[FIXED] Access ServletContext in a ConstraintValidator

Issue

I wish to validate the input using a constraint validator. My problem is that I need some information contained in ServletContext, for example the path of properties file, to validate the request bean. I find that with Spring I can use @Autowired annotation, but unfortunately I can't use this framework.

The constraint:

@Constraint(validateBy = MyValidationClass.class)
@Target(PARAMETER)
@Retention(RUNTIME)
public @interface  MyValidation {
    ...
}

And what I wish do in constraint validator is something like this:

@Override
public boolean isValid(RequestBean value, ConstraintValidatorContext context) {
    Properties props = servletContext.getAttribute("ws.props")
    // my validation
}

How can I achieve this?

Solution

This might not be the best solution. (EDIT: You could find a better solution in my EDIT at the end)

But I guess you could just create a ServletContainerInitializer that stores the ServletContext in a statical variable and access this inside the initializer.

What I don't find very nice here is that you than have a deep dependency to a static method. But otherwise you might find a way to hook into the process that instantiates the ConstraintValidator.

EDIT: I just looked up the Hibernator Validator documentation. And I guess this chapter here would be interesting for you, if you are using the Hibernator Validator implementation: https://docs.jboss.org/hibernate/stable/validator/reference/en-US/html_single/#__code_constraintvalidatorfactory_code

According to this I would create an own ConstraintValidatorFactory and a new interface ServletContextAware with one setter setServletContext(ServletContext). Then the validator factory can check if the class that should be instantiated implements this interface and set the ServletContext. The new ConstraintValidatorFactory could be used to create a new ValidatorFactory that will be used to create the required validators.

Just some not-checked code examples:

interface ServletContextArea {
    public void setServletContext(ServletContext context);
}


public class ServletContextConstraintValidatorFactory implements ConstraintValidatorFactory {
    private ServletContext servletContext;

    public ServletContextConstraintValidatorFactory(ServletContext servletContext) {
        this.servletContext = servletContext;
    }

    @Override
    public <T extends ConstraintValidator<?, ?>> T getInstance(Class<T> key) {
        // create instance from key as validator

        if(validator instanceof ServletContextAware) {
            ((ServletContextAware) validator).setServletContext(this.servletContext);
        }
        //...

        return validator;
    }

    @Override
    public void releaseInstance(ConstraintValidator<?, ?> instance) {
        //...
    }
}

// somewhere in the code where you have the servletContext available
ValidatorFactory validatorFactory = Validation.byDefaultProvider()
    .configure()
    .constraintValidatorFactory( new ServletContextConstraintValidatorFactory(servletContext) )
    .buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

Answered By - chris922
Answer Checked By - Candace Johnson (JavaFixing Volunteer)