Validation in Spring Boot

In this article, via a Gradle project, let us see how to validate a sample application and show the output in the browser. The application is prepared as of type Spring Boot and in this article let us see how to execute via the command line as well.

Example Project

Project Structure:

As this is the Gradle project, we need to check for 

build.gradle

buildscript {
    ext {
        springBootVersion = '2.3.1.RELEASE'
    }
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

group = 'gfg'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 8

repositories {
    mavenCentral()
}

dependencies {
    implementation('org.springframework.boot:spring-boot-starter-data-jpa')
    
    // This is very much essential for validation
    implementation('org.springframework.boot:spring-boot-starter-validation')
    implementation('org.springframework.boot:spring-boot-starter-web')
    runtimeOnly('com.h2database:h2')
    testImplementation('org.springframework.boot:spring-boot-starter-test')
    testImplementation('org.junit.jupiter:junit-jupiter-engine:5.0.1')

    // these dependencies are needed when running with Java 11, since they
    // are no longer part of the JDK
    implementation('javax.xml.bind:jaxb-api:2.3.1')
    implementation('org.javassist:javassist:3.23.1-GA')
}

test{
    useJUnitPlatform()
}

gradlew.bat (Gradle startup script for Windows)

@if "%DEBUG%" == "" @echo off
@rem ##########################################################################
@rem
@rem  Gradle startup script for Windows
@rem
@rem ##########################################################################

@rem Set local scope for the variables with windows NT shell
if "%OS%"=="Windows_NT" setlocal

set DIRNAME=%~dp0
if "%DIRNAME%" == "" set DIRNAME=.
set APP_BASE_NAME=%~n0
set APP_HOME=%DIRNAME%

@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
set DEFAULT_JVM_OPTS=

@rem Find java.exe
if defined JAVA_HOME goto findJavaFromJavaHome

set JAVA_EXE=java.exe
%JAVA_EXE% -version >NULL 2>&1
if "%ERRORLEVEL%" == "0" goto init

echo.
echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
echo.
echo Please set the JAVA_HOME variable in your environment to match the
echo location of your Java installation.

goto fail

:findJavaFromJavaHome
set JAVA_HOME=%JAVA_HOME:"=%
set JAVA_EXE=%JAVA_HOME%/bin/java.exe

if exist "%JAVA_EXE%" goto init

echo.
echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
echo.
echo Please set the JAVA_HOME variable in your environment to match the
echo location of your Java installation.

goto fail

:init
@rem Get command-line arguments, handling Windows variants

if not "%OS%" == "Windows_NT" goto win9xME_args

:win9xME_args
@rem Slurp the command line arguments.
set CMD_LINE_ARGS=
set _SKIP=2

:win9xME_args_slurp
if "x%~1" == "x" goto execute

set CMD_LINE_ARGS=%*

:execute
@rem Setup the command line

set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar

@rem Execute Gradle
"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%

:end
@rem End local scope for the variables with windows NT shell
if "%ERRORLEVEL%"=="0" goto mainEnd

:fail
rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
rem the _cmd.exe /c_ return code!
if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
exit /b 1

:mainEnd
if "%OS%"=="Windows_NT" endlocal

:omega

Now let us see the main application file from which the application starts to execute

SampleValidationApplication.java

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SampleValidationApplication {

    public static void main(String[] args) {
        SpringApplication.run(SampleValidationApplication.class, args);
    }
}

Let us see the necessary files that are helpful to produce the validation errors in a meaningful and clear way

ErrorHandlingControllerAdviceSample.java

import javax.validation.ConstraintViolation;
import javax.validation.ConstraintViolationException;

import org.springframework.http.HttpStatus;
import org.springframework.validation.FieldError;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.ResponseStatus;

@ControllerAdvice
class ErrorHandlingControllerAdviceSample {

  @ExceptionHandler(ConstraintViolationException.class)
  @ResponseStatus(HttpStatus.BAD_REQUEST)
  @ResponseBody
  ValidationErrorResponse onConstraintValidationException(ConstraintViolationException e) {
    ValidationErrorResponse error = new ValidationErrorResponse();
    for (ConstraintViolation violation : e.getConstraintViolations()) {
      error.getViolations().add(new Violation(violation.getPropertyPath().toString(), violation.getMessage()));
    }
    return error;
  }

