Request parameters cannot bind to Optional<List<String>> [SPR-13418]

[spring-projects-issues]

Kazuki Shimizu opened SPR-13418 and commented

Request parameter cannot bind to Optional<List<String>> at the @RequestMapping method.

I define the following method as handler method(@RequestMapping method).

@RequestMapping(path="search")
public String search(@RequestParam(defaultValue="word1,word2,word3") Optional<List<String>> words, Model model) {
    List<String> searchWords = words.get();
    System.out.println(searchWords);
    //...
}

I submit a request to http://localhost:8080/myApp/search?words=aaa&words=bbb.
In this case, i was expected a printing as follow:

[aaa, bbb]

But actually, printed as follow:

[aaa]

In this case, request parameters can be bind to first element only.

In addition, i submit a request to http://localhost:8080/myApp/search. (without request parameters)
In this case, printed as follow:

[word1, word2, word3]

In this case,default value converted by conversion service was applied.

This behavior is bug or specification ?

I will submit a repro project at the later.

---

Affects: 4.2.1

Issue Links:

• Support for java.util.Optional as a @RequestParam [SPR-11829] #16448 Support for java.util.Optional as a @RequestParam
• RequestPartMethodArgumentResolver should defensively handle MethodParameter nesting level and java.util.Optional access [SPR-13850] #18423 RequestPartMethodArgumentResolver should defensively handle MethodParameter nesting level and java.util.Optional access
• Request params Optional<List<String> and List<String> are inconsistent [SPR-15676] #20235 Request params Optional<List and List are inconsistent
• MultipartFile argument requires multipart request even when optional (and empty) [SPR-13849] #18422 MultipartFile argument requires multipart request even when optional (and empty)

0 votes, 5 watchers

[spring-projects-issues]

Kazuki Shimizu commented

I've submit PR of repro project.

[spring-projects-issues]

Rossen Stoyanchev commented

It looks like when a request parameter has 2 values the ArrayToObjectConverter kicks in, which tries to convert the first value in the array to the target Object. Since ObjectToOptionalConverter can do just that, we end up with only the first request parameter value used. The case when the @RequestParam default value is used works because in that scenario the conversion is from a comma-separated String.

As a workaround in this case you can remove Optional. The use of defaultValue implies its optional and it will always have a value.

[spring-projects-issues]

Rossen Stoyanchev commented

Juergen Hoeller, it seems that ObjectToOptionalConverter ought to be registered earlier, perhaps ahead of the collection converters?

[spring-projects-issues]

Juergen Hoeller commented

Rossen Stoyanchev, indeed, worth a try...

Juergen

[spring-projects-issues]

Kazuki Shimizu commented

Thanks for comments!!

As a workaround in this case you can remove Optional.

I know the workaround and tried it.
Actually, i want to use without defaultValue attribute as follow.
(in other words, i want to apply a default value that decided by programmatic)

e.g.)

@RequestMapping(path="search")
public String search(@RequestParam String type, @RequestParam Optional<List<String>> words, Model model) {
    model.addAttribute("words", String.valueOf(words.orElseGet(()->defaultValue(type))));
    // ...
}

private List<String> defaultValue(String type){
    // it is dummy code.
    return "1".equals(type) ?
            Arrays.asList("word1", "word2", "word3") :
            Arrays.asList("word4", "word5", "word6");
}

[spring-projects-issues]

Juergen Hoeller commented

Let's do this in a broader fashion for 4.3, making sure Optional declarations work for collections across the framework. In the end, we never really defined the semantics there.

For the time being, when not using defaultValue, you could also declare @RequestParam(required=false). Optional is effectively just a syntactic variation of that.

Juergen

[spring-projects-issues]

Tor Arne Kvaløy commented

As of version 4.3.2 I still only get the first element in the list.

@RequestParam(required = false) Optional<List<String>> locations