Here is a common problem with custom Ant tasks. A typical task is implemented using multiple classes, so classes that don't extend org.apache.tools.ant.Task class don't necessarily have to have a dependency on Ant APIs. For example, it is pretty easy to pass Ant properties in a hashtable instead of passing the entire project object. This makes the custom task's code more generic and reusable.

One little issue that still remains is logging. Ant users are accustomed to running Ant with -verbose option which tells Ant tasks to print more detailed information. Oftentimes, -verbose is the only way to debug a build.

Unfortunately, using Ant logging requires access to Project or Task objects. As a result, the dependency on Ant APIs permeates the code that otherwise could have remained generic.

My solution for this is to use a simple class that implements org.apache.commons.logging.Log interface so that we can use jakarta commons logging (JCL) APIs instead of using Ant logging directly. The class is called AntCommonsLogger.

To initialize AntCommonsLogger, users can either invoke "antCommonsLoggerInit" task in the beginning of a project or call AntCommonsLogger.init( getProject()) somewhere in their custom task class. After that, AntCommonsLogger becomes the default logger so that any class can use the the familiar commons logging pattern without any changes:

private static Log logger = LogFactory.getLog(CustomTask.class.getName());
...
logger.info("message");
logger.debug("message");
logger.trace("message");

"info" messages (i.e. calls to logger.info()) display during normal Ant execution, "debug" messages display if "-verbose" was specified and "trace" messages display if "-debug" was specified. This is a bit counterintuitive but this is the best we could do given that Ant's "verbose" does not have a direct counterpart in JCL.

To begin using AntCommonsLogger, download myarch-antuil and add antCommonsLoggerInit task definition to your project, e.g.:

    <taskdef resource="com/myarch/antutil/tasks.properties">
        <classpath>
            <pathelement path="${basedir}/myarch-antutil.jar"/>
            <!-- lib.dir must contain commons-logging -->
            <fileset dir="${lib.dir}" />
        </classpath>
    </taskdef>

You also need to add myarch-util.jar and commons-logging.jar to the classpath of your custom tasks.

Note that calling antCommonsLoggerInit makes AntCommonsLogger the default logger for this JVM instance. This means that all Java classes invoked by this Ant script (e.g., using "java" task) that use JCL, will use AntCommonsLogger instead of java.util logging or log4j. If this is not what you want, call AntCommonsLogger.init(getProject()) at the begging of your custom task and AntCommonsLogger.restorePreviousDefault() at the end.

Download myarch-antuil with AntCommonsLogger

Somebody asked me about examples for PAnt Jython wrapper. Here are some. I'll be updating this page with more examples in the future.

Following is a simple echo task. Note that pant.py has to be on your "python.path". You can set it by adding it to your ANT_OPTS environment variable (ANT_OPTS=-Dpython.path=python_path).

        <script language="jython">
from pant import *
pant=PAnt(project)
pant.execTask(name="echo", message="foo")
        </script>

Following is a copy task example. Note the use of "nested" function to denore nested elements. "expandproperties" is assigned an empty dictionary since it does not have any attributes.

pant = PAnt( project )
pant.copy(todir="${test.prop}", fileset=nested(dir=".", include=nested(name="*.xml")), 
          filterchain=nested(expandproperties={}) ) 

Following is an example of Exec task. Multiple "env" elements are distinguished by adding the suffix "_number". The suffix can in fact be anything, PAnt, simply ignores the substring starting with underbar. This example also demonstrates how you can mix and match python variables and Ant properties in the same piece of code.

shellFile="myshell.sh"
commandLine="options"
pant.exec(dir="${bin.dir}", executable=shellFile,  failonerror="true", resultproperty="result.code",
          env_1=nested(key="key1", value='${val1}'),
          env_2=nested(key="key2", value='${val2}'),
          env_3=nested(key="key3", value='${val3}'),
          arg=nested(line=commandLine) )

In my previous post I blogged about my attempts to replace XML-based syntax for invoking Ant tasks using Jython scripts. But I wasn't fully satisfied with the result - I did not like that fact that I had to pass a task name as a parameter to PAnt.execTask, e.g. pant.execTask("mkdir", dir=buildDir). It just was not intuitive enough. In Ant a task is equivalent to a subroutine, so I really wanted to use the task name as a function name. So I played a bit with dynamic dispatching in Jython and after a simple override of __getattr__ I was able to invoke Ant tasks using this syntax:
pant.mkdir(dir=buildDir)

PAnt (my Ant wrapper) treats any method call as a request to execute an Ant task (except for explicit calls to "execTask" method). This allows for an elegant (in my mind) and concise syntax. The updated PAnt script can be downloaded from here.

