BooleanQueryParser

1. What is it?

BooleanQueryParser (BQP) is a software that deals with simple boolean algebra. It contains a small domain specific language that is almolst the same as Java (link).

N.B For now, the only operators that are supported are following:

• relational: < > <= >=
• equality:   == !=
• and or:      && ||
• special: ->
  Special operator -> checks whenever element is present in collection or not(A -> [word1, word2, word3])

What is the difference between BQP and bunch of if-else statements?

It allows you to have dynamic conditions. Whenever your conditional logic changes, if-else java blocks have to be rewritten, application has to be re-builded and re-deployed. In case of BQP you just deploy modified query.
Therefore it is useful whenever you deal with parts of application logic that are highly volatile.

2. How it works?

It is absolutely trivial to use.

String query = "A || $true == (C && D) || $false";
QueryRunner qr = new QueryRunner();
Boolean result = qr.runQuery(query, valueMap);

There are 3 important components

• Map of parameters: This collection contains parameters that are going to be used to resolve the query. It always has to be Java map with String as a key and Object as a value (java.util.Map<String, Object>).
• Query string: Query saved as a java.lang.String. E.g "A || $true == (C && D) || $false"
• QueryRunner object: stargarth.interpreter.QueryRunner is an engine that interprets the query/AST. It takes string query/AST and parameter map as an input. It evaluates the query and returns boolean as an output.
  
  

3. Demo

There are two ways of running queries:
   1. Run it as it is
   2. Build abstract syntax tree (AST) from query string and use it to run queries

stargarth.parser.AbstractSyntaxTree is an internal query representation that QueryRunner is using to evaluate the query.
Running queries with AST as an input has huge benefits when same query is being run multiple times. This is due to the fact that whenever you run with AST rather than query string you skip whole parsing phase.

1 Run query as is:

//Get data
Map<String, Object> valueMap = new HashMap<String, Object>();
valueMap.put("A", false);
valueMap.put("C", true);
valueMap.put("D", true);
valueMap.put("E", "elo");

//Create query
String query = "A || $true == (C && D) || $false";

//Run it
QueryRunner qr = new QueryRunner();
Boolean result = qr.runQuery(query, valueMap);
//true
System.out.println(result);

valueMap.put("C", false);
result = qr.runQuery(query, valueMap);
//false
System.out.println(result);

2 Create AST and utilize use it as input for runner:

Map<String, Object> valueMap = new HashMap<String, Object>();
valueMap.put("A", false);
valueMap.put("C", true);
valueMap.put("D", true);
valueMap.put("E", "elo");

//Create query
String query = "A || $true == (C && D) || $false";

//Generate AST
QueryRunner qr = new QueryRunner();
AbstractSyntaxTree ast = qr.generateAst(query);
//Use it to run query
Boolean result = qr.runQuery(ast, valueMap);
//true
System.out.println(result);
		
valueMap.put("C", false);
result = qr.runQuery(ast, valueMap);
//false
System.out.println(result);

All contributions and feedback are deeply appreciated =)

Proper readme will be added soon™