substring function

[curtis-cantrell]

I'd love to contribute a substring function, but I see a couple of pull request that already deal with extending function capability that has been hanging around for a few years.

Example: Adding ability to define Functions #354

So, I'm not sure if add this would be used or not...

In a project I"m working on uses jayway, and we have an json file that has a property that is a series of bytes represented as a String. Kind'of like this: "bytes: "000100010010"

I'd like to be able to get just a single character... with substring(3,4,$.bytes)

I added a Substring function, updated the PathFunctionFactory, and wrote unit test... What are the chances something like this could be added?

Thank you,
Curtis Cantrell

package com.jayway.jsonpath.internal.function.text;

import java.util.List;

import com.jayway.jsonpath.internal.EvaluationContext;
import com.jayway.jsonpath.internal.PathRef;
import com.jayway.jsonpath.internal.function.Parameter;
import com.jayway.jsonpath.internal.function.PathFunction;

public class Substring implements PathFunction {
	
	/**
	 * Returns a new string that is a substring of this string. 
	 * <p>
	 * The substring begins at the specified beginIndex and extends to the character at index endIndex – 1. 
	 * <p>
	 * Thus the length of the substring is endIndex-beginIndex. 
	 * <p>
	 * In other words you can say that beginIndex is inclusive and endIndex is exclusive while getting the substring.
	 */
	@Override
    public Object invoke(String currentPath, PathRef parent, Object model, EvaluationContext ctx, List<Parameter> parameters) {
		
        String retVal = null;
        
        if (parameters != null) {
        	
        	 if (parameters.size() != 3)
        	 {
        		 throw new RuntimeException("Function substring must have 3 parameters 'substring(int, int, string)'");
        	 }
        		 
        	 Parameter begin = parameters.get(0);
        	 Parameter end = parameters.get(1);
        	 Parameter text = parameters.get(2);
        	 
        	 if (!(begin.getValue() instanceof Integer))
        	 {
        		 throw new RuntimeException("The begining index must be a number");
        	 }
        	 
        	 if (!(end.getValue() instanceof Integer))
        	 {
        		 throw new RuntimeException("The ending index must be a number");
        	 }

        	 if (!(text.getValue() instanceof String))
        	 {
        		 throw new RuntimeException("Function substring must be invoked with a String parameter");
        	 }
        	 
        	 Integer beginingIndex = (Integer)begin.getValue();
        	 Integer endingIndex = (Integer)end.getValue();
        	 String  textString = (String)text.getValue();
        	 
        	 retVal =  textString.substring(beginingIndex,  endingIndex);
        	 
        }
        return retVal;
    }

}

[kallestenflo]

Crete a PR