JavaTM Platform, Enterprise Edition, v 5.0
javax.el
Class MethodExpression
java.lang.Object
javax.el.Expression
javax.el.MethodExpression
- All Implemented Interfaces:
- Serializable
public abstract class MethodExpression - extends Expression
An Expression that refers to a method on an object.
The ExpressionFactory.createMethodExpression(javax.el.ELContext, java.lang.String, java.lang.Class>, java.lang.Class>[]) 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 getMethodInfo(javax.el.ELContext) and invoke(javax.el.ELContext, java.lang.Object[]) 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(javax.el.ELContext, java.lang.Object, java.lang.Object)
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
PropertyNotFoundException 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.
- Since:
- JSP 2.1
- See Also:
ELResolver ,
Expression ,
ExpressionFactory ,
Serialized Form
Method Summary |
abstract MethodInfo |
getMethodInfo(ELContext context)
Evaluates the expression relative to the provided context, and
returns information about the actual referenced method. |
abstract Object |
invoke(ELContext context,
Object[] params)
If a String literal is specified as the expression, returns the
String literal coerced to the expected return type of the method
signature. |
MethodExpression
public MethodExpression()
getMethodInfo
public abstract MethodInfo getMethodInfo(ELContext context)
- Evaluates the expression relative to the provided context, and
returns information about the actual referenced method.
- 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
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.
invoke
public abstract Object invoke(ELContext context,
Object[] params)
- If a String literal is specified as the expression, returns the
String literal coerced to the expected return type of the method
signature. An
ELException is thrown if
expectedReturnType is void or if the coercion of the String literal
to the expectedReturnType yields an error (see Section "1.16 Type
Conversion" of the EL specification).
If not a String literal, 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.
Any parameters passed to this method is ignored if isLiteralText()
is true.
- 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
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 a String literal is specified and
expectedReturnType of the MethodExpression is void or if the coercion of the String literal
to the expectedReturnType yields an error (see Section "1.16 Type
Conversion").
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.
Copyright 2003 Sun Microsystems, Inc. All rights reserved
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