JAXM Distributor Service

The JAXM distributor service and the Coffee Break have made arrangements regarding their exchange of XML documents. These arrangements include what kinds of messages they will send, the form of those messages, and what kind of JAXM messaging they will do. If they had agreed to do one-way messaging, they would also have had to use messaging providers that talk to each other and had to use the same profile. In this scenario, the parties have agreed to use request-response messaging, so a messaging provider is not needed.

All of the messages they send conform to an agreed-upon XML structure, which is specified in a DTD for each kind of message. This allows them to exchange messages even though they use different document formats internally.

The four kinds of messages exchanged by the Coffee Break server and the JAXM distributor are specified by the following DTDs:

request-prices.dtd

price-list.dtd

coffee-order.dtd

confirm.dtd

<INSTALL>/j2eetutorial/examples/cb/jaxm/dtds

The dtds directory also contains a sample of what the XML documents specified in the DTDs might look like. The corresponding XML files for each of the DTDs are as follows:

request-prices.xml

price-list.xml

coffee-order.xml

confirm.xml

Because of the DTDs, both parties know ahead of time what to expect in a particular kind of message and can therefore extract its content using the JAXM API.

<INSTALL>/j2eetutorial/examples/cb/jaxm/service

JAXM Service

The JAXM coffee distributor, the JAXM server in this scenario, provides the response part of the request-response paradigm. When JAXM messaging is being used, the server code is a servlet. The core part of each servlet is made up of three javax.servlet.HttpServlet methods: init, doPost, and onMessage. The init and doPost methods set up the response message, and the onMessage method gives the message its content.

Returning the Price List

This section takes you through the servlet PriceListServlet. This servlet creates the message with the current price list that is returned to the method call, invoked in PriceListRequest.

Any servlet extends a javax.servlet class. Being part of a Web application, this servlet extends HttpServlet. It first creates a static MessageFactory object that will be used later to create the SOAPMessage object that is returned. Then it declares the MessageFactory object msgFactory, which will be used to create a SOAPMessage object that has the headers and content of the original request message.

public class PriceListServlet extends HttpServlet { 
  MessageFactory msgFactory;

Every servlet has an init method. This init method initializes the servlet with the configuration information that the application server passed to it. Then it simply initializes msgFactory with the default implementation of the MessageFactory class.

public void init(ServletConfig servletConfig) 
                  throws ServletException { 
  super.init(servletConfig);
  try { 
    // Initialize it to the default.
    msgFactory = MessageFactory.newInstance();
  } catch (SOAPException ex) { 
    throw new ServletException(
      "Unable to create message factory" + ex.getMessage()); 
  } 
}

The next method defined in PriceListServlet is doPost, which does the real work of the servlet by calling the onMessage method. (The onMessage method is discussed later in this section.) the application server passes the doPost method two arguments. The first argument, the HttpServletRequest object req, holds the content of the message sent in PriceListRequest. The doPost method gets the content from req and puts it in the SOAPMessage object msg so that it can pass it to the onMessage method. The second argument, the HttpServletResponse object resp, will hold the message generated by executing the method onMessage.

In the following code fragment, doPost calls the methods getHeaders and putHeaders, defined immediately after doPost, to read and write the headers in req. It then gets the content of req as a stream and passes the headers and the input stream to the method MessageFactory.createMessage. The result is that the SOAPMessage object msg contains the request for a price list. Note that in this case, msg does not have any headers because the message sent in PriceListRequest did not have any headers.

public void doPost( HttpServletRequest req, HttpServletResponse
      resp) throws ServletException, IOException { 
  try { 
    // Get all the headers from the HTTP request. 
    MimeHeaders headers = getHeaders(req); 
    // Get the body of the HTTP request. 
    InputStream is = req.getInputStream(); 
    // Now internalize the contents of the HTTP request and 
    // create a SOAPMessage 
    SOAPMessage msg = msgFactory.createMessage(headers, is);

Next, the code declares the SOAPMessage object reply and populates it by calling the method onMessage.

