Validation of the Input Document

The most obvious enhancement we can make to this program is to validate the input document before we try to process it. As I previously pointed out, we can run into unexpected output, no output, or abnormal termination if the input document doesn't conform to the expected structure. There are two ways we can handle this.

The first way is to add additional code to the program in several places to deal with unexpected conditions. For example, in the main method we would check to see that there was at least one Row Node in the NodeList. We would want to do the same thing when checking for ColumnXX children of the Row Nodes in the CSVRowWriter write method. In addition, we would want to verify that the Row Node's children were Element Nodes and that their names started with Column before we tried to process them as columns. This is a lot of code to add, and you can easily imagine the code you would need to add in more complex applications.

Fortunately, there's an easy way out. The second alternative is to validate the document against a DTD or schema before we process it, letting the DOM API do the heavy lifting. In both the Java and C++ implementations we have to add only a line or two of code. After having given you this teaser, I'll wait until Chapter 5 to actually show you the code. There are, however, other considerations having to do with whether or not we should validate against a schema. I'll discuss these in Chapter 12.

You should now ask, “So what do I validate against?” Ah, there's the question! In Chapter 4 I'll introduce the W3C XML Schema Recommendation and in Chapter 5 the specific schema that can be used for this program and the one developed in the next chapter.