org.zkoss.xel
Class Expressions

java.lang.Object
  extended by org.zkoss.xel.Expressions

public class Expressions
extends java.lang.Object

Utilities to use XEL.

Since:
3.0.0
Author:
tomyeh

Field Summary
static Expression DUMMY_EXPRESSION
          An dummy expression that does nothing.
static FunctionMapper EMPTY_MAPPER
          An empty function mapper, i.e., it has no function defined at all.
static VariableResolver EMPTY_RESOLVER
          An empty variable resolver, i.e., it has no variable defined at all.
 
Constructor Summary
Expressions()
           
 
Method Summary
static java.lang.Object evaluate(XelContext ctx, java.lang.String expression, java.lang.Class<?> expectedType)
          Evaluates an expression.
static java.lang.Class<? extends ExpressionFactory> getExpressionFactoryClass()
          Returns the implementation of the expression factory that is used by the whole system, or null to use the system default.
static ExpressionFactory newExpressionFactory()
          Instantiates an instance of ExpressionFactory.
static ExpressionFactory newExpressionFactory(java.lang.Class<? extends ExpressionFactory> expfcls)
          Instantiates an instance of ExpressionFactory.
static void setExpressionFactoryClass(java.lang.Class<? extends ExpressionFactory> expfcls)
          Sets the implementation of the expression factory that shall be used by the whole system, or null to use the system default.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

EMPTY_MAPPER

public static final FunctionMapper EMPTY_MAPPER
An empty function mapper, i.e., it has no function defined at all. It is serializable.


EMPTY_RESOLVER

public static final VariableResolver EMPTY_RESOLVER
An empty variable resolver, i.e., it has no variable defined at all. It is serializable.


DUMMY_EXPRESSION

public static final Expression DUMMY_EXPRESSION
An dummy expression that does nothing. It is usually used as a flag to denote exceptional cases. It it serializable.

Constructor Detail

Expressions

public Expressions()
Method Detail

newExpressionFactory

public static final ExpressionFactory newExpressionFactory()
                                                    throws XelException
Instantiates an instance of ExpressionFactory.

The default class is ELFactory, which supports EL 2.0. If you run under JVM 1.5 or later and deploy zel.jar in your class path, the default class is then ELFactory which supports EL 2.2. To override it, you can specify the class by calling setExpressionFactoryClass(java.lang.Class), or use newExpressionFactory(Class) instead.

For the ZK user, you can override it with zk.xml or org.zkoss.zk.ui.util.Configuration.

Throws:
XelException - if the specified class failed to load, or instantiate.

newExpressionFactory

public static final ExpressionFactory newExpressionFactory(java.lang.Class<? extends ExpressionFactory> expfcls)
Instantiates an instance of ExpressionFactory.

The default class is ELFactory, which supports EL 2.0. If you run under JVM 1.5 or later and deploy zel.jar in your class path, the default class is then ELFactory which supports EL 2.2. To override it, you can specify the class by calling setExpressionFactoryClass(java.lang.Class), or specifying the class you prefer in the expfcls argument.

For the ZK user, you can override it with zk.xml or org.zkoss.zk.ui.util.Configuration.

Parameters:
expfcls - the class that implements ExpressionFactory, or null to use the default.
Throws:
XelException - if the specified class failed to load, or instantiate.

evaluate

public static final java.lang.Object evaluate(XelContext ctx,
                                              java.lang.String expression,
                                              java.lang.Class<?> expectedType)
                                       throws XelException
Evaluates an expression.

Parameters:
ctx - the context information to evaluate the expression It can be null, in which case no functions are supported for this invocation.
expression - the expression to be evaluated. Note: the expression is enclosed with ${ and }, regardless of what implementation is used.
expectedType - the expected type of the result of the evaluation
Throws:
XelException

setExpressionFactoryClass

public static final void setExpressionFactoryClass(java.lang.Class<? extends ExpressionFactory> expfcls)
Sets the implementation of the expression factory that shall be used by the whole system, or null to use the system default.

Default: null - it means ELFactory, which supports EL 2.0. If you run under JVM 1.5 or later and deploy zel.jar in your class path, the default class is then ELFactory which supports EL 2.2.

Note: you can only specify an implementation that is compatible with JSP EL here, since all built-in pages depend on it.

Parameters:
expfcls - the implementation class, or null to use the default. Note: expfcls must implement ExpressionFactory. If null, the system default is used.

getExpressionFactoryClass

public static final java.lang.Class<? extends ExpressionFactory> getExpressionFactoryClass()
Returns the implementation of the expression factory that is used by the whole system, or null to use the system default.

See Also:
setExpressionFactoryClass(java.lang.Class)


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