java - 连接到 postgres Spring MVC 时出现 NullPointerException

Question

我写了这段代码:

Controller :

@Controller
@RequestMapping("/groups")
public class GroupController {

    @Autowired
    private GroupService groupService;

    @RequestMapping
    public String list(Model model) {
        model.addAttribute("groups", groupService.getAllGroups());
        return "groups";
    }
}

数据库连接

    public class dbConnect {

    public dbConnect(){}

    private JdbcTemplate jdbcTemplate;

    public JdbcTemplate getJdbcTemplate() {
        return jdbcTemplate;
    }
    public void DatabaseConnection(){
        DriverManagerDataSource driverManagerDataSource = new DriverManagerDataSource();
        driverManagerDataSource.setDriverClassName("org.postgresql.Driver");
        driverManagerDataSource.setUrl("jdbc:postgres://xxx");
        driverManagerDataSource.setUsername("x");
        driverManagerDataSource.setPassword("xss");
        this.jdbcTemplate=new JdbcTemplate(driverManagerDataSource);
    }
}

群组仓库接口(interface)

public interface GroupRepository {

    List<Group> getAllGroups();
}

群组 repo 实现

@Repository
public class InMemoryGroupRepository implements GroupRepository {

    public InMemoryGroupRepository(){}

    private dbConnect data;

    //@Autowired
    public InMemoryGroupRepository(dbConnect dbConnect) {
        this.data = dbConnect;
    }


    public List<Group> getAllGroups() {
        return data.getJdbcTemplate().query("SELECT id_grupy, nazwa, id_egzaminatora, haslo, egzaminatorzy_id_egzaminatora FROM grupy", new RowMapper<Group>() {
            public Group mapRow(ResultSet rs, int rowNum)
                    throws SQLException {
                Group group = new Group();
                group.setId_grupy(rs.getInt(1));
                group.setNazwa(rs.getString(2));
                group.setId_egzaminatora(rs.getInt(3));
                group.setHaslo(rs.getString(4));
                group.setEgzaminatorzy_id_egzaminatora(rs.getInt(5));
                return group;
            }
        });
    }
}

群组服务接口(interface)

public interface GroupService {
    List<Group> getAllGroups();
}

群组服务实现

@Service
public class GroupServiceImpl implements GroupService {

    @Autowired
    private GroupRepository groupRepository;

    public List<Group> getAllGroups() {
        return groupRepository.getAllGroups();
    }
}

当我尝试输入“/groups”时，出现此错误:

我认为问题是无法建立数据库连接。我们排除了几乎所有可能的错误。我们尝试使用 ArrayList 而不是使用数据库，效果很好。我该如何修复它？

Answer 1

您的数据库配置有错误。 dbConnect 类不是由 Spring 管理的，因此您会得到 NPE，因为它没有注入(inject)到您的存储库中。我建议使用下面的配置:

@Configuration
class PersistenceConfig {

    @Bean
    public DataSource dataSource() {
        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName("org.postgresql.Driver");
        dataSource.setUrl("jdbc:postgres://xxx");
        dataSource.setUsername("x");
        dataSource.setPassword("xss");

        return dataSource;
    }

    @Bean
    public JdbcTemplate jdbcTemplate(DataSource dataSource) {
        return new JdbcTemplate(dataSource);
    }

}

和存储库实现:

@Repository
public class GroupPostgresRepository implements GroupRepository {

    private final JdbcTemplate jdbcTemplate;

    public GroupPostgresRepository(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    public List<Group> getAllGroups() {
        final String sql = "SELECT id_grupy, nazwa, id_egzaminatora, haslo, egzaminatorzy_id_egzaminatora FROM grupy";

        return jdbcTemplate.query(sql, (rs, rowNum) -> {
            Group group = new Group();
            group.setId_grupy(rs.getInt(1));
            group.setNazwa(rs.getString(2));
            group.setId_egzaminatora(rs.getInt(3));
            group.setHaslo(rs.getString(4));
            group.setEgzaminatorzy_id_egzaminatora(rs.getInt(5));
            return group;
        });
    }

}