How to transfer a logic to JSON and execute it in Java?

HelenBarskaya
March 27, 2024
107 views
0 votes
2 Answers

I have an object with fields a and b. For example, I need to add object.a+10 logic to JSON, and then pass this JSON to Java and perform an action on the object and its field a.

I want to write, for example, like this:

{
"object" : {
             "a": 1,
             "b": 10
           },
"operand1": "object.a",
"operand2": "10",
"operation": "+"
}

Or like this:

{
"object" : {
             "a": 1,
             "b": 10
           },
"action": "object.a + 10",
}

Is it possible? How can this be better implemented?

Tags: java json

Answers

You can use the first option and turn operation into a enum so that it can handle some operation.

Don’t forget to add appropriate exception handling etc.

public class Calculation {
    private Operand object;
    private String operand1;
    private String operand2;
    private OperationEnum operation;
    
    // . . .

    public int calculate(){
       int number1 = Integer.parseInt(operand1 );
       int number2 = Integer.parseInt(operand1 );
       return operation.apply(number1, number2);
    }

}

public enum OperationEnum{
    PLUS("+", (a, b) -> a + b),
    MINUS("-", (a, b) -> a - b),
    DIVIDE("/", (a, b) -> {
        if (b == 0) throw new ArithmeticException("Cannot divide by zero");
        return a / b;
    }),
    MULTIPLY("*", (a, b) -> a * b);

    private final String symbol;
    private final BiFunction<Integer, Integer, Integer> operation;

    Operation(String symbol, BiFunction<Integer, Integer, Integer> operation) {
        this.symbol = symbol;
        this.operation = operation;
    }

    public int apply(int a, int b) {
        return operation.apply(a, b);
    }
    // . . .
}

- Chaosfire
- March 27, 2024 at 12:37 pm
- 0 votes
0
Seems that you want to support both supplying directly a value as an operand and a reference to a value. The example with the reference is basically a JSONPath (well, almost).

JSONPath defines a string syntax for selecting and extracting JSON
(RFC 8259) values from within a given JSON value.

For simple use cases you could write your own simplified implementation, but for anything more complex you should use a library. I would suggest Jayway JsonPath, it is a java implementation of the JSONPath specification.
```
Map<String, Object> data = //parse json, use a library!!!

ToIntFunction<String> jsonPathOperandResolver = val -> JsonPath.parse(data).read("$." + val);
ToIntFunction<String> directValueOperandResolver = Integer::parseInt;

//analyze the value and pick the correct resolver
//for operand1 it's json path
int operand1 = jsonPathOperandResolver.applyAsInt(data.get("operand1").toString());
//for operand2 it's direct value
int operand2 = directValueOperandResolver.applyAsInt(data.get("operand2").toString());
//apply the operation on 1st and 2nd operand
```
The most important (missing part) in this example is that you write the logic to select the correct resolver based on the value. A simplified example, based on delegation may look like this:
```
class DelegatingOperandResolver implements ToIntFunction<String> {

  @Override
  public int applyAsInt(String value) {
    try {
      return directValueOperandResolver.applyAsInt(value);
    } catch (NumberFormatException exc) {
      return jsonPathOperandResolver.applyAsInt(value);
    }
  }
}
```
I would also strongly suggest to rethink your json structure and pick something, which does not constrain you into using Map<String, Object>. Basically something, which would allow you to parse into custom object, something like this:
```
public record CalculationData(String firstOperand, String secondOperand, String operation,
                              Map<String, Object> objToReferValueIn) {
}
```
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