JAXB objects initialized with default values

问题

There is little problem with JAXB.

Given:

Java 1.5; jaxb -jars from jaxws-2_0.
.xsd scheme and generated JAXB classes.
Every simple element in .xsd has default value. And as result class members has annotations like "@XmlElement(name = "cl_fname", required = true, defaultValue = "[______]")"

Required

Get java object (root element) which fully represent xml and every member initialized by default values.

when I try to marshall xml without explicitly setting values, default values doesn't make sence... is there any way to marshall xml populated with default values without customization of generated classes?

example of .xsd:

<xs:element name="document">
    <xs:complexType>
        <xs:sequence>
            <xs:element ref="d_int"/>
            <xs:element ref="d_double"/>
            <xs:element ref="d_string"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>

<xs:element name="d_int" type="xs:int" default="-1"/>
<xs:element name="d_double" type="xs:double" default="-1.0"/>
<xs:element name="d_string" type="xs:string" default="false"/>

and java class:

public class Document {
    @XmlElement(name = "d_int", defaultValue = "-1")
    protected int dInt;
    @XmlElement(name = "d_double", defaultValue = "-1.0")
    protected double dDouble;
    @XmlElement(name = "d_string", required = true, defaultValue = "Default")
    protected String dString;
...
}

回答1:

default value that is in annotations works only after unmarshalling.
unmarshal this

<document>
   <d_int/>
   <d_double/>
   <d_string/>
</document>

and you will get object with default values (-1, -1.0, "Default")

If you want set default values to marshalling, you should do this

public class Document {
    @XmlElement(name = "d_int", defaultValue = "-1")
    protected int dInt = 100;
    @XmlElement(name = "d_double", defaultValue = "-1.0")
    protected double dDouble = -100;
    @XmlElement(name = "d_string", required = true, defaultValue = "Default")
    protected String dString = "def";
...
}

jaxb generate default values only for unmarshalling

回答2:

For an initialization of the class members from XSD supplied defaults, you can use the default-value-plugin of XJC.

See the website of the plugin.

Note that the ant task definition as explained in that documentation did not work for me. As explained here, the class paths for XJC and the plugin have to be separated. Specifying the path to the plugin when calling it works for me:

<xjc schema="some.xsd" >
    <arg value="-Xdefault-value"/>
    <classpath>
        <pathelement location="lib/xjc-plugins/jaxb2-default-value-1.1.jar"/>
    </classpath>
</xjc>

来源：https://stackoverflow.com/questions/12040826/jaxb-objects-initialized-with-default-values

标签

jaxb

xsd

default-value