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Tutorial - The J2EE 1.4 Tutorial

Tutorial

This tutorial walks you through how to use the SAAJ API. First, it covers the basics of creating and sending a simple SOAP message. Then you will learn more details about adding content to messages, including how to create SOAP faults and attributes. Finally, you will learn how to send a message and retrieve the content of the response. After going through this tutorial, you will know how to perform the following tasks:

In the section Code Examples, you will see the code fragments from earlier parts of the tutorial in runnable applications, which you can test yourself. To see how the SAAJ API can be used in server code, see the SAAJ part of the Coffee Break case study (SAAJ Coffee Supplier Service), which shows an example of both the client and the server code for a web service application.

A SAAJ client can send request-response messages to web services that are implemented to do request-response messaging. This section demonstrates how you can do this.

Creating and Sending a Simple Message

This section covers the basics of creating and sending a simple message and retrieving the content of the response. It includes the following topics:

Creating a Message

The first step is to create a message using a MessageFactory object. The SAAJ API provides a default implementation of the MessageFactory class, thus making it easy to get an instance. The following code fragment illustrates getting an instance of the default message factory and then using it to create a message. 

MessageFactory factory = MessageFactory.newInstance();
SOAPMessage message = factory.createMessage();

As is true of the newInstance method for SOAPConnectionFactory, the newInstance method for MessageFactory is static, so you invoke it by calling MessageFactory.newInstance.

Parts of a Message

A SOAPMessage object is required to have certain elements, and, as stated previously, the SAAJ API simplifies things for you by returning a new SOAPMessage object that already contains these elements. So message, which was created in the preceding line of code, automatically has the following:

I.  A SOAPPart object that contains

        A.  A SOAPEnvelope object that contains

                 1.  An empty SOAPHeader object

                 2.  An empty SOAPBody object

The SOAPHeader object is optional and can be deleted if it is not needed. However, if there is one, it must precede the SOAPBody object. The SOAPBody object can hold either the content of the message or a fault message that contains status information or details about a problem with the message. The section Using SOAP Faults walks you through how to use SOAPFault objects.

Accessing Elements of a Message

The next step in creating a message is to access its parts so that content can be added. There are two ways to do this. The SOAPMessage object message, created in the preceding code fragment, is the place to start.

The first way to access the parts of the message is to work your way through the structure of the message. The message contains a SOAPPart object, so you use the getSOAPPart method of message to retrieve it: 

SOAPPart soapPart = message.getSOAPPart();

Next you can use the getEnvelope method of soapPart to retrieve the SOAPEnvelope object that it contains. 

SOAPEnvelope envelope = soapPart.getEnvelope();

You can now use the getHeader and getBody methods of envelope to retrieve its empty SOAPHeader and SOAPBody objects. 

SOAPHeader header = envelope.getHeader();
SOAPBody body = envelope.getBody();

The second way to access the parts of the message is to retrieve the message header and body directly, without retrieving the SOAPPart or SOAPEnvelope. To do so, use the getSOAPHeader and getSOAPBody methods of SOAPMessage: 

SOAPHeader header = message.getSOAPHeader();
SOAPBody body = message.getSOAPBody();

This example of a SAAJ client does not use a SOAP header, so you can delete it. (You will see more about headers later.) Because all SOAPElement objects, including SOAPHeader objects, are derived from the Node interface, you use the method Node.detachNode to delete header. 

header.detachNode();

Adding Content to the Body

The SOAPBody object contains either content or a fault. To add content to the body, you normally create one or more SOAPBodyElement objects to hold the content. You can also add subelements to the SOAPBodyElement objects by using the addChildElement method. For each element or child element, you add content by using the addTextNode method.

When you create any new element, you also need to create an associated Name object so that it is uniquely identified. One way to create Name objects is by using SOAPEnvelope methods, so you can use the envelope variable from the earlier code fragment to create the Name object for your new element. Another way to create Name objects is to use SOAPFactory methods, which are useful if you do not have access to the SOAPEnvelope.

Note: The SOAPFactory class also lets you create XML elements when you are not creating an entire message or do not have access to a complete SOAPMessage object. For example, JAX-RPC implementations often work with XML fragments rather than complete SOAPMessage objects. Consequently, they do not have access to a SOAPEnvelope object, and this makes using a SOAPFactory object to create Name objects very useful. In addition to a method for creating Name objects, the SOAPFactory class provides methods for creating Detail objects and SOAP fragments. You will find an explanation of Detail objects in Overview of SOAP Faults and Creating and Populating a SOAPFault Object.

Name objects associated with SOAPBodyElement or SOAPHeaderElement objects must be fully qualified; that is, they must be created with a local name, a prefix for the namespace being used, and a URI for the namespace. Specifying a namespace for an element makes clear which one is meant if more than one element has the same local name.

The following code fragment retrieves the SOAPBody object body from message, uses a SOAPFactory to create a Name object for the element to be added, and adds a new SOAPBodyElement object to body. 

