introsde-2016-assignment-1

TASK

This first assignment is divided in two main parts. The first part is based on the third laboratory session. In particular, it was required to work with XPath, a query language that uses path expressions to navigate the XML and queries information inside them. This first part is moreover divided in four points.

For the first point it is necessary to use XPath to implement method getWeight(personID) and getHeight(personID), which return weight (or height) of a person with that ID. Instead, make a function printAll() that prints all people in the database.xml with detail.

The database.xml file contains 20 person and has the following structure:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<people>
	<person id="1">
        	<firstname>George R. R.</firstname>
        	<lastname>Martin</lastname>
        	<birthdate>1984-09-20T18:00:00.000+02:00</birthdate>
        	<healthprofile>
            		<lastupdate>2014-09-20T18:00:00.000+02:00</lastupdate>
            		<weight>90</weight>
            		<height>1.70</height>
            		<bmi>31.14</bmi>
        	</healthprofile>
    	</person>
    ....   
</people>   

The third point concerns a function printHealthProfile(personID) that accepts an ID as parameter and prints the HealthProfile of the person with that ID. Finally, it is needed another function printPersonFromWeight(weight, operator) which accepts a weight and an operator (=, > or <) as parameters and prints people that fulfill that condition.

On the other hand, the second part of the assignment is based on the forth laboratory session. This second part is about JAXB which allows to map XML to Java Classes. In particular, the first step concerns the creation of an person.xsd file (XML schema) from the XML document database.xml. Through this XSD file is possible to automatically generate four classes thanks to the Java compiler XJC. The classes, which will be generated in peoplestore.generated package, are HealthprofileType.java, ObjectFactory.java, PeopleType.java and PersonType.java.

These classes are necessary to do the marshalling to XML and the unmarshalling from XML. The XMLMarshaller.java class handles the marshalling to XML, printing the content and saving it to people.xml file. The XMLUnMarshaller.java class handles the unmarshalling from people.xml.

Moreover, they can be used also for marshalling to JSON thanks to MOXy library. Marshalling to people.json is done by the JSONMarshaller.java class.

After completing these two parts of the assignment, it is necessary create a target in the build.xml file execute.evaluation which:

1. runs printAll()
2. runs printHealthProfile(personID) with ID = 5
3. runs printPersonFromWeight(weight, operator) with weight > 90
4. runs XMLMarshaller, it creates 3 persons using java and marshals them to XML, printing the content and saving to people.xml file
5. runs XMLUnMarshaller, un-marshaling from people.xml
6. runs JSONMarshaller, it creates 3 persons using java and marshals them to JSON, printing the content and saving to people.json file.

CODE

XPathAdvance

The first part of the assignment has been implemented in the XPathAdvance.java class, which is based on the XPathTestAdvance seen in laboratory. Besides loading the database.xml file, the XPathAdvance class contains getWeight(personID), getHeight(personID), printAll(), printHealthProfile(personID) and printPersonFromWeight(weight, operator) methods. These methods work in almost the same way.

For example, this is the printPersonFromWeight(weight, operator) method:

public void printPersonFromWeight(int weight, String operator) throws XPathExpressionException {
		XPathExpression expr = xpath
				.compile("/people/person/healthprofile[weight" + operator + "" + weight + "]/parent::person");
		NodeList nodes = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
		System.out.println("People with weight " + operator + " " + weight + "Kg:");
		for (int i = 0; i < nodes.getLength(); i++) {
			System.out.println(nodes.item(i).getTextContent());
		}
}

The method evaluates the compiled XPath expression in database.xml and returns the result in a list of node. Later, it prints the result.

For the second part of the assign three different classes were used: XMLMarshaller, XMLUnMarshaller and JSONMarshaller. To work correctly, these classes need the classes generated from people.xsd using XJC.

XMLMarshaller

The XMLMarshaller instantiates a new JAXB Context. After that, it creates a new marshaller using the JAXB Context and set its properties.

