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

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `MethodExpression()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `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.
    `boolean` | `isParametersProvided()` Return whether this MethodExpression was created with parameters.
    `boolean` | `isParmetersProvided()` Deprecated.

    - ### 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() or isParmetersProvided() 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.

    - #### isParametersProvided

          public boolean isParametersProvided()

      Return whether this MethodExpression was created with parameters.

      This method must return `true` if and only if parameters are specified in the EL, using the expr-a.expr-b(...) syntax.

      Returns:
        `true` if the MethodExpression was created with parameters, `false` otherwise.
      Since:
        EL 2.2

    - #### isParmetersProvided

          @Deprecated
          public boolean isParmetersProvided()

      Deprecated.
      Use isParametersProvided instead.

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