How to disable spring boot parameter split

Question

We have many @RestController receiving phrases in common language written by users. Phrases can be very long and contains punctuation, like periods and, of course, commas.

Simplified controller example:

@RequestMapping(value = "/countphrases", method = RequestMethod.PUT)
public String countPhrases(
    @RequestParam(value = "phrase", required = false) String[] phrase) {

  return "" + phrase.length;
}

Spring boot default behaviour is to split parameters values at comma, so the previous controller called with this url:

[...]/countphrases?phrase=john%20and%20me,%20you%and%her

Will return "2" istead of "1" like we want. In fact with the comma split the previous call is equivalent to:

[...]/countphrases?phrase=john%20and%20me&phrase=you%and%her

We work with natural language and we need to analyze phrases exactly how the users wrote them and to know exactly how many they wrote.

We tried this solution: https://stackoverflow.com/a/42134833/1085716 after adapting it to our spring boot version (2.0.5):

@Configuration
public class MvcConfig implements WebMvcConfigurer {

    @Override
    public void addFormatters(FormatterRegistry registry) {
        // we hoped this code could remove the "split strings at comma"
        registry.removeConvertible(String.class, Collection.class);
    }
}

But it doesn't work.

Anyone know how to globally remove the "spring boot split string parameters at comma" behaviour in spring boot 2.0.5?

POST, PUT, PATCH are used when posting data into a service, and here you usually use the body because then you can take advantage of SSL and the data sent is encrypted. GET usually returns a body, but the data returned is filtered by what query params you are sending. For example you do a search in a search engine. You want to GET the results filtered on what you searched for "bananas". The query string contains bananas, it will return in the body my results. — Toerktumlare, Sep 11 '19 at 11:04
Some solutions are here https://stackoverflow.com/questions/4998748/how-to-prevent-parameter-binding-from-interpreting-commas-in-spring-3-0-5 — xtian, Feb 24 '22 at 21:29

score 5 · Accepted Answer · answered Sep 11 '19 at 12:14

I find the solution. To override a default conversion we must add a new one. If we remove the old one only it doesn't work.

The correct (example) code should be:

@Configuration
public class MvcConfig implements WebMvcConfigurer {

    @Override
    public void addFormatters(FormatterRegistry registry) {
        registry.removeConvertible(String.class, String[].class);
        registry.addConverter(String.class, String[].class, noCommaSplitStringToArrayConverter());
    }

    @Bean
    public Converter<String, String[]> noCommaSplitStringToArrayConverter() {
        return new Converter<String, String[]>() {
            @Override
            public String[] convert(String source) {
                String[] arrayWithOneElement = {source};
                return arrayWithOneElement;
            }
        };
    }
}

This way any controller like the one in the main question will not split parameters values:

[...]/countphrases?phrase=a,b will return 1 (and fq=["a,b"])
[...]/countphrases?phrase=a,b&phrase=c,d will return 2 (and fq=["a,b", "c,d"])

I don't think so, because the formatters are defined top level. It should be investigated. — Znheb, Mar 24 '21 at 14:31
@dobry, can be done using binder - https://stackoverflow.com/a/20375369/363867 — Musa, Mar 31 '22 at 21:44

score 1 · Answer 2 · answered Oct 15 '21 at 16:24

Replacing your formatter registry with a completely new list could make you loose some needed default formatters that would come with the framework. This will also disable all String-To-Collections parsing for the entire application, on every endpoint, such that if you want to a request filter such as the following at another endpoint, it won't work:

identifiers = 12,34,45,56,67

Solution: Just change your delimiter into something else... # or ; or $

identifiers = 12;23;34;45;56

This is what I have been doing, so I don't mess with all the goodies in the formatter registry.

In our use case your solution was not possibile because the parameter values were human written text and there was no pre-processing available, something like "replace all commas with pipe before calling the api". We didn't have this level of control so we had to change the spring boot behaviour. — Znheb, Oct 26 '21 at 08:23

How to disable spring boot parameter split

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