Passing and validating RequestParam in spring-boot rest api

UPDATED: 13 February 2018
In my previous article Creating first rest api in spring-boot we learned how you can create rest api. Now lets learn how you can pass parameters to api and validate it. In this example I'm going to use code from my previous article or you can head to Spring Tutorials page.

@RequestParam
Annotation which indicates that a method parameter should be bound to a web request parameter.

Source code (HelloWorldController.java)
import javax.validation.constraints.Size;

import org.springframework.http.ResponseEntity;
import org.springframework.validation.annotation.Validated;
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;

/**
 * @author javaQuery
 * @since 2018-01-31
 * @github https://github.com/javaquery/spring-boot-examples
 */
@RestController
@RequestMapping("/api")
@Validated
public class HelloWorldController {
 
 /**
  * This will send Hello {name-from-parameter} in response with HTTP status code 200.
  * @since 2018-02-01
  * @param firstname
  * @param lastname
  * @return
  */
   @GetMapping("/hello")
   public ResponseEntity<?> sayHello(
     @RequestParam @Size(min= 1, max = 5, message = "firstname length must be between 1 and 5") String firstname,
     @RequestParam String middlename,
     @RequestParam(required = false) String lastname){
    /* check lastname value */
    lastname = lastname != null ? lastname : "{lastname-is-optional}";
    return ResponseEntity.ok("Hello " + firstname + " " + middlename + " " + lastname);
   }
}
Request parameter syntax
Using @RequestParam spring rest api accept parameters from the request. You can also use various annotation from package javax.validation.constraints with @RequestParam.
@RequestParam <data_type> <variable_name>;

Lets quickly understand annotations used in HelloWorldController.java. As we already discussed few annotations in Creating first rest api in spring-boot so we will talk about new annotations only.

  • @Validated - To perform validation on each method of controller if any.
  • @RequestParam - To accept web request parameter in variable. (Note: All variable annotated with @RequestParam are compulsory/mandatory for request, until you set required = false @RequestParam(required = false) for that parameter)
Request parameter variations
@RequestParam @Size(min= 1, max = 5 , message = "firstname length must be between 1 and 5") String firstname
- @Size of package javax.validation.constraints is used to validate length of parameter in request and will throw ConstraintViolationException if data is not valid.
@RequestParam String middlename
- Accept mandatory parameter in variable middlename. If parameter is not present in request then spring will throw MissingServletRequestParameterException.
@RequestParam(required = false) String lastname
- Accept optional parameter in variable lastname.

Exception Handling
For exception org.springframework.web.bind.MissingServletRequestParameterException and javax.validation.ConstraintViolationException, spring will send 500 (Internal Server Error) in response so we'll catch those exception and send customized response.

Source code (RestExceptionHandler.java)
Used to catch exception thrown.
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

import javax.servlet.http.HttpServletRequest;
import javax.validation.ConstraintViolation;
import javax.validation.ConstraintViolationException;

import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.MissingServletRequestParameterException;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.context.request.WebRequest;
import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;

/**
 * @author javaQuery
 * @since2018-02-01
 */
@Order(Ordered.HIGHEST_PRECEDENCE)
@ControllerAdvice()
public class RestExceptionHandler extends ResponseEntityExceptionHandler{
 
   @Override
   protected ResponseEntity<Object> handleMissingServletRequestParameter(MissingServletRequestParameterException ex, HttpHeaders headers,
     HttpStatus status, WebRequest request) {
    String error = ex.getParameterName() + " parameter is missing.";
    return new ResponseEntity<Object>(new ErrorResponse<>(Arrays.asList(error)), HttpStatus.BAD_REQUEST);
   }
 
   /**
    * Exception thrown when {@link org.springframework.validation.annotation.Validated} is used in controller.
    * @param ex
    * @param request
    * @return
    */
   @ExceptionHandler(ConstraintViolationException.class)
   protected ResponseEntity<?> handleConstraintViolationException(ConstraintViolationException ex, HttpServletRequest request) {
    try {
     List<String> messages = ex.getConstraintViolations().stream().map(ConstraintViolation::getMessage).collect(Collectors.toList());
     return new ResponseEntity<>(new ErrorResponse<>(messages), HttpStatus.BAD_REQUEST);
    } catch (Exception e) {
     return new ResponseEntity<>(new ErrorResponse<>(Arrays.asList(ex.getMessage())), HttpStatus.INTERNAL_SERVER_ERROR);
    }
   }
}
Source code (ErrorResponse.java)
Used to wrap the error message for response.
import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonInclude.Include;

/**
 * @author javaQuery
 * @since 2018-02-01
 * 
 * @param <T>
 */
@JsonIgnoreProperties(ignoreUnknown = true)
@JsonInclude(Include.NON_NULL)
public class ErrorResponse<T> {
   private List<T> errors = new ArrayList<>(1);
 
   public ErrorResponse(List<T> errors) {
    this.errors = errors;
   }
 
   public List<T> getErrors() {
    return errors;
   }
}

Request/Response
cURL GET http://localhost:8080/api/hello
-code 400
-body {"errors":["firstname parameter is missing."]}
cURL GET http://localhost:8080/api/hello?firstname=&middlename=v
-code 400
-body {"errors":["firstname length must be between 1 and 5"]}
cURL GET http://localhost:8080/api/hello?firstname=vicky&middlename=v
-code 200
-body Hello vicky v {lastname-is-optional}
cURL GET http://localhost:8080/api/hello?firstname=vicky&middlename=v&lastname=thakor
-code 200
-body Hello vicky v thakor

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