Handling ConversionException in Spring Framework: A Deep Dive

Posted Sep 24, 2023

By Exception Decoded 2 min read

Many developers working within the Java ecosystem will agree that Spring Framework significantly simplifies the development of enterprise-level applications. The framework provides a rich set of features and utilities, out of which a few can sometimes catch us off guard if we aren’t familiar - an example of such is the ConversionException.

In this comprehensive guide, we’ll be dissecting ConversionException in Spring, its causes, and how to handle it effectively.

Understanding ConversionException

In Spring, ConversionException is a sub-class of NestedRuntimeException. It encapsulates exceptions that arise due to data type conversion issues, such as converting String to Integer or Object to String.

  
public class ConversionException extends NestedRuntimeException

This exception generally occurs when the PropertyEditor fails to convert a string into the required type of property.

Causes of ConversionException

The most prevalent cause of a ConversionException is when Spring fails to convert a string, usually sourced from a properties file, XML configuration, or Controller’s request parameter, to a specific target type.

For instance, when Spring tries to convert the string value "one hundred" to an Integer:

  
Integer value = Integer.parseInt("one hundred");

This prompts a NumberFormatException, which is then wrapped into a ConversionException.

Understanding PropertyEditor and PropertyEditorSupport

Before diving into handling ConversionException, it’s important to reiterate how Spring handles type conversion. Spring intrigues PropertyEditor instances to perform data type conversions.

PropertyEditor is an interface in the java.beans package. However, implementing PropertyEditor from scratch isn’t straightforward. Thus, Spring provides a handy base class named PropertyEditorSupport.

Let’s create a simple custom editor, ExpiryDateEditor, which transforms String to LocalDate and vice versa:

  
public class ExpiryDateEditor extends PropertyEditorSupport {
    private String format = "dd-MM-yyyy";
    
    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        LocalDate date = LocalDate.parse(text, DateTimeFormatter.ofPattern(format));
        setValue(date);
    }
    
    @Override
    public String getAsText() {
        return ((LocalDate) getValue()).format(DateTimeFormatter.ofPattern(format));
    }
}

Registering Custom PropertyEditor in Spring

To use our custom PropertyEditor, we need to register it on the required bean. The process is straightforward:

  
public class Product {
    private LocalDate expiryDate;

    // setters and getters
}

public class ProductController {
    @InitBinder
    public void initBinder(WebDataBinder binder) {
        binder.registerCustomEditor(LocalDate.class, new ExpiryDateEditor());
    }
}

Handling ConversionException

In the event of a ConversionException, we can apply a global exception handling mechanism using ControllerAdvice and ExceptionHandler:

  
@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ConversionException.class)
    public ResponseEntity<String> handleConversionException(ConversionException ex) {
        return new ResponseEntity<>("Failed to convert value: " + ex, HttpStatus.BAD_REQUEST);
    }
}

This will catch any ConversionException thrown across our application and send a proper message to the client, thus ensuring a uniformed and clean error response scheme.

Conclusion

Understanding the Spring Framework ConversionException and how to handle it productively is integral for any Spring application’s robustness and resilience. By mastering these practices, we improve our applications and enhance our abilities as Spring developers.