SOAPBody body = message.getSOAPBody();
SOAPFactory soapFactory = SOAPFactory.newInstance();
Name bodyName = soapFactory.createName("GetLastTradePrice",
  "m", "http://wombat.ztrade.com");
SOAPBodyElement bodyElement = body.addBodyElement(bodyName);

At this point, body contains a SOAPBodyElement object identified by the Name object bodyName, but there is still no content in bodyElement. Assuming that you want to get a quote for the stock of Sun Microsystems, Inc., you need to create a child element for the symbol using the addChildElement method. Then you need to give it the stock symbol using the addTextNode method. The Name object for the new SOAPElement object symbol is initialized with only a local name because child elements inherit the prefix and URI from the parent element. 

Name name = soapFactory.createName("symbol");
SOAPElement symbol = bodyElement.addChildElement(name);
symbol.addTextNode("SUNW");

You might recall that the headers and content in a SOAPPart object must be in XML format. The SAAJ API takes care of this for you, building the appropriate XML constructs automatically when you call methods such as addBodyElement, addChildElement, and addTextNode. Note that you can call the method addTextNode only on an element such as bodyElement or any child elements that are added to it. You cannot call addTextNode on a SOAPHeader or SOAPBody object because they contain elements and not text.

The content that you have just added to your SOAPBody object will look like the following when it is sent over the wire: 

<SOAP-ENV:Envelope
 xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
  <SOAP-ENV:Body>
    <m:GetLastTradePrice xmlns:m="http://wombat.ztrade.com">
      <symbol>SUNW</symbol>
    </m:GetLastTradePrice>
  </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

Let's examine this XML excerpt line by line to see how it relates to your SAAJ code. Note that an XML parser does not care about indentations, but they are generally used to indicate element levels and thereby make it easier for a human reader to understand.

Here is the SAAJ code: 

SOAPMessage message = messageFactory.createMessage();
SOAPHeader header = message.getSOAPHeader();
SOAPBody body = message.getSOAPBody();

Here is the XML it produces: 

<SOAP-ENV:Envelope
 xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
  <SOAP-ENV:Header/>
  <SOAP-ENV:Body>
    . . .
  </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

The outermost element in this XML example is the SOAP envelope element, indicated by SOAP-ENV:Envelope. Note that Envelope is the name of the element, and SOAP-ENV is the namespace prefix. The interface SOAPEnvelope represents a SOAP envelope.

The first line signals the beginning of the SOAP envelope element, and the last line signals the end of it; everything in between is part of the SOAP envelope. The second line is an example of an attribute for the SOAP envelope element. Because a SOAP envelope element always contains this attribute with this value, a SOAPMessage object comes with it automatically included. xmlns stands for "XML namespace," and its value is the URI of the namespace associated with Envelope.

The next line is an empty SOAP header. We could remove it by calling header.detachNode after the getSOAPHeader call.

The next two lines mark the beginning and end of the SOAP body, represented in SAAJ by a SOAPBody object. The next step is to add content to the body.

Here is the SAAJ code: 

Name bodyName = soapFactory.createName("GetLastTradePrice",
  "m", "http://wombat.ztrade.com");
SOAPBodyElement bodyElement = body.addBodyElement(bodyName);

Here is the XML it produces: 

<m:GetLastTradePrice
 xmlns:m="http://wombat.ztrade.com">
 . . . .
</m:GetLastTradePrice>

These lines are what the SOAPBodyElement bodyElement in your code represents. GetLastTradePrice is its local name, m is its namespace prefix, and http://wombat.ztrade.com is its namespace URI.

Here is the SAAJ code: 

Name name = soapFactory.createName("symbol");
SOAPElement symbol = bodyElement.addChildElement(name);
symbol.addTextNode("SUNW");

Here is the XML it produces: 

<symbol>SUNW</symbol>

The String "SUNW" is the text node for the element <symbol>. This String object is the message content that your recipient, the stock quote service, receives.

The following example shows how to add multiple SOAPElement objects and add text to each of them. The code first creates the SOAPBodyElement object purchaseLineItems, which has a fully qualified name associated with it. That is, the Name object for it has a local name, a namespace prefix, and a namespace URI. As you saw earlier, a SOAPBodyElement object is required to have a fully qualified name, but child elements added to it, such as SOAPElement objects, can have Name objects with only the local name. 

SOAPBody body = message.getSOAPBody();
Name bodyName = soapFactory.createName("PurchaseLineItems",
  "PO", "http://sonata.fruitsgalore.com");
SOAPBodyElement purchaseLineItems =
  body.addBodyElement(bodyName);

Name childName = soapFactory.createName("Order");
SOAPElement order =
  purchaseLineItems.addChildElement(childName);

childName = soapFactory.createName("Product");
SOAPElement product = order.addChildElement(childName);
product.addTextNode("Apple");

childName = soapFactory.createName("Price");
SOAPElement price = order.addChildElement(childName);
price.addTextNode("1.56");

childName = soapFactory.createName("Order");
SOAPElement order2 =
  purchaseLineItems.addChildElement(childName);

childName = soapFactory.createName("Product");
SOAPElement product2 = order2.addChildElement(childName);
product2.addTextNode("Peach");

childName = soapFactory.createName("Price");
SOAPElement price2 = order2.addChildElement(childName);
price2.addTextNode("1.48");

