Spring-boot 过滤器处理与查询参数

Question

In a REST endpoint, I want to receive filters as query parameters. Each filter is defined in a key-value pair separated by commas as follows:

www.example.com/things?filter=key:value,key2:value2,key3:value3

This example means that the list of Things I'm trying to get must have the key as value , and the key2 as value2 and key3 as value3

In this endpoint I can receive multiple filters, like this:

www.example.com/things?filter=key:value&filter=key2:value2,key3:value3

This means that the list of things must have key as value or ( key2 as value2 and key3 as value3 )

In spring-boot, the way to receive multiple query parameters that have the same name is by defining in your controller a @RequestParam("filter") String[] filters . But here's the issue: whenever I'll send just a single filter query parameter, I'll get an array of Strings formed by each key-pair value. If I send multiple filter , I'll get an array with each filter (as expected).

This means that for the first example, I will have an array of size 3 for each key pair, while in the second example I would receive an array of Size 2.

I need that, whenever I send just a single filter as query param, the @RequestParam tag delivers an array of size 1 with the whole String to be parsed later. Is there a way to achieve this?

Answer 1

There might be better ways to achieve what you're after, but this is my suggestion.

A quick proof of concept, using Spring Boot 2.2.1.RELEASE , printing every filter on a separate line

import org.springframework.util.MultiValueMap;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/things")
public class ThingController {

    @GetMapping
    public void filters(@RequestParam MultiValueMap<String, String> filters) {
        System.out.println("Filters:");
        filters.get("filter").forEach(System.out::println);
    }
}

---

A curl command using only a single filter query param:

curl -v 'http://localhost:8080/things/?filter=key:value,key2:value2,key3:value3'

Prints:

Filters:
key:value,key2:value2,key3:value3

---

A curl command using only multiple filter query params:

curl -v 'http://localhost:8080/things/?filter=key:value&filter=key2:value2,key3:value3'

Prints:

Filters:
key:value
key2:value2,key3:value3

Answer 2

What you want to achieve is actually the default behaviour. If you declare an array in @RequestParam you will have the query parameters in the array no matter the number of parameters you send.

EDIT: For example, given this controller:

@GetMapping("/things")
public ResponseEntity getThings(@RequestParam("filter") String[] filters) {

    return ResponseEntity.ok(filters);
}

You can call it in two different ways:

• www.example.com/things?filter=key:value,key2:value2,key3:value3
• www.example.com/things?filter=key:value&filter=key2:value2&filter=key3:value3

Both of them map to the same array:

[
 "key:value",
 "key2:value2",
 "key3:value3"
]

EDIT2: I just checked that you can't mix the two ways. If you do so, the comma separated items will be in the same array item. Maybe that was happening to you