Generate Java classes with JAXB from a DTD file - how can I modify the DTD?

Question

I want to generate Java classes from a dtd file using JAXB.

The dtd looks like this:

<!--Contents-->
    <!ELEMENT persons (header, content) >
    <!ELEMENT groups (header, content) >

<!--Header-->
    <!ELEMENT header (version) >
    <!ELEMENT version(#PCDATA) >

<!--Content-->
    <!ELEMENT content(person, group)* >

<!--Person-->
    <!ELEMENT person(p_id, p_name) >
    <!ELEMENT p_id (#PCDATA) >
    <!ELEMENT p_name (#PCDATA) >    

<!--Group-->
    <!ELEMENT group(g_id) >
    <!ELEMENT g_id(#PCDATA) >

When generating the classes with JAXB I get the following ones:

• ObjectFactory
• Content
• Person
• Persons
• Group
• Groups

In the Content class the method to retreive all the persons and groups is

public List<Object> getPersonOrGroup() {
    if (personOrGroup == null) {
        personOrGroup = new ArrayList<Object>();
    }
    return this.personOrGroup;
}

Is there anything I can change in the dtd file so the generation of Java classes will make the persons and groups separated in the Content java class, so to retreive all persons and groups would be to make a call to Content.getPersons() and Content.getGroups() respectivly?

Solution 1

In his response, mavrav seems to tell that it's impossible with DTD. I don't know well how to use DTD. But if you can, translate your DTD in XML schema.

I tried with this shema:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
        xmlns:hr="http://mycompany.com/schema"
        elementFormDefault="qualified"
        targetNamespace="http://mycompany.com/schema">
    <!-- Contents -->
    <xs:element name="persons">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="header" />
                <xs:element name="content" />
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:element name="groups">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="header" />
                <xs:element name="content" />
            </xs:sequence>
        </xs:complexType>
    </xs:element>

    <!-- Header -->
    <xs:element name="header">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="version" type="xs:string" />
            </xs:sequence>
        </xs:complexType>
    </xs:element>

    <!-- Content -->
    <xs:element name="content">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="person" maxOccurs="unbounded" />
                <xs:element name="group" maxOccurs="unbounded" />
            </xs:sequence>
        </xs:complexType>
    </xs:element>

    <!-- Person -->
    <xs:element name="person">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="p_id" type="xs:integer" />
                <xs:element name="p_name" type="xs:string" />
            </xs:sequence>
        </xs:complexType>
    </xs:element>

    <!-- Group -->
    <xs:element name="group">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="g_id" type="xs:integer" />
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

After I generated Java classes with the following cmd:

xjc -p com.mypackage schema.xsd

And it gives me the following code for the Content class:

@XmlRootElement(name = "content")
public class Content {

    @XmlElement(required = true)
    protected List<Object> person;
    @XmlElement(required = true)
    protected List<Object> group;

    public List<Object> getPerson() {
        if (person == null) {
            person = new ArrayList<Object>();
        }
        return this.person;
    }

    public List<Object> getGroup() {
        if (group == null) {
            group = new ArrayList<Object>();
        }
        return this.group;
    }
}

Solution 2

xjc -dtd -d generatedsrc -p com.examples log4j.dtd

will generate the classes in directory generatedsrc and the package used will be com.examples.

you can find more information here: http://www.javaworld.com/community/node/7622

Comments

[lpacheco]

I don't think that article answers @Rox question. His problem is that when generating the Java code from the DTD xjc creates a single List<Object> whenever an element can hold more than one type of data, mixing objects of different classes. I have the same problem. The article only explains how to generate Java code from DTD using xjc, and doesn't even mention this particular case.