The foundation of Web services lies in the sending and receiving of messages in a standard format so that all systems can understand them. Typically, that format is SOAP. A SOAP message can be generated and sent manually, but the SOAP with Attachments API for Java (SAAJ) -- an offshoot of the Java API for XML Messaging (JAXM) -- automates many of the required steps, such as creating connections or creating and sending the actual messages. This tip chronicles the creation and sending of a synchronous SOAP message.

The process involves five steps:

1. Creating a SOAP connection
2. Creating a SOAP message
3. Populating the message
4. Sending the message
5. Retrieving the reply

SAAJ is available as part of the Java Web Services Developer Pack 1.2 (see Resources). This package also includes a copy of the Tomcat Web server (so you can host your own service) and sample applications.

Installation issues

Setting up the Java Web Services Developer Pack 1.2 is easy -- as long as you send your messages through the included Tomcat Web server. To send messages through a standalone application, as I do here, you need to take the following steps:

1. Download the JWSDP 1.2 from http://java.sun.com/webservices/downloads/webservicespack.html.
2. Install it according to the directions.
3. If you're using Java 1.4, you need to override the XML-related classes provided with it. Create the following directory:
   <JAVA_HOME>/jre/lib/endorsed
   and copy the files from:
   <JWSDP_HOME>/jaxp/lib/endorsed
   into it. (JAVA_HOME and JWSDP_HOME refer to your Java installation and your JWSDP installation, respectively.)
4. Add the following files to your classpath:
   • <JWSDP_HOME>/saaj/lib/saaj-api.jar
   • <JWSDP_HOME>/saaj/lib/saaj-impl.jar
   • <JWSDP_HOME>/jwsdp-shared/lib/commons-logging.jar
   • <JWSDP_HOME>/jwsdp-shared/lib/mail.jar
   • <JWSDP_HOME>/jwsdp-shared/lib/activation.jar
   • <JWSDP_HOME>/jaxp/lib/endorsed/dom.jar
   • <JWSDP_HOME>/jaxp/lib/endorsed/xercesImpl.jar
   • <JWSDP_HOME>/jaxp/lib/endorsed/sax.jar
   • <JWSDP_HOME>/jaxp/lib/endorsed/xalan.jar

Now you should be able to send a message from anywhere on your system using a standalone program.

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The structure of a SOAP message

I'll start by showing you the structure of the message itself. A basic SOAP message consists of an envelope with two main parts: the header and the body. The application determines how these parts are used, but the overall message must follow a specific XML structure, such as:

                
                <SOAP-ENV:Envelope 
        xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" 
        xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance" 
        xmlns:xsd="http://www.w3.org/1999/XMLSchema"> 
    <SOAP-ENV:Header />
    <SOAP-ENV:Body> 
        <ns1:getPrice xmlns:ns1="urn:xmethods-BNPriceCheck" 
             SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"> 
                  <isbn xsi:type="xsd:string">0672324229</isbn> 
        </ns1:getPrice> 
    </SOAP-ENV:Body> 
</SOAP-ENV:Envelope> 
            

Here, the header is empty and the body contains the payload, or the message to be delivered. In this case, it's a message requesting the price of a book.

Notice the structure of the message. The Envelope contains the Header and Body elements, and all three are part of the http://schemas.xmlsoap.org/soap/envelope/ namespace. The application sends the message using a SOAPConnection.

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Creating the connection and the message

The first step is to create the overall class and the connection:

                import javax.xml.soap.SOAPConnectionFactory;
import javax.xml.soap.SOAPConnection;

public class SOAPTip {
    
   public static void main(String args[]) {
        
      try {
      
         //First create the connection
         SOAPConnectionFactory soapConnFactory = 
                            SOAPConnectionFactory.newInstance();
         SOAPConnection connection = 
                             soapConnFactory.createConnection();
         


         //Close the connection            
         connection.close();
            
        } catch(Exception e) {
            System.out.println(e.getMessage());
        }
    }
}

The application can send SOAP messages directly using a SOAPConnection, which is now part of the SAAJ package, or indirectly using a messaging provider, which remains in the JAXM package. In this case, the application creates the SOAPConnection object using a factory.