// Create a JaxBContext
JAXBContext jaxbContext = JAXBContext.newInstance("peoplestore.generated");
// Create the Marshaller Object using the JaxB Context
Marshaller marshaller = jaxbContext.createMarshaller();
// Set it to true if you need the XML output to formatted
marshaller.setProperty("jaxb.formatted.output", new Boolean(true));

Now, people can be created through the generated classes using java.

ObjectFactory factory = new ObjectFactory();

PeopleType people = factory.createPeopleType();

PersonType person = factory.createPersonType();
List<PersonType> personList = people.getPerson();
			
XMLGregorianCalendar randomBirthdate = DatatypeFactory.newInstance().newXMLGregorianCalendar(randomBirthdate());
person.setBirthdate(randomBirthdate);
person.setFirstname("Daniele");
person.setId(1);
person.setLastname("Dellagiacoma");
HealthprofileType healthprofile = factory.createHealthprofileType();
			
GregorianCalendar c = new GregorianCalendar();
c.setTime(new Date());
XMLGregorianCalendar lastupdate = DatatypeFactory.newInstance().newXMLGregorianCalendar(c);
healthprofile.setLastupdate(lastupdate);
healthprofile.setHeight(1.80);
healthprofile.setWeight(70);
healthprofile.setBmi(healthprofile.getWeight()/(Math.pow(healthprofile.getHeight(), 2)));

person.setHealthprofile(healthprofile);

personList.add(person);

Finally, a JAXB Element of type People is created and used to print the content and save it to people.xml file.

JAXBElement<PeopleType> peopleElement = factory.createPeople(people);
// Marshal the People object to XML and print the output to console
marshaller.marshal(peopleElement, System.out);
// Marshal the People object to XML and write the output to the people.xml file
marshaller.marshal(peopleElement, new FileOutputStream(xmlDocument));

JSONMarshaller

The JSONMarshaller is the same as XMLMarshaller, except that it uses MOXy library to format the otput object as a json. It do that setting the MarshallerProperties in this way:

// Set the Marshaller media type to JSON
marshaller.setProperty(MarshallerProperties.MEDIA_TYPE, "application/json");
// Set it to true if you need to include the JSON root element in the JSON output
marshaller.setProperty(MarshallerProperties.JSON_INCLUDE_ROOT, true);

For this reason is necessary to enable MOXy at the beginning

//enables MOXy
System.setProperty("javax.xml.bind.context.factory", "org.eclipse.persistence.jaxb.JAXBContextFactory");

XMLUnMarshaller

On the other hand, the XMLUnMarshaller create an JAXB context and the UnMarshaller object using the context. After that, it uses people.xsd schema to validate subsequent unmarshal operations.

// Create a JaxBContext
JAXBContext jaxbContext = JAXBContext.newInstance("peoplestore.generated");
// Create the Unmarshaller Object using the JaxB Context
Unmarshaller unMarshaller = jaxbContext.createUnmarshaller();
SchemaFactory schemaFactory = SchemaFactory.newInstance("http://www.w3.org/2001/XMLSchema");
Schema schema = schemaFactory.newSchema(new File("people.xsd"));
unMarshaller.setSchema(schema);

Now, it can use a People element to get the value of each person in the file people.xml.

JAXBElement<PeopleType> peopleElement = (JAXBElement<PeopleType>) unMarshaller.unmarshal(xmlDocument);

//Create root object type from the JAXBElement object using its getValue() method
PeopleType people = peopleElement.getValue();

Finally, it prints all the person in people.xml and their information.

DEPLOYMENT

First of all, it is necessary to run the following command on terminal window in the folder where the build.xml file is:

ant compile

This instruction will download ivy.jar into ivy folder, and all libraries that are specified in ivi.xml fil will be downloaded into lib folder. Moreover, the target generate creates the folder bookstore/generated with four classes in it (HealthprofileType, ObjectFactory, PeopleType and PersonType).

After that, the following command can be used to run all the instructions described above.

ant execute.evaluation

The build.xml file has been implemented modifying the build.xml used during the forth laboratory.