Back in 2002 or 2003, while working at an internet service provider (Wanadoo Netherlands, now called Online), we were constantly integrating frontend applications created by one team with backend applications created by another. To improve integration, our development team created a technology that would evolve into the contract-first development tool now known as XINS. It worked like a charm for the people involved (architects, developers, IT opeations, management and testers), getting nothing but praise.
But that is a while ago, and the landscape has changed; so how does XINS fare after about 8 years? Looking back, what is arguably good, bad and ugly about it?
- The contract first approach really pays off in terms of quality and productivity. Once the contract is agreed upon by the involved developers and/or development teams, there’s suddenly a lot less room for discussion. And it’s fail fast; the contract is validated at both sides (client and server). This approach makes XINS unique and a real productivity monster. Developers are able to focus on the actual implementation code and hardly have to deal with after-the-implementation-discussions on integration issues;
- Strong operational excellence (like failover, load balancing, error handling, logging, etc.) increases productivity and improves overall quality of these aspects. Part of the functionality is built into the framework, the rest is generated from the specifications.
- From specifications, test forms can be generated. This is not only great for developers testing their own stuff, but also for other development teams, for testers and operations. It’s easy to peek at XINS-based applications.
- Performance has always been very good, with automated performance tests in place to detect regressions. The overhead of the XINS runtime is typically less than a millisecond.
- As long as it goes over HTTP, XINS supports various transport protocols, like JSON, XML-RPC, SOAP and the default: a simple browser-friendly protocol (HTTP GET/POST in, XML out).
- XINS still uses DTDs for validation of the specification files, instead of using the much more powerful XML Schema standard (or even RelaxNG).
- The XML-based specification files use custom file name extensions, like
.fnc, for function definitions,
.typfor types, etc. This typically confuses editors and disables syntax highlighting.
- Unit testing of function implementation classes is hard, they they require generated code (their superclasses). Nowadays, such classes would normally be POJOs.
- The default protocol has some quirks: e.g. it requires XML support in the browser (which Safari does not offer), it is impossible to send empty strings (because these are interpreted as nulls) and errors are returned using the
200 OKstatus, which is not in accordance with the HTML spec, etc.
- XINS 2.3 still uses various non-standard data type classes; this will be fixed in XINS 3.0. Examples of such data types include the
Map<String,String>in XINS 3) and the
Elementclass (XINS 3 will use the W3C DOM API instead).
- XINS tries to be too much at once; it not only generates stuff (code, documentation and test forms), but it also compiles compiles Java code, generates Javadoc, produces a WAR file, enforces an approach to application configurations, etc.
- As a tool, XINS does not fit in well in the current ecosystem of (Java) build tools and IDEs. It has its own source directory structure, it has its own build system, it does not integrate directly with Maven, etc.
- All transport protocols are supported, as long as it is HTTP. Local calls are supported, but then everything needs to be wrapped in
HttpServletResponseobjects. Especially for binary data, this introduces a lot of overhead: binary data is converted to an inefficient format (Base64 or hex), transported in the inefficient format (overhead!) and then converted back to the binary format. Note that this involves storing the data in memory (more than) twice on the server side!
- XINS hardly evolves: the community is minimal and development is slow.
Crowning the Successor
Overall, XINS is a productivity monster that addresses a topic no other tool appears to cover as good. But it has its share of issues; and integration with other processes and tools makes it less developer-friendly.
There is definitely room for an improved contract-first technology, especially if it would offer the following properties and features:
- Strong generation of code, documentation and browser-accessible test forms, similar to XINS.
- A runtime environment (client- and server-side) that provides strong operational excellence, similar to XINS.
- No attempt to be a one-size-fits-all; instead, make it easy to integrate this technology in existing contexts (tools, processes and technologies).
- Easy to pick up for current Java developers; this requires easy integration with modern build tools and IDEs.
- Transport-independence, supporting local calls, HTTP (including browser compatibility and efficient binary data handling), as well as other transports, with solid data type conversion.
- Strong integration with an existing component technology, such as Jigsaw or OSGi.
- Reusing an existing specification technology, such as WebIDL.
There is plenty of room for improving XINS, especially when it comes to adaptation to the current Java ecosystem. Still, in its current form, XINS is a mature technology that really shines when it comes to productivity and operational excellence.