我应该如何在Spring中使用FindOne

Question

我刚刚通过阅读《 Spring Boot in Action》一书开始学习Spring Boot，我正在复制本书中的示例，尝试自己运行它们，但是使用findOne时遇到了问题。 该项目应该是一个简单的阅读清单。 这是代码：

界面：

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

Reader类：

@Entity
public class Reader implements UserDetails {
    private static final long serialVersionUID = 1L;

    @Id
    private String username;
    private String fullname;
    private String password;

    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getFullname() {
        return fullname;
    }
    public void setFullname(String fullname) {
        this.fullname = fullname;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }

    // UserDetails methods
    @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;
    }
}

SecurityConfig

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Autowired
    private ReaderRepository readerRepository;
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
                .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);
                    }
                });
    }
}

错误：

错误画面

我希望有人能帮助我，因为我迷路了。 谢谢。

Answer 1

java: method findOne in interface org.springframework.data.repository.query.QueryByExampleExecutor<T> cannot be applied to given types; required: org.springframework.data.domain.Example<S> found: java.lang.String reason: cannot infer type-variable(s) S (argument mismatch; java.lang.String cannot be converted to org.springframework.data.domain.Example<S>)

非常简单。 您需要在此处传递Example对象。 这是代码。

Reader  r = new Reader().
r.setUserName("somename");

readerRepository.findOne(Example.of(r));