    SOAPMessage reply = null;
    reply = onMessage(msg);

If reply has anything in it, its contents are saved, the status of resp is set to OK, and the headers and content of reply are written to resp. If reply is empty, the status of resp is set to indicate that there is no content.

    if (reply != null) { 
    // Need to call saveChanges because we're going to use the 
    // MimeHeaders to set HTTP response information. These 
    // MimeHeaders are generated as part of the save. 
      if (reply.saveRequired()) { 
        reply.saveChanges(); 
      } 
      resp.setStatus(HttpServletResponse.SC_OK); 
      putHeaders(reply.getMimeHeaders(), resp); 
      // Write out the message on the response stream. 
      OutputStream os = resp.getOutputStream(); 
      reply.writeTo(os); 
      os.flush(); 
    } else 
      resp.setStatus(HttpServletResponse.SC_NO_CONTENT); 
  } catch (Exception ex) { 
      throw new ServletException( "JAXM POST failed " +
                  ex.getMessage()); 
  } 
}

The methods getHeaders and putHeaders are not standard methods in a servlet the way init, doPost, and onMessage are. The method doPost calls getHeaders and passes it the HttpServletRequest object req that the application server passed to it. It returns a MimeHeaders object populated with the headers from req.

static MimeHeaders getHeaders(HttpServletRequest req) {

  Enumeration enum = req.getHeaderNames(); 
  MimeHeaders headers = new MimeHeaders(); 
  while (enum.hasMoreElements()) { 
    String headerName = (String)enum.nextElement(); 
    String headerValue = req.getHeader(headerName); 
    StringTokenizer values = new StringTokenizer(
                          headerValue, ","); 
    while (values.hasMoreTokens()) {
      headers.addHeader(headerName,
        values.nextToken().trim());
    }
  }

  return headers; 
}

The doPost method calls putHeaders and passes it the MimeHeaders object headers, which was returned by the method getHeaders. The method putHeaders writes the headers in headers to res, the second argument passed to it. The result is that res, the response that the application server will return to the method call, now contains the headers that were in the original request.

static void putHeaders(MimeHeaders headers,
                      HttpServletResponse res) {
  Iterator it = headers.getAllHeaders(); 
  while (it.hasNext()) { 
    MimeHeader header = (MimeHeader)it.next();
    String[] values = headers.getHeader(header.getName()); 
    if (values.length == 1) 
      res.setHeader(header.getName(),
      header.getValue()); 
    else { 
      StringBuffer concat = new StringBuffer(); 
      int i = 0; 
      while (i < values.length) { 
        if (i != 0) concat.append(',');
        concat.append(values[i++]); 
      }
      res.setHeader(header.getName(), concat.toString()); 
    } 
  } 
}

The method onMessage is the application code for responding to the message sent by PriceListRequest and internalized into msg. It uses the static MessageFactory object fac to create the SOAPMessage object message and then populates it with the distributor's current coffee prices.

The method doPost invokes onMessage and passes it msg. In this case, onMessage does not need to use msg because it simply creates a message containing the distributor's price list. The onMessage method in ConfirmationServlet (Returning the Order Confirmation), on the other hand, uses the message passed to it to get the order ID.

public SOAPMessage onMessage(SOAPMessage msg) { 
  SOAPMessage message = null; 
  try { 
    message = fac.createMessage();

    SOAPPart part = message.getSOAPPart(); 
    SOAPEnvelope envelope = part.getEnvelope(); 
    SOAPBody body = envelope.getBody();

    Name bodyName = envelope.createName("price-list",
          "PriceList", "http://sonata.coffeebreak.com");
    SOAPBodyElement list = body.addBodyElement(bodyName);

    Name coffeeN = envelope.createName("coffee");
    SOAPElement coffee = list.addChildElement(coffeeN);

