src/main/java/org/apache/commons/jexl2/package.html - commons-jexl - Git at Google

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     <head>
         <title>Package Documentation for org.apache.commons.jexl2 Package</title>
     </head>
     <body bgcolor="white">
         Provides a framework for evaluating JEXL expressions.
         <br/><br/>
         <ul>
             <li><a href="#intro">Introduction</a></li>
             <li><a href="#example">Brief Example</a></li>
             <li><a href="#usage">Using JEXL</a></li>
             <li><a href="#configuration">Configuring JEXL</a></li>
             <li><a href="#customization">Customizing JEXL</a></li>
         </ul>

         <h2><a name="intro">Introduction</a></h2>
         <p>
             JEXL is a library intended to facilitate the implementation of dynamic and scripting features in applications
             and frameworks.
         </p>

         <h2><a name="example">A Brief Example</a></h2>
         <p>
             When evaluating expressions, JEXL merges an
             {@link org.apache.commons.jexl2.Expression}
             with a
             {@link org.apache.commons.jexl2.JexlContext}.
             An Expression is created using
             {@link org.apache.commons.jexl2.JexlEngine#createExpression(java.lang.String)},
             passing a String containing valid JEXL syntax.  A simple JexlContext can be created using
             a {@link org.apache.commons.jexl2.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:
         </p>
         <pre>
             // Create a JexlEngine (could reuse one instead)
             JexlEngine jexl = new JexlEngine();
             // Create an expression object
             String jexlExp = "foo.innerFoo.bar()";
             Expression e = jexl.createExpression( jexlExp );

             // Create a context and add data
             JexlContext jc = new MapContext();
             jc.set("foo", new Foo() );

             // Now evaluate the expression, getting the result
             Object o = e.evaluate(jc);
         </pre>


         <h2><a name="usage">Using JEXL</a></h2>
         The API is composed of three levels addressing different functional needs:
         <ul>
             <li>Dynamic invocation of setters, getters, methods and constructors</li>
             <li>Script expressions known as JEXL expressions</li>
             <li>JSP/JSF like expression known as UnifiedJEXL expressions</li>
         </ul>

         <h3><a name="usage_note">Important note</a></h3>
         The only public packages you should use are:
         <ul>
             <li>org.apache.commons.jexl2</li>
             <li>org.apache.commons.jexl2.introspection</li>
         </ul>
         The following packages follow a "use at your own maintenance cost" policy.
         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
         the community through the mailing list first.
         <ul>
             <li>org.apache.commons.jexl2.parser</li>
             <li>org.apache.commons.jexl2.scripting</li>
             <li>org.apache.commons.jexl2.internal</li>
             <li>org.apache.commons.jexl2.internal.introspection</li>
         </ul>

         <h3><a name="usage_api">Dynamic invocation</a></h3>
         <p>
             These functionalities are close to the core level utilities found in
             <a href="http://commons.apache.org/beanutils/">BeanUtils</a>.
             For basic dynamic property manipulations and method invocation, you can use the following
             set of methods:
         </p>
         <ul>
             <li>{@link org.apache.commons.jexl2.JexlEngine#newInstance}</li>
             <li>{@link org.apache.commons.jexl2.JexlEngine#setProperty}</li>
             <li>{@link org.apache.commons.jexl2.JexlEngine#getProperty}</li>
             <li>{@link org.apache.commons.jexl2.JexlEngine#invokeMethod}</li>
         </ul>
         The following example illustrate their usage:
         <pre>
             // test outer class
             public static class Froboz {
                 int value;
                 public Froboz(int v) { value = v; }
                 public void setValue(int v) { value = v; }
                 public int getValue() { return value; }
             }
             // test inner class
             public static class Quux {
                 String str;
                 Froboz froboz;
                 public Quux(String str, int fro) {
                     this.str = str;
                     froboz = new Froboz(fro);
                 }
                 public Froboz getFroboz() { return froboz; }
                 public void setFroboz(Froboz froboz) { this.froboz = froboz; }
                 public String getStr() { return str; }
                 public void setStr(String str) { this.str = str; }
             }
             // test API
             JexlEngine jexl = nex JexlEngine();
             Quux quux = jexl.newInstance(Quux.class, "xuuq", 100);
             jexl.setProperty(quux, "froboz.value", Integer.valueOf(100));
             Object o = jexl.getProperty(quux, "froboz.value");
             assertEquals("Result is not 100", new Integer(100), o);
             jexl.setProperty(quux, "['froboz'].value", Integer.valueOf(1000));
             o = jexl.getProperty(quux, "['froboz']['value']");
             assertEquals("Result is not 1000", new Integer(1000), o);
         </pre>

