Working with XML

Working with XML
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In this section we'll show how to create XML from the beans generated earlier. XML (or better an XML document) exists in various flavours: you might want to have it serialized into a String or you may prefer character or byte streams (typically instances of Writer or OutputStream). In other cases, a DOM representation is more useful. Feeding SAX events to a pipeline may be more efficient on other occasions.

The important questions are: how do I create a serialized XML document (a String, a character or byte stream)? And, vice versa, how do I read such a document and convert it back into Java objects?

Writing XML Documents

In the case of JaxMe, you'll start from simple Java beans whose source has typically been generated. An address implementation is constructed by instantiating an AddressImpl (which implements Address). For example:

import java.io.FileWriter;
import java.io.Writer;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;

import org.apache.ws.jaxme.examples.misc.address.Address;
import org.apache.ws.jaxme.examples.misc.address.AddressType.EmailDetailsType.EmailType;
import org.apache.ws.jaxme.examples.misc.address.AddressType.PhoneDetailsType.PhoneType;
import org.apache.ws.jaxme.examples.misc.address.impl.AddressImpl;
import org.apache.ws.jaxme.examples.misc.address.impl.AddressTypeImpl.EmailDetailsTypeImpl;
import org.apache.ws.jaxme.examples.misc.address.impl.AddressTypeImpl.EmailDetailsTypeImpl.EmailTypeImpl;
import org.apache.ws.jaxme.examples.misc.address.impl.AddressTypeImpl.PhoneDetailsTypeImpl;
import org.apache.ws.jaxme.examples.misc.address.impl.AddressTypeImpl.PhoneDetailsTypeImpl.PhoneTypeImpl;
import org.apache.ws.jaxme.examples.misc.address.impl.AddressTypeImpl.NameTypeImpl;
import org.apache.ws.jaxme.examples.misc.address.impl.AddressTypeImpl.PostalTypeImpl;

public class AddressCreator {

  public static void writeAddress(Writer pWriter) throws JAXBException {
    // Create the element:
    Address addr = new AddressImpl();
    addr.setName(new NameTypeImpl());
    addr.getName().setFirst("Jane");
    addr.getName().setLast("Doe");
    addr.setPostal(new PostalTypeImpl());
    addr.getPostal().setStreet("34 Main Street");
    addr.getPostal().setCity("Boston");
    addr.getPostal().setState("MA");
    addr.getPostal().setZIP("02215");
    addr.setEmailDetails(new EmailDetailsTypeImpl());

    /* Lots of similar lines omitted for brevity ...
     * ...
     */

    // And save it into the file "Address.xml"
    JAXBContext context = JAXBContext.newInstance("org.apache.ws.jaxme.examples.misc.address");
    Marshaller marshaller = context.createMarshaller();
    marshaller.marshal(addr, pWriter);
  }

  public static void main(String[] args) throws Exception {
    FileWriter fw = new FileWriter("Address.xml");
    writeAddress(fw);
    fw.close();
  }
}

The complete example code can be found in the JaxMe distribution (src/java/org/apache/ws/jaxme/examples/misc/address/AddressCreator.java).

There are several things you should note here:

The class and property names directly correspond to element and attribute names.
Although the Address document uses namespaces, attributes, and child elements, the example does not require that the developers have extensive knowledge of XML. For example, you do not need to care for character escaping. This is particularly useful when those without great knowledge of xml wish to develop code against an existing schema.
Complex child elements are java beans themselves, like the Address element. For example, this means that the Name element has to be instantiated.
To convert the object into an XML string, the JAXBContext and Marshaller are used. These objects are specified by JAXB. The example uses no JaxMe specific features and should run with any compliant JAXB implementation.

Reading XML

The example on writing XML was surprisingly simple. In fact, the only nasty part was creating the object, which requires invocation of lots of setters and getters. Quite opposed to the marshalling, which took place in three lines. And, as we soon will see: unmarshalling (the process of reading a document) is by no means more complex.

To demonstrate the unmarshalling process, we'll quote an example from the JaxMe distribution again. This time it's the file src/java/org/apache/ws/jaxme/examples/misc/address/AddressPrinter.java:

package org.apache.ws.jaxme.examples.misc.address;

import java.io.File;
import java.io.FileInputStream;
import java.io.StringWriter;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

import org.apache.ws.jaxme.examples.misc.address.Address;
import org.xml.sax.InputSource;


public class AddressPrinter {
  public static Address getAddress(InputSource pSource) throws JAXBException {
    JAXBContext context = JAXBContext.newInstance("org.apache.ws.jaxme.examples.misc.address");
    Unmarshaller unmarshaller = context.createUnmarshaller();
    return (Address) unmarshaller.unmarshal(pSource);
  }

  public static String getAddressAsString(Address pAddress) throws JAXBException {
    StringWriter sw = new StringWriter();
    JAXBContext context = JAXBContext.newInstance("org.apache.ws.jaxme.examples.misc.address");
    Marshaller marshaller = context.createMarshaller();
    marshaller.marshal(pAddress, sw);
    return sw.toString();
  }

  public static void main(String[] args) throws Exception {
    File f = new File("Address.xml");
    InputSource isource = new InputSource(new FileInputStream(f));
    isource.setSystemId(f.toURL().toString());
    Address addr = getAddress(isource);

    // A simpler variant might be:
    // Address addr = unmarshaller.unmarshal(f);

    if (addr.getName() == null) {
      System.out.println("Loaded address without name.");
    } else {
      System.out.println("Loaded address " + addr.getName().getLast() +
                         ", " + addr.getName().getFirst() + ".");
    }
    System.out.println("Details:" + getAddressAsString(addr));
  }
}

How this example works:

It reads the file Address.xml. This is the very same file created in the first example. JaxMe supports true round-tripping.
An instance of InputSource is constructed. The InputSource is part of the SAX API and can be viewed as an abstract data source from which XML can be read. Typically, the InputSource will be backed by an InputStream or a Writer.
The method getAddress() is invoked to convert the XML document into an instance of Address. These are the promised three lines, again using classes and methods specified by JAXB.
Finally the method getAddressAsString is invoked to convert the Address instance back into a printable String, which we may use to verify that everything went fine. (It is always nice to see a result being displayed on the screen. :-)