1. JAXB Overview
Vladimir Gapeyev

2. XML data binding Java: XML: ObjectFactory f = <book>
new ObjectFactory();
Book b = f.createBook();
b.setTitle(“Compilers”);
List a = b.getAuthor();
a.add(“Aho”);
a.add(“Sethi”);
a.add(“Ullman”);
b.setPages(796);
<book>
<title>Compilers</title>
<author>Aho</author>
<author>Sethi</author>
<author>Ullman</author>
<pages>796</pages>
</book>
12/5/2018
JAXB Overview

3. Schema-based XML data binding
compile
Schema
Classes
instance of
conforms
unmarshal
Objects
Documents
marshal
12/5/2018
JAXB Overview

4. JAXB: Java Architecture for XML Binding
Specification:
Subset of XML Schema
Default bindings
XML names  Java names
Schema atomic types  predefined Java types
Schema structured types  Java interfaces
javax.xml.bind – framework interfaces
Language for binding customization
Reference implementation:
Schema-to-Java compliler
Generates classes as well
12/5/2018
JAXB Overview

5. Mapping for atomic types
xs:string 
java.lang.string
xs:decimal
java.math.BigDecimal
xs:int
int
xs:QName
javax.xml.namespace.QName
xs:date
java.util.Calendar
Etc…
12/5/2018
JAXB Overview

6. Elements with simple content
interface Zip extends
javax.xml.bind.Element {
int getValue();
void setValue(int); }
<xs:element name=“zip”
type=“xs:int” />
12/5/2018
JAXB Overview

7. Elements with sequence and repetition
<xs:element name=“book” >
<xs:ComplexType>
<xs:sequence>
<xs:element name=“title”
type=“xs:string”/>
<xs:element name=“author”
type=“xs:string”
maxOccurs=“unbounded”/>
<xs:element name=“pages”
type=“xs:int”/>
</xs:sequence>
</xs:ComplexType>
</xs:element>
interface Book extends
BookType,
javax.xml.bind.Element {}
interface BookType {
String getTitile();
void setTitle(String x);
List getAuthor();
int getPages();
void setPages(int x); }
12/5/2018
JAXB Overview

8. Elements with choice <xs:complexType name=“volume”>
<xs:choice>
<xs:element
ref=“book”/>
ref=“journal”/>
</xs:choice>
</xs:complexType>
interface Volume {
BookType getBook();
void setBook(BookType);
JournalType getJournal();
void setJournal(JournalType); }
12/5/2018
JAXB Overview

9. Customization: isSet() method
<xs:annotation><xs:appinfo>
<jxb:globalBindings generateIsSetMethod=“true"/>
</xs:appinfo></xs:annotation>
<xs:complexType
name=“volume”>
<xs:choice>
<xs:element
ref=“book”/>
ref=“journal”/>
</xs:choice>
</xs:complexType>
interface Volume {
BookType getBook();
void setBook(BookType);
boolean isSetBook();
JournalType getJournal();
void setJournal(JournalType);
boolean isSetJournal(); }
12/5/2018
JAXB Overview

10. No roundtripping interface T { type t { getA(); setA();
getB(); setB(); }
type t {
(element a, element b) |
(element b, element a) }
Type t members: <a/><b/> and <b/><a/>
unmarshal; marshal =/= identity
unmarshal; marshal; unmarshal = unmarshal
12/5/2018
JAXB Overview

11. “General content style”
<xs:complexType name=“t”>
<xs:choice
maxOccurs=“unbounded”>
<element ref=“book”/>
<element ref=“journal”/>
</xs:choice>
</xs:complexType>
interface T {
List getBookOrJournal() }
Plus a constraint:
The only list members are
Book objects
Journal objects
12/5/2018
JAXB Overview

12. Model groups, by default
<xs:group name="bookName">
<xs:sequence>
<xs:element name="title"
type="xs:string"/>
<xs:element name="author"
type="xs:string“/>
</xs:sequence>
</xs:group>
<xs:complexType name="bookType">
<xs:group ref="bookName"/>
<xs:element name="pages"
type="xs:int"/>
</xs:complexType>
interface BookType {
String getTitle();
void setTitle(String x);
String getAuthor();
void setAuthor(String);
int getPages();
void setPages(int x); }
12/5/2018
JAXB Overview

13. Model groups, customized
<xs:group name="bookName">
<xs:sequence>
<xs:element name="title"
type="xs:string"/>
<xs:element name="author"
type="xs:string“/>
</xs:sequence>
</xs:group>
<xs:complexType name="bookType">
<xs:group ref="bookName"/>
<xs:element name="pages"
type="xs:int"/>
</xs:complexType>
interface BookName {
String getTitle();
void setTitle(String x);
String getAuthor();
void setAuthor(String); }
interface BookType {
BookName getBookName();
void setBookName(BookName);
int getPages();
void setPages(int x);
12/5/2018
JAXB Overview

14. Summary of observations
Mapping often loses static typing information – need to employ dynamic constraints
Complex content models with choice are most problematic
Alternative mapping styles
No good declarative specifications for the mappings
12/5/2018
JAXB Overview

15. Opportunities Formal specification of mapping styles
Formulate desired mapping properties
Verify that the mapping styles enjoy the properties
A toolkit for generating mapping compilers (as opposed to a single compiler)
12/5/2018
JAXB Overview