Java 8 从每个字段中删除字符串值，其中 "string" 值来自自定义对象

Question

我经历了 link：Is it possible in Java to check if objects fields are null and then add default value to all those attributes? 并实施了与下面相同的解决方案 -

注意：我正在使用 Swagger/Open API 规范（使用 springdoc-openapi-ui） 并且在制作 POST 请求所有字符串字段的默认值为 "string" 我真的想将其设置为 null 或 space .

任何 quick 指针 ?

public static Object getObject(Object obj) {
        for (Field f : obj.getClass().getFields()) {
            f.setAccessible(true);
            try {
                if (f.get(obj) == "string") {
                    f.set(obj, null);
                }
            } catch (IllegalArgumentException | IllegalAccessException e) {
                log.error("Error While Setting default values for String");
            }
        }
   return obj;
}

REST 端点

@GetMapping(value = "/employees")
public ResponseEntity<PagedModel<EmployeeModel>> findEmployees(
        EmployeeDto geoDto,
        @Parameter(hidden=true) String sort,
        @Parameter(hidden=true) String order,
        @Parameter(hidden=true) Pageable pageRequest) {

    EmployeeDto dto = (EmployeeDto) CommonsUtil.getObject(geoDto);

    Page<CountryOut> response = countryService..............;
    PagedModel<EmployeeModel> model = employeePagedAssembler.toModel(response, countryOutAssembler);

    return new ResponseEntity<>(model, HttpStatus.OK);
}

Answer 1

我想你可以做得更简单一些。如果控制EmployeeDto，例如：

@Accessors(chain = true)
@Getter
@Setter
@ToString
static class EmployeeDto {

    private String firstname;
    private String lastname;
    private int age;

}

您可以遍历 class 的字段并使用 MethodHandles 调用所需的 setter，当某些 getter return 您感兴趣的 string（和字符串使用 equals 进行比较，而不是 ==）。这甚至可以做成一个小型图书馆。这是一个开始：

private static final Lookup LOOKUP = MethodHandles.lookup();

/**
 * this computes all the know fields of some class (EmployeeDTO in your case) and their getter/setter
 */
private static final Map<Class<?>, Map<Entry<String, ? extends Class<?>>, Entry<MethodHandle, MethodHandle>>> ALL_KNOWN =
    Map.of(
        EmployeeDto.class, metadata(EmployeeDto.class)
    );
private Map<String, Entry<MethodHandle, MethodHandle>> MAP;

/**
 * For example this will hold : {"firstname", String.class} -> getter/setter to "firstname"
 */
private static Map<Entry<String, ? extends Class<?>>, Entry<MethodHandle, MethodHandle>> metadata(Class<?> cls) {
    return Arrays.stream(cls.getDeclaredFields())
                 .map(x -> new SimpleEntry<>(x.getName(), x.getType()))
                 .collect(Collectors.toMap(
                     Function.identity(),
                     entry -> {
                         try {
                             return new SimpleEntry<>(
                                 LOOKUP.findGetter(cls, entry.getKey(), entry.getValue()),
                                 LOOKUP.findSetter(cls, entry.getKey(), entry.getValue()));
                         } catch (Throwable t) {
                             throw new RuntimeException(t);
                         }
                     }
                 ));
}

根据这些信息你可以提供一个public方法供用户调用，所以你需要提供你的DTO的实际实例，DTOclass，Class您想要 "default to" 的字段、要检查的相等性和实际 defaultValue.

    public static <T, R> T defaulter(T initial,
                                  Class<T> dtoClass,
                                  Class<R> fieldType,
                                  R equality,
                                  R defaultValue) throws Throwable {

    Set<Entry<MethodHandle, MethodHandle>> all =
        ALL_KNOWN.get(dtoClass)
                 .entrySet()
                 .stream()
                 .filter(x -> x.getKey().getValue() == fieldType)
                 .map(Entry::getValue)
                 .collect(Collectors.toSet());

    for (Entry<MethodHandle, MethodHandle> getterAndSetter : all) {
        R whatWeGot = (R) getterAndSetter.getKey().invoke(initial);
        if (Objects.equals(whatWeGot, equality)) {
            getterAndSetter.getValue().invoke(initial, defaultValue);
        }
    }

    return initial;

}

您的来电者可以这样称呼它：

public static void main(String[] args) throws Throwable {
    EmployeeDto employeeDto = new EmployeeDto()
        .setFirstname("string")
        .setLastname("string");

    EmployeeDto withDefaults = defaulter(employeeDto, EmployeeDto.class, String.class, "string", "defaultValue");

    System.out.println(withDefaults);
}

Java 8 从每个字段中删除字符串值，其中 "string" 值来自自定义对象

Java 8 to remove string value from each field where "string" value comes of the Custom Object

java

java-8

spring-rest