Intellij Springboot problems on startup - spring-boot

Question

I am really new with spring boot, so I started with some tutorials to create a simple Rest example (my final goal is to integrate it with mongodb, but I need to start!).
I created a new project on IntelliJ with Spring Initializr and choosed Web and Mongodb as features.
Then I added only a class,
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
#RestController
public class HelloController {
#RequestMapping("/")
public String index() {
return "Greetings from Spring Boot!";
}
}
When I run the project, the console is
2018-09-03 20:08:33.139 INFO 1363 --- [ main]
test.test.TestApplication : Starting TestApplication on
MacBook-Pro-di-Stefano.local with PID 1363
(/Users/stefanomiceli/IdeaProjects/test/target/classes started by
stefanomiceli in /Users/stefanomiceli/IdeaProjects/test)
2018-09-03 20:08:33.141 INFO 1363 --- [ main]
test.test.TestApplication : No active profile set,
falling back to default profiles: default
2018-09-03 20:08:33.173 INFO 1363 --- [ main]
ConfigServletWebServerApplicationContext : Refreshing
org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext#15713d56: startup date [Mon Sep 03 20:08:33 PDT 2018]; root of context hierarchy
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by
org.springframework.cglib.core.ReflectUtils$1
(file:/Users/stefanomiceli/.m2/repository/org/springframework/spring-
core/5.0.8.RELEASE/spring-core-5.0.8.RELEASE.jar) to method
java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
WARNING: Please consider reporting this to the maintainers of
org.springframework.cglib.core.ReflectUtils$1
WARNING: Use --illegal-access=warn to enable warnings of further
illegal reflective access operations
WARNING: All illegal access operations will be denied in a future
release
2018-09-03 20:08:33.950 INFO 1363 --- [ main]
o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with
port(s): 8080 (http)
2018-09-03 20:08:33.969 INFO 1363 --- [ main]
o.apache.catalina.core.StandardService : Starting service [Tomcat]
2018-09-03 20:08:33.969 INFO 1363 --- [ main]
org.apache.catalina.core.StandardEngine : Starting Servlet Engine:
Apache Tomcat/8.5.32
2018-09-03 20:08:33.972 INFO 1363 --- [ost-startStop-1]
o.a.catalina.core.AprLifecycleListener : The APR based Apache Tomcat
Native library which allows optimal performance in production
environments was not found on the java.library.path:
[/Users/stefanomiceli/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.]
2018-09-03 20:08:34.021 INFO 1363 --- [ost-startStop-1] o.a.c.c.C.
[Tomcat].[localhost].[/] : Initializing Spring embedded
WebApplicationContext
2018-09-03 20:08:34.021 INFO 1363 --- [ost-startStop-1]
o.s.web.context.ContextLoader : Root WebApplicationContext:
initialization completed in 852 ms
2018-09-03 20:08:34.059 INFO 1363 --- [ost-startStop-1]
o.s.b.w.servlet.ServletRegistrationBean : Servlet dispatcherServlet
mapped to [/]
2018-09-03 20:08:34.061 INFO 1363 --- [ost-startStop-1]
o.s.b.w.servlet.FilterRegistrationBean : Mapping filter:
'characterEncodingFilter' to: [/*]
2018-09-03 20:08:34.062 INFO 1363 --- [ost-startStop-1]
o.s.b.w.servlet.FilterRegistrationBean : Mapping filter:
'hiddenHttpMethodFilter' to: [/*]
2018-09-03 20:08:34.062 INFO 1363 --- [ost-startStop-1]
o.s.b.w.servlet.FilterRegistrationBean : Mapping filter:
'httpPutFormContentFilter' to: [/*]
2018-09-03 20:08:34.062 INFO 1363 --- [ost-startStop-1]
o.s.b.w.servlet.FilterRegistrationBean : Mapping filter:
'requestContextFilter' to: [/*]
2018-09-03 20:08:34.143 INFO 1363 --- [ main]
o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path
[/**/favicon.ico] onto handler of type [class
org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-09-03 20:08:34.310 INFO 1363 --- [ main]
s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for
#ControllerAdvice:
org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext#15713d56: startup date [Mon Sep 03 20:08:33 PDT 2018]; root of context hierarchy
2018-09-03 20:08:34.344 INFO 1363 --- [ main]
s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto
public
org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>>
org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2018-09-03 20:08:34.345 INFO 1363 --- [ main]
s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces= [text/html]}" onto public org.springframework.web.servlet.ModelAndView
org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2018-09-03 20:08:34.362 INFO 1363 --- [ main]
o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path
[/webjars/**] onto handler of type [class
org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-09-03 20:08:34.362 INFO 1363 --- [ main]
o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto
handler of type [class
org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-09-03 20:08:34.550 INFO 1363 --- [ main]
org.mongodb.driver.cluster : Cluster created with
settings {hosts=[localhost:27017], mode=SINGLE,
requiredClusterType=UNKNOWN, serverSelectionTimeout='30000 ms',
maxWaitQueueSize=500}
2018-09-03 20:08:34.582 INFO 1363 --- [localhost:27017]
org.mongodb.driver.connection : Opened connection
[connectionId{localValue:1, serverValue:55}] to localhost:27017
2018-09-03 20:08:34.585 INFO 1363 --- [localhost:27017]
org.mongodb.driver.cluster : Monitor thread successfully
connected to server with description
ServerDescription{address=localhost:27017, type=STANDALONE,
state=CONNECTED, ok=true, version=ServerVersion{versionList=[4, 0,
1]}, minWireVersion=0, maxWireVersion=7, maxDocumentSize=16777216,
logicalSessionTimeoutMinutes=30, roundTripTimeNanos=1582641}
2018-09-03 20:08:34.739 INFO 1363 --- [ main]
o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX
exposure on startup
2018-09-03 20:08:34.768 INFO 1363 --- [ main]
o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s):
8080 (http) with context path ''
2018-09-03 20:08:34.772 INFO 1363 --- [ main]
test.test.TestApplication : Started TestApplication in
1.834 seconds (JVM running for 7.413)
But when I go on localhost:8080/ I get 404 error. What did I do wrong in my helloworld? Is there anything that should I make before running the application?

Answer 1

You need to either
Fix the project structure in order to place the Application Entry Point (TestApplication in this case) in the base package (see image below).
Or use #ComponentScan like this (not recommended):
#SpringBootApplication
#ComponentScan("prova") // add the names of the packages where the controllers, services, repositories, etc, are going to be stored.
public class TestApplication {
public static void main(String[] args) {
SpringApplication.run(TestApplication.class, args);
}
}

Answer 2

Your package structure is wrong:
prova.HelloController
test.test.TestApplication
The HelloController must be on the same level or below TestApplication.

Answer 3

You can do it 2 ways.
1.(preferable) Your controller package naming should be test.test.prova
i.e. Your springboot application should follow the package naming structure of Main class.
e.g. If your Main class has package name = com.test, so the controller package name should be com.test.controller
Another way is adding #ComponentScan to your Main class.
e.g.#SpringBootApplication
#ComponentScan("prova")