使用@RequestParams 时，可以使用 Spring Boot 中的 Query by Example 来替代条件逻辑吗？

如何解决使用@RequestParams 时，可以使用 Spring Boot 中的 Query by Example 来替代条件逻辑吗？

我有以下用于 Spring Boot 应用程序的代码：

实体：

@Proxy(lazy = false)
public class Vehicle {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  private String type;
  private String make;
  private String model;
  private Integer year;

控制器：

@RequestMapping("/vehicles")
public class VehicleController {

  @Autowired
  private VehicleService vehicleService;

  //GET method to get all vehicles,or specify a parameter
  @GetMapping
  @ResponseStatus(HttpStatus.OK)
  public List<Vehicle> getAllVehicles(
      @RequestParam(required = false) Map<String,String> allParams) {
    return vehicleService.getVehicles(allParams);
  }

服务：

  private VehicleRepository vehicleRepository;

  /**
   * Gets the full list of vehicles based on the provided parameters. If no parameters are
   * presented,then returns the entire list of vehicles
   *
   * @param allParams A map of all possible parameters that can be passed through
   * @return list of vehicles
   */
  @Override
  public List<Vehicle> getVehicles(Map<String,String> allParams) {
    //gather all of the possible parameters that can be passed through
    String type = allParams.get("type");
    String make = allParams.get("make");
    String model = allParams.get("model");
    Integer year;
    try {
      year = Integer.parseInt(allParams.get("year"));
    } catch (NumberFormatException n) {
      year = 0;
    }

    if (type != null && make != null && model != null && year != 0) {
      return vehicleRepository.findByTypeAndMakeAndModelAndYear(type,make,model,year);
    }
    if (make != null && type == null && model != null && year != 0) {
      return vehicleRepository.findByMakeAndModelAndYear(make,year);
    }
    if (type != null && make == null && model != null && year != 0) {
      return vehicleRepository.findByTypeAndModelAndYear(type,year);
    }
    if (type != null && make != null && model == null && year != 0) {
      return vehicleRepository.findByTypeAndMakeAndYear(type,year);
    }
    if (model != null && type == null && make == null && year != 0) {
      return vehicleRepository.findByModelAndYear(model,year);
    }
    if (make != null && type == null && model == null && year != 0) {
      return vehicleRepository.findByMakeAndYear(make,year);
    }
    if (type != null && make == null && model == null && year != 0) {
      return vehicleRepository.findByTypeAndYear(type,year);
    }
    if (type != null && make != null && model != null) {
      return vehicleRepository.findByTypeAndMakeAndModel(type,model);
    }
    if (make != null && type == null && model != null) {
      return vehicleRepository.findByMakeAndModel(make,model);
    }
    if (type != null && make == null && model != null) {
      return vehicleRepository.findByTypeAndModel(type,model);
    }
    if (type != null && make != null) {
      return vehicleRepository.findByTypeAndMake(type,make);
    }
    if (type != null) {
      return vehicleRepository.findByType(type);
    }
    if (make != null) {
      return vehicleRepository.findByMake(make);
    }
    if (model != null) {
      return vehicleRepository.findByModel(model);
    }
    if (year != 0) {
      return vehicleRepository.findByYear(year);
    }

    return vehicleRepository.findAll();
  }

存储库：

public interface VehicleRepository extends JpaRepository<Vehicle,Long> {

  List<Vehicle> findByTypeAndMakeAndModelAndYear(String type,String make,String model,Integer year);

  List<Vehicle> findByMakeAndModelAndYear(String make,Integer year);

  List<Vehicle> findByTypeAndModelAndYear(String type,Integer year);

  List<Vehicle> findByTypeAndMakeAndYear(String type,Integer year);

  List<Vehicle> findByModelAndYear(String model,Integer year);

  List<Vehicle> findByMakeAndYear(String make,Integer year);

  List<Vehicle> findByTypeAndYear(String type,Integer year);

  List<Vehicle> findByTypeAndMakeAndModel(String type,String model);

  List<Vehicle> findByMakeAndModel(String make,String model);

  List<Vehicle> findByTypeAndModel(String type,String model);

  List<Vehicle> findByTypeAndMake(String type,String make);

  List<Vehicle> findByType(String type);

  List<Vehicle> findByMake(String make);

  List<Vehicle> findByModel(String model);

  List<Vehicle> findByYear(Integer year);

}

显然，服务层有很多条件逻辑来覆盖传递参数的多种组合。虽然它实现了我对通过的任何查询进行解释的目标（即 http://localhost:8080/vehicles?make=&model=&year=&type=），但我想弄清楚是否有一种方法可以重构代码以使其更高效。 Spring的逐个查询是否足以解决这个问题，还是有更好的方法？ （或者这段代码是否和我能做到的一样好？）

解决方法

我推荐Spring JPA ExampleMatcher。它是最简单的 JPA 查询方法之一。您创建一个 probe 变量来定义对数据库的搜索。查询中仅包含非空值，有关详细信息，Spring Data JPA Query by Example。此外，我已将 Lombok 库用于 @Data 注释。如果您不喜欢，可以丢弃它。

Vehicle.java

@Data
@Entity
@Table
public class Vehicle {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String type;
    private String make;
    private String model;
    private Integer year;
}

车辆控制器.java

@RequestMapping("/vehicles")
@RestController
public class VehicleController{

    @Autowired
    private VehicleService vehicleService;

    //GET method to get all vehicles,or specify a parameter
    @GetMapping
    @ResponseStatus(HttpStatus.OK)
    public List<Vehicle> getAllVehicles(
            @RequestParam(required = false) Map<String,String> allParams) {
        return vehicleService.getVehicles(allParams);
    }
}

VehicleRepository.java

public interface VehicleRepository extends JpaRepository<Vehicle,Long> {
}

车辆服务.java

@Service
public class VehicleService {
    @Autowired
    private VehicleRepository vehicleRepository;

    public List<Vehicle> getVehicles(Map<String,String> allParams) {
        if (allParams.isEmpty()) {
            return vehicleRepository.findAll();
        }
        Vehicle probe = new Vehicle();
        if (allParams.containsKey("type")) {
            probe.setType(allParams.get("type"));
        }
        if (allParams.containsKey("make")) {
            probe.setMake(allParams.get("make"));
        }
        if (allParams.containsKey("year")) {
            probe.setYear(Integer.parseInt(allParams.get("year")));
        }
        if (allParams.containsKey("model")) {
            probe.setModel(allParams.get("model"));
        }
        Example<Vehicle> example = Example.of(probe,ExampleMatcher.matchingAll()
                        .withIgnoreCase());
        return vehicleRepository.findAll(example);
    }
}