Java example source code file (Resolver.java)

This example Java source code file (Resolver.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

classloader, entityresolver, fileinputstream, hashtable, inputsource, inputstream, ioexception, net, network, not, resolver, sax, string, urlconnection, us\-ascii, util, xml

The Resolver.java Java example source code

/*
 * Copyright (c) 2009, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.xml.internal.dtdparser;

import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.Hashtable;

/**
 * This entity resolver class provides a number of utilities which can help
 * managment of external parsed entities in XML.  These are commonly used
 * to hold markup declarations that are to be used as part of a Document
 * Type Declaration (DTD), or to hold text marked up with XML.
 * <p/>
 * <P> Features include: 

 * <p/>
 * <LI> Static factory methods are provided for constructing SAX InputSource
 * objects from Files, URLs, or MIME objects.  This eliminates a class of
 * error-prone coding in applications.
 * <p/>
 * <LI> Character encodings for XML documents are correctly supported: 

 * <p/>
 * <LI> The encodings defined in the RFCs for MIME content types
 * (2046 for general MIME, and 2376 for XML in particular), are
 * supported, handling <em>charset=... attributes and accepting
 * content types which are known to be safe for use with XML;
 * <p/>
 * <LI> The character encoding autodetection algorithm identified
 * in the XML specification is used, and leverages all of
 * the JDK 1.1 (and later) character encoding support.
 * <p/>
 * <LI> The use of MIME typing may optionally be disabled, forcing the
 * use of autodetection, to support web servers which don't correctly
 * report MIME types for XML.  For example, they may report text that
 * is encoded in EUC-JP as being US-ASCII text, leading to fatal
 * errors during parsing.
 * <p/>
 * <LI> The InputSource objects returned by this class always
 * have a <code>java.io.Reader available as the "character
 * stream" property.
 * <p/>
 * </UL>
 * <p/>
 * <LI> Catalog entries can map public identifiers to Java resources or
 * to local URLs.  These are used to reduce network dependencies and loads,
 * and will often be used for external DTD components.  For example, packages
 * shipping DTD files as resources in JAR files can eliminate network traffic
 * when accessing them, and sites may provide local caches of common DTDs.
 * Note that no particular catalog syntax is supported by this class, only
 * the notion of a set of entries.
 * <p/>
 * </UL>
 * <p/>
 * <P> Subclasses can perform tasks such as supporting new URI schemes for
 * URIs which are not URLs, such as URNs (see RFC 2396) or for accessing
 * MIME entities which are part of a <em>multipart/related group
 * (see RFC 2387).  They may also be used to support particular catalog
 * syntaxes, such as the <a href="http://www.oasis-open.org/html/a401.htm">
 * SGML/Open Catalog (SOCAT)</a> which supports the SGML notion of "Formal
 * Public Identifiers (FPIs).
 *
 * @author David Brownell
 * @author Janet Koenig
 * @version 1.3 00/02/24
 */
public class Resolver implements EntityResolver {
    private boolean ignoringMIME;

    // table mapping public IDs to (local) URIs
    private Hashtable id2uri;

    // tables mapping public IDs to resources and classloaders
    private Hashtable id2resource;
    private Hashtable id2loader;

    //
    // table of MIME content types (less attributes!) known
    // to be mostly "OK" to use with XML MIME entities.  the
    // idea is to rule out obvious braindamage ("image/jpg")
    // not the subtle stuff ("text/html") that might actually
    // be (or become) safe.
    //
    private static final String types [] = {
        "application/xml",
        "text/xml",
        "text/plain",
        "text/html", // commonly mis-inferred
        "application/x-netcdf", // this is often illegal XML
        "content/unknown"
    };

    /**
     * Constructs a resolver.
     */
    public Resolver() {
    }

    /**
     * Returns an input source, using the MIME type information and URL
     * scheme to statically determine the correct character encoding if
     * possible and otherwise autodetecting it.  MIME carefully specifies
     * the character encoding defaults, and how attributes of the content
     * type can change it.  XML further specifies two mandatory encodings
     * (UTF-8 and UTF-16), and includes an XML declaration which can be
     * used to internally label most documents encoded using US-ASCII
     * supersets (such as Shift_JIS, EUC-JP, ISO-2022-*, ISO-8859-*, and
     * more).
     * <p/>
     * <P> This method can be used to access XML documents which do not
     * have URIs (such as servlet input streams, or most JavaMail message
     * entities) and to support access methods such as HTTP POST or PUT.
     * (URLs normally return content using the GET method.)
     * <p/>
     * <P>  The caller should set the system ID in order for relative URIs
     * found in this document to be interpreted correctly.</em> In some cases,
     * a custom resolver will need to be used; for example, documents
     * may be grouped in a single MIME "multipart/related" bundle, and
     * relative URLs would refer to other documents in that bundle.
     *
     * @param contentType The MIME content type for the source for which
     *                    an InputSource is desired, such as <em>text/xml;charset=utf-8.
     * @param stream      The input byte stream for the input source.
     * @param checkType   If true, this verifies that the content type is known
     *                    to support XML documents, such as <em>application/xml.
     * @param scheme      Unless this is "file", unspecified MIME types
     *                    default to US-ASCII.  Files are always autodetected since most
     *                    file systems discard character encoding information.
     */
    public static InputSource createInputSource(String contentType,
                                                InputStream stream,
                                                boolean checkType,
                                                String scheme) throws IOException {
        InputSource retval;
        String charset = null;

