elutils.java

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/*
 * Copyright 2002-2004 the original author or authors.
 *
 * Licensed 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 de.mindmatters.faces.el;

import java.lang.reflect.Method;

import javax.faces.context.FacesContext;
import javax.faces.el.ReferenceSyntaxException;
import javax.faces.el.ValueBinding;
import javax.servlet.jsp.el.ELException;
import javax.servlet.jsp.el.FunctionMapper;
import javax.servlet.jsp.el.VariableResolver;

import org.apache.commons.el.Coercions;
import org.apache.commons.el.ComplexValue;
import org.apache.commons.el.ConditionalExpression;
import org.apache.commons.el.NamedValue;

/**
 * Utility class for interpreting and evaluating parsed JSF reference
 * expressions.
 * 
 * @author Andreas Kuhrwahl
 * @see ELParser
 * 
 */
public final class ELUtils {

    /** The servlet-api based VariableResolver. */
    private static final VariableResolver VARIABLE_RESOLVER = new ELVariableResolver();

    /** The function mapper. */
    private static final FunctionMapper FUNCTION_MAPPER = new FunctionMapper() {

        public Method resolveFunction(final String prefix,
                final String localName) {
            throw new ReferenceSyntaxException(
                    "Functions not supported in expressions. Function: "
                            + prefix + ":" + localName);
        }

    };

    /**
     * It's a static class!
     */
    private ELUtils() {
    }

    /**
     * Returns the name of the base of the given expression
     * <code>expression</code> if any.
     * 
     * @param context
     *            {@link FacesContext} for the current request
     * @param expression
     *            The parsed expression.
     * @return The name of the base of the given expression or <code>null</code>
     *         if not present
     */
    private static String resolveToBase(final FacesContext context,
            final Object expression) {
        String beanName = null;
        if (context == null) {
            throw new NullPointerException("FacesContext");
        }
        Object currentExpression = expression;
        while (currentExpression instanceof ConditionalExpression) {
            try {
                ConditionalExpression conditionalExpression = (ConditionalExpression) expression;
                boolean condition = Coercions.coerceToBoolean(
                        conditionalExpression.getCondition().evaluate(
                                VARIABLE_RESOLVER, FUNCTION_MAPPER,
                                ELParser.LOGGER), ELParser.LOGGER)
                        .booleanValue();
                if (condition) {
                    currentExpression = conditionalExpression.getTrueBranch();
                } else {
                    currentExpression = conditionalExpression.getFalseBranch();
                }
            } catch (ELException ex) {
                throw new ReferenceSyntaxException(ex.getMessage(), ex);
            }
        }
        if (currentExpression instanceof NamedValue) {
            beanName = ((NamedValue) currentExpression).getName();
        } else if (currentExpression instanceof ComplexValue) {
            ComplexValue complexValue = (ComplexValue) currentExpression;
            beanName = resolveToBase(context, (Object) complexValue.getPrefix());
        }
        return beanName;
    }

    /**
     * Returns the name of the base of the given JSF reference expression string
     * <code>expressionString</code> if any.
     * 
     * @param context
     *            {@link FacesContext} for the current request
     * @param expressionString
     *            The reference expression
     * @return The name of the base of the given expression or <code>null</code>
     *         if not present
     */
    public static String resolveToBase(final FacesContext context,
            final String expressionString) {
        try {
            return resolveToBase(context, ELParser.getCurrentInstance()
                    .parseExpression(expressionString));
        } catch (ReferenceSyntaxException ex) {
            return null;
        }
    }

    /**
     * Returns the name of the base of the given ValueBinding
     * <code>valueBinding</code> if any.
     * 
     * @param context
     *            {@link FacesContext} for the current request
     * @param valueBinding
     *            The ValueBinding
     * @return The name of the base of the given ValueBinding or
     *         <code>null</code> if not present
     */
    public static String resolveToBase(final FacesContext context,
            final ValueBinding valueBinding) {
        return resolveToBase(context, valueBinding.getExpressionString());
    }

}