[java] How do I retrieve query parameters in Spring Boot?

I am developing a project using Spring Boot. I've a controller which accepts GET requests.

Currently I'm accepting requests to the following kind of URLs:

http://localhost:8888/user/data/002

but I want to accept requests using query parameters:

http://localhost:8888/user?data=002

Here's the code of my controller:

@RequestMapping(value="/data/{itemid}", method = RequestMethod.GET)
public @ResponseBody
item getitem(@PathVariable("itemid") String itemid) {   
    item i = itemDao.findOne(itemid);              
    String itemname = i.getItemname();
    String price = i.getPrice();
    return i;
}

To accept both @PathVariable and @RequestParam in the same /user endpoint:

@GetMapping(path = {"/user", "/user/{data}"})
public void user(@PathVariable(required=false,name="data") String data,
                 @RequestParam(required=false) Map<String,String> qparams) {
    qparams.forEach((a,b) -> {
        System.out.println(String.format("%s -> %s",a,b));
    }
  
    if (data != null) {
        System.out.println(data);
    }
}

Testing with curl:

• curl 'http://localhost:8080/user/books'
• curl 'http://localhost:8080/user?book=ofdreams&name=nietzsche'

In Spring boot: 2.1.6, you can use like below:

    @GetMapping("/orders")
    @ApiOperation(value = "retrieve orders", response = OrderResponse.class, responseContainer = "List")
    public List<OrderResponse> getOrders(
            @RequestParam(value = "creationDateTimeFrom", required = true) String creationDateTimeFrom,
            @RequestParam(value = "creationDateTimeTo", required = true) String creationDateTimeTo,
            @RequestParam(value = "location_id", required = true) String location_id) {

        // TODO...

        return response;

@ApiOperation is an annotation that comes from Swagger api, It is used for documenting the apis.

I was interested in this as well and came across some examples on the Spring Boot site.

   // get with query string parameters e.g. /system/resource?id="rtze1cd2"&person="sam smith" 
// so below the first query parameter id is the variable and name is the variable
// id is shown below as a RequestParam
    @GetMapping("/system/resource")
    // this is for swagger docs
    @ApiOperation(value = "Get the resource identified by id and person")
    ResponseEntity<?> getSomeResourceWithParameters(@RequestParam String id, @RequestParam("person") String name) {

        InterestingResource resource = getMyInterestingResourc(id, name);
        logger.info("Request to get an id of "+id+" with a name of person: "+name);

        return new ResponseEntity<Object>(resource, HttpStatus.OK);
    }

See here also

While the accepted answer by afraisse is absolutely correct in terms of using @RequestParam, I would further suggest to use an Optional<> as you cannot always ensure the right parameter is used. Also, if you need an Integer or Long just use that data type to avoid casting types later on in the DAO.

@RequestMapping(value="/data", method = RequestMethod.GET)
public @ResponseBody
Item getItem(@RequestParam("itemid") Optional<Integer> itemid) { 
    if( itemid.isPresent()){
         Item i = itemDao.findOne(itemid.get());              
         return i;
     } else ....
}