  @ExceptionHandler(MethodArgumentNotValidException.class)
  @ResponseStatus(HttpStatus.BAD_REQUEST)
  @ResponseBody
  ValidationErrorResponse onMethodArgumentNotValidException(MethodArgumentNotValidException e) {
    ValidationErrorResponse error = new ValidationErrorResponse();
    for (FieldError fieldError : e.getBindingResult().getFieldErrors()) {
      error.getViolations().add(new Violation(fieldError.getField(), fieldError.getDefaultMessage()));
    }
    return error;
  }

}

ValidationErrorResponse.java

import java.util.ArrayList;
import java.util.List;

public class ValidationErrorResponse {

  private List<Violation> violations = new ArrayList<>();

  public List<Violation> getViolations() {
    return violations;
  }

  public void setViolations(List<Violation> violations) {
    this.violations = violations;
  }
}

Violation.java

public class Violation {

  private final String fieldName;

  private final String message;

  public Violation(String fieldName, String message) {
    this.fieldName = fieldName;
    this.message = message;
  }

  public String getFieldName() {
    return fieldName;
  }

  public String getMessage() {
    return message;
  }
}

ValidateGivenParametersByController.java

This is the controller file where we can put the annotations for conditional checking

import javax.validation.ConstraintViolationException;
import javax.validation.constraints.Min;
import javax.validation.constraints.Max;
import javax.validation.constraints.Email;
import javax.validation.constraints.Positive;
import javax.validation.constraints.NegativeOrZero;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RestController;

@RestController
@Validated
class ValidateGivenParametersByController {

  @GetMapping("/validatePathVariable/{id}")
  ResponseEntity<String> validatePathVariable(@PathVariable("id") @Min(5) int id) {
    return ResponseEntity.ok("valid");
  }

  @GetMapping("/validateRequestParameterWithMin")
  ResponseEntity<String> validateRequestParameterWithMin(@RequestParam("id") @Min(0) int id) {
    return ResponseEntity.ok("valid");
  }
  
  @GetMapping("/validateRequestParameterWithMax")
  ResponseEntity<String> validateRequestParameterWithMax(@RequestParam("id") @Max(5) int id) {
    return ResponseEntity.ok("valid");
  }
  
  @GetMapping("/validateRequestParameterWithEmailId")
  ResponseEntity<String> validateRequestParameterWithEmailId(@Email @RequestParam(name = "emailId")  String emailId) {
    return ResponseEntity.ok("valid");
  }
  
  @GetMapping("/validateRequestParameterWithPositive")
  ResponseEntity<String> validateRequestParameterWithPositive(@Positive @RequestParam(name = "id")  int id) {
    return ResponseEntity.ok("valid");
  }
  
  @GetMapping("/validateRequestParameterWithNegativeOrZero")
  ResponseEntity<String> validateRequestParameterWithNegativeOrZero(@NegativeOrZero @RequestParam(name = "id")  int id) {
    return ResponseEntity.ok("valid");
  }

  @ExceptionHandler(ConstraintViolationException.class)
  @ResponseStatus(HttpStatus.BAD_REQUEST)
  @ResponseBody
  String handleConstraintViolationException(ConstraintViolationException e) {
    return "Given input is not valid due to validation error: " + e.getMessage();
  }

}

Via the command line, we can execute the project as follows

Now let us test the following

Test 1:

http://localhost:8080/validatePathVariable/90 

 This is valid as we have the code as id should be @Min(5)). At the same time, if we pass as 

http://localhost:8080/validatePathVariable/1

the error will be thrown

Test 2:

http://localhost:8080/validateRequestParameterWithMin?id=-10

Here @Min(0) is applied and hence we can see below the validation error message

Test 3:

http://localhost:8080/validateRequestParameterWithMax?id=10

Here @Max(5) is applied and hence 

Test 4:

http://localhost:8080/validateRequestParameterWithEmailId?emailId=a.com 

Here emailId is not properly given

Test 5:

http://localhost:8080/validateRequestParameterWithPositive?id=-200 

So only positive numbers alone are accepted

Test 6:

http://localhost:8080/validateRequestParameterWithNegativeOrZero?id=100

So only negative or zero only accepted

Conclusion

Throughout the entire project, we can use the necessary annotation and validate the input fields. We also can give a proper error message and make the software more productive.