Spring error: nested exception is java.lang.IllegalArgumentException: Class name must not be null

I am currently working on a Spring Security project: Web-application with registration & log-in functions.

The code that will be given later below is from a Udemy course and I am just learning it.

The code seems correct to me, but it throws an exception like this.

(root cause)
org.springframework.beans.factory.UnsatisfiedDependencyException: Error 
creating bean with name 'demoSecurityConfig': Unsatisfied dependency 
expressed through field 'userService'; nested exception is 
org.springframework.beans.factory.UnsatisfiedDependencyException: Error 
creating bean with name 'userServiceImpl': Unsatisfied dependency expressed 
through field 'userDao'; nested exception is 
org.springframework.beans.factory.UnsatisfiedDependencyException: Error 
creating bean with name 'userDaoImpl': Unsatisfied dependency expressed 
through field 'sessionFactory'; nested exception is 
org.springframework.beans.factory.BeanCreationException: Error creating 
bean with name 'sessionFactory' defined in 
com.luv2code.springsecurity.demo.config.DemoAppConfig: Invocation of init 
method failed; nested exception is java.lang.IllegalArgumentException: 
Class name must not be null

If you look at the thrown exception, it has multiple nested exceptions on and on until it reaches the DemoAppConfig.class, so it looks like the @Autowired annotations work fine to me.

For me, it looks like the fundamental problem of this exception is caused by this.

java.lang.IllegalArgumentException: Class name must not be null

However, I can't find a solution to fix this issue. I found a post that talks about this issue which was written in 2013. It says that I need to import these dependencies

<dependencies>
  <!-- ... other dependency elements ... -->
  <dependency>
    <groupId>org.springframework.security</groupId>
    <artifactId>spring-security-web</artifactId>
    <version>3.2.0.CI-SNAPSHOT</version>
  </dependency>
  <dependency>
    <groupId>org.springframework.security</groupId>
    <artifactId>spring-security-config</artifactId>
    <version>3.2.0.CI-SNAPSHOT</version>
  </dependency>
</dependencies>

<repositories>
  <!-- ... possibly other repository elements ... -->
  <repository>
    <id>spring-snapshots</id>
    <url>https://repo.springsource.org/snapshot</url>
  </repository>
</repositories>

However, It does not work.

As it seems that the main cause of the problem is in DemoAppConfig.class, I will only copy and paste the portion of the source code of wired classes, which is enough to show you how they are wired to each other, except the DemoAppConfig.class.

Here is the code.

DemoSecurityConfig.class

@Configuration
@EnableWebSecurity
public class DemoSecurityConfig extends WebSecurityConfigurerAdapter {

	//UserService는 UserDetailsService를 extends하는 interface이다.
	@Autowired
	private UserService userService;

UserService.class

public interface UserService extends UserDetailsService{

	User findByUserName(String userName);
	
	void save(CrmUser crmUser);
}

UserServiceImpl.class

@Service
    public class UserServiceImpl implements UserService{
    
    	@Autowired
    	private UserDao userDao;
    	@Autowired
    	private BCryptPasswordEncoder passwordEncoder;

UserDao.class

public interface UserDao {
	User findByUserName(String userName);
	
	void save(User user);
}

UserDaoImpl.class

@Repository
public class UserDaoImpl implements UserDao {

	// need to inject the session factory
	@Autowired
	private SessionFactory sessionFactory;

DemoAppConfig.class

@Configuration
@EnableWebMvc
@ComponentScan(basePackages="com.luv2code.springsecurity.demo")
@PropertySource("classpath:persistence-oracle.properties")
public class DemoAppConfig {
	
	@Autowired
	private Environment env;

	private Logger logger = Logger.getLogger(getClass().getName());
	
	// define a bean for ViewResolver
	
	@Bean
	public ViewResolver viewResolver() {
		InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
		
		viewResolver.setPrefix("/WEB-INF/view/");
		viewResolver.setSuffix(".jsp");
		
		return viewResolver;
	}
	
	@Bean
	public DataSource securityDataSource() {
		
		ComboPooledDataSource securityDataSource
			= new ComboPooledDataSource();
		
		try {
			securityDataSource.setDriverClass(env.getProperty("jdbc.driver"));
		} catch (PropertyVetoException e) {
			// TODO Auto-generated catch block
			throw new RuntimeException(e);
		}
		
		logger.info(">>> jdbc.url=" + env.getProperty("jdbc.url"));
		logger.info(">>> jdbc.user=" + env.getProperty("jdbc.user"));
		
		securityDataSource.setJdbcUrl(env.getProperty("jdbc.url"));
		securityDataSource.setUser(env.getProperty("jdbc.user"));
		securityDataSource.setPassword(env.getProperty("jdbc.password"));
		
		securityDataSource.setInitialPoolSize(getIntProperty("connection.pool.initialPoolSize"));
		securityDataSource.setMinPoolSize(getIntProperty("connection.pool.minPoolSize"));
		securityDataSource.setMaxPoolSize(getIntProperty("connection.pool.maxPoolSize"));
		securityDataSource.setMaxIdleTime(getIntProperty("connection.pool.maxIdleTime"));
		
		return securityDataSource;
	}
	
	private int getIntProperty(String propName) {
		String propVal = env.getProperty(propName);
		
		int intPropVal = Integer.parseInt(propVal);
		
		return intPropVal;
	}
	
	private Properties getHibernateProperties() {

		// set hibernate properties
		Properties props = new Properties();

		props.setProperty("hibernate.dialect", env.getProperty("hibernate.dialect"));
		props.setProperty("hibernate.show_sql", env.getProperty("hibernate.show_sql"));
	
		return props;				
	}

	
	@Bean
	public LocalSessionFactoryBean sessionFactory(){
		
		// create session factories
		LocalSessionFactoryBean sessionFactory = new LocalSessionFactoryBean();
		
		// set the properties
		sessionFactory.setDataSource(securityDataSource());
		sessionFactory.setPackagesToScan(env.getProperty("hiberante.packagesToScan"));
		sessionFactory.setHibernateProperties(getHibernateProperties());
		
		return sessionFactory;
	}
	
	@Bean
	@Autowired
	public HibernateTransactionManager transactionManager(SessionFactory sessionFactory) {
		
		// setup transaction manager based on session factory
		HibernateTransactionManager txManager = new HibernateTransactionManager();
		txManager.setSessionFactory(sessionFactory);

		return txManager;
	}	
	
	
}

Let me know if you need more information, and thank you for your support.