        if (contentType != null) {
            int index;

            contentType = contentType.toLowerCase();
            index = contentType.indexOf(';');
            if (index != -1) {
                String attributes;

                attributes = contentType.substring(index + 1);
                contentType = contentType.substring(0, index);

                // use "charset=..." if it's available
                index = attributes.indexOf("charset");
                if (index != -1) {
                    attributes = attributes.substring(index + 7);
                    // strip out subsequent attributes
                    if ((index = attributes.indexOf(';')) != -1)
                        attributes = attributes.substring(0, index);
                    // find start of value
                    if ((index = attributes.indexOf('=')) != -1) {
                        attributes = attributes.substring(index + 1);
                        // strip out rfc822 comments
                        if ((index = attributes.indexOf('(')) != -1)
                            attributes = attributes.substring(0, index);
                        // double quotes are optional
                        if ((index = attributes.indexOf('"')) != -1) {
                            attributes = attributes.substring(index + 1);
                            attributes = attributes.substring(0,
                                    attributes.indexOf('"'));
                        }
                        charset = attributes.trim();
                        // XXX "\;", "\)" etc were mishandled above
                    }
                }
            }

            //
            // Check MIME type.
            //
            if (checkType) {
                boolean isOK = false;
                for (int i = 0; i < types.length; i++)
                    if (types[i].equals(contentType)) {
                        isOK = true;
                        break;
                    }
                if (!isOK)
                    throw new IOException("Not XML: " + contentType);
            }

            //
            // "text/*" MIME types have hard-wired character set
            // defaults, as specified in the RFCs.  For XML, we
            // ignore the system "file.encoding" property since
            // autodetection is more correct.
            //
            if (charset == null) {
                contentType = contentType.trim();
                if (contentType.startsWith("text/")) {
                    if (!"file".equalsIgnoreCase(scheme))
                        charset = "US-ASCII";
                }
                // "application/*" has no default
            }
        }

        retval = new InputSource(XmlReader.createReader(stream, charset));
        retval.setByteStream(stream);
        retval.setEncoding(charset);
        return retval;
    }


    /**
     * Creates an input source from a given URI.
     *
     * @param uri       the URI (system ID) for the entity
     * @param checkType if true, the MIME content type for the entity
     *                  is checked for document type and character set encoding.
     */
    static public InputSource createInputSource(URL uri, boolean checkType)
            throws IOException {

        URLConnection conn = uri.openConnection();
        InputSource retval;

        if (checkType) {
            String contentType = conn.getContentType();
            retval = createInputSource(contentType, conn.getInputStream(),
                    false, uri.getProtocol());
        } else {
            retval = new InputSource(XmlReader.createReader(conn.getInputStream()));
        }
        retval.setSystemId(conn.getURL().toString());
        return retval;
    }


    /**
     * Creates an input source from a given file, autodetecting
     * the character encoding.
     */
    static public InputSource createInputSource(File file)
            throws IOException {
        InputSource retval;
        String path;

        retval = new InputSource(XmlReader.createReader(new FileInputStream(file)));

        // On JDK 1.2 and later, simplify this:
        //    "path = file.toURL ().toString ()".
        path = file.getAbsolutePath();
        if (File.separatorChar != '/')
            path = path.replace(File.separatorChar, '/');
        if (!path.startsWith("/"))
            path = "/" + path;
        if (!path.endsWith("/") && file.isDirectory())
            path = path + "/";

        retval.setSystemId("file:" + path);
        return retval;
    }


    /**
     * <b>SAX:
     * Resolve the given entity into an input source.  If the name can't
     * be mapped to a preferred form of the entity, the URI is used.  To
     * resolve the entity, first a local catalog mapping names to URIs is
     * consulted.  If no mapping is found there, a catalog mapping names
     * to java resources is consulted.  Finally, if neither mapping found
     * a copy of the entity, the specified URI is used.
     * <p/>
     * <P> When a URI is used, 
     * createInputSource</a> is used to correctly deduce the character
     * encoding used by this entity.  No MIME type checking is done.
     *
     * @param name Used to find alternate copies of the entity, when
     *             this value is non-null; this is the XML "public ID".
     * @param uri  Used when no alternate copy of the entity is found;
     *             this is the XML "system ID", normally a URI.
     */
    public InputSource resolveEntity(String name, String uri)
            throws IOException {
        InputSource retval;
        String mappedURI = name2uri(name);
        InputStream stream;

