javax.el
Class MethodExpression
java.lang.Object
javax.el.Expression
javax.el.MethodExpression
- All Implemented Interfaces:
- java.io.Serializable
- Direct Known Subclasses:
- TreeMethodExpression
public abstract class MethodExpression
- extends Expression
An Expression that refers to a method on an object. The
ExpressionFactory.createMethodExpression(ELContext, String, Class, 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(ELContext)
and
invoke(ELContext, 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(ELContext, Object, 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.
- 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 java.lang.Object |
invoke(ELContext context,
java.lang.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. |
Methods inherited from class java.lang.Object |
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait |
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:
- The context of this evaluation
- Throws:
java.lang.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 java.lang.Object invoke(ELContext context,
java.lang.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:
java.lang.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.