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PatternTesting Exception (patterntesting-exception) is a framework round about exceptions. It wraps some common exception (like IOException) to provide some more information as the original exception (e.g. the filename with the absolute pathname). On the other it allows you to provoke exceptions for better testing.
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/*
 * $Id: SAXHelper.java,v 1.11 2016/12/18 21:57:35 oboehm Exp $
 *
 * Copyright (c) 2008 by Oliver Boehm
 *
 * 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 orimplied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * (c)reated 17.12.2008 by oliver ([email protected])
 */
package patterntesting.exception.xml;

import java.io.*;

import org.apache.commons.io.IOUtils;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.*;
import org.xml.sax.SAXException;

import patterntesting.annotation.check.runtime.MayReturnNull;

/**
 * The class SAXHelper was introduced to be able to provide better
 * SAXExceptions.
 *
 * @author oliver
 * @version $Revision: 1.11 $
 * @since 17.12.2008
 */
public final class SAXHelper {

    private static final Logger LOG = LoggerFactory.getLogger(SAXHelper.class);

    /** The Constant DRIVER_PROPERTY. */
    public static final String DRIVER_PROPERTY = "org.xml.sax.driver";

    /** The Constant DRIVER_RESOURCE. */
    public static final String DRIVER_RESOURCE = "META-INF/services/" + DRIVER_PROPERTY;

    /** Utility class - no need to instantiate it. */
    private SAXHelper() {}

    /**
     * Transforms a SAXException with too less infos into a better SAXException
     * with more infos.
     * 
     * NOTE: Amonst other things the system property "org.xml.sax.driver" are
     * used to get a better exception. Normally this should be synchronized
     * because other threads may changes this system property so that this
     * method may misinterpret this property. But it is very unlikely (except
     * for testing) that this happen. So no synchronization is done to avoid
     * blocked threads. So in some very, very rare circumstances the "better
     * SAXException" may be perhaps confuses you (or the tester ;-).
     * 
     *
     * @param saxe the saxe
     * @return the sAX exception
     */
    public static SAXException betterSAXException(final SAXException saxe) {
        String msg = saxe.getMessage();
        String className = parseMessage(msg);
        if (className == null) {
            if (LOG.isTraceEnabled()) {
                LOG.trace("unknown message '" + msg + "' - returning " + saxe
                        + "...");
            }
            return saxe;
        }
        if (isDriverPropertySetWith(className)) {
            if (LOG.isTraceEnabled()) {
                LOG.trace("conflict with property " + DRIVER_PROPERTY + "="
                        + className + " detected");
            }
            msg = msg + " - check property \"" + DRIVER_PROPERTY + "\"";
            return betterSAXException(saxe, msg);
        } else if (isDriverResourceSetWith(className)) {
            if (LOG.isTraceEnabled()) {
                LOG.trace("conflict with resource " + DRIVER_RESOURCE + "="
                        + className + " detected");
            }
            msg = msg + " - check system resource \"" + DRIVER_RESOURCE + "\"";
            return betterSAXException(saxe, msg);
        } else {
            return saxe;
        }
    }

    /**
     * Better sax exception.
     *
     * @param saxe the saxe
     * @param newMessage the new message
     *
     * @return the sAX exception
     */
    public static SAXException betterSAXException(final SAXException saxe, final String newMessage) {
        Exception cause = saxe.getException();
        SAXException betterException = new SAXException(newMessage, cause);
        betterException.setStackTrace(saxe.getStackTrace());
        return betterException;
    }

    @MayReturnNull
    private static String parseMessage(final String msg) {
        String prefix = "SAX2 driver class ";
        if (msg.startsWith(prefix)) {
            return StringUtils.substringBetween(msg, prefix, " ");
        } else {
            return null;
        }
    }

    private static boolean isDriverPropertySetWith(final String className) {
        String prop = System.getProperty(DRIVER_PROPERTY);
        return className.equals(prop);
    }

    private static boolean isDriverResourceSetWith(final String className) {
        InputStream in = ClassLoader.getSystemResourceAsStream(DRIVER_RESOURCE);
        if (in == null) {
            return false;
        }
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    in, "UTF8"));
            String driver = reader.readLine();
            reader.close();
            if (StringUtils.isBlank(driver)) {
                LOG.warn("no classname found in " + DRIVER_RESOURCE);
                return false;
            }
            return driver.equals(className);
        } catch (IOException ioe) {
            LOG.warn("Cannot read " + DRIVER_RESOURCE + ":", ioe);
            return false;
        } finally {
            IOUtils.closeQuietly(in);
        }
    }

}