         <h3><a name="usage_jexl">JEXL script expression</a></h3>
         <p>
             If your needs require simple expression evaluation capabilities, the core JEXL features
             will most likely fit.
             The main methods are:
         </p>
         <ul>
             <li>{@link org.apache.commons.jexl2.JexlEngine#createExpression}</li>
             <li>{@link org.apache.commons.jexl2.JexlEngine#createScript}</li>
             <li>{@link org.apache.commons.jexl2.Expression#evaluate}</li>
         </ul>
         The following example illustrates their usage:
         <pre>
             JexlEngine jexl = nex JexlEngine();

             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");
             Quux quux = (Quux) create.evaluate(jc);
             Object o = assign.evaluate(jc);
             assertEquals("Result is not 10", new Integer(10), o);
             o = check.evaluate(jc);
             assertEquals("Result is not 10", new Integer(10), o);
         </pre>

         <h3><a name="usage_ujexl">UnifiedJEXL script expressions</a></h3>
         <p>
             If you are looking for JSP-EL like and basic templating features, you can
             use UnifiedJEXL.
         </p>
         The main methods are:
         <ul>
             <li>{@link org.apache.commons.jexl2.UnifiedJEXL#parse}</li>
             <li>{@link org.apache.commons.jexl2.UnifiedJEXL.Expression#evaluate}</li>
             <li>{@link org.apache.commons.jexl2.UnifiedJEXL.Expression#prepare}</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();
         </pre>
         <h3>Expressions Script and UnifiedJEXL.Expression: differences</h3>
         <h4>Expression</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
         everything after the first semi-colon and just returns the result from
         the first command.
         </p>
         <h4>Script</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.
         </p>
         <h4>UnifiedJEXL.Expression</h4>
         <p>
         This is ideal to produce text. 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
         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>

         <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.
         </p>
         <p>
             {@link org.apache.commons.jexl2.JexlEngine#setLenient} 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.jexl2.JexlEngine#setSilent} 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.jexl2.JexlEngine#setDebug} 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.jexl2.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
             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
             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.
         </p>
         <p>Both JexlEngine and UnifiedJEXL are thread-safe; the same instance can be shared between different
             threads and proper synchronization is enforced in critical areas.</p>
         <p>{@link org.apache.commons.jexl2.JexlEngine#setCache} 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.jexl2.JexlEngine#setFunctions} extends JEXL scripting by registering functions in
             namespaces.
         </p>
         This can be used as in:
         <pre><code>
             public static MyMath {
                 public double cos(double x) {
                     return Math.cos(x);
                 }
             }
             Map&lt;String, Object> funcs = new HashMap&lt;String, Object>();
             funcs.put("math", new MyMath());
             JexlEngine jexl = new JexlEngine();
             jexl.setFunctions(funcs);

             JexlContext jc = new MapContext();
             jc.set("pi", Math.PI);

             e = JEXL.createExpression("math:cos(pi)");
             o = e.evaluate(jc);
             assertEquals(Double.valueOf(-1),o);
         </code></pre>
         If the <i>namespace</i> is a Class and that class declares a constructor that takes a JexlContext (or
         a class extending JexlContext), one <i>namespace</i> instance is created on first usage in an
         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.
         <p>
             {@link org.apache.commons.jexl2.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.
         </p>
         <p>
             {@link org.apache.commons.jexl2.JexlArithmetic}
             is the class to derive if you need to change how operators behave. 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.
         </p>
         <p>
             {@link org.apache.commons.jexl2.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.
         </p>
         <p>
             {@link org.apache.commons.jexl2.introspection.UberspectImpl}
             is the class to derive if you need to add introspection or reflection capabilities for some objects.
             The code already reflects public fields as properties on top of Java-beans conventions.
         </p>
     </body>
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	<html>
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	contributor license agreements. See the NOTICE file distributed with
	this work for additional information regarding copyright ownership.
	The ASF licenses this file to You under the Apache License, Version 2.0
	(the "License"); you may not use this file except in compliance with
	the License. You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
	limitations under the License.
	-->
	<head>
	<title>Package Documentation for org.apache.commons.jexl2 Package</title>
	</head>
	<body bgcolor="white">
	Provides a framework for evaluating JEXL expressions.
	<br/><br/>
	<ul>
	<li><a href="#intro">Introduction</a></li>
	<li><a href="#example">Brief Example</a></li>
	<li><a href="#usage">Using JEXL</a></li>
	<li><a href="#configuration">Configuring JEXL</a></li>
	<li><a href="#customization">Customizing JEXL</a></li>
	</ul>