The SAAJ code in the preceding example produces the following XML in the SOAP body: 

<PO:PurchaseLineItems
 xmlns:PO="http://sonata.fruitsgalore.com">
  <Order>
    <Product>Apple</Product>
    <Price>1.56</Price>
  </Order>

  <Order>
    <Product>Peach</Product>
    <Price>1.48</Price>
  </Order>
</PO:PurchaseLineItems>

Getting a SOAPConnection Object

The SAAJ API is focused primarily on reading and writing messages. After you have written a message, you can send it using various mechanisms (such as JMS or JAXM). The SAAJ API does, however, provide a simple mechanism for request-response messaging.

To send a message, a SAAJ client can use a SOAPConnection object. A SOAPConnection object is a point-to-point connection, meaning that it goes directly from the sender to the destination (usually a URL) that the sender specifies.

The first step is to obtain a SOAPConnectionFactory object that you can use to create your connection. The SAAJ API makes this easy by providing the SOAPConnectionFactory class with a default implementation. You can get an instance of this implementation using the following line of code. 

SOAPConnectionFactory soapConnectionFactory = 
  SOAPConnectionFactory.newInstance();

Now you can use soapConnectionFactory to create a SOAPConnection object. 

SOAPConnection connection = 
  soapConnectionFactory.createConnection();

You will use connection to send the message that you created.

Sending a Message

A SAAJ client calls the SOAPConnection method call on a SOAPConnection object to send a message. The call method takes two arguments: the message being sent and the destination to which the message should go. This message is going to the stock quote service indicated by the URL object endpoint. 

java.net.URL endpoint = new URL(
  "http://wombat.ztrade.com/quotes");

SOAPMessage response = connection.call(message, endpoint);

The content of the message you sent is the stock symbol SUNW; the SOAPMessage object response should contain the last stock price for Sun Microsystems, which you will retrieve in the next section.

A connection uses a fair amount of resources, so it is a good idea to close a connection as soon as you are finished using it. 

connection.close();

Getting the Content of a Message

The initial steps for retrieving a message's content are the same as those for giving content to a message: Either you use the Message object to get the SOAPBody object, or you access the SOAPBody object through the SOAPPart and SOAPEnvelope objects.

Then you access the SOAPBody object's SOAPBodyElement object, because that is the element to which content was added in the example. (In a later section you will see how to add content directly to the SOAPPart object, in which case you would not need to access the SOAPBodyElement object to add content or to retrieve it.)

To get the content, which was added with the method SOAPElement.addTextNode, you call the method Node.getValue. Note that getValue returns the value of the immediate child of the element that calls the method. Therefore, in the following code fragment, the getValue method is called on bodyElement, the element on which the addTextNode method was called.

To access bodyElement, you call the getChildElements method on soapBody. Passing bodyName to getChildElements returns a java.util.Iterator object that contains all the child elements identified by the Name object bodyName. You already know that there is only one, so calling the next method on it will return the SOAPBodyElement you want. Note that the Iterator.next method returns a Java Object, so you need to cast the Object it returns to a SOAPBodyElement object before assigning it to the variable bodyElement. 

SOAPBody soapBody = response.getSOAPBody();
java.util.Iterator iterator = 
  soapBody.getChildElements(bodyName);
SOAPBodyElement bodyElement =
  (SOAPBodyElement)iterator.next();
String lastPrice = bodyElement.getValue();
System.out.print("The last price for SUNW is "); 
System.out.println(lastPrice);

If more than one element had the name bodyName, you would have to use a while loop using the Iterator.hasNext method to make sure that you got all of them. 

while (iterator.hasNext()) {
  SOAPBodyElement bodyElement = 
    (SOAPBodyElement)iterator.next();
  String lastPrice = bodyElement.getValue();
  System.out.print("The last price for SUNW is ");
  System.out.println(lastPrice);
}

At this point, you have seen how to send a very basic request-response message and get the content from the response. The next sections provide more detail on adding content to messages.

Adding Content to the Header

To add content to the header, you create a SOAPHeaderElement object. As with all new elements, it must have an associated Name object, which you can create using the message's SOAPEnvelope object or a SOAPFactory object.

For example, suppose you want to add a conformance claim header to the message to state that your message conforms to the WS-I Basic Profile. The following code fragment retrieves the SOAPHeader object from message and adds a new SOAPHeaderElement object to it. This SOAPHeaderElement object contains the correct qualified name and attribute for a WS-I conformance claim header. 

SOAPHeader header = message.getSOAPHeader();
Name headerName = soapFactory.createName("Claim",
  "wsi", "http://ws-i.org/schemas/conformanceClaim/");
SOAPHeaderElement headerElement =
  header.addHeaderElement(headerName);
headerElement.addAttribute(soapFactory.createName(
  "conformsTo"), "http://ws-i.org/profiles/basic1.0/");

At this point, header contains the SOAPHeaderElement object headerElement identified by the Name object headerName. Note that the addHeaderElement method both creates headerElement and adds it to header.