Meanwhile, I've started using this wrapper in earnest in a large-scale enterprise build system that I'm working on. So far, I've been absolutely thrilled with the results. This makes writing any non-trivial Ant target so much easier. I'm really hoping that this could make build script development less dull and daunting.

It's pretty easy to create an Ant file for a simple project. A simple Ant script typically contains ubiquitous "init", "compile", "test", "war" (or "jar), "build" targets all wired together. It's easy to change and easy to understand and the script's flow has a declarative, rule-based feel to it. The problem is, projects and their build files rarely stay simple for long. Soon we need to add "validate.xml" target, junit reports, deployment to your application server and so on. Then we begin supporting multiple environments; we discover that our local desktop configuration is different from how integration environment is configured so we add numerous property files, "ftp" tasks and multiple "copy" targets for various application files. Before we know it, the build script becomes a convoluted mess of XML tags and there is nothing declarative about it anymore; it's morphed into a full-fledged, very procedural program. Perhaps we even had to resort to using ant-contrib "if" and "for" targets to implement procedural logic in Ant. And nothing is uglier than an "if" with complex conditions expressed in XML.

A better approach would be to implement "procedural" portion of the build script in Java or any of the scripting languages that Ant supports. The problem is, configuring and invoking Ant tasks from Java or a scripting language leads to verbose code. For example:

    execTask = project.createTask("exec")
    execTask.setOutputproperty(outputPropertyName)
    execTask.setErrorProperty(errorPropertyName)
    execTask.setResultProperty(resultPropertyName)
    execTask.setExecutable(execName)
    arg=execTask.createArg()
    arg.setLine(paramString)

Doing the same thing in XML is shorter and cleaner:

<exec executable="${execName}" outputPropert="p1" 
    errorProperty="p2" resultProperty="p3">
    <arg line="${params}" />
</exec>

So what can we do to make task invocation syntax more concise and easier to understand? In fact, the syntax could be drastically simplified with the help of simple Ant "adapters" that can be developed for popular scripting languages since Groovy, Ruby and python all have fairly intuitive syntax for supporting lists, dictionaries and other data structures. I developed such an adapter for jython. It uses python named arguments and dictionary syntax, so executing a "copy" task looks like this:

pant=PAnt(project)
pant.exTask("copy", todir="testdir",  fileset={"dir":".","includes":"*.xml"} )

"PAnt" is the name of the "ant adapter" class for Jython. The class configures and executes Ant tasks based on the provided arguments using Ant task configuration API.

"pant" module also comes with a simple helper function called "nested" so that named arguments can be consistently used for nested elements. With syntax highlighting supported by most editors/IDEs (e.g., you can try PyDev for jython/python development), it allows for better visual distinctions between attribute names and values:

pant.exTask("copy", todir="testdir",  fileset=nested(dir=".", includes="*.xml") )

To use "PAnt" from Ant, you can develop custom tasks using "scriptdef" or simply embed python code directly into a target:

    <target name="test.pant" >
        <script language="jython">
from pant import *
pant=PAnt(project)
pant.execTask(name="echo", message="foo")
        </script>
    </target>

The "pant" module itself is just a few lines of code as you can see from its code. Don't forget to properly setup your "python.path" if you want to make it globally available to all your Ant scripts.

There is also an open-source project Gant that provides similar (in fact, much more extensive) capabilities for Groovy, but I have not had a chance to play with it; I specifically wanted to use python/jython because jython can also be used for WebSphere Application Server administration.

In my mind scripting language-based approach for writing build files provides for much more flexible and easier to understand and maintain scripts. When you start implementing your Ant logic in python, you'll see that Ant targets become much more coarse-grained, since there is no need to create internal targets (the ones that are never invoked by the users) to simulate subroutines or conditional targets to simulate "if" statements . It is also nice to be able to use all the capabilities of a full-blown programming language as oppose a limited subset of procedural tasks that Ant provides (such as "condition"). Being able to user properly scoped variables instead of inherently global Ant properties is another great benefit.

At the same time, it is still possible to use Ant targets for expressing a flow wiring together major functions of the build script. I would prefer something less XML-like for this purpose too, but that's a task for another day.

Download PAnt

XML is everywhere these days. It is used for passing data around, for specifying metadata and even as a programming language for tools such as Ant and Jetty.

