Is there an easy way to turn empty form inputs into null strings in Spring MVC?

问题

I'm using Spring MVC and SimpleJdbcInsert to insert objects into a MySQL database. I'd like to set the blank input to NULL in the database rather than ''. I have quite a few fields, and I'm hoping for a way to do this without manually checking every value.

Thanks!

---

UPDATE

So I'm an idiot. Several errors combined on my part led me to believe the correct answers below were not correct. I'd written a PropertyEditorSupport like this:

class StringEditor extends PropertyEditorSupport {

    public void setAsText(String text) {
        String value = text.trim();
        if ("" == value) {
            setValue(null);  
        } else {  
            setValue(value);  
        }
    }

}  

There are two problems:

1. no getAsText, so my form was getting populated with "null" strings!
2. my equality check is C++, not Java. When I tried the recommended setter, I just reloaded the post, which already contained the "null" strings. Once I cleaned all that up, everything started working.

Thanks for the help, and sorry for my "operator error"!

Brett

回答1:

The class you're looking for is:

org.springframework.beans.propertyeditors.StringTrimmerEditor

If you construct it with a true it will convert empty/whitespace strings to null. How to get it registered onto the binder depends on if you want it to be the default or only apply to certain views.

e.g., on a single controller you can just add

@InitBinder
public void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(String.class, new StringTrimmerEditor(true));
}

instructions here

回答2:

I know this is old, but I wasted about 2 or 3 hours until I found a very easy way to apply a StringTrimmerEditor with a binder for all my controllers.

Once again: I must remember to RTFM.

In spring 3.2 you can create a @ControllerAdvice-annottated controller class and use the @InitBinder-annotated method just like the example @Affe gave.

http://docs.spring.io/spring/docs/3.2.x/spring-framework-reference/html/mvc.html#mvc-ann-initbinder-advice

Here is an example:

@ControllerAdvice
@Controller
public class AppBindingInitializer {

    @InitBinder
    public void initBinder(WebDataBinder binder) {
        binder.registerCustomEditor(String.class, new StringTrimmerEditor(true));
    }

}

Hope it helps someone.

回答3:

Perhaps you can use a custom Binder

回答4:

Set the default value for your optional fields to NULL - actually is it not NULL by default?

Parse your input string and then explicitly specify only populated columns with

 usingColumns

oh, and I'd advise to always sanitise your inputs...

来源：https://stackoverflow.com/questions/2977649/is-there-an-easy-way-to-turn-empty-form-inputs-into-null-strings-in-spring-mvc