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package javax.el;

/**
 * An Expression that refers to a method on an object.
 *
 * 

The {@link javax.el.ExpressionFactory#createMethodExpression} method * can be used to parse an expression string and return a concrete instance * of MethodExpression that encapsulates the parsed expression. * The {@link FunctionMapper} is used at parse time, not evaluation time, * so one is not needed to evaluate an expression using this class. * However, the {@link ELContext} is needed at evaluation time.

* *

The {@link #getMethodInfo} and {@link #invoke} methods will evaluate the * expression each time they are called. The {@link 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 * {@link javax.el.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 * 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 {@link Expression} javadocs. * * @see ELResolver * @see Expression * @see ExpressionFactory * @since JSP 2.1 */ public abstract class MethodExpression extends Expression { // Evaluation /** * Evaluates the expression relative to the provided context, and * returns information about the actual referenced method. * * @param context The context of this evaluation * @return an instance of MethodInfo containing information * about the method the expression evaluated to. * @throws NullPointerException if context is null * @throws PropertyNotFoundException if one of the property * resolutions failed because a specified variable or property * does not exist or is not readable. * @throws MethodNotFoundException if no suitable method can be found. * @throws 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. */ public abstract MethodInfo getMethodInfo(ELContext context); /** * 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. * * @param context The context of this evaluation. * @param params The parameters to pass to the method, or * null if no parameters. * @return the result of the method invocation (null if * the method has a void return type). * @throws NullPointerException if context is null * @throws PropertyNotFoundException if one of the property * resolutions failed because a specified variable or property * does not exist or is not readable. * @throws MethodNotFoundException if no suitable method can be found. * @throws 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"). * @throws 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. */ public abstract Object invoke(ELContext context, Object[] params); /** * 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.

* * @return true if the MethodExpression was created with * parameters, false otherwise. * @since EL 2.2 */ public boolean isParametersProvided() { return false; } /** * Use isParametersProvided instead. */ @Deprecated public boolean isParmetersProvided() { return isParametersProvided(); } }




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