## javax.el
Class MethodExpression

    java.lang.Object
      javax.el.Expression
          javax.el.MethodExpression

All Implemented Interfaces:
  Serializable

Direct Known Subclasses:
  MethodExpressionImpl, MethodExpressionLiteral

    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

Constructor Summary
`MethodExpression()`

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.

Methods inherited from class javax.el.Expression
`equals, getExpressionString, hashCode, isLiteralText`

Methods inherited from class java.lang.Object
`clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### MethodExpression

    public MethodExpression()

Method Detail

### 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 "1.18 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 "1.18 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 © 2007 Mort Bay Consulting. All Rights Reserved.