spring_security登录demo

1.在配置文件中关联登录service
```
security:authentication-manager
<security:authentication-provider user-service-ref="userService">

        <security:password-encoder ref="passwordEncoder"></security:password-encoder>
    </security:authentication-provider>
    
</security:authentication-manager>
```

2.在service中新建service类继承UserDetailsService类,重写loadUserByUsername方法
```
@Service("userService")
public class UserServiceImpl implements UserService {

@Autowired
private SysUserDao sysUserDao;
@Override
public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
    SysUser sysUser = sysUserDao.findByName(username);
    if (sysUser != null) {
        Set<GrantedAuthority> set = new HashSet<>();
        GrantedAuthority grantedAuthority = new SimpleGrantedAuthority("ROLE_USER");
        set.add(grantedAuthority);
        UserDetails user = new User(username, sysUser.getPassword(), set);
        return user;
    }
    return null;
}

}
```