A conformance claim header has no content. This code produces the following XML header: 

<SOAP-ENV:Header>
  <wsi:Claim conformsTo="http://ws-i.org/profiles/basic1.0/"
   xmlns:wsi="http://ws-i.org/schemas/conformanceClaim/"/>
</SOAP-ENV:Header>

For more information about creating SOAP messages that conform to WS-I, see the Messaging section of the WS-I Basic Profile.

For a different kind of header, you might want to add content to headerElement. The following line of code uses the method addTextNode to do this. 

headerElement.addTextNode("order");

Now you have the SOAPHeader object header that contains a SOAPHeaderElement object whose content is "order".

Adding Content to the SOAPPart Object

If the content you want to send is in a file, SAAJ provides an easy way to add it directly to the SOAPPart object. This means that you do not access the SOAPBody object and build the XML content yourself, as you did in the preceding section.

To add a file directly to the SOAPPart object, you use a javax.xml.transform.Source object from JAXP (the Java API for XML Processing). There are three types of Source objects: SAXSource, DOMSource, and StreamSource. A StreamSource object holds an XML document in text form. SAXSource and DOMSource objects hold content along with the instructions for transforming the content into an XML document.

The following code fragment uses the JAXP API to build a DOMSource object that is passed to the SOAPPart.setContent method. The first three lines of code get a DocumentBuilderFactory object and use it to create the DocumentBuilder object builder. Because SOAP messages use namespaces, you should set the NamespaceAware property for the factory to true. Then builder parses the content file to produce a Document object. 

DocumentBuilderFactory dbFactory = 
  DocumentBuilderFactory.newInstance();
dbFactory.setNamespaceAware(true);
DocumentBuilder builder = dbFactory.newDocumentBuilder();
Document document =
  builder.parse("file:///music/order/soap.xml");
DOMSource domSource = new DOMSource(document);

The following two lines of code access the SOAPPart object (using the SOAPMessage object message) and set the new Document object as its content. The SOAPPart.setContent method not only sets content for the SOAPBody object but also sets the appropriate header for the SOAPHeader object. 

SOAPPart soapPart = message.getSOAPPart();
soapPart.setContent(domSource);

The XML file you use to set the content of the SOAPPart object must include Envelope and Body elements: 

<SOAP-ENV:Envelope 
xmlns="http://schemas.xmlsoap.org/soap/envelope/">
  <SOAP-ENV:Body>
  ...
  </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

You will see other ways to add content to a message in the sections Adding a Document to the SOAP Body and Adding Attachments.

Adding a Document to the SOAP Body

In addition to setting the content of the entire SOAP message to that of a DOMSource object, you can add a DOM document directly to the body of the message. This capability means that you do not have to create a javax.xml.transform.Source object. After you parse the document, you can add it directly to the message body: 

SOAPBody body = message.getSOAPBody();
SOAPBodyElement docElement = body.addDocument(document);

Manipulating Message Content Using SAAJ or DOM APIs

Because SAAJ nodes and elements implement the DOM Node and Element interfaces, you have many options for adding or changing message content:

  • Use only DOM APIs.
  • Use only SAAJ APIs.
  • Use SAAJ APIs and then switch to using DOM APIs.
  • Use DOM APIs and then switch to using SAAJ APIs.

The first three of these cause no problems. After you have created a message, whether or not you have imported its content from another document, you can start adding or changing nodes using either SAAJ or DOM APIs.

But if you use DOM APIs and then switch to using SAAJ APIs to manipulate the document, any references to objects within the tree that were obtained using DOM APIs are no longer valid. If you must use SAAJ APIs after using DOM APIs, you should set all your DOM typed references to null, because they can become invalid. For more information about the exact cases in which references become invalid, see the SAAJ API documentation.

The basic rule is that you can continue manipulating the message content using SAAJ APIs as long as you want to, but after you start manipulating it using DOM, you should no longer use SAAJ APIs.

Adding Attachments

An AttachmentPart object can contain any type of content, including XML. And because the SOAP part can contain only XML content, you must use an AttachmentPart object for any content that is not in XML format.

Creating an AttachmentPart Object and Adding Content

The SOAPMessage object creates an AttachmentPart object, and the message also must add the attachment to itself after content has been added. The SOAPMessage class has three methods for creating an AttachmentPart object.

The first method creates an attachment with no content. In this case, an AttachmentPart method is used later to add content to the attachment. 

AttachmentPart attachment = message.createAttachmentPart();

You add content to attachment by using the AttachmentPart method setContent. This method takes two parameters: a Java Object for the content, and a String object for the MIME content type that is used to encode the object. Content in the SOAPBody part of a message automatically has a Content-Type header with the value "text/xml" because the content must be in XML. In contrast, the type of content in an AttachmentPart object must be specified because it can be any type.

