There are times when I want to create a data structure in Mirth, and output the contents of that data structure while debugging the code. Luckily, JSON.stringify() is available not only in modern browsers but also in Mirth.
var o = {
mrn: '8675309',
labs: [
'blood bank',
'microbiology',
'toxicology'
]
};
console.log(JSON.stringify(o, null, '\t'));
However, there are any types of Mirth mapped variables, the JSON.stringify() method blows up on itself with a message similar to
DETAILS: Java class "[B" has no public instance field or method named "toJSON".
This is how we fix it.
Consider the following code. Assume that a variable has been mapped to mrn using Mirth’s mapper transformer or a call to channelMap.put(). This code explodes with the aforementioned error.
var o = {
mrn: $('mrn'),
labs: [
'blood bank',
'microbiology',
'toxicology'
]
};
Oddly, if we call logger.error($('mrn')), the mapped variable shows up correctly. Our assumption is that $('mrn') would return a string if the mapped variable was in fact a string (as opposed to a javascript object, for example). However, if we then call logger.error(typeof $('mrn')), we get “object.” This should be our first clue that not all is what it seems.
Since I am not a Java programmer, I searched the internet trying to find what [B represents. I’ve found that [B is some kind of a byte array in Java, and thus Mirth or maybe even Rhino implements a mapped variable as a byte array. When JSON.stringify() is called on our data structure, toJSON() is called on each individual element in the structure… since the Java byte array [B does not implement toJSON(), an exception is thrown.
So, our goal is to convert the [B object into a javascript string since a javascript string does implement the toJSON() method. My original instinct was to simply called toString() on the mapped variable, but that failed similarly.
I eventually found that explicitly constructing a javascript string with the new keyword would get the job done. This is the working code for printing a data structure with a mapped variable.
var o = {
mrn: new String($('mrn')),
labs: [
'blood bank',
'microbiology',
'toxicology'
]
};
logger.error(JSON.stringify(o, null, '\t'));