Spring Mvc Injection Error(Injection of autowired dependencies failed)

Question

I'm really new in Spring MVC. I write a demo(use annotation),but it doesn't work. here is the construction of my demo

public class WebInitializer extends
    AbstractAnnotationConfigDispatcherServletInitializer {

@Override
protected Class<?>[] getRootConfigClasses() {
    return new Class<?>[] { RootConfigure.class };
}

@Override
protected Class<?>[] getServletConfigClasses() {
    return new Class<?>[] { Configure.class };
}

@Override
protected String[] getServletMappings() {
    return new String[] { "/" };
}

}

in Configure.java,I declare the 'ContackDAO' bean ,like this:

@Configuration
@ComponentScan(basePackages = "base")
@EnableWebMvc
public class Configure extends WebMvcConfigurerAdapter {

@Bean
public ViewResolver getViewResolver() {
    InternalResourceViewResolver resolver = new   InternalResourceViewResolver();
    resolver.setPrefix("/WEB-INF/views/");
    resolver.setSuffix(".jsp");
    return resolver;
}

@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
    registry.addResourceHandler("/resources/**").addResourceLocations(
            "/resources/");
}

@Bean
public ContactDAO getContactDAO() {
    return new ContactDAOImpl();
}
} 

in MainControl.java .I need to use ContackDAO,so I write this:

@Controller
public class MainControl {
@Autowired
private ContactDAO contactDAO;

@RequestMapping(value="/")
public String listContact() throws IOException{
    System.out.println(contactDAO.getBean());// getBean() returns "hello"
    return "hello";
}
}

when I run this demo, I get errors:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mainControl': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private base.dao.ContactDAO base.contorl.MainControl.contactDAO; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [base.dao.ContactDAO] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

what's wrong in my demo? Can you help me?

I find if I put the code:

@Bean
public ContactDAO getContactDAO() {
    return new ContactDAOImpl();
}

into RootConfigure.class

@Configuration
@ComponentScan(basePackages = { "base" }, excludeFilters = { @Filter(type =     FilterType.ANNOTATION, value = EnableWebMvc.class) })
public class RootConfigure {
@Bean
public ContactDAO getContactDAO() {
    return new ContactDAOImpl();
}
}

,the demo run successfully.I don't know why...

Answer 1

希望您不要错过contactDAO的二传手。

Answer 2

Before answering your question, a good practice is to follow the proper package structure.

i.e. in Your case you can put the configuration like this:

        base.dao.config 
        base.dao.impl

        base.mvc.config
        base.mvc.impl

And then include all these in top most configuration. This way it would be a clear separation about configuration for each type of beans that is again for @Repository , @Service and @Controller

To Answer your question about why. because you are excluding your mvc configuration class in the RootConfig.java using excludeFilters.

check the link for excludeFilters in the RootConfig.java

You need to understand first what @EnableWebMvc does and what the excludeFilters does which is explained in below link

ComponentScan

Some SO questions related to similar thing:

excludeFilters not working

And one more: Filter Specific Packages in Component Scan