When XML is generated by various development and run-time tools (e.g., for serializing Java objects into SOAP), its complexity and readability don't matter much since humans have to deal with raw XML only occasionally (e.g., to troubleshoot a problem).

However, more often than not, XML is written directly by developers mostly with the help of a validating XML editor/IDE (that is, if developers are lucky and Schema/DTD are available). WSDL (in the case of WSDL-to-Java approach), XML schema and Ant build files are a just a few examples when this is the case.

Using XML as a mark-up language for otherwise mostly text documents (e.g., XHTML) it's not a totally bad idea. However, XML is ill-suited for specifying complex metadata which dynamic dependencies or for wiring command-based logic (e.g., Ant) or for defining domain-specific languages. That is, ill-suited for humans.

For starters, XML is unlike any other programming language (or a natural language). Consider a basic XML construct: <name>value</name>. In any other language it would've been written as "name=value" (or "name:=value", or something similar). An assignment is a construct familiar to most of us from math, even though we may not understand the intricacies of r-value versus l-value. It is intuitive. XML relegates this basic construct to attributes that can only be used as part of an element. Using attributes, a simple assignment can be expressed as <name value="my value" />, which is a bit easier to understand than a purely element-based construct. However, "value" attribute in still seems kind of redundant.

Another annoying feature of XML is closing tags. Closing tags is what makes XML verbose. (What's interesting, SGML, which XML is derived from, did not require closing tags, so one could write something like <TAG/this/.) In most programming languages we express grouping and nesting using brackets or parenthesis or braces. This is true for function arguments, arrays, lists, maps/dictionaries, tuples, you name it, in any modern programming language. XML creators for some reason decided that repeating the name of a variable (tag) is the way to go. This is a great choice for XML parsers but a poor alternative when XML is written/read by humans.

Closing tags do help when the nesting level runs deep. But it does hurt in cases when there is a need to express a simple construct with just a few (or one!) data items. Problem is, our brain can only process limited number of items at a time, so intermixing data that needs to be processed with tags that serve as delimiters for this data makes comprehension more difficult. For simple lists, a comma-delimited format could be a better choice in many situations.

In general, repeating the same set of tags over and over again to define repetitive groups makes XML difficult to read, especially when each element contains just text:

    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>

Compare this with a simple property/comma delimited format: welcome-file-list= index.html, index.htm, index.jsp

Finally, what's up with angle brackets? I suppose, brackets could be justified when an element has multiple attributes. In many cases, however, elements don't have attributes and so an angle bracket is simply a way to distinguish a tag name from data. This is again, counter-intuitive and different from many modern programming language. Normally, variable names are not bracketed or quoted, instead, values are. Also, if there was a need to use a special symbol for denoting variables, wouldn't using "$" or "${}" be a more intuitive option for most of us?

Of course, XML has many advantages, the key one being that it is very easy to develop grammars for XML documents (using DTD or Schema). Another one is the fact that grammars are extensible via namespaces. Finally, any XML grammar can be parsed by any XML parser; to a parser an XML document is just a hierarchy of elements.

This simplicity, however, comes at a great price. Expressiveness of XML is extremely limited. It only has a limited number of constructs and no operators. While it's adequate for its role as a markup language for text files, it puts a lot of constraints on any more-or-less complex metadata format, let alone something requiring procedural logic, such as Ant or XSLT. As a result, intuitiveness of XML-based grammars suffers.

I'm not saying that we must stop using XML altogether. It has its place. But we should not be applying it blindly just because it's the only widely available tool for creating domain-specific languages. For starters, BNF/EBNF, should be part of any developer's arsenal (along with ANTLR). And good old name/value pair and comma-delimited formats should be seriously considered for simple situations that do not require support for hierarchical structures.

Bobby Wolf posted a great article about a wide-spread problem plaguing many SOA implementations: over-engineering of SOA infrastructure, meaning that people rollout products that are not particularly required to implement their business services. He specifically talks about ESBs, but I would say that "you ain't gonna need it" principle should be applied to any component of a SOA stack. For example, why implement a super-expensive BPM suite (or a BPEL engine) when an organization is simply trying to build some data services? Or why pay for a registry if there are only a handful of services in place?

What many people don't realize is just how many SOA-related features are already provided by application servers. Open-source Glassfish server supports JAXR Web services repositories, XSLT mediations, JBI integration and provides extensive Web services monitoring capabilities. It can be augmented by several open-source JBI-based ESBs, such as OpenESB. Other application servers provide similar set of features, although using different technologies (e.g., SCA instead of JBI in IBM products). With an application server being so powerful, there should be a very good reason and business rationale for upgrading to commercial SOA/integration products.