Each AttachmentPart object has one or more MIME headers associated with it. When you specify a type to the setContent method, that type is used for the header Content-Type. Note that Content-Type is the only header that is required. You may set other optional headers, such as Content-Id and Content-Location. For convenience, SAAJ provides get and set methods for the headers Content-Type, Content-Id, and Content-Location. These headers can be helpful in accessing a particular attachment when a message has multiple attachments. For example, to access the attachments that have particular headers, you can call the SOAPMessage method getAttachments and pass it a MIMEHeaders object containing the MIME headers you are interested in.

The following code fragment shows one of the ways to use the method setContent. The Java Object in the first parameter can be a String, a stream, a javax.xml.transform.Source object, or a javax.activation.DataHandler object. The Java Object being added in the following code fragment is a String, which is plain text, so the second argument must be "text/plain". The code also sets a content identifier, which can be used to identify this AttachmentPart object. After you have added content to attachment, you must add it to the SOAPMessage object, something that is done in the last line. 

String stringContent = "Update address for Sunny Skies " + 
  "Inc., to 10 Upbeat Street, Pleasant Grove, CA 95439";

attachment.setContent(stringContent, "text/plain");
attachment.setContentId("update_address");

message.addAttachmentPart(attachment);

The attachment variable now represents an AttachmentPart object that contains the string stringContent and has a header that contains the string "text/plain". It also has a Content-Id header with "update_address" as its value. And attachment is now part of message.

The other two SOAPMessage.createAttachment methods create an AttachmentPart object complete with content. One is very similar to the AttachmentPart.setContent method in that it takes the same parameters and does essentially the same thing. It takes a Java Object containing the content and a String giving the content type. As with AttachmentPart.setContent, the Object can be a String, a stream, a javax.xml.transform.Source object, or a javax.activation.DataHandler object.

The other method for creating an AttachmentPart object with content takes a DataHandler object, which is part of the JavaBeans Activation Framework (JAF). Using a DataHandler object is fairly straightforward. First, you create a java.net.URL object for the file you want to add as content. Then you create a DataHandler object initialized with the URL object: 

URL url = new URL("http://greatproducts.com/gizmos/img.jpg");
DataHandler dataHandler = new DataHandler(url);
AttachmentPart attachment = 
  message.createAttachmentPart(dataHandler);
attachment.setContentId("attached_image");

message.addAttachmentPart(attachment);

You might note two things about this code fragment. First, it sets a header for Content-ID using the method setContentId. This method takes a String that can be whatever you like to identify the attachment. Second, unlike the other methods for setting content, this one does not take a String for Content-Type. This method takes care of setting the Content-Type header for you, something that is possible because one of the things a DataHandler object does is to determine the data type of the file it contains.

Accessing an AttachmentPart Object

If you receive a message with attachments or want to change an attachment to a message you are building, you need to access the attachment. The SOAPMessage class provides two versions of the getAttachments method for retrieving its AttachmentPart objects. When it is given no argument, the method SOAPMessage.getAttachments returns a java.util.Iterator object over all the AttachmentPart objects in a message. When getAttachments is given a MimeHeaders object, which is a list of MIME headers, getAttachments returns an iterator over the AttachmentPart objects that have a header that matches one of the headers in the list. The following code uses the getAttachments method that takes no arguments and thus retrieves all the AttachmentPart objects in the SOAPMessage object message. Then it prints the content ID, the content type, and the content of each AttachmentPart object. 

java.util.Iterator iterator = message.getAttachments();
while (iterator.hasNext()) {
  AttachmentPart attachment = 
    (AttachmentPart)iterator.next();
  String id = attachment.getContentId();
  String type = attachment.getContentType();
  System.out.print("Attachment " + id + 
    " has content type " + type);
  if (type == "text/plain") {
    Object content = attachment.getContent();
    System.out.println("Attachment " +
      "contains:\n" + content);
  }
}

Adding Attributes

An XML element can have one or more attributes that give information about that element. An attribute consists of a name for the attribute followed immediately by an equal sign (=) and its value.

The SOAPElement interface provides methods for adding an attribute, for getting the value of an attribute, and for removing an attribute. For example, in the following code fragment, the attribute named id is added to the SOAPElement object person. Because person is a SOAPElement object rather than a SOAPBodyElement object or SOAPHeaderElement object, it is legal for its Name object to contain only a local name. 

Name attributeName = envelope.createName("id");
person.addAttribute(attributeName, "Person7");

These lines of code will generate the first line in the following XML fragment. 

<person id="Person7">
  ...
</person>

The following line of code retrieves the value of the attribute whose name is id. 

String attributeValue = 
  person.getAttributeValue(attributeName);

If you had added two or more attributes to person, the preceding line of code would have returned only the value for the attribute named id. If you wanted to retrieve the values for all the attributes for person, you would use the method getAllAttributes, which returns an iterator over all the values. The following lines of code retrieve and print each value on a separate line until there are no more attribute values. Note that the Iterator.next method returns a Java Object, which is cast to a Name object so that it can be assigned to the Name object attributeName. (The examples in DOMExample.java and DOMSrcExample.java use code similar to this.) 

