使用杰克逊的弹簧过滤响应字段

Question

我正在尝试过滤嵌套对象中的字段：

class Response {

  // These objects themselves can have many fields within
  private final PropA a;
  private final PropB b;

  @JsonCreator
  public Response(PropA a, PropB b) { ... }
}

我想要一个通用的“过滤器助手”来实现上述逻辑。这是我到目前为止所拥有的（遵循与this project类似的方法）

public class FilterHelper {

    private final ObjectMapper objectMapper;

    public FilterHelper(ObjectMapper objectMapper) {
        this.objectMapper = objectMapper;
        this.objectMapper.addMixIn(Object.class, MyFilterMixin.class);
    }

    @JsonFilter("myfilter")
    public static class MyFilterMixin {
    }

    private static class MyFilter extends SimpleBeanPropertyFilter {
        private final Set<String> properties;

        public MyFilter(Set<String> properties) {
            super();
            this.properties = properties;
        }

        @Override
        public void serializeAsField(final Object pojo, final JsonGenerator jgen, final SerializerProvider provider,
                                     final PropertyWriter writer) throws Exception {

            System.out.println("************************** " + writer.getName());
            if (properties.contains(writer.getName())) {
                writer.serializeAsField(pojo, jgen, provider);
            } else if (!jgen.canOmitFields()) {
                writer.serializeAsOmittedField(pojo, jgen, provider);
            }
        }
    }

    public String filter(T obj, Set<String> fields) {

        FilterProvider filterProvider = new SimpleFilterProvider().addFilter("myfilter", new MyFilter(fields));

        return objectMapper.writer(filterProvider).writeValueAsString(obj);
    }
}

当我使用?fields=one,two 作为查询参数点击此端点时，我希望从打印到控制台的行中看到该顶级Response 对象中的每个字段，如下所示：

******************* a
******************* a1
******************* a2
******************* ..etc
******************* b
******************* b1
******************* b2
******************* ..etc

但我只看到顶级 a 和 b 字段的输出，然后在从端点获取 500 状态代码之前出现错误：

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot resolve PropertyFilter with id 'myfilter'; no FilterProvider configured (through reference chain: com.google.common.collect.SingletonImmutableList[0])

值得一提的是，我以某种方式让它工作了，但经过一些我不记得的更改后它被破坏了。

Answer 1

除非您需要为不同的字段提供自定义序列化，否则您不应挂钩 serializeAsField，而应覆盖 #include 变体方法：

• com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter#include(com.fasterxml.jackson.databind.ser.BeanPropertyWriter)
• com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter#include(com.fasterxml.jackson.databind.ser.PropertyWriter)

如下：

private static class MyFilter extends SimpleBeanPropertyFilter {
    private final Set<String> properties;

    public MyFilter(Set<String> properties) {
        super();
        this.properties = properties;
    }

    @Override
    protected boolean include(BeanPropertyWriter writer) {
        return !this.properties.contains(writer.getName());
    }

    @Override
    protected boolean include(PropertyWriter writer) {
        return !this.properties.contains(writer.getName());
    }
}

甚至还有一个静态工厂提供了一个com.fasterxml.jackson.databind.ser.PropertyFilter 来过滤掉一组特定的字段：

com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter#serializeAllExcept(java.util.Set<java.lang.String>)

额外问题

在过滤器助手级别，您将过滤后的对象序列化为 JSON，然后将其反序列化（使用过滤后的字段）到您作为端点响应返回的对象。

解决方案/替代方案

您可以简单地省略中间步骤，只需使用过滤字段谓词对结果Response 进行消毒并将结果 JSON 作为ResponseEntity 返回：

FilterHelper:

@Component
public class FilterHelper {

    private final ObjectMapper objectMapper;

    @Autowired
    public FilterHelper(ObjectMapper objectMapper) {
        this.objectMapper = objectMapper;
        this.objectMapper.addMixIn(Object.class, MyFilterMixin.class);
    }

    @JsonFilter("myfilter")
    public static class MyFilterMixin {
    }

    private static class MyFilter extends SimpleBeanPropertyFilter {
        private final Set<String> properties;

        public MyFilter(Set<String> properties) {
            super();
            this.properties = properties;
        }

        @Override
        protected boolean include(BeanPropertyWriter writer) {
            return !this.properties.contains(writer.getName());
        }

        @Override
        protected boolean include(PropertyWriter writer) {
            return !this.properties.contains(writer.getName());
        }
    }

    public String filter(Object dto, Set<String> fields) {
        if (fields == null || fields.isEmpty()) {
            return "";
        }

        FilterProvider filterProvider = new SimpleFilterProvider()
                .addFilter("myfilter", SimpleBeanPropertyFilter.serializeAllExcept(fields));
        try {
            return objectMapper.writer(filterProvider).writeValueAsString(dto);
        } catch (JsonProcessingException e) {
            return "";
        }
    }
}

Controller:

@GetMapping(value = "/", produces = MediaType.APPLICATION_JSON_VALUE)
@ResponseStatus(OK)
ReponseEntity<String> someEndpoint(@RequestParam(name = "fields") Set<String> fields) {
  Response response = getResponseFromSomewhere();
  return ResponseEntity.ok(filterHelper.filter(response, fields));
}