org.apache.el
public final class MethodExpressionImpl extends MethodExpression implements Externalizable
Expression
that refers to a method on an object.
The ExpressionFactory#createMethodExpression method
can be used to parse an expression string and return a concrete instance
of
MethodExpression
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 MethodExpressionImpl and MethodExpressionImpl 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 two methods, the ELResolver#getValue
method is used to resolve all properties up to but excluding the last
one. This provides the base
object on which the method
appears. If the base
object is null, a
NullPointerException
must be thrown. At the last resolution,
the final property
is then coerced to a String
,
which provides the name of the method to be found. A method matching the
name and expected parameters provided at parse time is found and it is
either queried or invoked (depending on the method called on this
MethodExpression
).
See the notes about comparison, serialization and immutability in the Expression javadocs.
Version: $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: markt $
See Also: javax.el.ELResolver javax.el.Expression javax.el.ExpressionFactory javax.el.MethodExpression
Constructor Summary | |
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MethodExpressionImpl() | |
MethodExpressionImpl(String expr, Node node, FunctionMapper fnMapper, VariableMapper varMapper, Class expectedType, Class[] paramTypes) |
Method Summary | |
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boolean | equals(Object obj)
Determines whether the specified object is equal to this
Expression .
|
String | getExpressionString()
Returns the original String used to create this Expression ,
unmodified.
|
MethodInfo | getMethodInfo(ELContext context)
Evaluates the expression relative to the provided context, and returns
information about the actual referenced method.
|
int | hashCode()
Returns the hash code for this Expression .
|
Object | invoke(ELContext context, Object[] params)
Evaluates the expression relative to the provided context, invokes the
method that was found using the supplied parameters, and returns the
result of the method invocation.
|
boolean | isLiteralText() |
void | readExternal(ObjectInput in) |
void | writeExternal(ObjectOutput out) |
Parameters: expr node fnMapper expectedType paramTypes
Expression
.
The result is true
if and only if the argument is not
null
, is an Expression
object that is the
of the same type (ValueExpression
or
MethodExpression
), and has an identical parsed
representation.
Note that two expressions can be equal if their expression Strings are
different. For example, ${fn1:foo()}
and
${fn2:foo()}
are equal if their corresponding
FunctionMapper
s mapped fn1:foo
and
fn2:foo
to the same method.
Parameters: obj
the Object
to test for equality.
Returns: true
if obj
equals this
Expression
; false
otherwise.
See Also: java.util.Hashtable java.lang.Object#equals(java.lang.Object)
Expression
,
unmodified.
This is used for debugging purposes but also for the purposes of comparison (e.g. to ensure the expression in a configuration file has not changed).
This method does not provide sufficient information to re-create an
expression. Two different expressions can have exactly the same
expression string but different function mappings. Serialization should
be used to save and restore the state of an Expression
.
Returns: The original expression String.
See Also: javax.el.Expression#getExpressionString()
Parameters: context The context of this evaluation
Returns: an instance of MethodInfo
containing information
about the method the expression evaluated to.
Throws: NullPointerException
if context is null
or the base object is
null
on the last resolution. PropertyNotFoundException
if one of the property resolutions failed because a specified
variable or property does not exist or is not readable. MethodNotFoundException
if no suitable method can be found. ELException
if an exception was thrown while performing property or
variable resolution. The thrown exception must be included as
the cause property of this exception, if available.
See Also: javax.el.MethodExpression#getMethodInfo(javax.el.ELContext)
Expression
.
See the note in the MethodExpressionImpl method on how two expressions can be
equal if their expression Strings are different. Recall that if two
objects are equal according to the equals(Object)
method,
then calling the hashCode
method on each of the two
objects must produce the same integer result. Implementations must take
special note and implement hashCode
correctly.
Returns: The hash code for this Expression
.
See Also: MethodExpressionImpl java.util.Hashtable java.lang.Object#hashCode()
Parameters: context
The context of this evaluation. params
The parameters to pass to the method, or null
if no parameters.
Returns: the result of the method invocation (null
if the
method has a void
return type).
Throws: NullPointerException
if context is null
or the base object is
null
on the last resolution. PropertyNotFoundException
if one of the property resolutions failed because a specified
variable or property does not exist or is not readable. MethodNotFoundException
if no suitable method can be found. ELException
if an exception was thrown while performing property or
variable resolution. The thrown exception must be included as
the cause property of this exception, if available. If the
exception thrown is an InvocationTargetException
,
extract its cause
and pass it to the
ELException
constructor.
See Also: javax.el.MethodExpression#invoke(javax.el.ELContext,
java.lang.Object[])