'If then Else' loops with Conditional Operators from Java code to XML or something else

Question

There are some "if then else" loops with conditional statements in my java program that keep changing almost every day. We cannot keep changing the code, doing a build and deploying it. Hence we decided to bring the whole "if then else" loops to outside the java code. One idea that I have is to represent the entire "if then else" into XML file. This way when the "if then else" loop changes, we will not change the code but just update the xml which would be in some file. This way there would not be any code change. My first question is: is XML the right approach?

If xml is the right approach then, how do I put conditional statements that is present in java code (if then else) into xml. This my second question. Then my plan is to read this xml during runtime and execute the "if then else" loop. Now how will I execute the "if then else" loop with conditional statements in java again during run time? This is my third question.

My idea is (it could be dumb): If I go with XML approach, I can traverse easily through XML using a DOM processor. I can put the conditional statements in an xml node or element as 'text'. Example of conditional statements within xml would be:

(((if x == 100 || x == 200) && (y != 0)) || (a > 1 && b < 20))

Now how do I execute the above conditional statement in java? Especially with all the "&&"and "||" operators. I do not know. Any help here please.

The question could be little confusing. I tried to put sense into it as much as I can.

Answer 1

XML will be hard to update every day. Maybe harder then recompiling and deploying. This is the moment when you want to do some scripting. There are lots of scripting languages out here. Pick one that will suite your needs. I don't have any experience with scripting (yet), but I heard Lua is used sometimes. Wikipedia has a demo list of some applications/games that use Lua for quickly changing logic here.

Another approach might be to use a Java interpreter like Beanshell. Beanshell will compile at runtime Java code in string form to real executable byte code in RAM. This will allow you to write a little Java script apart from the code.

Always be careful with evil script injections.

Answer 2

Many people use XSLT with exactly this objective. Of course, changes to a program in any language deserve to be thoroughly tested before being put into production. But there are degrees of risk, and separating your code into a rarely-changing Java part and a frequently-changing XSLT part can make it easier to manage the testing so you only run the tests for the parts that have changed.

It's not clear to me from your question whether the frequently-changing parts of the code are in fact manipulating XML. If they are, then XSLT invoked from the Java would be a good solution. If not, then other scripting languages might be more appropriate.