Problem Statement

Json Expression Evaluator

1. Write a full expression parser and evaluator, that takes in an Expression and a Json
2. Expression will contain:
   1. Variable (which will start with $), could also be nested (dot separated)
   2. Constant:
      1. String within quotes
      2. Boolean - true or false
      3. Decimal
      4. Number
   3. Logical Operator:
      1. AND
      2. OR
      3. NOT
      4. ( ) (Brackets)
   4. Comparison Operators 1) == 2) EXISTS
3. Evaluation will be done on a json string input. Use variable values from this json, to evaluate it against the json.
4. Returns true if expression is true on evaluation against a json

Sample Examples

1. Expression: "$color == 'red'"

   Json: {"color":"red","size":10,"cost":100.0,"mattress":{"name":"king"},"big":true,"legs":[{"length":4}]}

   Output: true

2. Exp: "$mattress.name == 'king' AND $cost == 100.0"

   Json: {"color":"red","size":10,"cost":100.0,"mattress":{"name":"king"},"big":true,"legs":[{"length":4}]}

   Output: true

3. Exp: "NOT EXISTS $color"

   Json: {"color":"red","size":10,"cost":100.0,"mattress":{"name":"king"},"big":true,"legs":[{"length":4}]}

   output: false

4. Exp: "( $cost == 100.0 AND ( $mattress.big == false ) ) OR $size == 100"

   Json: {"color":"red","size":10,"cost":100.0,"mattress":{"name":"king"},"big":true,"legs":[{"length":4}]}

   Output: false

Modules

1. InputData.java: This module reads the input & returns the data

2. Init.java: This module is the entry point of the application. Application starts its execution from here. It reads the input data and give it to Parser to process

3. Parser.java: This module will take the input & process it.

4. JSONParser.java: This module will take the string representation of json & converts it into json object.

5. JSONObject.java: This module will take the json object created by JSONParser.java & json specific operations have been defined here.

6. ExpressionParser.java: This module will take the string representation of expression & split it into tokens

7. Condition.java: This module takes a condition in string format & converts it into a condition object, which will be used in ExpressionEvaluator.java

8. ExpressionEvaluator.java: This module will take care of the evaluation of the expression based on the json object.

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Sub-modules

1. Stack.java: This sub-module will help in evaluation of expression condition. Example: to get the topmost token etc
2. JSONParserHelper.java: This sub-module contains helper functions

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Assumptions

1. I have assumed the given input is valid. (Both expression & json).

2. I have assumed the input format is as same as shown below. Valid expressions formats 1. "$color == 'red'" 2. "$mattress.name == 'king' AND $cost == 100.0" 3. "NOT EXISTS $color" 4. "( $cost == 100.0 AND ( $mattress.big == false ) ) OR $size == 100" etc

      Valid JSON Strings formats
      1. {"color":"red","size":10,"cost":100.0,"mattress":{"name":"king"},"big":true,"legs":[{"length":4}]}
   

3. If the expression contains any keys whose value is Array, then I am considering it as null. Example:

   expression: "$legs.length == 4" Json: {"color":"red","size":10,"cost":100.0,"mattress":{"name":"king"},"big":true,"legs":[{"length":4}]}

   Here in the json 'legs' is a key , whose 'value' is array. When one says 'legs.length', we don't know which element in the array to check. So these kind of expressions will be yield to "false" result.

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Cons

1. Circuit break pattern is not implemented.
2. Restrictions in the inputs.
3. No test cases

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How To Execute?

1. Install java & set up the env variables
2. Import the project into IntelliJ or Eclipse IDE and start executing from Init.java

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Read Author

Name: Sachin Kalsi

Ph: +91 9945746470

email: sachinkalsi15@gmail.com

website: https://sachinkalsi.github.io/

Github: https://github.com/sachinkalsi

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NOTE:

1. PLEASE LET ME KNOW AT ANY TIME IF YOU FIND ANY DIFFICULTY/TROUBLE IN EXECUTING THE APPLICATION.