	<h2><a name="intro">Introduction</a></h2>
	<p>
	JEXL is a library intended to facilitate the implementation of dynamic and scripting features in applications
	and frameworks.
	</p>

	<h2><a name="example">A Brief Example</a></h2>
	<p>
	When evaluating expressions, JEXL merges an
	{@link org.apache.commons.jexl2.Expression}
	with a
	{@link org.apache.commons.jexl2.JexlContext}.
	An Expression is created using
	{@link org.apache.commons.jexl2.JexlEngine#createExpression(java.lang.String)},
	passing a String containing valid JEXL syntax. A simple JexlContext can be created using
	a {@link org.apache.commons.jexl2.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:
	</p>
	<pre>
	// Create a JexlEngine (could reuse one instead)
	JexlEngine jexl = new JexlEngine();
	// Create an expression object
	String jexlExp = "foo.innerFoo.bar()";
	Expression e = jexl.createExpression( jexlExp );

	// Create a context and add data
	JexlContext jc = new MapContext();
	jc.set("foo", new Foo() );

	// Now evaluate the expression, getting the result
	Object o = e.evaluate(jc);
	</pre>


	<h2><a name="usage">Using JEXL</a></h2>
	The API is composed of three levels addressing different functional needs:
	<ul>
	<li>Dynamic invocation of setters, getters, methods and constructors</li>
	<li>Script expressions known as JEXL expressions</li>
	<li>JSP/JSF like expression known as UnifiedJEXL expressions</li>
	</ul>

	<h3><a name="usage_note">Important note</a></h3>
	The only public packages you should use are:
	<ul>
	<li>org.apache.commons.jexl2</li>
	<li>org.apache.commons.jexl2.introspection</li>
	</ul>
	The following packages follow a "use at your own maintenance cost" policy.
	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
	the community through the mailing list first.
	<ul>
	<li>org.apache.commons.jexl2.parser</li>
	<li>org.apache.commons.jexl2.scripting</li>
	<li>org.apache.commons.jexl2.internal</li>
	<li>org.apache.commons.jexl2.internal.introspection</li>
	</ul>

	<h3><a name="usage_api">Dynamic invocation</a></h3>
	<p>
	These functionalities are close to the core level utilities found in
	<a href="http://commons.apache.org/beanutils/">BeanUtils</a>.
	For basic dynamic property manipulations and method invocation, you can use the following
	set of methods:
	</p>
	<ul>
	<li>{@link org.apache.commons.jexl2.JexlEngine#newInstance}</li>
	<li>{@link org.apache.commons.jexl2.JexlEngine#setProperty}</li>
	<li>{@link org.apache.commons.jexl2.JexlEngine#getProperty}</li>
	<li>{@link org.apache.commons.jexl2.JexlEngine#invokeMethod}</li>
	</ul>
	The following example illustrate their usage:
	<pre>
	// test outer class
	public static class Froboz {
	int value;
	public Froboz(int v) { value = v; }
	public void setValue(int v) { value = v; }
	public int getValue() { return value; }
	}
	// test inner class
	public static class Quux {
	String str;
	Froboz froboz;
	public Quux(String str, int fro) {
	this.str = str;
	froboz = new Froboz(fro);
	}
	public Froboz getFroboz() { return froboz; }
	public void setFroboz(Froboz froboz) { this.froboz = froboz; }
	public String getStr() { return str; }
	public void setStr(String str) { this.str = str; }
	}
	// test API
	JexlEngine jexl = nex JexlEngine();
	Quux quux = jexl.newInstance(Quux.class, "xuuq", 100);
	jexl.setProperty(quux, "froboz.value", Integer.valueOf(100));
	Object o = jexl.getProperty(quux, "froboz.value");
	assertEquals("Result is not 100", new Integer(100), o);
	jexl.setProperty(quux, "['froboz'].value", Integer.valueOf(1000));
	o = jexl.getProperty(quux, "['froboz']['value']");
	assertEquals("Result is not 1000", new Integer(1000), o);
	</pre>

