these
traces will carry the exact caller location the Expression was
created from.
</p>
<p>
- {@link org.apache.commons.jexl3.JexlEngine#setClassLoader}
indicates to a JexlEngine which class loader to use to solve a class name; this
affects
- how JexlEngine.newInstance and the 'new' script method operates.
This is mostly usefull in cases where
+ {@link org.apache.commons.jexl3.JexlBuilder#loader} indicates to a
JexlEngine which class loader to use to solve a class name; this affects
+ how JexlEngine.newInstance and the 'new' script method operates.
This is mostly useful in cases where
you rely on JEXL to dynamically load and call plugins for your
application.
</p>
<p>
- JexlEngine and UnifiedJEXL expression caches can be configured as
well. If you intend to use JEXL
+ JexlEngine and JxltEngine expression caches can be configured as
well. If you intend to use JEXL
repeatedly in your application, these are worth configuring since
expression parsing is quite heavy.
Note that all caches created by JEXL are held through
SoftReference; under high memory pressure, the GC will be able
to reclaim those caches and JEXL will rebuild them if needed. By
default, a JexlEngine does not create a cache
- whilst UnifiedJEXL does.
+ whilst JxltEngine does.
</p>
- <p>Both JexlEngine and UnifiedJEXL are thread-safe; the same instance
can be shared between different
+ <p>Both JexlEngine and JxltEngine are thread-safe, all their inner
fields are final; the same instance can be shared between different
threads and proper synchronization is enforced in critical
areas.</p>
- <p>{@link org.apache.commons.jexl3.JexlEngine#setCache} will set how
many expressions can be simultaneously cached by the
+ <p>{@link org.apache.commons.jexl3.JexlBuilder#cache} will set how
many expressions can be simultaneously cached by the
JEXL engine. UnifiedJEXL allows to define the cache size through
its constructor.</p>
<p>
- {@link org.apache.commons.jexl3.JexlEngine#setFunctions} extends
JEXL scripting by registering functions in
- namespaces.
+ {@link org.apache.commons.jexl3.JexlEngine#namespaces} extends
JEXL scripting by registering your own classes as
+ namespaces allowing your own functions to be exposed at will.
</p>
This can be used as in:
<pre><code>
@@ -255,13 +291,12 @@
}
Map<String, Object> funcs = new HashMap<String, Object>();
funcs.put("math", new MyMath());
- JexlEngine jexl = new JexlEngine();
- jexl.setFunctions(funcs);
+ JexlEngine jexl = new JexlBuilder().namespaces(funcs).create();
JexlContext jc = new MapContext();
jc.set("pi", Math.PI);
- e = JEXL.createExpression("math:cos(pi)");
+ JexlExpression e = JEXL.createExpression("math:cos(pi)");
o = e.evaluate(jc);
assertEquals(Double.valueOf(-1),o);
</code></pre>
@@ -270,30 +305,48 @@
expression; this instance lifetime is limited to the expression
evaluation.
<h2><a name="customization">JEXL Customization</a></h2>
- If you need to make JEXL treat some objects in a specialized manner or
tweak how it
- reacts to some settings, you can derive most of its inner-workings.
However, using the protected methods
- or internal package classes imply you might have to re-adapt your code
when new JEXL versions are released.
+
<p>
- {@link org.apache.commons.jexl3.JexlEngine} is meant to be
- extended and lets you capture your own configuration defaults wrt
cache sizes and various flags.
- Implementing your own cache - instead of the basic LinkedHashMap
based one - would be
- another possible extension.
+ The {@link org.apache.commons.jexl3.JexlContext}, {@link
org.apache.commons.jexl3.JexlBuilder} and
+ {@link org.apache.commons.jexl3.JexlEngine$Options} are
+ the most likely interfaces you'll want to implement for
customization. Since they expose variables and options,
+ they are the primary targets. Before you do so, have a look at
{@link org.apache.commons.jexl3.JexlEvalContext}
+ and {@link org.apache.commons.jexl3.ObjectContext} which may
already cover some of your needs.
+ </p>
+ <p>
+ The {@link org.apache.commons.jexl3.NamespaceResolver} may also be
of interest since it allows resolving namespaces (sic)
+ without having to store them in a map.
</p>
<p>
{@link org.apache.commons.jexl3.JexlArithmetic}
- is the class to derive if you need to change how operators behave.
For example, this would
+ is the class to derive if you need to change how operators behave
or add types upon which they
+ operate. For example, this would
be the case if you wanted '+' to operate on arrays; you'd need to
derive JexlArithmetic and
implement your own version of Add.
+ Note however that you can not change the operator precedence.
+ </p>
+
+ <h2><a name="extension">JEXL Extending</a></h2>
+ If you need to make JEXL treat some objects in a specialized manner or
tweak how it
+ reacts to some settings, you can derive most of its inner-workings.
The classes and methods are rarely private or
+ final - only when the inner contract really requires it. However,
using the protected methods
+ and internal package classes imply you might have to re-adapt your
code when new JEXL versions are released.
+ <p>
+ {@link org.apache.commons.jexl3.internal.Engine} can be
+ extended to let you capture your own configuration defaults wrt
cache sizes and various flags.
+ Implementing your own cache - instead of the basic LinkedHashMap
based one - would be
+ another possible extension.
</p>
<p>
- {@link org.apache.commons.jexl3.Interpreter}
+ {@link org.apache.commons.jexl3.internal.Interpreter}
is the class to derive if you need to add more features to the
evaluation
itself; for instance, you want pre- and post- resolvers for
variables or nested scopes for
- for variable contexts or add factory based support to the 'new'
operator.
+ for variable contexts.
</p>
<p>
{@link org.apache.commons.jexl3.internal.introspection.Uberspect}
- is the class to derive if you need to add introspection or
reflection capabilities for some objects.
+ is the class to derive if you need to add introspection or
reflection capabilities for some objects, for
+ instance adding factory based support to the 'new' operator.
The code already reflects public fields as properties on top of
Java-beans conventions.
</p>
</body>
