因此，我可以使用以下代码修复此问题：
对于SecurityConfig.java:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    private UserDetailServiceImpl customUserDetailsService;

    //Spring injecting for you, IoC
    public SecurityConfig(UserDetailServiceImpl customUserDetailsService) {
        this.customUserDetailsService = customUserDetailsService;
    }

    @Autowired
    public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
        auth.userDetailsService(customUserDetailsService)
            .passwordEncoder(new BCryptPasswordEncoder());
    }

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .csrf().disable() //We don't need CSRF for this example
            .authorizeRequests()
            .anyRequest().authenticated() // all request requires a logged in user
            .and()
            .formLogin()
            .loginProcessingUrl("/login") //the URL on which the clients should post the login information
            .usernameParameter("username") //the username parameter in the queryString, default is 'username'
            .passwordParameter("password");
    }
}

在这里，你可以配置哪些url被请求登录，如果你想自定义登录url、用户名和密码字段，你还可以配置表单。
您的主要问题是，您没有在类中注入“UserDetailServiceImpl”。
这里的提示：您可以像我上面所做的那样使用构造函数，而不是使用@Autowired，spring将为您注入，因此您不必使用注解。
这是一个很好的方法，当你创建单元测试后，你可以很容易地模拟构造类进行测试。

我用了这个答案，它对我很有效：
https://stackoverflow.com/a/42191609/1010619

@EnableWebSecurity
@Configuration
public class AppSecurityConfig extends WebSecurityConfigurerAdapter {

    private UserDetailsService userDetailsService;

public AppSecurityConfig(UserDetailsService userDetailsService) {
    super();
    this.userDetailsService = userDetailsService;
    }

    @Autowired
    public void configureGlobal(AuthenticationManagerBuilder builder, PasswordEncoder passwordEncoder) throws Exception {
    builder.userDetailsService(userDetailsService).passwordEncoder(passwordEncoder);
    }

    // @formatter:off
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
            .antMatchers("/webjars/**", "/static/**").permitAll()
            .antMatchers("/", "/index", "/home", "/register", "/user/confirmRegistration").permitAll()
            .antMatchers("/user/**").hasAnyRole("ADMIN", "USER")
            .anyRequest().authenticated()
            .and()
            .formLogin().loginPage("/loginCustom").permitAll().loginProcessingUrl("/doLogin")
            .and()
            .logout().permitAll().logoutUrl("/logout").logoutSuccessUrl("/")
            .and()
            .csrf().disable()
            ;
    }// @formatter:on 

    public UserDetailsService getUserDetailsService() {
    return userDetailsService;
    }

    @Autowired
    public void setUserDetailsService(UserDetailsService userDetailsService) {
    this.userDetailsService = userDetailsService;
    }

    @Bean
    public PasswordEncoder passwordEncoder() {
    BCryptPasswordEncoder bCryptPasswordEncoder = new BCryptPasswordEncoder();
    return bCryptPasswordEncoder;
    }

}

您正在尝试在SecurityConfig中使用UserDetailServiceImpl，但是您尚未注入UserDetailServiceImpl bean，这将导致该错误。仅执行此操作是不够的：
private UserDetailServiceImpl customUserDetailsService;
您需要注入UserDetailServiceImpl bean。