Iterator iterator = person.getAllAttributes();
while (iterator.hasNext()){
  Name attributeName = (Name) iterator.next();
  System.out.println("Attribute name is " + 
    attributeName.getQualifiedName());
  System.out.println("Attribute value is " + 
    element.getAttributeValue(attributeName));
}

The following line of code removes the attribute named id from person. The variable successful will be true if the attribute was removed successfully. 

boolean successful = person.removeAttribute(attributeName);

In this section you have seen how to add, retrieve, and remove attributes. This information is general in that it applies to any element. The next section discusses attributes that can be added only to header elements.

Header Attributes

Attributes that appear in a SOAPHeaderElement object determine how a recipient processes a message. You can think of header attributes as offering a way to extend a message, giving information about such things as authentication, transaction management, payment, and so on. A header attribute refines the meaning of the header, whereas the header refines the meaning of the message contained in the SOAP body.

The SOAP 1.1 specification defines two attributes that can appear only in SOAPHeaderElement objects: actor and mustUnderstand. The next two sections discuss these attributes.

See HeaderExample.java for an example that uses the code shown in this section.

The Actor Attribute

The actor attribute is optional, but if it is used, it must appear in a SOAPHeaderElement object. Its purpose is to indicate the recipient of a header element. The default actor is the message's ultimate recipient; that is, if no actor attribute is supplied, the message goes directly to the ultimate recipient.

An actor is an application that can both receive SOAP messages and forward them to the next actor. The ability to specify one or more actors as intermediate recipients makes it possible to route a message to multiple recipients and to supply header information that applies specifically to each of the recipients.

For example, suppose that a message is an incoming purchase order. Its SOAPHeader object might have SOAPHeaderElement objects with actor attributes that route the message to applications that function as the order desk, the shipping desk, the confirmation desk, and the billing department. Each of these applications will take the appropriate action, remove the SOAPHeaderElement objects relevant to it, and send the message on to the next actor.

Note: Although the SAAJ API provides the API for adding these attributes, it does not supply the API for processing them. For example, the actor attribute requires that there be an implementation such as a messaging provider service to route the message from one actor to the next.

An actor is identified by its URI. For example, the following line of code, in which orderHeader is a SOAPHeaderElement object, sets the actor to the given URI. 

orderHeader.setActor("http://gizmos.com/orders");

Additional actors can be set in their own SOAPHeaderElement objects. The following code fragment first uses the SOAPMessage object message to get its SOAPHeader object header. Then header creates four SOAPHeaderElement objects, each of which sets its actor attribute. 

SOAPHeader header = message.getSOAPHeader();
SOAPFactory soapFactory = SOAPFactory.newInstance();

String nameSpace = "ns";
String nameSpaceURI = "http://gizmos.com/NSURI";

Name order = soapFactory.createName("orderDesk",
  nameSpace, nameSpaceURI);
SOAPHeaderElement orderHeader =
  header.addHeaderElement(order);
orderHeader.setActor("http://gizmos.com/orders");

Name shipping = 
  soapFactory.createName("shippingDesk",
    nameSpace, nameSpaceURI);
SOAPHeaderElement shippingHeader =
  header.addHeaderElement(shipping);
shippingHeader.setActor("http://gizmos.com/shipping");

Name confirmation = 
  soapFactory.createName("confirmationDesk",
    nameSpace, nameSpaceURI);
SOAPHeaderElement confirmationHeader =
  header.addHeaderElement(confirmation);
confirmationHeader.setActor(
  "http://gizmos.com/confirmations");

Name billing = soapFactory.createName("billingDesk",
  nameSpace, nameSpaceURI);
SOAPHeaderElement billingHeader =
  header.addHeaderElement(billing);
billingHeader.setActor("http://gizmos.com/billing");

The SOAPHeader interface provides two methods that return a java.util.Iterator object over all the SOAPHeaderElement objects that have an actor that matches the specified actor. The first method, examineHeaderElements, returns an iterator over all the elements that have the specified actor. 

java.util.Iterator headerElements =
  header.examineHeaderElements("http://gizmos.com/orders");

The second method, extractHeaderElements, not only returns an iterator over all the SOAPHeaderElement objects that have the specified actor attribute but also detaches them from the SOAPHeader object. So, for example, after the order desk application did its work, it would call extractHeaderElements to remove all the SOAPHeaderElement objects that applied to it. 

java.util.Iterator headerElements =
  header.extractHeaderElements("http://gizmos.com/orders");

Each SOAPHeaderElement object can have only one actor attribute, but the same actor can be an attribute for multiple SOAPHeaderElement objects.

