Why does I'm getting Inferred type 'S' for type parameter 'S' is not within its bound; in my SecurityConfig?

Question

The error: Inferred type 'S' for type parameter 'S' is not within its bound; should extend 'br.com.allen.readinglist.model.Reader'. I tried to read in other questions but none that I tried worked. And I'm not even understanding what the error is.

[Edit] The error is in the line: return readerRepository.findOne(username); of SecurityConfig.

SecurityConfig Class:

package br.com.allen.readinglist.security;

import br.com.allen.readinglist.repository.ReaderRepository;
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.core.userdetails.UserDetails;
import org.springframework.security.core.userdetails.UserDetailsService;
import org.springframework.security.core.userdetails.UsernameNotFoundException;

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Autowired
    private ReaderRepository readerRepository;

    @Override
    protected void configure(HttpSecurity httpSecurity) throws Exception{
        httpSecurity.authorizeRequests().antMatchers("/").access("hasRole('READER')").antMatchers("/**").permitAll().and().formLogin().loginPage("/login").failureUrl("/login?error=true");
    }

    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception{
        auth.userDetailsService(new UserDetailsService() {
            @Override
            public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
                return readerRepository.findOne(username);
            }
        });
    }
}

ReaderRepository Class:

package br.com.allen.readinglist.repository;

import br.com.allen.readinglist.model.Reader;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface ReaderRepository extends JpaRepository<Reader, String> {
}

Reader class:

package br.com.allen.readinglist.model;

import lombok.*;
import org.springframework.security.core.GrantedAuthority;
import org.springframework.security.core.authority.SimpleGrantedAuthority;
import org.springframework.security.core.userdetails.UserDetails;

import javax.persistence.Entity;
import javax.persistence.Id;
import java.util.Arrays;
import java.util.Collection;

@Entity
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Reader implements UserDetails {
    private static final long serialVersionUID = 1L;
    @Id
    private String username;
    private String fullname;
    private String password;

    @Override
    public Collection<? extends GrantedAuthority> getAuthorities(){
        return Arrays.asList(new SimpleGrantedAuthority("READER"));
    }

    @Override
    public boolean isAccountNonExpired(){
        return true;
    }

    @Override
    public boolean isAccountNonLocked(){
        return true;
    }

    @Override
    public boolean isCredentialsNonExpired(){
        return true;
    }

    @Override
    public boolean isEnabled(){
        return true;
    }
}

Answer 1

You need

Optional<Reader> findByUsername(String username);

instead of

<S extends T> Optional<S> findOne(Example<S> example)

https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/repository/query/QueryByExampleExecutor.html