Add Spring Boot Custom Validation Module (#18873)

* Add Spring Boot Custom Validation Module

* Moved classes to com.baeldung.validation.custommessage package

Author: sandipk09roy-pixel

spring-boot-modules/spring-boot-custom-validation/src/main/java/com/baeldung/validation/custommessage/AppConfig.java

@@ -0,0 +1,19 @@
+package com.baeldung.validation.custommessage;
+
+import org.springframework.context.MessageSource;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.support.ResourceBundleMessageSource;
+
+@Configuration
+public class AppConfig {
+
+    @Bean
+    public MessageSource messageSource() {
+        ResourceBundleMessageSource source = new ResourceBundleMessageSource();
+        source.setBasename("ValidationMessages");
+        source.setDefaultEncoding("UTF-8");
+        source.setUseCodeAsDefaultMessage(true);
+        return source;
+    }
+}

spring-boot-modules/spring-boot-custom-validation/src/main/java/com/baeldung/validation/custommessage/LogbackPing.java

@@ -0,0 +1,11 @@
+package com.baeldung.validation.custommessage;
+import ch.qos.logback.core.util.StatusPrinter;
+import org.slf4j.LoggerFactory;
+import ch.qos.logback.classic.LoggerContext;
+
+public class LogbackPing {
+    public static void ping() {
+        LoggerContext context = (LoggerContext) LoggerFactory.getILoggerFactory();
+        StatusPrinter.print(context);
+    }
+}

spring-boot-modules/spring-boot-custom-validation/src/main/java/com/baeldung/validation/custommessage/SpringBootCustomValidationApplication.java

@@ -0,0 +1,12 @@
+package com.baeldung.validation.custommessage;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class SpringBootCustomValidationApplication {
+    public static void main(String[] args) {
+        LogbackPing.ping(); // Ensures logback-core is included
+        SpringApplication.run(SpringBootCustomValidationApplication.class, args);
+    }
+}

spring-boot-modules/spring-boot-custom-validation/src/main/java/com/baeldung/validation/custommessage/UserController.java

@@ -0,0 +1,29 @@
+// Minor change to trigger PR comparison
+package com.baeldung.validation.custommessage;
+
+import org.springframework.http.ResponseEntity;
+import org.springframework.validation.BindingResult;
+import org.springframework.validation.FieldError;
+import org.springframework.web.bind.annotation.*;
+
+import jakarta.validation.Valid;
+import java.util.List;
+import java.util.stream.Collectors;
+
+@RestController
+@RequestMapping("/register")
+public class UserController {
+
+    @PostMapping
+    public ResponseEntity<?> registerUser(@RequestBody @Valid UserDTO userDTO, BindingResult result) {
+        if (result.hasErrors()) {
+            List<String> errors = result.getFieldErrors()
+                .stream()
+                .map(FieldError::getDefaultMessage)
+                .collect(Collectors.toList());
+            return ResponseEntity.badRequest().body(errors);
+        }
+
+        return ResponseEntity.ok("User registered successfully");
+    }
+}

spring-boot-modules/spring-boot-custom-validation/src/main/java/com/baeldung/validation/custommessage/UserDTO.java

@@ -0,0 +1,42 @@
+package com.baeldung.validation.custommessage;
+
+import jakarta.validation.constraints.Email;
+import jakarta.validation.constraints.Min;
+import jakarta.validation.constraints.NotBlank;
+
+public class UserDTO {
+
+    @NotBlank(message = "{user.name.notblank}")
+    private String name;
+
+    @Email(message = "{user.email.invalid}")
+    private String email;
+
+    @Min(value = 18, message = "{user.age.min}")
+    private int age;
+
+    // Getters and setters
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+}