How to programmatically replace Spring's NumberFormatException with a user-friendly text?

Question

I am working on a Spring web app and i have an entity that has an Integer property which the user can fill in when creating a new entity using a JSP form. The controller method called by this form is below :

@RequestMapping(value = {"/newNursingUnit"}, method = RequestMethod.POST)
public String saveNursingUnit(@Valid NursingUnit nursingUnit, BindingResult result, ModelMap model) 
{
    boolean hasCustomErrors = validate(result, nursingUnit);
    if ((hasCustomErrors) || (result.hasErrors()))
    {
        List<Facility> facilities = facilityService.findAll();
        model.addAttribute("facilities", facilities);

        setPermissions(model);

        return "nursingUnitDataAccess";
    }

    nursingUnitService.save(nursingUnit);
    session.setAttribute("successMessage", "Successfully added nursing unit \"" + nursingUnit.getName() + "\"!");
    return "redirect:/nursingUnits/list";
}

The validate method simply checks if the name already exists in the DB so I did not include it. My issue is that, when I purposely enter text in the field, I would like to have a nice message such as "The auto-discharge time must be a number!". Instead, Spring returns this absolutely horrible error :

Failed to convert property value of type [java.lang.String] to required type [java.lang.Integer] for property autoDCTime; nested exception is java.lang.NumberFormatException: For input string: "sdf"

I fully understand why this is happening but i cannot for the life of me figure out how to, programmatically, replace Spring's default number format exception error message with my own. I am aware of message sources which can be used for this type of thing but I really want to achieve this directly in the code.

EDIT

As suggested, i built this method in my controller but i'm still getting Spring's "failed to convert property value..." message :

@ExceptionHandler({NumberFormatException.class})
private String numberError()
{
   return "The auto-discharge time must be a number!";
}

OTHER EDIT

Here is the code for my entity class :

@Entity
@Table(name="tblNursingUnit")
public class NursingUnit implements Serializable 
{
private Integer id;
private String name;
private Integer autoDCTime;
private Facility facility;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
public Integer getId() 
{
    return id;
}

public void setId(Integer id) 
{
    this.id = id;
}

@Size(min = 1, max = 15, message = "Name must be between 1 and 15 characters long")
@Column(nullable = false, unique = true, length = 15)
public String getName() 
{
    return name;
}

public void setName(String name) 
{
    this.name = name;
}

@NotNull(message = "The auto-discharge time is required!")
@Column(nullable = false)
public Integer getAutoDCTime() 
{
    return autoDCTime;
}

public void setAutoDCTime(Integer autoDCTime) 
{
    this.autoDCTime = autoDCTime;
}

@ManyToOne (fetch=FetchType.EAGER)
@NotNull(message = "The facility is required")
@JoinColumn(name = "id_facility", nullable = false)
public Facility getFacility()
{
    return facility;
}

public void setFacility(Facility facility)
{
    this.facility = facility;
}

@Override
public boolean equals(Object obj) 
{
    if (obj instanceof NursingUnit)
    {
        NursingUnit nursingUnit = (NursingUnit)obj;
        if (Objects.equals(id, nursingUnit.getId()))
        {
            return true;
        }
    }
    return false;
}

@Override
public int hashCode() 
{
    int hash = 3;
    hash = 29 * hash + Objects.hashCode(this.id);
    hash = 29 * hash + Objects.hashCode(this.name);
    hash = 29 * hash + Objects.hashCode(this.autoDCTime);
    hash = 29 * hash + Objects.hashCode(this.facility);
    return hash;
}

@Override
public String toString()
{
    return name + " (" + facility.getCode() + ")";
}
}

YET ANOTHER EDIT

I am able to make this work using a message.properties file on the classpath containing this :

typeMismatch.java.lang.Integer={0} must be a number!

And the following bean declaration in a config file :

@Bean
public ResourceBundleMessageSource messageSource() 
{
    ResourceBundleMessageSource resource = new ResourceBundleMessageSource();
    resource.setBasename("message");
    return resource;
}

This gives me the correct error message instead of the Spring generic TypeMismatchException / NumberFormatException which i can live with but still, I want to do everything programmatically wherever possible and I'm looking for an alternative.

Thank you for your help!

Answer 1

Solution 1: StaticMessageSource as Spring bean

This gives me the correct error message instead of the Spring generic TypeMismatchException / NumberFormatException which i can live with but still, I want to do everything programmatically wherever possible and I'm looking for an alternative.

Your example uses ResourceBundleMessageSource which uses resource bundles (such as property files). If you want to use everything programmatically, then you could use a StaticMessageSource instead. Which you can then set as a Spring bean named messageSource. For example:

@Configuration
public class TestConfig {
    @Bean
    public MessageSource messageSource() {
        StaticMessageSource messageSource = new StaticMessageSource();
        messageSource.addMessage("typeMismatch.java.lang.Integer", Locale.getDefault(), "{0} must be a number!");
        return messageSource;
    }
}

This is the simplest solution to get a user friendly message.

(Make sure the name is messageSource.)