	<h3><a name="usage_jexl">JEXL script expression</a></h3>
	<p>
	If your needs require simple expression evaluation capabilities, the core JEXL features
	will most likely fit.
	The main methods are:
	</p>
	<ul>
	<li>{@link org.apache.commons.jexl2.JexlEngine#createExpression}</li>
	<li>{@link org.apache.commons.jexl2.JexlEngine#createScript}</li>
	<li>{@link org.apache.commons.jexl2.Expression#evaluate}</li>
	</ul>
	The following example illustrates their usage:
	<pre>
	JexlEngine jexl = nex JexlEngine();

	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");
	Quux quux = (Quux) create.evaluate(jc);
	Object o = assign.evaluate(jc);
	assertEquals("Result is not 10", new Integer(10), o);
	o = check.evaluate(jc);
	assertEquals("Result is not 10", new Integer(10), o);
	</pre>

	<h3><a name="usage_ujexl">UnifiedJEXL script expressions</a></h3>
	<p>
	If you are looking for JSP-EL like and basic templating features, you can
	use UnifiedJEXL.
	</p>
	The main methods are:
	<ul>
	<li>{@link org.apache.commons.jexl2.UnifiedJEXL#parse}</li>
	<li>{@link org.apache.commons.jexl2.UnifiedJEXL.Expression#evaluate}</li>
	<li>{@link org.apache.commons.jexl2.UnifiedJEXL.Expression#prepare}</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();
	</pre>
	<h3>Expressions Script and UnifiedJEXL.Expression: differences</h3>
	<h4>Expression</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
	everything after the first semi-colon and just returns the result from
	the first command.
	</p>
	<h4>Script</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.
	</p>
	<h4>UnifiedJEXL.Expression</h4>
	<p>
	This is ideal to produce text. 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
	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>

	<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.
	</p>
	<p>
	{@link org.apache.commons.jexl2.JexlEngine#setLenient} 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.jexl2.JexlEngine#setSilent} 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.jexl2.JexlEngine#setDebug} 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.jexl2.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
	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
	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.
	</p>
	<p>Both JexlEngine and UnifiedJEXL are thread-safe; the same instance can be shared between different
	threads and proper synchronization is enforced in critical areas.</p>
	<p>{@link org.apache.commons.jexl2.JexlEngine#setCache} 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.jexl2.JexlEngine#setFunctions} extends JEXL scripting by registering functions in
	namespaces.
	</p>
	This can be used as in:
	<pre><code>
	public static MyMath {
	public double cos(double x) {
	return Math.cos(x);
	}
	}
	Map<String, Object> funcs = new HashMap<String, Object>();
	funcs.put("math", new MyMath());
	JexlEngine jexl = new JexlEngine();
	jexl.setFunctions(funcs);

	JexlContext jc = new MapContext();
	jc.set("pi", Math.PI);

	e = JEXL.createExpression("math:cos(pi)");
	o = e.evaluate(jc);
	assertEquals(Double.valueOf(-1),o);
	</code></pre>
	If the <i>namespace</i> is a Class and that class declares a constructor that takes a JexlContext (or
	a class extending JexlContext), one <i>namespace</i> instance is created on first usage in an
	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.
	<p>
	{@link org.apache.commons.jexl2.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.
	</p>
	<p>
	{@link org.apache.commons.jexl2.JexlArithmetic}
	is the class to derive if you need to change how operators behave. 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.
	</p>
	<p>
	{@link org.apache.commons.jexl2.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.
	</p>
	<p>
	{@link org.apache.commons.jexl2.introspection.UberspectImpl}
	is the class to derive if you need to add introspection or reflection capabilities for some objects.
	The code already reflects public fields as properties on top of Java-beans conventions.
	</p>
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