Struts example source code file (MethodExpressionImpl.java)

This example Struts source code file (MethodExpressionImpl.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Struts tags/keywords

class, class, elexception, evaluationcontext, evaluationcontext, functionmapper, io, methodexpressionimpl, methodexpressionimpl, methodnotfoundexception, node, node, object, string, variablemapper

The Struts MethodExpressionImpl.java source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.struts2.el;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

import javax.el.ELContext;
import javax.el.ELException;
import javax.el.ELResolver;
import javax.el.Expression;
import javax.el.ExpressionFactory;
import javax.el.FunctionMapper;
import javax.el.MethodExpression;
import javax.el.MethodInfo;
import javax.el.MethodNotFoundException;
import javax.el.PropertyNotFoundException;
import javax.el.VariableMapper;

import org.apache.struts2.el.lang.EvaluationContext;
import org.apache.struts2.el.lang.ExpressionBuilder;
import org.apache.struts2.el.parser.Node;
import org.apache.struts2.el.util.ReflectionUtil;


/**
 * An <code>Expression that refers to a method on an object.
 * 
 * <p>
 * <code>The {@link ExpressionFactory#createMethodExpression} method
 * can be used to parse an expression string and return a concrete instance
 * of <code>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.</p>
 *
 * <p>The {@link #getMethodInfo} and {@link #invoke} methods will evaluate the 
 * expression each time they are called. The {@link ELResolver} in the 
 * <code>ELContext is used to resolve the top-level variables and to 
 * determine the behavior of the <code>. and [] 
 * operators. For any of the two methods, the {@link ELResolver#getValue} 
 * method is used to resolve all properties up to but excluding the last 
 * one. This provides the <code>base object on which the method
 * appears. If the <code>base object is null, a 
 * <code>NullPointerException must be thrown. At the last resolution, 
 * the final <code>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
 * <code>MethodExpression).

 *
 * <p>See the notes about comparison, serialization and immutability in 
 * the {@link Expression} javadocs.
 *
 * @see javax.el.ELResolver
 * @see javax.el.Expression
 * @see javax.el.ExpressionFactory
 * @see javax.el.MethodExpression
 * 
 * @author Jacob Hookom [jacob@hookom.net]
 * @version $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: markt $
 */
public final class MethodExpressionImpl extends MethodExpression implements
        Externalizable {

    private Class expectedType;

    private String expr;

    private FunctionMapper fnMapper;

    private VariableMapper varMapper;

    private transient Node node;

    private Class[] paramTypes;

    /**
     * 
     */
    public MethodExpressionImpl() {
        super();
    }

    /**
     * @param expr
     * @param node
     * @param fnMapper
     * @param expectedType
     * @param paramTypes
     */
    public MethodExpressionImpl(String expr, Node node,
            FunctionMapper fnMapper, VariableMapper varMapper,
            Class expectedType, Class[] paramTypes) {
        super();
        this.expr = expr;
        this.node = node;
        this.fnMapper = fnMapper;
        this.varMapper = varMapper;
        this.expectedType = expectedType;
        this.paramTypes = paramTypes;
    }

    /**
     * Determines whether the specified object is equal to this
     * <code>Expression.
     * 
     * <p>
     * The result is <code>true if and only if the argument is not
     * <code>null, is an Expression object that is the
     * of the same type (<code>ValueExpression or
     * <code>MethodExpression), and has an identical parsed
     * representation.
     * </p>
     * 
     * <p>
     * Note that two expressions can be equal if their expression Strings are
     * different. For example, <code>${fn1:foo()} and
     * <code>${fn2:foo()} are equal if their corresponding
     * <code>FunctionMappers mapped fn1:foo and
     * <code>fn2:foo to the same method.
     * </p>
     * 
     * @param obj
     *            the <code>Object to test for equality.
     * @return <code>true if obj equals this
     *         <code>Expression; false otherwise.
     * @see java.util.Hashtable
     * @see java.lang.Object#equals(java.lang.Object)
     */
    public boolean equals(Object obj) {
        return (obj instanceof MethodExpressionImpl && obj.hashCode() == this
                .hashCode());
    }

