How to read a formatted text file into objects

[Kjeld Sigtermans]

Hello,

I have a text file that has a formatted structure containing 0-n lines, each line having the same length, containing properties, who each claim their own position in the line. For example, position 1 through 10 contains property A, position 11-16 contains property B, etc.

What would be an effective way to 'unmarshall' each line to an instance of a class containing property A, B, etc.? Other than explicitly programming to create a new instance, store pos 1-10 to property A, etc.?

E.g. this line:

foo......?bar..!

should result in an instance of a pojo having thePojo.getA() == "foo......?" and thePojo.getB() == "bar..!"

Obviously there is also the problem of how to assign each pojo property name to its corresponding property in the line.

Perhaps I should use XSLT or Freemarker to turn the file into XML and then unmarshall it?

Cheers,
Kjeld

[Rob Spoor]

Since you know exactly how each line is built you can substring each line; for instance, after reading a line (BufferedReader comes into mind), you can use line.substring(0, 10), line.substring(10, 16), etc. The order is fixed as well, so it could be as simple as this:

thePojo.setA(line.substring(0, 10));
thePojo.setB(line.substring(10, 16));
thePojo.setC(line.substring(16, 25)); // if you need characters 17-25

Note that from a human's perspective String start at 1, but in Java (and most other programming languages) they start at 0. So if you say characters 1 to 10, in Java that's 0 to 9, and you use 10 as upper bound of substring because the upper bound is exclusive.

[Kjeld Sigtermans]

Thanks Bob.

But what if I would not want to hardcode the positions in my Java code, and also not hardcode the mapping between line properties and object properties? Instead, specifying this in a mapping file of some sort.
As I said, this is the solution I try to avoid...

Other than explicitly programming to create a new instance, store pos 1-10 to property A, etc.?

Thanks,
Kjeld