View Drools Generated Code

When we execute rules, behind the scene java code is generated which is actually getting executed, to see this java code you need to set configuration path where you want java code generated by drools to be stored.

PackageBuilderConfiguration configuration = new PackageBuilderConfiguration();
configuration.setDumpDir(new File("XYZ"));

final KnowledgeBuilder kbuilder = KnowledgeBuilderFactory
.newKnowledgeBuilder(configuration);

Set XYZ as a directory path where you would like drools to store generated code. e.g. XYZ = "c:/drools/codegen"

When you run your program the java classes generated for the .drl files are stored at the path XYZ.

This generated code is really helpful to understand the behavior in lot of situations.

Drools - An overview

For Java based applications the most challenging part has always been the business logic maintenance, and pick any applications which you find complex and if we ask ourself how complex it would be moving forward, the answer will always be nX times.

What do we do ? Drools comes for Rescue as a Rule Engine.

Drools provides mechanism:

a. To write business logic in simple english language
b. Easy to maintain and very simple to extend
c. Reusability of logic by defining keywords in a DSL file and using them in DSLR file.

But be careful nothing comes free, everything takes cost in terms of memory and time space.

Use Drools if you really have :

a. Business logic which you think is getting cluttered with multiple if conditions because of variety of scenarios
b. You will have growing demand of increase in the complexity
c. The business logic changes would be frequent (1 - 2 times a year would also be frequent)
d. Your server's have enough of memory as it is a memory hungary tool, it provides performance at cost of memory

Choosing a technology stack is a big decision for the lifecycle of an application, so evaluate both pros and cons and if they fits in your application requirements go for it because it is one of the easiest to use and plug in Java based Rule Engine.

Some programmers might find it cumbersome as we are used to looking at the code which is being executed and loves to debug it and understand it and see what is actually happening, latest version of Drools 5.0 address this by providing JMX support and functionality to see the generated Java Code.

Good Luck with your Rule Engine !!