1 /*
   2  * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package com.sun.xml.internal.bind.api;
  27 
  28 import javax.xml.bind.JAXBContext;
  29 import javax.xml.bind.Unmarshaller;
  30 import javax.xml.bind.ValidationEventHandler;
  31 import javax.xml.bind.annotation.XmlAnyElement;
  32 
  33 import com.sun.istack.internal.NotNull;
  34 import com.sun.istack.internal.Nullable;
  35 
  36 /**
  37  * Dynamically locates classes to represent elements discovered during the unmarshalling.
  38  *
  39  * <p>
  40  * <b>THIS INTERFACE IS SUBJECT TO CHANGE WITHOUT NOTICE.</b>
  41  *
  42  * <h2>Background</h2>
  43  * <p>
  44  * {@link JAXBContext#newInstance(Class...)} requires that application informs JAXB
  45  * about all the classes that it may see in the instance document. While this allows
  46  * JAXB to take time to optimize the unmarshalling, it is sometimes inconvenient
  47  * for applications.
  48  *
  49  * <p>
  50  * This is where {@link ClassResolver} comes to resucue.
  51  *
  52  * <p>
  53  * A {@link ClassResolver} instance can be specified on {@link Unmarshaller} via
  54  * {@link Unmarshaller#setProperty(String, Object)} as follows:
  55  *
  56  * <pre>
  57  * unmarshaller.setProperty( ClassResolver.class.getName(), new MyClassResolverImpl() );
  58  * </pre>
  59  *
  60  * <p>
  61  * When an {@link Unmarshaller} encounters (i) an unknown root element or (ii) unknown
  62  * elements where unmarshaller is trying to unmarshal into {@link XmlAnyElement} with
  63  * {@code lax=true}, unmarshaller calls {@link #resolveElementName(String, String)}
  64  * method to see if the application may be able to supply a class that corresponds
  65  * to that class.
  66  *
  67  * <p>
  68  * When a {@link Class} is returned, a new {@link JAXBContext} is created with
  69  * all the classes known to it so far, plus a new class returned. This operation
  70  * may fail (for example because of some conflicting annotations.) This failure
  71  * is handled just like {@link Exception}s thrown from
  72  * {@link ClassResolver#resolveElementName(String, String)}.
  73  *
  74  * @author Kohsuke Kawaguchi
  75  * @since 2.1
  76  */
  77 public abstract class ClassResolver {
  78     /**
  79      * JAXB calls this method when it sees an unknown element.
  80      *
  81      * <p>
  82      * See the class javadoc for details.
  83      *
  84      * @param nsUri
  85      *      Namespace URI of the unknown element. Can be empty but never null.
  86      * @param localName
  87      *      Local name of the unknown element. Never be empty nor null.
  88      *
  89      * @return
  90      *      If a non-null class is returned, it will be used to unmarshal this element.
  91      *      If null is returned, the resolution is assumed to be failed, and
  92      *      the unmarshaller will behave as if there was no {@link ClassResolver}
  93      *      to begin with (that is, to report it to {@link ValidationEventHandler},
  94      *      then move on.)
  95      *
  96      * @throws Exception
  97      *      Throwing any {@link RuntimeException} causes the unmarshaller to stop
  98      *      immediately. The exception will be propagated up the call stack.
  99      *      Throwing any other checked {@link Exception} results in the error
 100      *      reproted to {@link ValidationEventHandler} (just like any other error
 101      *      during the unmarshalling.)
 102      */
 103     public abstract @Nullable Class<?> resolveElementName(@NotNull String nsUri, @NotNull String localName) throws Exception;
 104 }