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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><!--NewPage--><HTML><HEAD><!-- Generated by javadoc (build 1.5.0_14) on Mon Jan 28 05:47:05 PST 2008 --><TITLE>MethodExpression (Java EE 5)</TITLE><META NAME="keywords" CONTENT="javax.el.MethodExpression class"><LINK REL ="stylesheet" TYPE="text/css" HREF="../../stylesheet.css" TITLE="Style"><SCRIPT type="text/javascript">function windowTitle(){ parent.document.title="MethodExpression (Java EE 5)";}</SCRIPT><NOSCRIPT></NOSCRIPT></HEAD><BODY BGCOLOR="white" onload="windowTitle();"><!-- ========= START OF TOP NAVBAR ======= --><A NAME="navbar_top"><!-- --></A><A HREF="#skip-navbar_top" title="Skip navigation links"></A><TABLE BORDER="0" WIDTH="100%" CELLPADDING="1" CELLSPACING="0" SUMMARY=""><TR><TD COLSPAN=2 BGCOLOR="#EEEEFF" CLASS="NavBarCell1"><A NAME="navbar_top_firstrow"><!-- --></A><TABLE BORDER="0" CELLPADDING="0" CELLSPACING="3" SUMMARY=""> <TR ALIGN="center" VALIGN="top"> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../overview-summary.html"><FONT CLASS="NavBarFont1"><B>Overview</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-summary.html"><FONT CLASS="NavBarFont1"><B>Package</B></FONT></A> </TD> <TD BGCOLOR="#FFFFFF" CLASS="NavBarCell1Rev"> <FONT CLASS="NavBarFont1Rev"><B>Class</B></FONT> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-tree.html"><FONT CLASS="NavBarFont1"><B>Tree</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../deprecated-list.html"><FONT CLASS="NavBarFont1"><B>Deprecated</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../index-all.html"><FONT CLASS="NavBarFont1"><B>Index</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../help-doc.html"><FONT CLASS="NavBarFont1"><B>Help</B></FONT></A> </TD> </TR></TABLE></TD><TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM></EM></TD></TR><TR><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> <A HREF="../../javax/el/MapELResolver.html" title="class in javax.el"><B>PREV CLASS</B></A> <A HREF="../../javax/el/MethodInfo.html" title="class in javax.el"><B>NEXT CLASS</B></A></FONT></TD><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> <A HREF="../../index.html?javax/el/MethodExpression.html" target="_top"><B>FRAMES</B></A> <A HREF="MethodExpression.html" target="_top"><B>NO FRAMES</B></A> <SCRIPT type="text/javascript"> <!-- if(window==top) { document.writeln('<A HREF="../../allclasses-noframe.html"><B>All Classes</B></A>'); } //--></SCRIPT><NOSCRIPT> <A HREF="../../allclasses-noframe.html"><B>All Classes</B></A></NOSCRIPT></FONT></TD></TR><TR><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2"> SUMMARY: NESTED | FIELD | <A HREF="#constructor_summary">CONSTR</A> | <A HREF="#method_summary">METHOD</A></FONT></TD><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">DETAIL: FIELD | <A HREF="#constructor_detail">CONSTR</A> | <A HREF="#method_detail">METHOD</A></FONT></TD></TR></TABLE><A NAME="skip-navbar_top"></A><!-- ========= END OF TOP NAVBAR ========= --><HR><!-- ======== START OF CLASS DATA ======== --><H2><FONT SIZE="-1">javax.el</FONT><BR>Class MethodExpression</H2><PRE><A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/Object.html" title="class or interface in java.lang">java.lang.Object</A> <IMG SRC="../../resources/inherit.gif" ALT="extended by "><A HREF="../../javax/el/Expression.html" title="class in javax.el">javax.el.Expression</A> <IMG SRC="../../resources/inherit.gif" ALT="extended by "><B>javax.el.MethodExpression</B></PRE><DL><DT><B>All Implemented Interfaces:</B> <DD><A HREF="http://java.sun.com/j2se/1.5/docs/api/java/io/Serializable.html" title="class or interface in java.io">Serializable</A></DD></DL><HR><DL><DT><PRE>public abstract class <B>MethodExpression</B><DT>extends <A HREF="../../javax/el/Expression.html" title="class in javax.el">Expression</A></DL></PRE><P>An <code>Expression</code> that refers to a method on an object. <p>The <A HREF="../../javax/el/ExpressionFactory.html#createMethodExpression(javax.el.ELContext, java.lang.String, java.lang.Class, java.lang.Class[])"><CODE>ExpressionFactory.createMethodExpression(javax.el.ELContext, java.lang.String, java.lang.Class<?