This is a presentation about XStream, the lightweight and easy-to-use open source Java™ library, used for serializing java objects into XML and de-serializing XML back into java objects.

1. Presented by
Angelin

2.  Lightweightand easy-to-use open source
Java™ library
 Usedfor serializing java objects into XML and
de-serializing XML back into java objects
 Usesreflection API for serialization and
deserialization

3.  xstream-[version].jarand xpp3-[version].jar
are required in the classpath.
 Instantiate
the XStream class:
XStream xstream = new XStream();

4.  To Serialize an object to a XML String use:
xstream.toXML(Object obj);
 ToDeserialize an object from an XML String
use:
xstream.fromXML(String xml);

5. import com.thoughtworks.xstream.XStream;
public class HelloWorld {
public static void main(String[] args) {
XStream xstream = new XStream();
String salutation = "Hello, World!";
String xml = xstream.toXML(salutation);
System.out.print(xml);
}
}
Output
<string>Hello, World!</string>

10. Output
<com.example.Person>
<name>Joe</name>
<age>23</age>
<phone>
<code>123</code>
<number>123456</number>
</phone>
<fax>
<code>123</code>
<number>112233</number>
</fax>
</com.example.Person>
Name: Joe
Age: 23
Phone:123-123456
Fax:123-112233

11.  Syntax: xstream.useAttributeFor(Class definedIn, String fieldName);

12.  Aliasingenables us to use different tag or
attribute names in the generated XML.
 The different types of aliasing that Xstream
supports are:
 Class aliasing
 Field aliasing
 Attribute aliasing
 Package aliasing
 Omitting fields and root tag of collection

13.  Xstream default serialization nature:
fully qualified class name <> element name
corresponding to the class
 Use Class Aliasing to get the class name
(without the package name) as the XML
element name
 To create alias for any class' name, use
xstream.alias(String alias, Class clsname);

14.  Syntax:
xstream.alias(String alias, Class clsName);
 Example:
xstream.alias(“Person", Person.class);
Before Class Aliasing After Class Aliasing
<com.example.Person> <Person>
<name>Joe</name> <name>Joe</name>
<age>23</age> <age>23</age>
<phone> <phone>
<code>123</code> <code>123</code>
<number>123456</number> <number>123456</number>
</phone> </phone>
<fax> <fax>
<code>123</code> <code>123</code>
<number>112233</number> <number>112233</number>
</fax> </fax>
</com.example.Person> </Person>

15.  Syntax:
xstream.aliasField(String alias, Class definedIn, String fieldName);
 Example:
xstream.aliasField("Name", Person.class, "name");
Before Field Aliasing After Field Aliasing
<Person> <Person>
<name>Joe</name> <Name>Joe</Name>
<age>23</age> <age>23</age>
<phone> <phone>
<code>123</code> <code>123</code>
<number>123456</number> <number>123456</number>
</phone> </phone>
<fax> <fax>
<code>123</code> <code>123</code>
<number>112233</number> <number>112233</number>
</fax> </fax>
</Person> </Person>

16.  Syntax:
xstream.aliasAttribute(Class definedIn, String fieldName, String
alias); // makes field as attribute and sets an alias name for it
 Example:
xstream.aliasAttribute(PhoneNumber.class, "code", "AreaCode");
xstream.aliasAttribute(PhoneNumber.class, "number", "Number");
Before Attribute Aliasing After Attribute Aliasing
<Person> <Person>
<name>Joe</name> <Name>Joe</Name>
<age>23</age> <age>23</age>
<phone> <phone AreaCode="123" Number="123456"/>
<code>123</code> <fax AreaCode="123" Number="112233"/>
<number>123456</number> </Person>
</phone>
<fax>
<code>123</code>
<number>112233</number>
</fax>
</Person>

17. xstream.aliasAttribute(PhoneNumber.class, "code", "AreaCode");
xstream.aliasAttribute(PhoneNumber.class, "number", "Number");
Is equivalent to
xstream.useAttributeFor(PhoneNumber.class, "code");
xstream.aliasField("AreaCode", PhoneNumber.class, "code");
xstream.useAttributeFor(PhoneNumber.class, "number");
xstream.aliasField("Number", PhoneNumber.class, "number");

