Spring启动和配置文件

Question

I am learning Spring, and in particular Spring Boot.

I am trying to do some basic injection, but I'm failing to do a basic one. It is probably a quite stupid error, but I can't figure it out - might be because I just woke up :)

This is my application class

package it.myapp.console.spring;

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

import it.myapp.console.menus.MainMenu;

@SpringBootApplication
@EnableAutoConfiguration
public class Application {

   public static void main(String[] args) {
      SpringApplication app = new SpringApplication(MainMenu.class);

      app.run(args);
   }
}

This is the MainMenu class

package it.myapp.console.menus;

import javax.annotation.Resource;

import org.springframework.boot.CommandLineRunner;

import it.myapp.console.test.TestBean;


public class MainMenu implements CommandLineRunner {

   @Resource
   private TestBean testBean;

   public void run(String... strings) throws Exception {

      System.out.println(testBean.doTest());
   }
}

This is my configuration class

package it.myapp.console.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

import it.myapp.console.test.TestBean;
import it.myapp.console.test.TestBeanImpl;

@Configuration
public class ConsoleSpringConfig {

   @Bean
   public TestBean getTest() {
      return new TestBeanImpl();
   }
}

TestBean and TestBeanImpl are quite trivial

package it.myapp.console.test;

public interface TestBean {
   String doTest();
}

and

package it.myapp.console.test;

public class TestBeanImpl implements TestBean {
   public String doTest() {
      return "aaa";
   }
}

What I receive is a really sad

***************************
APPLICATION FAILED TO START
***************************

Description:

A component required a bean of type '...TestBean' that could not be found.


Action:

Consider defining a bean of type '...TestBean' in your configuration.

I swear I've seen quite a few guides, they seem to do everything automagically but I am apparently missing the last bit.

I've tried to launch the application with the --debug option, but it doesn't mention the ConsoleSpringConfig class in any way, so I suppose I'm missing some way to declare that config should be found there.

Thanks for your help! Lorenzo

Answer 1

By default, the @SpringBootApplication allows to trigger auto-configuration and component scanning for the package where the class declaring this annotation is used.
Of course, you can change it by specifying the scanBasePackages attribute of the annotation.

In your case, you declare the annotation in the it.myapp.console.spring.Application class.

So only beans declared in the it.myapp.console.spring package and subpackage of it will be scanner by Spring.

But TestBeanImpl is not located in this base package :

package it.myapp.console.test;

public class TestBeanImpl implements TestBean {
   public String doTest() {
      return "aaa";
   }
}

So, it will not be scanned.

To solve your problem, you could move the TestBeanImpl class in the it.myapp.console.spring.test for example.

And as a general advise, all your beans should be located in the base package or subpackage of the Spring Boot Application to avoid this kind of problem.

Answer 2

Solved the problem by changing

  SpringApplication app = new SpringApplication(MainMenu.class);

into

  SpringApplication app = new SpringApplication(MainMenu.class, MailchimpConsoleSpringConfig.class);

I admit I copied that line and adapted it to my class name without reflecting on its semantics. It lists the first beans to load in the application, and the Java config bean must be in that list of course :)

Thanks for everyone help anyway!