A factory also creates the message itself:

                import javax.xml.soap.SOAPConnectionFactory;
import javax.xml.soap.SOAPConnection;
import javax.xml.soap.MessageFactory;
import javax.xml.soap.SOAPMessage;
import javax.xml.soap.SOAPPart;
import javax.xml.soap.SOAPEnvelope;
import javax.xml.soap.SOAPBody;

public class SOAPTip {
    
   public static void main(String args[]) {
        
      try {
     
         //First create the connection
         SOAPConnectionFactory soapConnFactory = 
                            SOAPConnectionFactory.newInstance();
         SOAPConnection connection = 
                             soapConnFactory.createConnection();
         
         //Next, create the actual message
         MessageFactory messageFactory = MessageFactory.newInstance();
         SOAPMessage message = messageFactory.createMessage();
         
         //Create objects for the message parts            
         SOAPPart soapPart =     message.getSOAPPart();
         SOAPEnvelope envelope = soapPart.getEnvelope();
         SOAPBody body =         envelope.getBody();


         //Close the connection            
         connection.close();
            
        } catch(Exception e) {
            System.out.println(e.getMessage());
        }
    }
}

First, you create the message itself by using the MessageFactory. This message already contains empty versions of the basic parts, such as the envelope and header. The SOAPPart contains the envelope, and the envelope contains the body. Create references to the needed objects, such as the SOAPBody.

Next, populate the SOAPBody:

                ...
import javax.xml.soap.SOAPBody;
import javax.xml.soap.SOAPElement;

public class SOAPTip {
    
   public static void main(String args[]) {
        
      try {
...
         //Create objects for the message parts            
         SOAPPart soapPart =     message.getSOAPPart();
         SOAPEnvelope envelope = soapPart.getEnvelope();
         SOAPBody body =         envelope.getBody();

        //Populate the body
        //Create the main element and namespace
        SOAPElement bodyElement = 
                  body.addChildElement(envelope.createName("getPrice" , 
                                                                "ns1", 
                                          "urn:xmethods-BNPriceCheck"));
        //Add content
        bodyElement.addChildElement("isbn").addTextNode("0672324229");

        //Save the message
        message.saveChanges();


        //Check the input
        System.out.println("\nREQUEST:\n");
        message.writeTo(System.out);
        System.out.println();


         //Close the connection            
         connection.close();
            
        } catch(Exception e) {
            System.out.println(e.getMessage());
        }
    }
}

The body of the SOAP message is just like any other XML element in that you can add a child element, such as getPrice. You can then add the isbn element and its text node just as you might with a typical DOM element.

With SAAJ you also have the opportunity to directly create the SOAPPart of the message using an external file. For example, the file prepped.msg contains the XML structure in the first listing, and can be called in lieu of building the document manually:

                ...
import javax.xml.soap.SOAPElement;

import java.io.FileInputStream;
import javax.xml.transform.stream.StreamSource;

public class SOAPTip {
    
   public static void main(String args[]) {
...
         //Create objects for the message parts            
         SOAPPart soapPart =     message.getSOAPPart();
         SOAPEnvelope envelope = soapPart.getEnvelope();
         SOAPBody body =         envelope.getBody();

         //Populate the Message
        StreamSource preppedMsgSrc = new StreamSource( 
                 new FileInputStream("prepped.msg"));
        soapPart.setContent(preppedMsgSrc);

         //Save the message
         message.saveChanges();
...
    }
}

The StreamSource class is typically used as part of an XSL Transformation, but here you can use it simply to obtain the FileInputStream. The result is a SOAP message that's ready to send.

