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/*
 * Copyright (c) 1997, 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0, which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package com.sun.xml.bind.marshaller;

import java.io.OutputStream;

import javax.xml.bind.JAXBContext;
import javax.xml.stream.XMLEventWriter;
import javax.xml.stream.XMLStreamWriter;
import javax.xml.transform.dom.DOMResult;

import org.w3c.dom.Node;

// be careful about changing this class. this class is supposed to be
// extended by users and therefore we are not allowed to break
// those user code.
//
// this means:
// - don't add any abstract method
// - don't change any existing method signature
// - don't remove any existing method.

/**
 * Implemented by the user application to determine URI {@code ->} prefix
 * mapping.
 * 
 * This is considered as an interface, though it's implemented
 * as an abstract class to make it easy to add new methods in
 * a future. 
 * 
 * @author
 *     Kohsuke Kawaguchi ([email protected])
 */
public abstract class NamespacePrefixMapper {

    private static final String[] EMPTY_STRING = new String[0];

    /**
     * Returns a preferred prefix for the given namespace URI.
     * 
     * This method is intended to be overrided by a derived class.
     *
     * 

* As noted in the return value portion of the javadoc, there * are several cases where the preference cannot be honored. * Specifically, as of JAXB RI 2.0 and onward: * *

    *
  1. * If the prefix returned is already in use as one of the in-scope * namespace bindings. This is partly necessary for correctness * (so that we don't unexpectedly change the meaning of QNames * bound to {@link String}), partly to simplify the marshaller. *
  2. * If the prefix returned is "" yet the current {@link JAXBContext} * includes classes that use the empty namespace URI. This allows * the JAXB RI to reserve the "" prefix for the empty namespace URI, * which is the only possible prefix for the URI. * This restriction is also to simplify the marshaller. *
* * @param namespaceUri * The namespace URI for which the prefix needs to be found. * Never be null. "" is used to denote the default namespace. * @param suggestion * When the content tree has a suggestion for the prefix * to the given namespaceUri, that suggestion is passed as a * parameter. Typicall this value comes from the QName.getPrefix * to show the preference of the content tree. This parameter * may be null, and this parameter may represent an already * occupied prefix. * @param requirePrefix * If this method is expected to return non-empty prefix. * When this flag is true, it means that the given namespace URI * cannot be set as the default namespace. * * @return * null if there's no prefered prefix for the namespace URI. * In this case, the system will generate a prefix for you. * * Otherwise the system will try to use the returned prefix, * but generally there's no guarantee if the prefix will be * actually used or not. * * return "" to map this namespace URI to the default namespace. * Again, there's no guarantee that this preference will be * honored. * * If this method returns "" when requirePrefix=true, the return * value will be ignored and the system will generate one. * * @since JAXB 1.0.1 */ public abstract String getPreferredPrefix(String namespaceUri, String suggestion, boolean requirePrefix); /** * Returns a list of namespace URIs that should be declared * at the root element. * *

* By default, the JAXB RI 1.0.x produces namespace declarations only when * they are necessary, only at where they are used. Because of this * lack of look-ahead, sometimes the marshaller produces a lot of * namespace declarations that look redundant to human eyes. For example, *

{@code
     * 
     * 
     *    ... 
     *    ... 
     *    ... 
     *   ...
     * 
     * }
* *

* The JAXB RI 2.x mostly doesn't exhibit this behavior any more, * as it declares all statically known namespace URIs (those URIs * that are used as element/attribute names in JAXB annotations), * but it may still declare additional namespaces in the middle of * a document, for example when (i) a QName as an attribute/element value * requires a new namespace URI, or (ii) DOM nodes as a portion of an object * tree requires a new namespace URI. * *

* If you know in advance that you are going to use a certain set of * namespace URIs, you can override this method and have the marshaller * declare those namespace URIs at the root element. * *

* For example, by returning new String[]{"urn:foo"}, * the marshaller will produce: *

{@code
     * 
     * 
     *    ... 
     *    ... 
     *    ... 
     *   ...
     * 
     * }
*

* To control prefixes assigned to those namespace URIs, use the * {@link #getPreferredPrefix(String, String, boolean)} method. * * @return * A list of namespace URIs as an array of {@link String}s. * This method can return a length-zero array but not null. * None of the array component can be null. To represent * the empty namespace, use the empty string "". * * @since * JAXB RI 1.0.2 */ public String[] getPreDeclaredNamespaceUris() { return EMPTY_STRING; } /** * Similar to {@link #getPreDeclaredNamespaceUris()} but allows the * (prefix,nsUri) pairs to be returned. * *

* With {@link #getPreDeclaredNamespaceUris()}, applications who wish to control * the prefixes as well as the namespaces needed to implement both * {@link #getPreDeclaredNamespaceUris()} and {@link #getPreferredPrefix(String, String, boolean)}. * *

* This version eliminates the needs by returning an array of pairs. * * @return * always return a non-null (but possibly empty) array. The array stores * data like (prefix1,nsUri1,prefix2,nsUri2,...) Use an empty string to represent * the empty namespace URI and the default prefix. Null is not allowed as a value * in the array. * * @since * JAXB RI 2.0 beta */ public String[] getPreDeclaredNamespaceUris2() { return EMPTY_STRING; } /** * Returns a list of (prefix,namespace URI) pairs that represents * namespace bindings available on ancestor elements (that need not be repeated * by the JAXB RI.) * *

* Sometimes JAXB is used to marshal an XML document, which will be * used as a subtree of a bigger document. When this happens, it's nice * for a JAXB marshaller to be able to use in-scope namespace bindings * of the larger document and avoid declaring redundant namespace URIs. * *

* This is automatically done when you are marshalling to {@link XMLStreamWriter}, * {@link XMLEventWriter}, {@link DOMResult}, or {@link Node}, because * those output format allows us to inspect what's currently available * as in-scope namespace binding. However, with other output format, * such as {@link OutputStream}, the JAXB RI cannot do this automatically. * That's when this method comes into play. * *

* Namespace bindings returned by this method will be used by the JAXB RI, * but will not be re-declared. They are assumed to be available when you insert * this subtree into a bigger document. * *

* It is NOT OK to return the same binding, or give * the receiver a conflicting binding information. * It's a responsibility of the caller to make sure that this doesn't happen * even if the ancestor elements look like: *

{@code
     *   
     *     
     *       
     *         ... JAXB marshalling into here.
     *       
     *     
     *   
     * }
* * @return * always return a non-null (but possibly empty) array. The array stores * data like (prefix1,nsUri1,prefix2,nsUri2,...) Use an empty string to represent * the empty namespace URI and the default prefix. Null is not allowed as a value * in the array. * * @since JAXB RI 2.0 beta */ public String[] getContextualNamespaceDecls() { return EMPTY_STRING; } }




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