| java.lang.Object
 javax.el.Expression
javax.el.ValueExpression
| ValueExpression | | abstract public class ValueExpression extends Expression (Code) | | An Expression that can get or set a value.
In previous incarnations of this API, expressions could only be
read. ValueExpression objects can now be used both to
retrieve a value and to set a value. Expressions that can have a value
set on them are referred to as l-value expressions. Those that
cannot are referred to as r-value expressions. Not all r-value expressions
can be used as l-value expressions (e.g. "${1+1}" or
"${firstName} ${lastName}"). See the EL Specification for
details. Expressions that cannot be used as l-values must always
return true from isReadOnly().
The
ExpressionFactory.createValueExpression method
can be used to parse an expression string and return a concrete instance
of ValueExpression that encapsulates the parsed expression.
The
FunctionMapper is used at parse time, not evaluation time,
so one is not needed to evaluate an expression using this class.
However, the
ELContext is needed at evaluation time.
The
ValueExpression.getValue ,
ValueExpression.setValue ,
ValueExpression.isReadOnly and
ValueExpression.getType methods will evaluate the expression each time they are
called. The
ELResolver in the ELContext is used to
resolve the top-level variables and to determine the behavior of the
. and [] operators. For any of the four methods,
the
ELResolver.getValue method is used to resolve all properties
up to but excluding the last one. This provides the base
object. At the last resolution, the ValueExpression will
call the corresponding
ELResolver.getValue ,
ELResolver.setValue ,
ELResolver.isReadOnly or
ELResolver.getType method, depending on which was called on
the ValueExpression.
See the notes about comparison, serialization and immutability in
the
Expression javadocs.
See Also: ELResolver
See Also: Expression
See Also: ExpressionFactory
since:
JSP 2.1 |
| Method Summary | |
| abstract public Class | getExpectedType()
Returns the type the result of the expression will be coerced to
after evaluation. | | abstract public Class | getType(ELContext context)
Evaluates the expression relative to the provided context, and
returns the most general type that is acceptable for an object to be
passed as the value parameter in a future call
to the
ValueExpression.setValue method.
This is not always the same as getValue().getClass().
For example, in the case of an expression that references an
array element, the getType method will return the
element type of the array, which might be a superclass of the type
of the actual element that is currently in the specified
array element.
Parameters:
context - The context of this evaluation. | | abstract public Object | getValue(ELContext context)
Evaluates the expression relative to the provided context, and
returns the resulting value.
The resulting value is automatically coerced to the type
returned by getExpectedType(), which was
provided to the ExpressionFactory when this
expression was created.
Parameters:
context - The context of this evaluation. | | abstract public boolean | isReadOnly(ELContext context)
Evaluates the expression relative to the provided context, and
returns true if a call to
ValueExpression.setValue will
always fail.
Parameters:
context - The context of this evaluation. | | abstract public void | setValue(ELContext context, Object value)
Evaluates the expression relative to the provided context, and
sets the result to the provided value.
Parameters:
context - The context of this evaluation.
Parameters:
value - The new value to be set.
throws:
NullPointerException - if context is null.
throws:
PropertyNotFoundException - if one of the propertyresolutions failed because a specified variable or property does not exist or is not readable.
throws:
PropertyNotWritableException - if the final variable orproperty resolution failed because the specifiedvariable or property is not writable.
throws:
ELException - if an exception was thrown while attempting toset the property or variable. |
| getExpectedType | | abstract public Class getExpectedType()(Code) | | Returns the type the result of the expression will be coerced to
after evaluation.
the expectedType passed to theExpressionFactory.createValueExpression methodthat created this ValueExpression. |
| getType | | abstract public Class getType(ELContext context)(Code) | | Evaluates the expression relative to the provided context, and
returns the most general type that is acceptable for an object to be
passed as the value parameter in a future call
to the
ValueExpression.setValue method.
This is not always the same as getValue().getClass().
For example, in the case of an expression that references an
array element, the getType method will return the
element type of the array, which might be a superclass of the type
of the actual element that is currently in the specified
array element.
Parameters:
context - The context of this evaluation. the most general acceptable type; otherwise undefined.
throws:
NullPointerException - if context is null.
throws:
PropertyNotFoundException - if one of the propertyresolutions failed because a specified variable or property does not exist or is not readable.
throws:
ELException - if an exception was thrown while performingproperty or variable resolution. The thrown exceptionmust be included as the cause property of this exception, ifavailable. |
| getValue | | abstract public Object getValue(ELContext context)(Code) | | Evaluates the expression relative to the provided context, and
returns the resulting value.
The resulting value is automatically coerced to the type
returned by getExpectedType(), which was
provided to the ExpressionFactory when this
expression was created.
Parameters:
context - The context of this evaluation. The result of the expression evaluation.
throws:
NullPointerException - if context is null.
throws:
PropertyNotFoundException - if one of the propertyresolutions failed because a specified variable or property does not exist or is not readable.
throws:
ELException - if an exception was thrown while performingproperty or variable resolution. The thrown exceptionmust be included as the cause property of this exception, ifavailable. |
| isReadOnly | | abstract public boolean isReadOnly(ELContext context)(Code) | | Evaluates the expression relative to the provided context, and
returns true if a call to
ValueExpression.setValue will
always fail.
Parameters:
context - The context of this evaluation. true if the expression is read-only orfalse if not.
throws:
NullPointerException - if context is null.
throws:
PropertyNotFoundException - if one of the propertyresolutions failed because a specified variable or property does not exist or is not readable.
throws:
ELException - if an exception was thrown while performingproperty or variable resolution. The thrown exceptionmust be included as the cause property of this exception, ifavailable.
throws:
NullPointerException - if context is null |
| setValue | | abstract public void setValue(ELContext context, Object value)(Code) | | Evaluates the expression relative to the provided context, and
sets the result to the provided value.
Parameters:
context - The context of this evaluation.
Parameters:
value - The new value to be set.
throws:
NullPointerException - if context is null.
throws:
PropertyNotFoundException - if one of the propertyresolutions failed because a specified variable or property does not exist or is not readable.
throws:
PropertyNotWritableException - if the final variable orproperty resolution failed because the specifiedvariable or property is not writable.
throws:
ELException - if an exception was thrown while attempting toset the property or variable. The thrown exceptionmust be included as the cause property of this exception, ifavailable. |
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