Two additional SOAPHeader methods--examineAllHeaderElements and extractAllHeaderElements--allow you to examine or extract all the header elements, whether or not they have an actor attribute. For example, you could use the following code to display the values of all the header elements: 

Iterator allHeaders = 
  header.examineAllHeaderElements();
while (allHeaders.hasNext()) {
  SOAPHeaderElement headerElement = 
    (SOAPHeaderElement)allHeaders.next();
  Name headerName = 
    headerElement.getElementName();
  System.out.println("\nHeader name is " + 
    headerName.getQualifiedName());
  System.out.println("Actor is " + 
    headerElement.getActor());
}
The mustUnderstand Attribute

The other attribute that must be added only to a SOAPHeaderElement object is mustUnderstand. This attribute says whether or not the recipient (indicated by the actor attribute) is required to process a header entry. When the value of the mustUnderstand attribute is true, the actor must understand the semantics of the header entry and must process it correctly to those semantics. If the value is false, processing the header entry is optional. A SOAPHeaderElement object with no mustUnderstand attribute is equivalent to one with a mustUnderstand attribute whose value is false.

The mustUnderstand attribute is used to call attention to the fact that the semantics in an element are different from the semantics in its parent or peer elements. This allows for robust evolution, ensuring that a change in semantics will not be silently ignored by those who may not fully understand it.

If the actor for a header that has a mustUnderstand attribute set to true cannot process the header, it must send a SOAP fault back to the sender. (See Using SOAP Faults.) The actor must not change state or cause any side effects, so that, to an outside observer, it appears that the fault was sent before any header processing was done.

The following code fragment creates a SOAPHeader object with a SOAPHeaderElement object that has a mustUnderstand attribute. 

SOAPHeader header = message.getSOAPHeader();

Name name = soapFactory.createName("Transaction", "t", 
  "http://gizmos.com/orders");

SOAPHeaderElement transaction = header.addHeaderElement(name);
transaction.setMustUnderstand(true);
transaction.addTextNode("5");

This code produces the following XML: 

<SOAP-ENV:Header>
  <t:Transaction 
     xmlns:t="http://gizmos.com/orders" 
     SOAP-ENV:mustUnderstand="1">
    5
  </t:Transaction>
</SOAP-ENV:Header>

You can use the getMustUnderstand method to retrieve the value of the mustUnderstand attribute. For example, you could add the following to the code fragment at the end of the preceding section: 

  System.out.println("mustUnderstand is " + 
    headerElement.getMustUnderstand());

Using SOAP Faults

In this section, you will see how to use the API for creating and accessing a SOAP fault element in an XML message.

Overview of SOAP Faults

If you send a message that was not successful for some reason, you may get back a response containing a SOAP fault element, which gives you status information, error information, or both. There can be only one SOAP fault element in a message, and it must be an entry in the SOAP body. Furthermore, if there is a SOAP fault element in the SOAP body, there can be no other elements in the SOAP body. This means that when you add a SOAP fault element, you have effectively completed the construction of the SOAP body.

A SOAPFault object, the representation of a SOAP fault element in the SAAJ API, is similar to an Exception object in that it conveys information about a problem. However, a SOAPFault object is quite different in that it is an element in a message's SOAPBody object rather than part of the try/catch mechanism used for Exception objects. Also, as part of the SOAPBody object, which provides a simple means for sending mandatory information intended for the ultimate recipient, a SOAPFault object only reports status or error information. It does not halt the execution of an application, as an Exception object can.

If you are a client using the SAAJ API and are sending point-to-point messages, the recipient of your message may add a SOAPFault object to the response to alert you to a problem. For example, if you sent an order with an incomplete address for where to send the order, the service receiving the order might put a SOAPFault object in the return message telling you that part of the address was missing.

Another example of who might send a SOAP fault is an intermediate recipient, or actor. As stated in the section Adding Attributes, an actor that cannot process a header that has a mustUnderstand attribute with a value of true must return a SOAP fault to the sender.

A SOAPFault object contains the following elements:

  • A fault code: Always required. The fault code must be a fully qualified name: it must contain a prefix followed by a local name. The SOAP 1.1 specification defines a set of fault code local name values in section 4.4.1, which a developer can extend to cover other problems. The default fault code local names defined in the specification relate to the SAAJ API as follows:
    • VersionMismatch: The namespace for a SOAPEnvelope object was invalid.
    • MustUnderstand: An immediate child element of a SOAPHeader object had its mustUnderstand attribute set to true, and the processing party did not understand the element or did not obey it.
    • Client: The SOAPMessage object was not formed correctly or did not contain the information needed to succeed.
    • Server: The SOAPMessage object could not be processed because of a processing error, not because of a problem with the message itself.
  • A fault string: Always required. A human-readable explanation of the fault.
  • A fault actor: Required if the SOAPHeader object contains one or more actor attributes; optional if no actors are specified, meaning that the only actor is the ultimate destination. The fault actor, which is specified as a URI, identifies who caused the fault. For an explanation of what an actor is, see The Actor Attribute.
  • A Detail object: Required if the fault is an error related to the SOAPBody object. If, for example, the fault code is Client, indicating that the message could not be processed because of a problem in the SOAPBody object, the SOAPFault object must contain a Detail object that gives details about the problem. If a SOAPFault object does not contain a Detail object, it can be assumed that the SOAPBody object was processed successfully.

Creating and Populating a SOAPFault Object

You have seen how to add content to a SOAPBody object; this section walks you through adding a SOAPFault object to a SOAPBody object and then adding its constituent parts.

