Spring @RequestParam<\/em> annotation can be used to extract the query parameters in a handler method.<\/strong> In this quick tutorial, we\u2019ll learn its usage.<\/p>\n Let\u2019s first expose an API which returns a list of users with a given first name and age:<\/p>\n And now, let\u2019s use cURL<\/em> to quickly test this out:<\/p>\n As we can see, the firstName<\/em> and age<\/em> are the query parameters that got correctly mapped to our handler method.<\/strong><\/p>\n The @RequestParam<\/em> annotation supports the usage of several attributes to cater to various common needs:<\/p>\n In the example we just covered, we\u2019ll notice that the names of the method argument and query parameter were the same (firstName<\/em> and age<\/em>). However, at times, we might feel the need to have different names. For that, we\u2019ll use its name<\/em> or value<\/em> attribute<\/strong>:<\/p>\n With this, the uName<\/em> and uAge<\/em> parameters will map to the firstName<\/em> and age<\/em> method arguments respectively:<\/p>\n By default, if we define a request parameter and don\u2019t pass it in the user request, we\u2019ll get an error.<\/strong><\/p>\n To avoid that, we can set the required<\/em> to false:<\/em><\/p>\n It\u2019ll assign data type defaults to all optional parameters.<\/strong> When we hit below URL:<\/p>\n the firstName<\/em> will get mapped to a null<\/em> value.<\/p>\n If we want to set the required<\/em> to false<\/em> and also map a default value to the concerned attribute, we\u2019ll have:<\/strong><\/p>\n Here, if we don\u2019t pass the firstName <\/em>query parameter, it\u2019ll assume it to be \u2018John\u2019<\/em>.<\/p>\n We can accept a list of query parameters in a Java List:<\/em><\/p>\n To use our new users API, <\/em>we\u2019ll have something as:<\/p>\n To retrieve all passed query parameters from a user request, we\u2019ll accept them as a Java Map<\/em>:<\/p>\n This comes handy when we want to retrieve all parameters without knowing their names:<\/p>\n In this tutorial, we learned how to work with @RequestParam<\/em> annotation in a Spring application.<\/p>\n@RequestParam<\/em> Annotation:<\/h3>\n
@RestController\npublic class UserController {\n ...\n @GetMapping(\"\/users\")\n public List<User> getUsers(@RequestParam String firstName, @RequestParam int age) {\n return userService.findUsersWith(firstName, age);\n }\n}\n<\/pre>\ncurl -XGET 'http:\/\/localhost:8080\/users?firstName=John&age=15'\n...\n[{firstName = John ,lastName = Mason ,age = 15}\n , {firstName = John ,lastName = Dash ,age = 15}] \n<\/pre>\nAttributes of @RequestParam<\/em>:<\/h3>\n
1. name<\/em>\/value<\/em>:<\/h3>\n
@GetMapping(\"\/users\")\npublic List<User> getUsers(@RequestParam(name=\"uName\") String firstName\n , @RequestParam(\"uAge\") int age) {\n return userService.findUsersWith(firstName, age); \n}\n<\/pre>\ncurl -XGET 'http:\/\/localhost:8080\/users?uName=John&uAge=15'\n<\/pre>\n
2. required<\/em>:<\/h3>\n
@GetMapping(\"\/users\") \npublic List<User> getUsers(@RequestParam(required=false) String firstName\n , @RequestParam int age) {\n return userService.findUsersWith(firstName, age); \n}\n<\/pre>\nhttp:\/\/localhost:8080\/users?age=15<\/pre>\n
3. defaultValue<\/em>:<\/h3>\n
@GetMapping(\"\/users\") \npublic List<User> getUsers(@RequestParam(defaultValue=\"John\") String firstName,\n @RequestParam int age) { \n return userService.findUsersWith(firstName, age); \n}\n<\/pre>\n@RequestParam<\/em> with Java List<\/em>:<\/h3>\n
@GetMapping(\"\/users\/v2\")\npublic List<User> getUsersWithGivenAges(@RequestParam List<Integer> age) {\n\u00a0\u00a0\u00a0\u00a0return userService.findUsersWithAges(age);\n}<\/pre>\ncurl -XGET 'http:\/\/localhost:8080\/users\/v2?age=10,15,20'\n\u00a0\nOr\n\u00a0\ncurl -XGET 'http:\/\/localhost:8080\/users\/v2?age=10&age=15&age=20'<\/pre>\n
Retrieve All Parameters:<\/h3>\n
@GetMapping(\"\/paramsEx\")\npublic Map<String, String> \n printParams(@RequestParam Map<String, String> allQueryParams) {\n System.out.println(allQueryParams); \n return allQueryParams; \n}\n<\/pre>\ncurl -XGET 'http:\/\/localhost:8080\/paramsEx?param1=A¶m2=B¶m3=2'\n...\n{param1=A, param2=B, param3=2}\n<\/pre>\nConclusion:<\/h3>\n