In my mind the right strategy for any SOA is to first implement some services that provide immediate value to the business stakeholders. These services should be implemented using the products already owned and used by an organization (or by using open source ones). After the initial success of this implementation, the organization can evaluate commercial products to see how these products will help implement next set of business requirements/goals more efficiently.

SOAP-based services currently dominate the enterprise landscape. Main reasons this are:

• SOAP tight coupling with WSDL. Until recently, SOAP was the only supported WSDL binding. WSDL, with all of its issues (such as the convoluted structure), remains the only widely accepted vendor-neutral way of defining services.
• In Java world, SOAP was promoted by adding its support to J2EE/Java EE via JAX-RPC and JAX-WS specifications. There is a way to create RESTful services using JAX-WS, however this approach has not gained wide acceptance due to a number of reasons (lack of standardized WSDL binding being one of them).
• Solid support by software vendors. SOAP is supported in all application servers; there are plenty of development tools (including Eclipse and NetBeans) that can help with creating SOAP-based services.
• Availability of a number of WS-* specifications that only work with SOAP. WS-* specs, such as WS-Security and WS-ReliableMessaging heavily rely on SOAP headers for passing message metadata.

SOAP, however, is far from perfect. It adds complexity and overhead and makes implementation of message intermediaries (e.g., gateway products) more difficult (XML message has to be parsed in order to obtain any information about the message, such as an operation name). On the other hand, the uptake of WS-* standards has been very slow, perhaps with the exception of WS-Security, so the benefit of WS-* integration with SOAP failed to materialize. Another supposed SOAP benefit is the protocol neutrality, i.e., a SOAP message looks the same over HTTP, JMS, RMI or any other supported protocol. However, most services are implemented using HTTP, or in some cases, JMS without any headers (unless WS-* is used), so this benefit has limited value.

So it is fair to say that in many instances, SOAP itself does not add any value to Web services implementation. Nevertheless, it's continued to be used because of the reasons listed above. But this situation might be changing in the future.

WSDL 2.0 fully supports HTTP binding. WSDL 2.0 stirred a lot of controversy (I personally think that it's a step forward from WSDL 1), however, it was finally accepted as a W3C recommendation in June, so we can fully expect that vendors support will follow.

Additionally, JAX-RS specification was created and included into Java EE 6. This will also promote development of RESTful services behind the firewall.

Currently, there a preconceived notion that REST is only good for Internet/WEB 2.0 environment, whereas enterprise services should all be using SOAP. The emergence of the two new standards will help change this notion.

Ideally, developers should be able to use the simplest binding that gets the job done. HTTP/REST can be a good choice for many "query-style" services. Services that accept more complex data can use "Plain Old XML" over HTTP post. Finally, services that have to rely on WS-* specifications will utilize SOAP. In all these cases, developers should be able to use same set of APIs for invoking the service and same set of annotations (obviously, with different parameters) for creating the service.

Perhaps this is how Web service development will be done in the future, but we are certainly not there yet.

This article on techtarget is a great illustration of my point from the previous post about the importance of the proper design patterns and techniques required to be able to benefit from XML appliance capabilities.

When implementing Web services Java developers tend to think in terms of Java classes that XML documents map to. Using XSLT (or even Schema) for implementing part of their processing logic is not on their list because the common thinking is that it is too expensive to do it in Java.

With XML appliances the situation is exactly the opposite. XSLT all of a sudden becomes one of the best performing part of an application (although, I would imagine that using Java hardware acceleration such as the one provided by Azul might once again change that). This could be a serious "paradigm shift" for many developers and architects.

Another obstacle to more effective usage of appliances could simply be the lack of XSLT skills. XSLT is essentially a functional language and so it comes with a learning curve attached, especially for complex transformations. It is important to have a good knowledge of XSLT to understand what kind of work can be "outsourced" to an appliance. Not that many developers have this knowledge today, but perhaps it will change with more widespread use of XML appliances.

XML appliances are capable of extremely fast XML parsing and transformation (sometimes the term "wire-speed" is used). The speed is achieved by using hardware acceleration, specially written XML parsers and XSLT engines (you won’t find Xerces on these devices) and optimized operating system (usually, a trimmed-down version of Linux or BSD).

