butorconfigentityresolver.java

一个实用工具类

/*
 * Copyright (C) butor.com. All rights reserved.
 *
 * This software is published under the terms of the GNU Library General
 * Public License (GNU LGPL), a copy of which has been included with this
 * distribution in the LICENSE.txt file. 
 */


package org.butor.config.lowlevel;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;

import java.net.URI;
import java.net.URISyntaxException;

import org.butor.log.Log;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

/**
 * @author sawanai
 *
 */
public class ButorConfigEntityResolver implements EntityResolver {

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

    /**
     * Allow the application to resolve external entities.
     *
     * <p>The Parser will call this method before opening any external
     * entity except the top-level document entity (including the
     * external DTD subset, external entities referenced within the
     * DTD, and external entities referenced within the document
     * element): the application may request that the parser resolve
     * the entity itself, that it use an alternative URI, or that it
     * use an entirely different input source.</p>
     *
     * <p>Application writers can use this method to redirect external
     * system identifiers to secure and/or local URIs, to look up
     * public identifiers in a catalogue, or to read an entity from a
     * database or other input source (including, for example, a dialog
     * box).</p>
     *
     * <p>If the system identifier is a URL, the SAX parser must
     * resolve it fully before reporting it to the application.</p>
     *
     * @param publicId The public identifier of the external entity
     *        being referenced, or null if none was supplied.
     * @param systemId The system identifier of the external entity
     *        being referenced.
     * @return An InputSource object describing the new input source,
     *         or null to request that the parser open a regular
     *         URI connection to the system identifier.
     * @exception org.xml.sax.SAXException Any SAX exception, possibly
     *            wrapping another exception.
     * @exception java.io.IOException A Java-specific IO exception,
     *            possibly the result of creating a new InputStream
     *            or Reader for the InputSource.
     * @see org.xml.sax.InputSource
     */
    public InputSource resolveEntity (String publicId, String systemId)
			throws SAXException, IOException {
    	
        try {
            // Wrap the systemId in a URI object to make it convenient
            // to extract the components of the systemId
            URI uri = new URI(systemId);

            // Check if external source is a file
            if ("file".equals(uri.getScheme())) {
                File file = new File(uri.getSchemeSpecificPart());
                //TODO
                String filename = "/org/butor/config/lowlevel/" +file.getName();
            	
                Log.logStr(this, Log.LOG_TYPE_INFO, "resolveEntity()", "getting resource [" +filename +"] ...");

            	InputStream inputStream = this.getClass().getResourceAsStream(filename);
                if (inputStream == null) {
                	Log.logStr(this, Log.LOG_TYPE_ERROR, "resolveEntity()", "Resource [" +filename +"] not found!");
                }
                return new InputSource(inputStream);
            }
            
        } catch (URISyntaxException e) {
        	//OK
        }

        // Returning null causes the caller to try accessing the systemid
        return null;
    }
}