35.2. Attributes
Overview
Apache CXF supports the use of
attribute elements and attributeGroup elements within the scope of a complexType element. When defining structures for an XML document attribute declarations provide a means of adding information that is specified within the tag, not the value that the tag contains. For example, when describing the XML element <value currency="euro">410<\value> in XML Schema the currency attribute is described using an attribute element as shown in Example 35.5, “XML Schema Defining and Attribute”.
The
attributeGroup element allows you to define a group of reusable attributes that can be referenced by all complex types defined by the schema. For example, if you are defining a series of elements that all use the attributes category and pubDate, you could define an attribute group with these attributes and reference them in all the elements that use them. This is shown in Example 35.7, “Attribute Group Definition”.
When describing data types for use in developing application logic, attributes whose
use attribute is set to either optional or required are treated as elements of a structure. For each attribute declaration contained within a complex type description, an element is generated in the class for the attribute, along with the appropriate getter and setter methods.
Defining an attribute in XML Schema
An XML Schema
attribute element has one required attribute, name, that is used to identify the attribute. It also has four optional attributes that are described in Table 35.2, “Optional Attributes Used to Define Attributes in XML Schema”.
| Attribute | Description |
|---|---|
use | Specifies if the attribute is required. Valid values are required, optional, or prohibited. optional is the default value. |
type | Specifies the type of value the attribute can take. If it is not used the schema type of the attribute must be defined in-line. |
default | Specifies a default value to use for the attribute. It is only used when the attribute element's use attribute is set to optional. |
fixed | Specifies a fixed value to use for the attribute. It is only used when the attribute element's use attribute is set to optional. |
Example 35.5, “XML Schema Defining and Attribute” shows an attribute element defining an attribute, currency, whose value is a string.
Example 35.5. XML Schema Defining and Attribute
<element name="value">
<complexType>
<xsd:simpleContent>
<xsd:extension base="xsd:integer">
<xsd:attribute name="currency" type="xsd:string"
use="required"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
</xsd:element>
If the
type attribute is omitted from the attribute element, the format of the data must be described in-line. Example 35.6, “Attribute with an In-Line Data Description” shows an attribute element for an attribute, category, that can take the values autobiography, non-fiction, or fiction.
Example 35.6. Attribute with an In-Line Data Description
<attribute name="category" use="required">
<simpleType>
<restriction base="xsd:string">
<enumeration value="autobiography"/>
<enumeration value="non-fiction"/>
<enumeration value="fiction"/>
</restriction>
</simpleType>
</attribute>Using an attribute group in XML Schema
Using an attribute group in a complex type definition is a two step process:
- Define the attribute group.An attribute group is defined using an
attributeGroupelement with a number ofattributechild elements. TheattributeGrouprequires anameattribute that defines the string used to refer to the attribute group. Theattributeelements define the members of the attribute group and are specified as shown in the section called “Defining an attribute in XML Schema”. Example 35.7, “Attribute Group Definition” shows the description of the attribute groupcatalogIndecies. The attribute group has two members:category, which is optional, andpubDate, which is required.Example 35.7. Attribute Group Definition
<attributeGroup name="catalogIndices"> <attribute name="category" type="catagoryType" /> <attribute name="pubDate" type="dateTime" use="required" /> </attributeGroup> - Use the attribute group in the definition of a complex type.You use attribute groups in complex type definitions by using the
attributeGroupelement with therefattribute. The value of therefattribute is the name given the attribute group that you want to use as part of the type definition. For example if you want to use the attribute groupcatalogIndeciesin the complex type dvdType, you would use <attributeGroup ref="catalogIndecies" /> as shown in Example 35.8, “Complex Type with an Attribute Group”.Example 35.8. Complex Type with an Attribute Group
<complexType name="dvdType"> <sequence> <element name="title" type="xsd:string" /> <element name="director" type="xsd:string" /> <element name="numCopies" type="xsd:int" /> </sequence> <attributeGroup ref="catalogIndices" /> </complexType>
Mapping attributes to Java
Attributes are mapped to Java in much the same way that member elements are mapped to Java. Required attributes and optional attributes are mapped to member variables in the generated Java class. The member variables are decorated with the
@XmlAttribute annotation. If the attribute is required, the @XmlAttribute annotation's required property is set to true.
The complex type defined in Example 35.9, “techDoc Description ” is mapped to the Java class shown in Example 35.10, “techDoc Java Class”.
Example 35.9. techDoc Description
<complexType name="techDoc">
<all>
<element name="product" type="xsd:string" />
<element name="version" type="xsd:short" />
</all>
<attribute name="usefullness" type="xsd:float"
use="optional" default="0.01" />
</complexType>Example 35.10. techDoc Java Class
@XmlType(name = "techDoc", propOrder = {
})
public class TechDoc {
@XmlElement(required = true)
protected String product;
protected short version;
@XmlAttribute
protected Float usefullness;
public String getProduct() {
return product;
}
public void setProduct(String value) {
this.product = value;
}
public short getVersion() {
return version;
}
public void setVersion(short value) {
this.version = value;
}
public float getUsefullness() {
if (usefullness == null) {
return 0.01F;
} else {
return usefullness;
}
}
public void setUsefullness(Float value) {
this.usefullness = value;
}
}
As shown in Example 35.10, “techDoc Java Class”, the
default attribute and the fixed attribute instruct the code generators to add code to the getter method generated for the attribute. This additional code ensures that the specified value is returned if no value is set.
Important
The
fixed attribute is treated the same as the default attribute. If you want the fixed attribute to be treated as a Java constant you can use the customization described in Section 38.5, “Customizing Fixed Value Attribute Mapping”.
Mapping attribute groups to Java
Attribute groups are mapped to Java as if the members of the group were explicitly used in the type definition. If the attribute group has three members, and it is used in a complex type, the generated class for that type will include a member variable, along with the getter and setter methods, for each member of the attribute group. For example, the complex type defined in Example 35.8, “Complex Type with an Attribute Group”, Apache CXF generates a class containing the member variables
category and pubDate to support the members of the attribute group as shown in Example 35.11, “dvdType Java Class”.
Example 35.11. dvdType Java Class
@XmlType(name = "dvdType", propOrder = {
"title",
"director",
"numCopies"
})
public class DvdType {
@XmlElement(required = true)
protected String title;
@XmlElement(required = true)
protected String director;
protected int numCopies;
@XmlAttribute
protected CatagoryType category;
@XmlAttribute(required = true)
@XmlSchemaType(name = "dateTime")
protected XMLGregorianCalendar pubDate;
public String getTitle() {
return title;
}
public void setTitle(String value) {
this.title = value;
}
public String getDirector() {
return director;
}
public void setDirector(String value) {
this.director = value;
}
public int getNumCopies() {
return numCopies;
}
public void setNumCopies(int value) {
this.numCopies = value;
}
public CatagoryType getCatagory() {
return catagory;
}
public void setCatagory(CatagoryType value) {
this.catagory = value;
}
public XMLGregorianCalendar getPubDate() {
return pubDate;
}
public void setPubDate(XMLGregorianCalendar value) {
this.pubDate = value;
}
}