Convert Java object to a Ballerina JSON value

Question

Is it possible to convert Java objects into Ballerina objects and/or JSON types? I want to use the POI Java package to read XLSX and make it available in Ballerina land as a record[] or json[] or something else.

Answer 1

Yes, you can achieve this using Java interoperability and the bindgen tool to generate Ballerina objects corresponding to Java objects. Check out the following resources for more information:

• Call Java Code from Ballerina
• Java Interoperability Guide

However, note that there is no direct way to convert Java objects to Ballerina records or JSON types. Here are a couple of options:

1. If you have a string representation in JSON format, you can use the fromJsonStringWithType function to convert it to an array of JSON or records.

   import ballerina/jballerina.java;
   
   type Employee record {|
       int id;
       string name;
       json...;
   |};
   
   // `jsonJavaStr` is the Java String that is in JSON format.
   function convertToEmployees(handle jsonJavaStr) returns Employee[]|error {
       string? jsonBalStr = java:toString(jsonJavaStr);
   
       if jsonBalStr is () {
           return error("expected non-empty string");
       }
   
       return jsonBalStr.fromJsonStringWithType();
   }
   

2. You could create the Java representation of json[] in an external function you implement (actual conversion would happen in Java). For example, creating a io.ballerina.runtime.api.values.BArray value using io.ballerina.runtime.api.creators.ValueCreator#createArrayValue.

   // `javaObj` is the reference to the Java object.
   function constructJsonArray(handle javaObj) returns json[] = external;
   

   This approach involves more work since you'll have to create a new array type and recursively parse/map the values too.