MethodExpression (Java EE 5 SDK)

javax.el Class MethodExpression

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

所有已实现的接口:

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.

从以下版本开始:

JSP 2.1

另请参见:

ELResolver, Expression, ExpressionFactory, Serialized Form

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.

参数:

context - The context of this evaluation

返回:

an instance of MethodInfo containing information about the method the expression evaluated to.

抛出异常:

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.

参数:

context - The context of this evaluation.

params - The parameters to pass to the method, or null if no parameters.

返回:

the result of the method invocation (null if the method has a void return type).

抛出异常:

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.

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