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Sending the message

With a synchronous message, sending the SOAP message and receiving a reply take place in a single step:

                ...
public class SOAPTip {
    
   public static void main(String args[]) {
        
...
         //Check the input
         System.out.println("\nREQUEST:\n");
         message.writeTo(System.out);
         System.out.println();

        //Send the message and get a reply   
            
        //Set the destination
        String destination = 
            "http://services.xmethods.net:80/soap/servlet/rpcrouter";
        //Send the message
        SOAPMessage reply = connection.call(message, destination);

         //Close the connection            
         connection.close();         
...
    }
}

MimeHeaders headers = message.getMimeHeaders();
headers.addHeader("SOAPAction", "urn:requiredSOAPAction");

The actual message is sent using the call() method, which takes the message itself and a destination as arguments and returns a second SOAPMessage as a reply. In earlier versions of JAXM, the destination had to be an Endpoint object or a URLEndpoint, but now it simply has to be an object. This example uses the "Book price checker" Web service hosted by XMethods, which returns the price of the book whose ISBN is listed in the request.

The call() method blocks until it receives the returned SOAPMessage.

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The response

The returned SOAPMessage, reply, is a SOAP message in the same form as the message sent, and as such can be manipulated just like any other XML message. SOAP allows you to transform the reply directly using XSLT:

                ...
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.Transformer;
import javax.xml.transform.Source;

import javax.xml.transform.stream.StreamResult;

public class SOAPTip {
    
   public static void main(String args[]) {
        
      try {
      
...
         //Send the message
         SOAPMessage reply = connection.call(message, destination);

        //Check the output
        System.out.println("\nRESPONSE:\n");
        //Create the transformer
        TransformerFactory transformerFactory = 
                           TransformerFactory.newInstance();
        Transformer transformer = 
                        transformerFactory.newTransformer();
        //Extract the content of the reply
        Source sourceContent = reply.getSOAPPart().getContent();
        //Set the output for the transformation
        StreamResult result = new StreamResult(System.out);
        transformer.transform(sourceContent, result);
        System.out.println();

         //Close the connection            
         connection.close();
...            
     }
}

Create the Transformer object as you would in any XSLT application. In this case, you just want to output the content, so there's no stylesheet. Here, the content itself is the entire SOAP part of the message (as opposed to the SOAP message itself, which might include attachments). You could also extract the envelope and body before processing. The result in this case is simply System.out, but can be any choice normally available to a transformation. Transform as usual.

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Next steps

This simple application just outputs the received message, but you can just as easily extract the information from the XML document. Also, while this tip demonstrates the synchronous sending and receiving of messages, the JAXM API, available as an optional download, allows for the use of a messaging provider for asynchronous delivery through the use of a ProviderConnection object rather than a SOAPConnection. The provider holds the message until it is delivered successfully.

JAXM also allows for the use of profiles, which make it easy to create specialized SOAP messages such as SOAP-RP or ebXML messages.

Resources

• Check out the status of various recommendations related to Web services at the W3C.
  
  
• Try SAAJ, available as part of the Java Web Services Developer Pack 1.2.
  
  
• Get IBM WebSphere Studio Application Developer, an easy-to-use, integrated development environment for building, testing, and deploying Web services.
  
  
• Find more resources on the developerWorks XML and Web Services zones. For a complete list of XML tips to date, check out the tips summary page.
  
  
• Find out how you can become an IBM Certified Developer in XML and related technologies.
  
  

About the author

Nicholas Chase, a Studio B author, has been involved in Web site development for companies such as Lucent Technologies, Sun Microsystems, Oracle, and the Tampa Bay Buccaneers. Nick has been a high school physics teacher, a low-level radioactive waste facility manager, an online science fiction magazine editor, a multimedia engineer, and an Oracle instructor. More recently, he was the Chief Technology Officer of Site Dynamics Interactive Communications in Clearwater, Florida, USA, and is the author of four books on Web development, including XML Primer Plus (Sams). He loves to hear from readers and can be reached at nicholas@nicholaschase.com.

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Table of contents

• Installation issues
• The structure of a SOAP message
• Creating the connection and the message
• Sending the message
• The response
• Next steps
• Resources
• About the author
• Comments

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