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XStream

Daily del.icio.us for February 10th through February 14th

by Vinny Carpenter on February 14, 2008

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Daily del.icio.us for May 25, 2007

by Vinny Carpenter on May 25, 2007

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Daily del.icio.us for May 22, 2007 through May 25, 2007

by Vinny Carpenter on May 25, 2007

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Declarative Caching Services for Spring

by Vinny Carpenter on May 19, 2006

Declarative Caching Services for Spring by Alex Ruiz — Caching is an essential practice that improves the performance of enterprise applications. In this article, Alex Ruiz demonstrates a declarative caching framework for Spring 2.0, which supports pluggable cache implementations.

spring, spring2.0, caching, aspectj, AOP, SpringAOP, XStream

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Life is beautiful with XMLBeans and XStream

by Vinny Carpenter on January 30, 2006

XML creation, parsing and processing with Java has gotten so much easier with tools like XMLBeans, XStream and many other such tools. I personally love XMLBeans and XStream and I try to use them for all of my XML processing needs. While they both consume XML, they solve different problems. XMLBeans allows you to process XML by binding it to Java types using XML schema that has been compiled to generate Java types that represent schema types. XStream on the other hand allows you to serialize objects to XML and back again using special reflective secret sauce.

I've been using these tools for many years now and so you tend to forget just how useful and powerful they are and how productive they make you. Case in point – A friend of mine came to me for help. He was building an application that would allow him to resale items from Amazon on his site and he wanted to use the Amazon eCommerce Web Services to search for products programmatically and update a local database that housed his content. Having played with Amazon E-Commerce Service (ECS) before, I offered to write up a simple application that would make the Web Services call, process the results and present them back to you.

Amazon's ECS is an API that allows you to access Amazon data and functionality through a Web site or Web-enabled application. ECS follows the standard Web services model: users of the service request data through XML over HTTP (REST) or SOAP and data is returned by the service as an XML-formatted stream of text. In addition to the WSDL, ECS also provides XML schemas for validating the XML output of REST requests. So I decide to use XMLBeans to create my type system using the XML Schema provided by Amazon. XMLBeans provides you with a utility (scomp) to compile your schema into Java XMLBeans classes and metadata. To generate the Java code, use the following command:

scomp –jar amznws.jar AWSECommerceService.xsd

This generates a jar file named amznws.jar, which will contain all of the code needed to bind an XML instance to the Java types representing your schema. In my application, I use HttpClient to make my REST request and then use the XMLBeans generated jar file to process the result. Here's a snippet of code from my sample class:

[code lang="java"]

if (StringUtils.isNotBlank(searchCriteria)) {
String url = "http://webservices.amazon.com/onca/xml?Service=AWSECommerceService&" +
"AWSAccessKeyId=*YOUR_KEY*&AssociateTag=*YOUR_TAG*&Operation=ItemSearch&SearchIndex=Books&" +
"Keywords=" + searchCriteria + "&ResponseGroup=Large,Images";

GetMethod method = new GetMethod(url);
List results = new ArrayList();

try {
int statusCode = client.executeMethod(method);

if (statusCode != HttpStatus.SC_OK) {
log.error("Method failed: " + method.getStatusLine());
}

// Read the response body.
InputStream in = method.getResponseBodyAsStream();
String xmlPayload = parseISToString(in);

// Set up the validation error listener.
ArrayList validationErrors = new ArrayList();
XmlOptions validationOptions = new XmlOptions();
validationOptions.setErrorListener(validationErrors);

ItemSearchResponseDocument items = ItemSearchResponseDocument.Factory.parse(xmlPayload);

if (items != null) {

ItemsDocument.Items[] itemsArray = items.getItemSearchResponse().getItemsArray();
for (int i = 0; i < itemsArray.length; i++) {
AmazonWSObject amzn = processResults(itemsArray, i);
results.add(i, amzn);
}

// During validation, errors are added to the ArrayList
boolean isValid = items.validate(validationOptions);

// Print the errors if the XML is invalid.
if (!isValid) {
for (Object validationError : validationErrors) {
log.error(">> " + validationError + "\n");
}
}
} else {
log.error("Search returned no results");
}
} catch (HttpException e) {
log.error("Fatal protocol violation: " + e.getMessage());
} catch (IOException e) {
log.error("Fatal transport error: " + e.getMessage());
log.error(e.toString());
} catch (XmlException e) {
log.error(e.toString());
} finally {
method.releaseConnection();
}

return results;
} else {
return null;
}

[/code]

As you can tell, HttpClient makes the REST call a snap and XMLBeans makes processing the results easy as well. In total, I spent 3-4 hours getting the application working and a lot of the time was spent figuring out the data set returned from Amazon and trying to come up with a meaningful example. Here is a zip file with the IDEA project that has all the stuff needed to make this work including a simple JSP and a JUnit test class.

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