How can I pass data back from a SOAP handler to a webservice client?

The two choices that seemed to work for me are both documented here. I didn't receive a response yet about whether using a ThreadLocal was fine or not, but I don't see why it shouldn't be.

My secoond method which was added to the original question was to go the route of the handler. While debugging the WS callout, I noticed that the invocationProperties map had the SOAP response as part of an internal packet structure within the responseContext object, but there appeared to be no way of getting to it. The ResponseContext was a set of name value pairs. However, when I read the source code for ResponseContext at this location, I saw that the code for the get method had a comment about returning null if it could not find an Application Scoped property, otherwise, it would read it from the packet invocationProperties, which seemed to be what I wanted. So I seached on how to set the scope on the key/value pair (Google: setting application-scope property for jaxws) that the context was introducing it low-and-behold, it was in the jax-ws spec that I referenced in the other thread.

I also did some reading about the Packet, https://jax-ws.java.net/nonav/jax-ws-20-fcs/arch/com/sun/xml/ws/api/message/Packet.html.

I hope this makes some sense for you. I was concerned that three wouldn't be anything to use JAXB against if the web service call resulted in a Soap FAULT, and I really wanted to log this packet, since it was being returned from a Payment Gateway which to this day has a number of undocumented results.

Good luck.

The solution was to use JAXB to convert the objects back to XML. I didn't really want to do this because it seems redundant to have the webservice client receive XML, convert it to a POJO, only to have that POJO converted back to XML, but it works.

Example of handler that passes out request / response message bodies:

public class MsgLogger implements SOAPHandler<SOAPMessageContext> {

    public static String REQEST_BODY = "com.evil.request";
    public static String RESPONSE_BODY = "com.evil.response";

    @Override
    public Set<QName> getHeaders() {
        return null;
    }

    @Override
    public boolean handleMessage(SOAPMessageContext context) {
        SOAPMessage msg = context.getMessage();
        Boolean beforeRequest = (Boolean) context.get(MessageContext.MESSAGE_OUTBOUND_PROPERTY);
        try {
            ByteArrayOutputStream baos = new ByteArrayOutputStream(32_000);
            context.getMessage().writeTo(baos);
            String key = beforeRequest ? REQEST_BODY : RESPONSE_BODY;
            context.put(key, baos.toString("UTF-8"));
            context.setScope(key, MessageContext.Scope.APPLICATION);
        } catch (SOAPException | IOException e) { }
        return true;
    }

    @Override
    public boolean handleFault(SOAPMessageContext context) {
        return true;
    }

    @Override
    public void close(MessageContext context) { }
}

To register handler and use preserved properties:

BindingProvider provider = (BindingProvider) port;
List<Handler> handlerChain = bindingProvider.getBinding().getHandlerChain();
handlerChain.add(new MsgLogger());
bindingProvider.getBinding().setHandlerChain(handlerChain);

Req req = ...;
Rsp rsp = port.serviceCall(req); // call WS Port

// Access saved message bodies:
Map<String, Object> responseContext = provider.getResponseContext();
String reqBody = (String) responseContext.get(MsgLogger.REQEST_BODY);
String rspBody = (String) responseContext.get(MsgLogger.RESPONSE_BODY);

TL;DR

Metro JAX WS RI docs says about MessageContext.Scope.APPLICATION property:

The message context object can also hold properties set by the client or provider. For instance, port proxy and dispatch objects both extend BindingProvider. A message context object can be obtained from both to represent the request or response context. Properties set in the request context can be read by the handlers, and the handlers may set properties on the message context objects passed to them. If these properties are set with the scope MessageContext.Scope.APPLICATION then they will be available in the response context to the client. On the server end, a context object is passed into the invoke method of a Provider.

metro-jax-ws/jaxws-ri/rt/src/main/java/com/sun/xml/ws/api/message/Packet.java contains property:

/**
 * Lazily created set of handler-scope property names.
 *
 * <p>
 * We expect that this is only used when handlers are present
 * and they explicitly set some handler-scope values.
 *
 * @see #getHandlerScopePropertyNames(boolean)
 */
private Set<String> handlerScopePropertyNames;

On other hand metro-jax-ws/jaxws-ri/rt/src/main/java/com/sun/xml/ws/client/ResponseContext.java is an implementation of Map with:

public boolean containsKey(Object key) {
    if(packet.supports(key))
        return packet.containsKey(key);    // strongly typed

    if(packet.invocationProperties.containsKey(key))
        // if handler-scope, hide it
        return !packet.getHandlerScopePropertyNames(true).contains(key);

    return false;
}

In SOAPHandler we can mark property as APPLICATION instead of default MessageContext.Scope.HANDLER:

/**
 * Property scope. Properties scoped as <code>APPLICATION</code> are
 * visible to handlers,
 * client applications and service endpoints; properties scoped as
 * <code>HANDLER</code>
 * are only normally visible to handlers.
 */
public enum Scope {APPLICATION, HANDLER};

by:

/**
 * Sets the scope of a property.
 *
 * @param name Name of the property associated with the
 *             <code>MessageContext</code>
 * @param scope Desired scope of the property
 * @throws java.lang.IllegalArgumentException if an illegal
 *             property name is specified
 */
public void setScope(String name,  Scope scope);