How fast are XML appliances? I’m not aware of published benchmarks; however, I did have a chance to conduct an informal performance testing of DataPower XI50 for a client and the results were quite impressive; for example we saw little to no overhead validating medium-size XML schemas.

Clearly, offloading as much XML processing as possible to an appliance could be a performance booster. So what kind of processing could be done on the device? Here are my recommendations based on the capabilities of the DataPower appliance; the situation could be slightly different with devices from other vendors. Read the rest of this entry »

A Web services registry is arguably one of the most important components of SOA. The registry provides a single source of information about all services in an enterprise.

There are a number of commercial registry/repository products but all of them are quite pricey. Also, smaller organizations or organizations just starting with SOA may not need the full power of a commercial registry/repository product; most of it functionality will remain unutilized. On the other hand, existing registries do not do a particularly good job of managing dependencies between services as well as between service consumers and service providers. Dependency management must be a key consideration in SOA since, unlike in the case of monolithic applications, an SOA consists of a large number of “moving parts”, that is, services. In a well developed SOA most services depend on other services and these services in turn may rely on some other services. Being able to manage and analyze services dependencies is required in order to be able to implement robust and maintainable SOA.

Open source Maven project has become something close to a de-facto standard in the area of dependency management for building Java-based projects and components. Read the rest of this entry »

Layer7 announced that its appliances will support Java-based custom assertions. Details are sketchy at this point but apparently Layer7 will provide a proprietary SDK for developing assertions. This could be much more powerful mechanism than XSLT-only facilities in IBM DataPower.

So how long before appliances begin supporting JBI and SCA components? The trick here of course is to make sure that an appliance is still a robust low-maintenance device that can't be brought down by a rogue application thread. But if Layer7 was able to figure it out for Java in general (I wonder if they use a general Sun JDK or some kind of a special JDK build), there is no reason why an appliance can't start supporting more advanced specifications such as JBI/SCA.

Several SOA vendors are trying to put together comprehensive suites of SOA products that in theory should be capable of addressing all aspects of SOA, including governance, integration, business process management and others.

Formation of SOA suites is having a tremendous impacts on how SOA products are selected as many organizations are being tempted to settle for "one stop shop" approach as opposed to doing proper product evaluation within each SOA product category. (Interesting discussion about SOA suites is available at ZDNet).

So what is a SOA suite and how offerings from different vendors support different aspects of SOA? The table below attempts to answer this question. Read the rest of this entry »

There is an interesting and somewhat controversial interview with ZapThink's Jason Bloomberg where he claims that SCA and JBI are just going to "muddy the waters" as opposed to provide real help to SOA architects.

I certainly agree with his assessment that SCA (can't really speak about JBI) is more of a generic component-centric programming model than a SOA implementation framework. I blogged about it before. However, I do think that SCA is going to provide a lot of value in the area of application architecture and just general component reuse. A technology or a framework does not have to be about SOA to be useful.

Developers working with REST and XML/HTTP services have traditionally used light-weight APIs, such as java.net classes or Apache HttpClient. Web services APIs provided by JAX-RPC were SOAP and "enterprise" only and they required J2EE libraries. The situation changed with the release of JAX-WS and its inclusion into Java SE 6. JAX-WS supports RESTful services; also, its Dispatch interface allows clients to work with XML directly as opposed to having to use object mapping or completely unwieldy SAAJ API. A nice example of using JAX-WS to implement a client for a RESTful service is available in Mark Hadley's blog.

However, I don't think that JAX-WS is going to become the primary way of implementing RESTful clients just yet. In many situations, HttpClient provides more flexibility and control over HTTP calls.

For example, it is very straightforward to turn on basic authentication for a client using HttpClient APIs: Read the rest of this entry »

Lori MacVitte from F5 had a few comments about my post on using XML appliances in ESB capacity. While I don't completely agree with some of her specific points about what ESB capabilities are missing from XML appliances (for example, parallel processing is employed by most appliance vendors, transactionality is also supported for relevant protocols (although no XML appliance can act as an XA transaction coordinator)), the overall observation is correct – there is (and there always will be) a big difference between software-based ESBs and hardware-based XML appliances.

Software ESBs are implemented on top of application servers or messaging products. As such, they are infinitely flexible. Even if certain feature (e.g., some fancy transformation) is not supported by the ESB product out of the box, it can always be custom-developed using Java or other language supported by the product. This custom code can use all the facilities of the underlying application server, such as transaction management, connection pooling and so forth. Read the rest of this entry »