    Name coffeeNm1 = envelope.createName("coffee-name");
    SOAPElement coffeeName =
                coffee.addChildElement(coffeeNm1);
    coffeeName.addTextNode("Arabica");

    Name priceName1 = envelope.createName("price"); 
    SOAPElement price1 = coffee.addChildElement(priceName1);
    price1.addTextNode("4.50");

    Name coffeeNm2 = envelope.createName("coffee-name"); 
    SOAPElement coffeeName2 =
                    coffee.addChildElement(coffeeNm2);
    coffeeName2.addTextNode("Espresso");

    Name priceName2 = envelope.createName("price"); 
    SOAPElement price2 = coffee.addChildElement(priceName2);
    price2.addTextNode("5.00");

    Name coffeeNm3 = envelope.createName("coffee-name"); 
    SOAPElement coffeeName3 =
                    coffee.addChildElement(coffeeNm3);
    coffeeName3.addTextNode("Dorada");

    Name priceName3 = envelope.createName("price"); 
    SOAPElement price3 = coffee.addChildElement(priceName3);
    price3.addTextNode("6.00");

    Name coffeeNm4 = envelope.createName("coffee-name"); 
    SOAPElement coffeeName4 =
                    coffee.addChildElement(coffeeNm4);
    coffeeName4.addTextNode("House Blend");

    Name priceName4 = envelope.createName("price"); 
    SOAPElement price4 = coffee.addChildElement(priceName4);
    price4.addTextNode("5.00");

    message.saveChanges();

  } catch(Exception e) { 
    e.printStackTrace(); 
  } 
  return message; 
  } 
}

Returning the Order Confirmation

ConfirmationServlet creates the confirmation message that is returned to the call method that is invoked in OrderRequest. It is very similar to the code in PriceListServlet except that instead of building a price list, its onMessage method builds a confirmation with the order number and shipping date.

The onMessage method for this servlet uses the SOAPMessage object passed to it by the doPost method to get the order number sent in OrderRequest. Then it builds a confirmation message with the order ID and shipping date. The shipping date is calculated as today's date plus two days.

public SOAPMessage onMessage(SOAPMessage message) {

  SOAPMessage confirmation = null;

  try {

    //retrieve the orderID element from the message received
    SOAPBody sentSB = message.getSOAPPart().
                      getEnvelope().getBody();
    Iterator sentIt = sentSB.getChildElements();
    SOAPBodyElement sentSBE =
                  (SOAPBodyElement)sentIt.next();
    Iterator sentIt2 = sentSBE.getChildElements();
    SOAPElement sentSE = (SOAPElement)sentIt2.next();

    //get the text for orderID to put in confirmation
    String sentID = sentSE.getValue();

    //create the confirmation message
    confirmation = fac.createMessage();
    SOAPPart sp = confirmation.getSOAPPart();
    SOAPEnvelope env = sp.getEnvelope();
    SOAPBody sb = env.getBody();
    Name newBodyName = env.createName("confirmation",
          "Confirm", "http://sonata.coffeebreak.com");
    SOAPBodyElement confirm = 
          sb.addBodyElement(newBodyName);

    //create the orderID element for confirmation
    Name newOrderIDName = env.createName("orderId");
    SOAPElement newOrderNo =
              confirm.addChildElement(newOrderIDName);
    newOrderNo.addTextNode(sentID);

     //create ship-date element
     Name shipDateName = env.createName("ship-date");
    SOAPElement shipDate = 
             confirm.addChildElement(shipDateName);

    //create the shipping date
    Date today = new Date();
    long msPerDay = 1000 * 60 * 60 * 24;
    long msTarget = today.getTime();
    long msSum = msTarget + (msPerDay * 2);
    Date result = new Date();
    result.setTime(msSum);
    String sd = result.toString();
    shipDate.addTextNode(sd);

    confirmation.saveChanges();

  } catch (Exception ex) {
    ex.printStackTrace();
  }
  return confirmation;
}