[FHIR] Add FHIR XML resource parsing support

[sameeragunarathne]

Description: This issue is to track the FHIR XML resource payload parse support to the ballerina fhir healthcare package.

[nimsara66]

Here's an implementation of a working Proof of Concept (PoC) for FHIR XML resource payload parse support in Ballerina:

FHIRParser.java

package nimsara66.fhir;

import ca.uhn.fhir.context.FhirContext;
import ca.uhn.fhir.parser.DataFormatException;
import ca.uhn.fhir.parser.IParser;
import org.hl7.fhir.instance.model.api.IBaseResource;
import io.ballerina.runtime.api.values.BXml;
import io.ballerina.runtime.api.values.BString;
import io.ballerina.runtime.api.utils.StringUtils;
import io.ballerina.runtime.api.utils.JsonUtils;
import io.ballerina.runtime.internal.ValueConverter;

public class FHIRParser {
    private static final FhirContext context = FhirContext.forR4();

    public static Object fhirXmlToJson(final BXml content) throws DataFormatException {
        IParser source = context.newXmlParser(); // new XML parser
        IBaseResource resource = source.parseResource(content.toString()); // parse the resource
        IParser target = context.newJsonParser(); // new JSON parser
        String jsonString = target.setPrettyPrint(true).encodeResourceToString(resource); // output JSON
        BString bstring = StringUtils.fromString(jsonString);
        return JsonUtils.parse(bstring);
    }
}

fair-lib.bal

import ballerina/jballerina.java;

public type Error distinct error;

# Convert FHIR XML to JSON
#
# + xmlValue - FHIR XML to be converted to JSON
# + return - Converted JSON or Error
public isolated function fhirXmlToJson(xml xmlValue) returns json|Error = @java:Method {
    'class: "nimsara66.fhir.FHIRParser"
} external;

Note:

• This implementation uses HAPI FHIR Structures FHIR R4 for parsing XML in a Java.

This PoC demonstrates the conversion of FHIR XML to JSON using a Java method invocation in Ballerina. Feel free to review and integrate it into the Ballerina FHIR healthcare package. If you have any questions or suggestions, please let me know!

[sameeragunarathne]

Thanks @nimsara66 for the contributions. We will evaluate this and come back.