Solution 2: custom BindingErrorProcessor for initBinder

This solution is lower level and less easy than solution 1, but may give you more control:

public class CustomBindingErrorProcessor extends DefaultBindingErrorProcessor {
    public void processPropertyAccessException(PropertyAccessException ex, BindingResult bindingResult) {
        Throwable cause = ex.getCause();
        if (cause instanceof NumberFormatException) {
            String field = ex.getPropertyName();
            Object rejectedValue = ex.getValue();
            String[] codes = bindingResult.resolveMessageCodes(ex.getErrorCode(), field);
            Object[] arguments = getArgumentsForBindError(bindingResult.getObjectName(), field);

            boolean useMyOwnErrorMessage = true; // just so that you can easily see to default behavior one line below
            String message = useMyOwnErrorMessage ? field + " must be a number!" : ex.getLocalizedMessage();
            FieldError error = new FieldError(bindingResult.getObjectName(), field, rejectedValue, true, codes, arguments, message);
            error.wrap(ex);
            bindingResult.addError(error);
        } else {
            super.processPropertyAccessException(ex, bindingResult);
        }
    }
}

@ControllerAdvice
public class MyControllerAdvice {
    @InitBinder
    public void initBinder(WebDataBinder binder) {
        BindingErrorProcessor customBindingErrorProcessor = new CustomBindingErrorProcessor();
        binder.setBindingErrorProcessor(customBindingErrorProcessor);
    }
}

It basically intercepts the call to DefaultBindingErrorProcessor.processPropertyAccessException and adds a custom FieldError message when binding failed with a NumberFormatException.

Example code without Spring Web/MVC

In case you want to try it without Spring Web/MVC, but just plain Spring, then you could use this example code.

public class MyApplication {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(MyConfig.class);
        Validator validator = context.getBean(LocalValidatorFactoryBean.class);

        // Empty person bean to be populated
        Person2 person = new Person2(null, null);
        // Data to be populated
        MutablePropertyValues propertyValues = new MutablePropertyValues(List.of(
                new PropertyValue("name", "John"),
                // Bad value
                new PropertyValue("age", "anInvalidInteger")
        ));

        DataBinder dataBinder = new DataBinder(person);
        dataBinder.setValidator(validator);
        dataBinder.setBindingErrorProcessor(new CustomBindingErrorProcessor());

        // Bind and validate
        dataBinder.bind(propertyValues);
        dataBinder.validate();

        // Get and print results
        BindingResult bindingResult = dataBinder.getBindingResult();
        bindingResult.getAllErrors().forEach(error -> 
                System.out.println(error.getDefaultMessage())
        );
        
        // Output:
        // "age must be a number!"
    }
}

@Configuration
class MyConfig {
    @Bean
    public LocalValidatorFactoryBean validator() {
        return new LocalValidatorFactoryBean();
    }
}

class Person2 {
    @NotEmpty
    private String name;

    @NotNull @Range(min = 20, max = 50)
    private Integer age;

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public Integer getAge() { return age; }
    public void setAge(Integer age) { this.age = age; }

    public Person2(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
}

Answer 2

@Martin, I asked you about the version because @ControllerAdvice is available starting with version 3.2.

I would recommend you to use @ControllerAdvice, which is an annotation that allows you to write code that is sharable between controllers(annotated with @Controller and @RestController), but it can also be applied only to controllers in specific packages or concrete classes.

ControllerAdvice is intended to be used with @ExceptionHandler, @InitBinder, or @ModelAttribute.

You set the target classes like this @ControllerAdvice(assignableTypes = {YourController.class, ...}).

@ControllerAdvice(assignableTypes = {YourController.class, YourOtherController.class})
public class YourExceptionHandler{
    //Example with default message
    @ExceptionHandler({NumberFormatException.class})
    private String numberError(){
        return "The auto-discharge time must be a number!";
    }

    //Example with exception handling
    @ExceptionHandler({WhateverException.class})
    private String whateverError(WhateverException exception){
        //do stuff with the exception
        return "Whatever exception message!";
    }

    @ExceptionHandler({ OtherException.class })
    protected String otherException(RuntimeException e, WebRequest request) {
        //do stuff with the exception and the webRequest
        return "Other exception message!";
    }
} 

What you need to keep in mind is that if you do not set the target and you define multiple exception handlers for the same exceptions in different @ControllerAdvice classes, Spring will apply the first handler that it finds. If multiple exception handlers are present in the same @ControllerAdvice class, an error will be thrown.

Answer 3

You can annotate a method with:

@ExceptionHandler({NumberFormatException.class})
public String handleError(){
   //example
   return "Uncorrectly formatted number!";
}

and implement whatever you want to do in case the exception of that type is thrown. The given code will handle exceptions happened in the current controller. For further reference consult this link.

To make global error handling you can use @ControllerAdvice in the following way:

@ControllerAdvice
public class ServiceExceptionHandler extends ResponseEntityExceptionHandler {

   @ExceptionHandler({NumberFormatException.class})
    public String handleError(){
       //example
       return "Uncorrectly formatted number!";
    }
} 

Answer 4

You may be able to override that messaging by providing an implementation of the Spring DefaultBindingErrorProcessor similar to what is done here: Custom Binding Error Message with Collections of Beans in Spring MVC

Answer 5

Handle NumberFormatException.

try {
 boolean hasCustomErrors = validate(result, nursingUnit);
}catch (NumberFormatException nEx){
 // do whatever you want
 // for example : throw custom Exception with the custom message.
}