Tomcat example source code file (ValueExpressionImpl.java)

This example Tomcat source code file (ValueExpressionImpl.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 - Tomcat tags/keywords

class, elexception, elexception, evaluationcontext, evaluationcontext, functionmapper, io, node, object, propertynotfoundexception, propertynotfoundexception, string, string, valueexpressionimpl, variablemapper

The Tomcat ValueExpressionImpl.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.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.PropertyNotFoundException;
import javax.el.PropertyNotWritableException;
import javax.el.ValueExpression;
import javax.el.VariableMapper;

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


/**
 * An <code>Expression that can get or set a value.
 * 
 * <p>
 * In previous incarnations of this API, expressions could only be read.
 * <code>ValueExpression objects can now be used both to retrieve a
 * value and to set a value. Expressions that can have a value set on them are
 * referred to as l-value expressions. Those that cannot are referred to as
 * r-value expressions. Not all r-value expressions can be used as l-value
 * expressions (e.g. <code>"${1+1}" or
 * <code>"${firstName} ${lastName}"). See the EL Specification for
 * details. Expressions that cannot be used as l-values must always return
 * <code>true from isReadOnly().
 * </p>
 * 
 * <p>
 * <code>The {@link ExpressionFactory#createValueExpression} method
 * can be used to parse an expression string and return a concrete instance
 * of <code>ValueExpression 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 #getValue}, {@link #setValue}, {@link #isReadOnly} and
 * {@link #getType} 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 four 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. At the last resolution, the <code>ValueExpression will 
 * call the corresponding {@link ELResolver#getValue}, 
 * {@link ELResolver#setValue}, {@link ELResolver#isReadOnly} or 
 * {@link ELResolver#getType} method, depending on which was called on 
 * the <code>ValueExpression.
 * </p>
 *
 * <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.ValueExpression
 * 
 * @author Jacob Hookom [jacob@hookom.net]
 * @version $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: markt $
 */
public final class ValueExpressionImpl extends ValueExpression implements
        Externalizable {

    private Class expectedType;

    private String expr;

    private FunctionMapper fnMapper;

    private VariableMapper varMapper;

    private transient Node node;

    public ValueExpressionImpl() {

    }

    /**
     * 
     */
    public ValueExpressionImpl(String expr, Node node, FunctionMapper fnMapper,
            VariableMapper varMapper, Class expectedType) {
        this.expr = expr;
        this.node = node;
        this.fnMapper = fnMapper;
        this.varMapper = varMapper;
        this.expectedType = expectedType;
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#equals(java.lang.Object)
     */
    public boolean equals(Object obj) {
        return (obj instanceof ValueExpressionImpl && obj.hashCode() == this
                .hashCode());
    }

    /*
     * (non-Javadoc)
     * 
     * @see javax.el.ValueExpression#getExpectedType()
     */
    public Class getExpectedType() {
        return this.expectedType;
    }

    /**
     * Returns the type the result of the expression will be coerced to after
     * evaluation.
     * 
     * @return the <code>expectedType passed to the
     *         <code>ExpressionFactory.createValueExpression method
     *         that created this <code>ValueExpression.
     * 
     * @see javax.el.Expression#getExpressionString()
     */
    public String getExpressionString() {
        return this.expr;
    }

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

    /*
     * (non-Javadoc)
     * 
     * @see javax.el.ValueExpression#getType(javax.el.ELContext)
     */
    public Class getType(ELContext context) throws PropertyNotFoundException,
            ELException {
        EvaluationContext ctx = new EvaluationContext(context, this.fnMapper,
                this.varMapper);
        return this.getNode().getType(ctx);
    }

    /*
     * (non-Javadoc)
     * 
     * @see javax.el.ValueExpression#getValue(javax.el.ELContext)
     */
    public Object getValue(ELContext context) throws PropertyNotFoundException,
            ELException {
        EvaluationContext ctx = new EvaluationContext(context, this.fnMapper,
                this.varMapper);
        Object value = this.getNode().getValue(ctx);
        if (this.expectedType != null) {
            return ELSupport.coerceToType(value, this.expectedType);
        }
        return value;
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#hashCode()
     */
    public int hashCode() {
        return this.expr.hashCode();
    }

    /*
     * (non-Javadoc)
     * 
     * @see javax.el.ValueExpression#isLiteralText()
     */
    public boolean isLiteralText() {
        try {
            return this.getNode() instanceof AstLiteralExpression;
        } catch (ELException ele) {
            return false;
        }
    }

    /*
     * (non-Javadoc)
     * 
     * @see javax.el.ValueExpression#isReadOnly(javax.el.ELContext)
     */
    public boolean isReadOnly(ELContext context)
            throws PropertyNotFoundException, ELException {
        EvaluationContext ctx = new EvaluationContext(context, this.fnMapper,
                this.varMapper);
        return this.getNode().isReadOnly(ctx);
    }

    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.fnMapper = (FunctionMapper) in.readObject();
        this.varMapper = (VariableMapper) in.readObject();
    }

    /*
     * (non-Javadoc)
     * 
     * @see javax.el.ValueExpression#setValue(javax.el.ELContext,
     *      java.lang.Object)
     */
    public void setValue(ELContext context, Object value)
            throws PropertyNotFoundException, PropertyNotWritableException,
            ELException {
        EvaluationContext ctx = new EvaluationContext(context, this.fnMapper,
                this.varMapper);
        this.getNode().setValue(ctx, value);
    }

    public void writeExternal(ObjectOutput out) throws IOException {
        out.writeUTF(this.expr);
        out.writeUTF((this.expectedType != null) ? this.expectedType.getName()
                : "");
        out.writeObject(this.fnMapper);
        out.writeObject(this.varMapper);
    }

    public String toString() {
        return "ValueExpression["+this.expr+"]";
    }
}