Spring Boot 预处理 JSON 数据

Question

我有一个 RESTful Spring Boot API，它有一个注册端点。

在我的@RestController 类中，我编写了一个简单的字符串值预处理器，用null 值修剪和替换只有空格的字符串。

  @InitBinder
  public void blankStringBinder(WebDataBinder dataBinder) {
    dataBinder.setDisallowedFields("password", "confirmPassword");
    StringTrimmerEditor stringTrimmerEditor = new StringTrimmerEditor(true);
    dataBinder.registerCustomEditor(String.class, stringTrimmerEditor);
  }

但是，当我从 Postman 以原始 JSON 提交数据时，没有进行修剪编辑。我在blankStringBinder 方法中放置了一个断点，我看到它在每个传入请求中都会被调用。

WebDataBinder 似乎适用于 form-data。有没有办法让它也适用于原始 JSON 数据？

Answer 1

如果您只想对少数String 字段执行此操作，请先创建一个自定义JsonDeserializer：

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonNode;

public class EmptyToNullCustomDeserializer extends JsonDeserializer<String> {
    @Override
    public String deserialize(JsonParser jp, DeserializationContext dc) throws IOException, JsonProcessingException {
        JsonNode node = jp.readValueAsTree();
        if (node.textValue().isEmpty()) {
            return null;
        }
        return node.textValue();
    }
}

然后在POJO的每个String上添加这个注解：@JsonDeserialize(using = EmptyToNullCustomDeserializer.class)。 例如：

@JsonDeserialize(using = EmptyToNullCustomDeserializer.class)
private String content;

---

编辑：

如果您有很多 String 字段要进行预处理，那么对每个字段进行注释可能会非常麻烦。

作为替代方案，您可以对 all String 字段进行预处理，而无需对其进行注释。为此，您必须首先修改EmptyToNullCustomDeserializer，使其父类为Jacksons StdDeserializer：

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import java.io.IOException;
import org.springframework.stereotype.Component;

@Component
public class EmptyToNullCustomDeserializer extends StdDeserializer<String> {
    protected EmptyToNullCustomDeserializer() {
        super(String.class);
    }

    @Override
    public String deserialize(JsonParser jp, DeserializationContext dc) throws IOException, JsonProcessingException {
        JsonNode node = jp.readValueAsTree();
        if (node.textValue().isEmpty()) {
            return null;
        }
        return node.textValue();
    }
}

然后通过将上述反序列化器添加到配置中来创建此组件以自定义 Jackson 对象映射器：

import java.util.List;
import lombok.AllArgsConstructor;
import lombok.NonNull;
import org.springframework.boot.autoconfigure.jackson.Jackson2ObjectMapperBuilderCustomizer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Primary;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
import org.springframework.stereotype.Component;

@Component
public class JacksonConfiguration {

    @Autowired
    private EmptyToNullCustomDeserializer emptyToNullCustomDeserializer;

    @Primary
    @Bean
    public Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder(List<Jackson2ObjectMapperBuilderCustomizer> customizers) {
        Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
        for (Jackson2ObjectMapperBuilderCustomizer customizer : customizers) {
            customizer.customize(builder);
        }
        return builder;
    }

    @Bean
    public Jackson2ObjectMapperBuilderCustomizer addEmptyToNullStringDeserialization() {
        return new Jackson2ObjectMapperBuilderCustomizer() {
            @Override
            public void customize(Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder) {
                jacksonObjectMapperBuilder.deserializerByType(String.class, emptyToNullCustomDeserializer);
            }

        };
    }
}

Answer 2

excellent answer from @sébastien-temprado 的小扩展：如果您需要“将空白字符串修剪为 null”（如问题所提）而不是“将空字符串修剪为 null”，请使用例如Apache Commons Lang StringUtils:

import org.apache.commons.lang3.StringUtils;

//[...]
@Override
public String deserialize(JsonParser jp, DeserializationContext dc) throws IOException, JsonProcessingException {
    JsonNode node = jp.readValueAsTree();
    
    return StringUtils.trimToNull(node.textValue());
}
//[...]