        // prefer explicit URI mappings, then bundled resources...
        if (mappedURI == null && (stream = mapResource(name)) != null) {
            uri = "java:resource:" + (String) id2resource.get(name);
            retval = new InputSource(XmlReader.createReader(stream));

            // ...and treat all URIs the same (as URLs for now).
        } else {
            URL url;
            URLConnection conn;

            if (mappedURI != null)
                uri = mappedURI;
            else if (uri == null)
                return null;

            url = new URL(uri);
            conn = url.openConnection();
            uri = conn.getURL().toString();
            // System.out.println ("++ URI: " + url);
            if (ignoringMIME)
                retval = new InputSource(XmlReader.createReader(conn.getInputStream()));
            else {
                String contentType = conn.getContentType();
                retval = createInputSource(contentType,
                        conn.getInputStream(),
                        false, url.getProtocol());
            }
        }
        retval.setSystemId(uri);
        retval.setPublicId(name);
        return retval;
    }


    /**
     * Returns true if this resolver is ignoring MIME types in the documents
     * it returns, to work around bugs in how servers have reported the
     * documents' MIME types.
     */
    public boolean isIgnoringMIME() {
        return ignoringMIME;
    }

    /**
     * Tells the resolver whether to ignore MIME types in the documents it
     * retrieves.  Many web servers incorrectly assign text documents a
     * default character encoding, even when that is incorrect.  For example,
     * all HTTP text documents default to use ISO-8859-1 (used for Western
     * European languages), and other MIME sources default text documents
     * to use US-ASCII (a seven bit encoding).  For XML documents which
     * include text encoding declarations (as most should do), these server
     * bugs can be worked around by ignoring the MIME type entirely.
     */
    public void setIgnoringMIME(boolean value) {
        ignoringMIME = value;
    }


    // maps the public ID to an alternate URI, if one is registered
    private String name2uri(String publicId) {
        if (publicId == null || id2uri == null)
            return null;
        return (String) id2uri.get(publicId);
    }


    /**
     * Registers the given public ID as corresponding to a particular
     * URI, typically a local copy.  This URI will be used in preference
     * to ones provided as system IDs in XML entity declarations.  This
     * mechanism would most typically be used for Document Type Definitions
     * (DTDs), where the public IDs are formally managed and versioned.
     *
     * @param publicId The managed public ID being mapped
     * @param uri      The URI of the preferred copy of that entity
     */
    public void registerCatalogEntry(String publicId,
                                     String uri) {
        if (id2uri == null)
            id2uri = new Hashtable(17);
        id2uri.put(publicId, uri);
    }


    // return the resource as a stream
    private InputStream mapResource(String publicId) {
        // System.out.println ("++ PUBLIC: " + publicId);
        if (publicId == null || id2resource == null)
            return null;

        String resourceName = (String) id2resource.get(publicId);
        ClassLoader loader = null;

        if (resourceName == null)
            return null;
        // System.out.println ("++ Resource: " + resourceName);

        if (id2loader != null)
            loader = (ClassLoader) id2loader.get(publicId);
        // System.out.println ("++ Loader: " + loader);
        if (loader == null)
            return ClassLoader.getSystemResourceAsStream(resourceName);
        return loader.getResourceAsStream(resourceName);
    }

    /**
     * Registers a given public ID as corresponding to a particular Java
     * resource in a given class loader, typically distributed with a
     * software package.  This resource will be preferred over system IDs
     * included in XML documents.  This mechanism should most typically be
     * used for Document Type Definitions (DTDs), where the public IDs are
     * formally managed and versioned.
     * <p/>
     * <P> If a mapping to a URI has been provided, that mapping takes
     * precedence over this one.
     *
     * @param publicId     The managed public ID being mapped
     * @param resourceName The name of the Java resource
     * @param loader       The class loader holding the resource, or null if
     *                     it is a system resource.
     */
    public void registerCatalogEntry(String publicId,
                                     String resourceName,
                                     ClassLoader loader) {
        if (id2resource == null)
            id2resource = new Hashtable(17);
        id2resource.put(publicId, resourceName);

        if (loader != null) {
            if (id2loader == null)
                id2loader = new Hashtable(17);
            id2loader.put(publicId, loader);
        }
    }
}