18.  Syntax:
xstream.aliasPackage(String alias, String packageName);
 Example:
xstream.aliasPackage("my.company", "com.example");
Before Field Aliasing After Field Aliasing
<com.example.Person> <my.company.Person>
<name>Joe</name> <name>Joe</name>
<age>23</age> <age>23</age>
<phone> <phone>
<code>123</code> <code>123</code>
<number>123456</number> <number>123456</number>
</phone> </phone>
<fax> <fax>
<code>123</code> <code>123</code>
<number>112233</number> <number>112233</number>
</fax> </fax>
</com.example.Person> </my.company.Person>

19.  Syntax:
xstream.omitField(Class definedIn, String fieldName);

23.  Syntax:
xstream.addImplicitCollection(Class definedIn, String collectionName);

25.  For converting particular types of objects
found in the object graph, to and from XML.
 Xstream provides converters for primitives,
String, File, Collections, arrays, and Dates.
 Types:
 Converters for converting common basic types in
Java into a single String, with no nested
elements
 Converters for converting items in collections
such as arrays, Lists, Sets and Maps into nested
elements

29.  To customize the information being serialized
or deserialized.
 They can be implemented and registered
using the
XStream.registerConverter() method
 Converters for objects that can store all
information in a single value should
implement SingleValueConverter.

34.  Annotations simplify the process of setting aliases and
registering converters etc.
 Annotations do not provide more functionality, but may
improve convenience.
Annotation Types Description
@XStreamAlias Annotation used to define an XStream class or
field value.
@XStreamAsAttribute Defines that a field should be serialized as an
attribute.
@XStreamConverter Annotation to declare a converter.
@XStreamImplicit An annotation for marking a field as an
implicit collection.
@XStreamInclude Annotation to force automated processing of
further classes.
@XStreamOmitField Declares a field to be omitted.

35.  processAnnotation() method to configure
Xstream to process annotations defined in
classes
 All super types, implemented interfaces, the
class types of the members and all their generic
types will be processed.
 For e.g. the statement
xstream.processAnnotations(Person.class);
will also process the annotations of its member
of type Company. So there is no need to
explicitly configure processAnnotation() for the
class Company.

36.  XStream can also be run in a lazy mode,
where it auto-detects the annotations while
processing the object graph and configures
the XStream instance on-the-fly.
 Example:
XStream xstream = new XStream() {
{
autodetectAnnotations(true);
}
};

37. Implications of using autodetectAnnotations
 Deserialization will fail if the type has not
already been processed either by having called
XStream's processAnnotations method or by
already having serialized this type. However,
@XStreamAlias is the only annotation that may
fail in this case
 May cause thread-unsafe operation
 will slow down the marshalling process until all
processed types have been examined once.

38.  Annotation used to define an XStream class or field value.
Xstream method Equivalent Xstream
Annotation
xstream.alias("Person", Person.class); @XStreamAlias("Person")
public class Person {
...
...
}

39.  Defines that a field should be serialized as an attribute.
Xstream method Equivalent Xstream
Annotation
xstream.aliasAttribute(Person.class, @XStreamAlias("Person")
"company", "Company"); public class Person {
...
...
@XStreamAsAttribute
@XStreamAlias("Company")
private Company company;
...
...
}

40.  Annotation to declare a converter.
Xstream method Equivalent Xstream Annotation
xstream.registerConverter(new @XStreamConverter(CompanyConverter.class)
CompanyConverter()); public class Company {
...
}
 To register the custom converter locally, i.e. only for the
member variable company defined in the Person class
Xstream method Equivalent Xstream Annotation
xstream.registerConverter(new @XStreamAlias("Person")
CompanyConverter()); public class Person {
...
@XStreamAsAttribute
@XstreamAlias("Company")
@XStreamConverter(CompanyConverter.class)
private Company company;
...
}

41.  An annotation for marking a field as an implicit collection.
Xstream method Equivalent Xstream Annotation
xstream.addImplicitCollection(Cu @XStreamAlias("Customers")
stomers.class, "customers"); public class Customers {
@XStreamImplicit
private List customers;
...
...
}

42.  Declares a field to be omitted.
Xstream method Equivalent Xstream Annotation
xstream.omitField(Person.class, @XStreamAlias("Person")
"phone"); public class Person {
...
@XStreamOmitField
private PhoneNumber phone;
@XStreamOmitField
private PhoneNumber fax;
...
}

43.  Used by base classes to improve annotation processing when
deserializing.
 Example:

44.  Annotation processing using autodetectAnnotations

45.  Annotation processing using processAnnotations