Создание файла с конфигурацией.

spring_online_calculator/src/main/java/WebConfiguration.java

@@ -0,0 +1,11 @@
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.servlet.config.annotation.CorsRegistry;
+import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
+
+@Configuration
+class WebConfiguration implements WebMvcConfigurer {
+    @Override
+    public void addCorsMappings(CorsRegistry registry){
+        registry.addMapping("/**").allowedMethods("*");
+    }
+}

spring_online_calculator/src/main/java/com/example/spring_online_calculator/SpringOnlineCalculatorApplication.java

@@ -14,9 +14,8 @@ public class SpringOnlineCalculatorApplication {
 		SpringApplication.run(SpringOnlineCalculatorApplication.class, args);
 	}
 
-	@CrossOrigin
 	@GetMapping("/String")
-	public String PrintName(@RequestParam(value = "Егор", defaultValue = "Иван") String str) {
+	public String PrintName(@RequestParam(value="Егор", defaultValue = "Егор") String str) {
 		return String.format("Привет, %s!", str);
 	}
 }