@RequestParam

@RequestParam主要用于接收url?后面的参数，get或post请求，只要后面的url?有参数都可以获取到对应的参数

@RequestParam注解有几个比较重要的属性
required 表示是否必须，默认为 true，必须。
defaultValue 可设置请求参数的默认值。
value 为接收url的参数名（相当于key值）。

对于对象也能够进行默认接收，前提是参数要与对象属性一致才能够进行注入

    @GetMapping("/requestParam")
    @ResponseBody
    public Map<String, String> requestParam(
            UserDto userDto,//通过一个实体类来接收，字段名必须一致
            @RequestParam(value = "id", required = false) String userId,
            @RequestParam(value = "name", required = false) String userName,
            @RequestParam(value = "pageIndex", required = true, defaultValue = "1") String pageIndex,
            @RequestParam(value = "pageSize", required = true, defaultValue = "5") String pageSize) {
        Map<String, String> map = new HashMap<>();
        map.put("userDto",userDto.toString());
        map.put("id", userId);
        map.put("name", userName);
        map.put("pageIndex", pageIndex);
        map.put("pageSize", pageSize);
        return map;
    }

无参数请求

{
  "pageIndex": "1",
  "name": null,
  "pageSize": "5",
  "id": null,
  "userDto": "UserDto{userName='null', password='null'}"
}

GET http://localhost:8080/requestParam?name=test1&id=2233&userName=nongcha&password=123456
{
  "pageIndex": "1",
  "name": "test1",
  "pageSize": "5",
  "id": "2233",
  "userDto": "UserDto{userName='nongcha', password='123456'}"
}