    /**
     * Returns the original String used to create this <code>Expression,
     * unmodified.
     * 
     * <p>
     * This is used for debugging purposes but also for the purposes of
     * comparison (e.g. to ensure the expression in a configuration file has not
     * changed).
     * </p>
     * 
     * <p>
     * This method does not provide sufficient information to re-create an
     * expression. Two different expressions can have exactly the same
     * expression string but different function mappings. Serialization should
     * be used to save and restore the state of an <code>Expression.
     * </p>
     * 
     * @return The original expression String.
     * 
     * @see javax.el.Expression#getExpressionString()
     */
    public String getExpressionString() {
        return this.expr;
    }

    /**
     * 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 <code>MethodInfo containing information
     *         about the method the expression evaluated to.
     * @throws NullPointerException
     *             if context is <code>null or the base object is
     *             <code>null on the last resolution.
     * @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.
     * @see javax.el.MethodExpression#getMethodInfo(javax.el.ELContext)
     */
    public MethodInfo getMethodInfo(ELContext context)
            throws PropertyNotFoundException, MethodNotFoundException,
            ELException {
        Node n = this.getNode();
        EvaluationContext ctx = new EvaluationContext(context, this.fnMapper,
                this.varMapper);
        return n.getMethodInfo(ctx, this.paramTypes);
    }

    /**
     * @return
     * @throws ELException
     */
    private Node getNode() throws ELException {
        if (this.node == null) {
            this.node = ExpressionBuilder.createNode(this.expr);
        }
        return this.node;
    }

    /**
     * Returns the hash code for this <code>Expression.
     * 
     * <p>
     * See the note in the {@link #equals} method on how two expressions can be
     * equal if their expression Strings are different. Recall that if two
     * objects are equal according to the <code>equals(Object) method,
     * then calling the <code>hashCode method on each of the two
     * objects must produce the same integer result. Implementations must take
     * special note and implement <code>hashCode correctly.
     * </p>
     * 
     * @return The hash code for this <code>Expression.
     * @see #equals
     * @see java.util.Hashtable
     * @see java.lang.Object#hashCode()
     */
    public int hashCode() {
        return this.expr.hashCode();
    }

    /**
     * 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.
     * 
     * @param context
     *            The context of this evaluation.
     * @param params
     *            The parameters to pass to the method, or <code>null
     *            if no parameters.
     * @return the result of the method invocation (<code>null if the
     *         method has a <code>void return type).
     * @throws NullPointerException
     *             if context is <code>null or the base object is
     *             <code>null on the last resolution.
     * @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. If the
     *             exception thrown is an <code>InvocationTargetException,
     *             extract its <code>cause and pass it to the
     *             <code>ELException constructor.
     * @see javax.el.MethodExpression#invoke(javax.el.ELContext,
     *      java.lang.Object[])
     */
    public Object invoke(ELContext context, Object[] params)
            throws PropertyNotFoundException, MethodNotFoundException,
            ELException {
        EvaluationContext ctx = new EvaluationContext(context, this.fnMapper,
                this.varMapper);
        return this.getNode().invoke(ctx, this.paramTypes, params);
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.io.Externalizable#readExternal(java.io.ObjectInput)
     */
    public void readExternal(ObjectInput in) throws IOException,
            ClassNotFoundException {
        this.expr = in.readUTF();
        String type = in.readUTF();
        if (!"".equals(type)) {
            this.expectedType = ReflectionUtil.forName(type);
        }
        this.paramTypes = ReflectionUtil.toTypeArray(((String[]) in
                .readObject()));
        this.fnMapper = (FunctionMapper) in.readObject();
        this.varMapper = (VariableMapper) in.readObject();
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.io.Externalizable#writeExternal(java.io.ObjectOutput)
     */
    public void writeExternal(ObjectOutput out) throws IOException {
        out.writeUTF(this.expr);
        out.writeUTF((this.expectedType != null) ? this.expectedType.getName()
                : "");
        out.writeObject(ReflectionUtil.toTypeNameArray(this.paramTypes));
        out.writeObject(this.fnMapper);
        out.writeObject(this.varMapper);
    }

    public boolean isLiteralText() {
        return false;
    }
}