>, java.lang.Class<?>[])</CODE></A> method can be used to parse an expression string and return a concrete instance of <code>MethodExpression</code> that encapsulates the parsed expression. The <A HREF="../../javax/el/FunctionMapper.html" title="class in javax.el"><CODE>FunctionMapper</CODE></A> is used at parse time, not evaluation time, so one is not needed to evaluate an expression using this class. However, the <A HREF="../../javax/el/ELContext.html" title="class in javax.el"><CODE>ELContext</CODE></A> is needed at evaluation time.</p> <p>The <A HREF="../../javax/el/MethodExpression.html#getMethodInfo(javax.el.ELContext)"><CODE>getMethodInfo(javax.el.ELContext)</CODE></A> and <A HREF="../../javax/el/MethodExpression.html#invoke(javax.el.ELContext, java.lang.Object[])"><CODE>invoke(javax.el.ELContext, java.lang.Object[])</CODE></A> methods will evaluate the expression each time they are called. The <A HREF="../../javax/el/ELResolver.html" title="class in javax.el"><CODE>ELResolver</CODE></A> in the <code>ELContext</code> is used to resolve the top-level variables and to determine the behavior of the <code>.</code> and <code>[]</code> operators. For any of the two methods, the <A HREF="../../javax/el/ELResolver.html#getValue(javax.el.ELContext, java.lang.Object, java.lang.Object)"><CODE>ELResolver.getValue(javax.el.ELContext, java.lang.Object, java.lang.Object)</CODE></A> method is used to resolve all properties up to but excluding the last one. This provides the <code>base</code> object on which the method appears. If the <code>base</code> object is null, a <code>PropertyNotFoundException</code> must be thrown. At the last resolution, the final <code>property</code> is then coerced to a <code>String</code>, 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 <code>MethodExpression</code>).</p> <p>See the notes about comparison, serialization and immutability in the <A HREF="../../javax/el/Expression.html" title="class in javax.el"><CODE>Expression</CODE></A> javadocs.<P><P><DL><DT><B>Since:</B></DT> <DD>JSP 2.1</DD><DT><B>See Also:</B><DD><A HREF="../../javax/el/ELResolver.html" title="class in javax.el"><CODE>ELResolver</CODE></A>, <A HREF="../../javax/el/Expression.html" title="class in javax.el"><CODE>Expression</CODE></A>, <A HREF="../../javax/el/ExpressionFactory.html" title="class in javax.el"><CODE>ExpressionFactory</CODE></A>, <A HREF="../../serialized-form.html#javax.el.MethodExpression">Serialized Form</A></DL><HR><P><!-- ======== CONSTRUCTOR SUMMARY ======== --><A NAME="constructor_summary"><!-- --></A><TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2"><B>Constructor Summary</B></FONT></TH></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><B><A HREF="../../javax/el/MethodExpression.html#MethodExpression()">MethodExpression</A></B>()</CODE><BR> </TD></TR></TABLE> <!-- ========== METHOD SUMMARY =========== --><A NAME="method_summary"><!-- --></A><TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2"><B>Method Summary</B></FONT></TH></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE>abstract <A HREF="../../javax/el/MethodInfo.html" title="class in javax.el">MethodInfo</A></CODE></FONT></TD><TD><CODE><B><A HREF="../../javax/el/MethodExpression.html#getMethodInfo(javax.el.ELContext)">getMethodInfo</A></B>(<A HREF="../../javax/el/ELContext.html" title="class in javax.el">ELContext</A> context)</CODE><BR> Evaluates the expression relative to the provided context, and returns information about the actual referenced method.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE>abstract <A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A></CODE></FONT></TD><TD><CODE><B><A HREF="../../javax/el/MethodExpression.html#invoke(javax.el.ELContext, java.lang.Object[])">invoke</A></B>(<A HREF="../../javax/el/ELContext.html" title="class in javax.el">ELContext</A> context, <A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/Object.html" title="class or interface in java.lang">Object</A>[] params)</CODE><BR> If a String literal is specified as the expression, returns the String literal coerced to the expected return type of the method signature.</TD>⌨️ 快捷键说明
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