As with adding content, the first step is to access the SOAPBody object. 

SOAPBody body = message.getSOAPBody();

With the SOAPBody object body in hand, you can use it to create a SOAPFault object. The following line of code creates a SOAPFault object and adds it to body. 

SOAPFault fault = body.addFault();

The SOAPFault interface provides convenience methods that create an element, add the new element to the SOAPFault object, and add a text node, all in one operation. For example, in the following lines of code, the method setFaultCode creates a faultcode element, adds it to fault, and adds a Text node with the value "SOAP-ENV:Server" by specifying a default prefix and the namespace URI for a SOAP envelope. 

Name faultName =
  soapFactory.createName("Server",
    "", SOAPConstants.URI_NS_SOAP_ENVELOPE);
fault.setFaultCode(faultName);
fault.setFaultActor("http://gizmos.com/orders");
fault.setFaultString("Server not responding");

The SOAPFault object fault, created in the preceding lines of code, indicates that the cause of the problem is an unavailable server and that the actor at http://gizmos.com/orders is having the problem. If the message were being routed only to its ultimate destination, there would have been no need to set a fault actor. Also note that fault does not have a Detail object because it does not relate to the SOAPBody object.

The following code fragment creates a SOAPFault object that includes a Detail object. Note that a SOAPFault object can have only one Detail object, which is simply a container for DetailEntry objects, but the Detail object can have multiple DetailEntry objects. The Detail object in the following lines of code has two DetailEntry objects added to it. 

SOAPFault fault = body.addFault();

Name faultName = soapFactory.createName("Client",
  "", SOAPConstants.URI_NS_SOAP_ENVELOPE);
fault.setFaultCode(faultName);
fault.setFaultString("Message does not have necessary info");

Detail detail = fault.addDetail();

Name entryName = soapFactory.createName("order",
  "PO", "http://gizmos.com/orders/");
DetailEntry entry = detail.addDetailEntry(entryName);
entry.addTextNode("Quantity element does not have a value");

Name entryName2 = soapFactory.createName("confirmation",
  "PO", "http://gizmos.com/confirm");
DetailEntry entry2 = detail.addDetailEntry(entryName2);
entry2.addTextNode("Incomplete address: no zip code");

See SOAPFaultTest.java for an example that uses code like that shown in this section.

Retrieving Fault Information

Just as the SOAPFault interface provides convenience methods for adding information, it also provides convenience methods for retrieving that information. The following code fragment shows what you might write to retrieve fault information from a message you received. In the code fragment, newMessage is the SOAPMessage object that has been sent to you. Because a SOAPFault object must be part of the SOAPBody object, the first step is to access the SOAPBody object. Then the code tests to see whether the SOAPBody object contains a SOAPFault object. If it does, the code retrieves the SOAPFault object and uses it to retrieve its contents. The convenience methods getFaultCode, getFaultString, and getFaultActor make retrieving the values very easy. 

SOAPBody body = newMessage.getSOAPBody();
if ( body.hasFault() ) {
  SOAPFault newFault = body.getFault();
  Name code = newFault.getFaultCodeAsName();
  String string = newFault.getFaultString();
  String actor = newFault.getFaultActor();

Next the code prints the values it has just retrieved. Not all messages are required to have a fault actor, so the code tests to see whether there is one. Testing whether the variable actor is null works because the method getFaultActor returns null if a fault actor has not been set. 

  System.out.println("SOAP fault contains: ");
  System.out.println("  Fault code = " + 
    code.getQualifiedName());
  System.out.println("  Fault string = " + string);

  if ( actor != null ) {
    System.out.println("  Fault actor = " + actor);
  }

The final task is to retrieve the Detail object and get its DetailEntry objects. The code uses the SOAPFault object newFault to retrieve the Detail object newDetail, and then it uses newDetail to call the method getDetailEntries. This method returns the java.util.Iterator object entries, which contains all the DetailEntry objects in newDetail. Not all SOAPFault objects are required to have a Detail object, so the code tests to see whether newDetail is null. If it is not, the code prints the values of the DetailEntry objects as long as there are any. 

Detail newDetail = newFault.getDetail();
if (newDetail != null) {
  Iterator entries = newDetail.getDetailEntries();
  while ( entries.hasNext() ) {
    DetailEntry newEntry = 
      (DetailEntry)entries.next();
    String value = newEntry.getValue();
    System.out.println("  Detail entry = " + value);
  }
}

In summary, you have seen how to add a SOAPFault object and its contents to a message as well as how to retrieve the contents. A SOAPFault object, which is optional, is added to the SOAPBody object to convey status or error information. It must always have a fault code and a String explanation of the fault. A SOAPFault object must indicate the actor that is the source of the fault only when there are multiple actors; otherwise, it is optional. Similarly, the SOAPFault object must contain a Detail object with one or more DetailEntry objects only when the contents of the SOAPBody object could not be processed successfully.

See SOAPFaultTest.java for an example that uses code like that shown in this section.