com.agilejava.docbkx.maven.ExpressionHandler.java Source code

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Here is the source code for com.agilejava.docbkx.maven.ExpressionHandler.java

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/*
 * #%L
 * Docbkx Maven Base
 * %%
 * Copyright (C) 2006 - 2014 Wilfred Springer, Cedric Pronzato
 * %%
 * 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.
 * #L%
 */
package com.agilejava.docbkx.maven;

import java.lang.reflect.Method;

import javax.servlet.jsp.el.ELException;
import javax.servlet.jsp.el.ExpressionEvaluator;
import javax.servlet.jsp.el.FunctionMapper;
import javax.servlet.jsp.el.VariableResolver;

import org.apache.commons.el.ExpressionEvaluatorImpl;

import org.apache.maven.plugin.logging.Log;

import org.xml.sax.ContentHandler;
import org.xml.sax.SAXException;

/**
 * A {@link ProcessingInstructionHandler} that evaluates expressions passed as data as JSP
 * expression language expressions.
 *
 * @author Wilfred Springer
 */
public class ExpressionHandler implements ProcessingInstructionHandler {
    /**
     * The name of the processing instruction.
     */
    private final String PI_NAME = "eval";

    /**
     * The object responsible for resolving variables.
     */
    private VariableResolver resolver;

    /**
     * The object used for logging.
     */
    private Log log;

    /**
     * A simplified function mapper that basically does not support any functions at all.
     */
    private FunctionMapper mapper = new FunctionMapper() {
        public Method resolveFunction(String prefix, String localName) {
            return null;
        }
    };

    /**
     * Constructs a new instance.
     * 
     * @param resolver
     *            The object used for resolving variables. (Not
     *            <code>null</code>.)
     * @param log
     *            The object used for logging. (Not <code>null</code>.)
     */
    public ExpressionHandler(VariableResolver resolver, Log log) {
        this.resolver = resolver;
        this.log = log;
    }

    // JavaDoc inherited
    /**
     * DOCUMENT ME!
     *
     * @param data DOCUMENT ME!
     * @param handler DOCUMENT ME!
     */
    public void handle(String data, ContentHandler handler) {
        ExpressionEvaluator evaluator = new ExpressionEvaluatorImpl();
        Object value;

        try {
            value = evaluator.evaluate(data, Object.class, resolver, mapper);

            if (value != null) {
                char[] result = value.toString().toCharArray();
                handler.characters(result, 0, result.length);
            } else {
                log.debug("Failed to resolve " + data);
            }
        } catch (ELException ele) {
            log.error("Failed to handle EL expression.", ele);
        } catch (SAXException saxe) {
            log.error("Failed to generate content.", saxe);
        }
    }

    // JavaDoc inherited
    /**
     * DOCUMENT ME!
     *
     * @param target DOCUMENT ME!
     *
     * @return DOCUMENT ME!
     */
    public boolean matches(String target) {
        return PI_NAME.matches(target);
    }
}