1/*
2 * Copyright (c) 2004, 2013, 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
26package javax.xml.bind;
27
28import javax.xml.namespace.QName;
29import java.io.Serializable;
30
31/**
32 * <p>JAXB representation of an Xml Element.</p>
33 *
34 * <p>This class represents information about an Xml Element from both the element
35 * declaration within a schema and the element instance value within an xml document
36 * with the following properties
37 * <ul>
38 *   <li>element's xml tag <b>{@code name}</b></li>
39 *   <li><b>{@code value}</b> represents the element instance's atttribute(s) and content model</li>
40 *   <li>element declaration's <b>{@code declaredType}</b> ({@code xs:element @type} attribute)</li>
41 *   <li><b>{@code scope}</b> of element declaration</li>
42 *   <li>boolean <b>{@code nil}</b> property. (element instance's <b>{@code xsi:nil}</b> attribute)</li>
43 * </ul>
44 *
45 * <p>The {@code declaredType} and {@code scope} property are the
46 * JAXB class binding for the xml type definition.
47 * </p>
48 *
49 * <p><b>{@code Scope}</b> is either {@link GlobalScope} or the Java class representing the
50 * complex type definition containing the schema element declaration.
51 * </p>
52 *
53 * <p>There is a property constraint that if <b>{@code value}</b> is {@code null},
54 * then {@code nil} must be {@code true}. The converse is not true to enable
55 * representing a nil element with attribute(s). If {@code nil} is true, it is possible
56 * that {@code value} is non-null so it can hold the value of the attributes
57 * associated with a nil element.
58 * </p>
59 *
60 * @author Kohsuke Kawaguchi, Joe Fialli
61 * @since 1.6, JAXB 2.0
62 */
63
64public class JAXBElement<T> implements Serializable {
65
66    /** xml element tag name */
67    final protected QName name;
68
69    /** Java datatype binding for xml element declaration's type. */
70    final protected Class<T> declaredType;
71
72    /** Scope of xml element declaration representing this xml element instance.
73     *  Can be one of the following values:
74     *  - {@link GlobalScope} for global xml element declaration.
75     *  - local element declaration has a scope set to the Java class
76     *     representation of complex type defintion containing
77     *     xml element declaration.
78     */
79    final protected Class scope;
80
81    /** xml element value.
82        Represents content model and attributes of an xml element instance. */
83    protected T value;
84
85    /** true iff the xml element instance has xsi:nil="true". */
86    protected boolean nil = false;
87
88    /**
89     * Designates global scope for an xml element.
90     */
91    public static final class GlobalScope {}
92
93    /**
94     * <p>Construct an xml element instance.</p>
95     *
96     * @param name          Java binding of xml element tag name
97     * @param declaredType  Java binding of xml element declaration's type
98     * @param scope
99     *      Java binding of scope of xml element declaration.
100     *      Passing null is the same as passing {@code GlobalScope.class}
101     * @param value
102     *      Java instance representing xml element's value.
103     * @see #getScope()
104     * @see #isTypeSubstituted()
105     */
106    public JAXBElement(QName name,
107                       Class<T> declaredType,
108                       Class scope,
109                       T value) {
110        if(declaredType==null || name==null)
111            throw new IllegalArgumentException();
112        this.declaredType = declaredType;
113        if(scope==null)     scope = GlobalScope.class;
114        this.scope = scope;
115        this.name = name;
116        setValue(value);
117    }
118
119    /**
120     * Construct an xml element instance.
121     *
122     * This is just a convenience method for {@code new JAXBElement(name,declaredType,GlobalScope.class,value)}
123     */
124    public JAXBElement(QName name, Class<T> declaredType, T value ) {
125        this(name,declaredType,GlobalScope.class,value);
126    }
127
128    /**
129     * Returns the Java binding of the xml element declaration's type attribute.
130     */
131    public Class<T> getDeclaredType() {
132        return declaredType;
133    }
134
135    /**
136     * Returns the xml element tag name.
137     */
138    public QName getName() {
139        return name;
140    }
141
142    /**
143     * <p>Set the content model and attributes of this xml element.</p>
144     *
145     * <p>When this property is set to {@code null}, {@code isNil()} must by {@code true}.
146     *    Details of constraint are described at {@link #isNil()}.</p>
147     *
148     * @see #isTypeSubstituted()
149     */
150    public void setValue(T t) {
151        this.value = t;
152    }
153
154    /**
155     * <p>Return the content model and attribute values for this element.</p>
156     *
157     * <p>See {@link #isNil()} for a description of a property constraint when
158     * this value is {@code null}</p>
159     */
160    public T getValue() {
161        return value;
162    }
163
164    /**
165     * Returns scope of xml element declaration.
166     *
167     * @see #isGlobalScope()
168     * @return {@code GlobalScope.class} if this element is of global scope.
169     */
170    public Class getScope() {
171        return scope;
172    }
173
174    /**
175     * <p>Returns {@code true} iff this element instance content model
176     * is nil.</p>
177     *
178     * <p>This property always returns {@code true} when {@link #getValue()} is null.
179     * Note that the converse is not true, when this property is {@code true},
180     * {@link #getValue()} can contain a non-null value for attribute(s). It is
181     * valid for a nil xml element to have attribute(s).</p>
182     */
183    public boolean isNil() {
184        return (value == null) || nil;
185    }
186
187    /**
188     * <p>Set whether this element has nil content.</p>
189     *
190     * @see #isNil()
191     */
192    public void setNil(boolean value) {
193        this.nil = value;
194    }
195
196    /* Convenience methods
197     * (Not necessary but they do unambiguously conceptualize
198     *  the rationale behind this class' fields.)
199     */
200
201    /**
202     * Returns true iff this xml element declaration is global.
203     */
204    public boolean isGlobalScope() {
205        return this.scope == GlobalScope.class;
206    }
207
208    /**
209     * Returns true iff this xml element instance's value has a different
210     * type than xml element declaration's declared type.
211     */
212    public boolean isTypeSubstituted() {
213        if(value==null)     return false;
214        return value.getClass() != declaredType;
215    }
216
217    private static final long serialVersionUID = 1L;
218}
219