Kotlin Language Features Related to Null Handling

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Any software engineer with a Java background would find the null handling features in the Kotlin language interesting. Let's summarize this topic with some examples. Nullable types: In Kotlin, types are non-nullable by default. If you want a variable to be able to hold a null value, you need to explicitly declare its type as nullable using the Type? syntax. For example, String? denotes a nullable string, while String represents a non-nullable string. Safe calls (?.): Kotlin introduces the safe call operator (?.) for handling nullable types. It allows you to safely invoke a method or access a property on a nullable object. If the object is null, the expression returns null instead of throwing a NullPointerException. Example: data class Person(val name: String, val age: Int, val address: String?) fun main() {     // Create a person with a nullable address     val person1 = Person("John Doe", 25, "123 Main Street")     val person2 = Person("Jane Doe", 30,...
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Fluent Interface Example in an Enterprise Integration Project

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While working on an enterprise integration project about virtual bank payments, I utilized a simple fluent interface approach. The purpose of the code is creating strongly typed objects from a generic SMO (ServiceMessageObject) instance.

Note: In the context of IBM integration technologies, ServiceMessageObject represents the “message”. In our example, it represents a Web Service request.

Old Code:

if (paymentInfo.getDataObject("totalAmount") != null) {
  totalAmount = paymentInfo.getDataObject("totalAmount");
  
  DataObject totalAmount2 = totalAmount.getDataObject("totalAmount");
  if (totalAmount2.getBigDecimal("amount") != null) {
   parameters.setAmount(totalAmount2.getBigDecimal("amount"));
  }
  
  String currencyCode = totalAmount2.getString("currencyCode");
  parameters.setCurrencyCode(currencyCode);  
     
 }
 Byte numberOfInstallments = paymentInfo.getByte("numberOfInstallments");
 if (numberOfInstallments != null) {
  parameters.setNumberOfInstallments(numberOfInstallments);
 }

if (transactionInfo.size() != 0) {
  if (((DataObject) transactionInfo.get(0)).getString("orderID") != null) {
   parameters.setOrderId(((DataObject) transactionInfo.get(0))
     .getString("orderID"));
   if (((DataObject) transactionInfo.get(0))
     .getString("transactionID") != null) {
    parameters.setTransactionID(((DataObject) transactionInfo
      .get(0)).getString("transactionID"));
   }
 parameters.setBankRefId(((DataObject) transactionInfo.get(0)).getString("bankReferenceID"));
//...more


It is really painful to read and modify this code. But actually, what it does is really simple. It should look simple.

New Code:

parameters.setCreditCardNumber(body
  .getDataObject("paymentInfo")
  .getDataObject("creditCardInfo")
  .getString("creditCardNumber"));

parameters.setCreditCardExpiryMonth(body
  .getDataObject("paymentInfo")
  .getDataObject("creditCardInfo")
  .getByte("creditCardExpiryMonth"));

parameters.setAmount(body
  .getDataObject("paymentInfo")
  .getDataObject("totalAmount")
  .getDataObject("totalAmount")
  .getBigDecimal("amount"));

parameters.setTransactionID(body
  .getListItem("transactionInfo")
  .getString("transactionID"));

This is a simple example of an internal DSL. The point I want to stress is this: “Use internal DSLs whenever you need better readability, among other things.”
This simple refactoring helped us a lot to read/modify the code easier than before.

To implement the DSL, what I did is hiding some details in a class that I named DataObjectWrapper. This class contains IBM's DataObject:

public class DataObjectWrapper {

    private DataObject dataObject;
    public DataObjectWrapper getListItem(String string) {
  
 List list = dataObject.getList(string);
  
 if (list.size() != 0) 
  return new DataObjectWrapper((DataObject)list.get(0));
   
 return new NullDataObject();  
    }

    public DataObjectWrapper getDataObject(String field) {

 if (dataObject.getDataObject(field) != null)
             return new DataObjectWrapper(dataObject.getDataObject(field));

 return new NullDataObject();
    }

    public String getString(String field) {
 return dataObject.getString(field);
    }

    public Byte getByte(String field) {
 return dataObject.getByte(field);
    }
}


To support fluent statements, NullDataObject is an important abstraction:

public class NullDataObject extends DataObjectWrapper {
    @Override
    public DataObjectWrapper getDataObject(String string) {
 return new NullDataObject();
    }

    @Override
    public String getString(String field) {
 return null;
    }
    // ...
}

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