如何启用“ALLOW_NUMERIC_LEADING_ZEROS”功能以允许 JSON 请求正文中的前导零？

Question

根据 JSON 规范，我知道 JSON 中的整数中不允许有前导零。但根据 Jackson 文档，Jackson 库中有一个属性，即ALLOW_NUMERIC_LEADING_ZEROS，启用后，在找到前导零时不会引发异常。

我通过设置以下属性启用了属性ALLOW_NUMERIC_LEADING_ZEROS，但仍然出现错误：Leading zeroes not allowed。

spring.jackson.parser.ALLOW_NUMERIC_LEADING_ZEROS=true

相关日志：

Caused by: com.fasterxml.jackson.core.JsonParseException: Invalid numeric value: Leading zeroes not allowed
at [Source: (PushbackInputStream); line: 8, column: 17]
    at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1804) ~[jackson-core-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:663) ~[jackson-core-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.core.base.ParserMinimalBase.reportInvalidNumber(ParserMinimalBase.java:539) ~[jackson-core-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._verifyNoLeadingZeroes(UTF8StreamJsonParser.java:1489) ~[jackson-core-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._parsePosNumber(UTF8StreamJsonParser.java:1341) ~[jackson-core-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser.nextFieldName(UTF8StreamJsonParser.java:1025) ~[jackson-core-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:376) ~[jackson-databind-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159) ~[jackson-databind-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:127) ~[jackson-databind-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:369) ~[jackson-databind-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159) ~[jackson-databind-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001) ~[jackson-databind-2.9.4.jar:2.9.4]
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3072) ~[jackson-databind-2.9.4.jar:2.9.4]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:235) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
    ... 63 more

我通过执行以下代码验证了属性ALLOW_NUMERIC_LEADING_ZEROS是否已启用：

@Autowired
private ObjectMapper objectMapper;

@PostMapping(path = "random_path", produces = MediaType.APPLICATION_JSON_VALUE, consumes = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Object> fun123( @RequestBody RandomClass obj) throws Exception {

    log.info(" isEnabled = " + objectMapper.getFactory().isEnabled(JsonParser.Feature.ALLOW_NUMERIC_LEADING_ZEROS));
    log.info(" isEnabled = " + objectMapper.isEnabled(JsonParser.Feature.ALLOW_NUMERIC_LEADING_ZEROS));

    /*
        When correct request is given i.e. no leading zeroes in json body , then this function is successfully executed and
        output is true for above two statements  => i.e. feature 'ALLOW_NUMERIC_LEADING_ZEROS' is enabled.

        When leading zeroes are present in json request body, this function is not executed as an exception 'HttpMessageNotReadableException'
        is generated with error message 'Invalid numeric value: Leading zeroes not allowed'
    */

  ....
}

根据UTF8StreamJsonParser.java 的code ，启用此属性时不应发生异常，但我不确定为什么会发生这种情况！ 知道这背后的原因是什么吗？

来自UTF8StreamJsonParser.java的相关代码：

/**
 * Method called when we have seen one zero, and want to ensure
 * it is not followed by another
 */
private final int _verifyNoLeadingZeroes() throws IOException
{
    // Ok to have plain "0"
    if (_inputPtr >= _inputEnd && !_loadMore()) {
        return INT_0;
    }
    int ch = _inputBuffer[_inputPtr] & 0xFF;
    // if not followed by a number (probably '.'); return zero as is, to be included
    if (ch < INT_0 || ch > INT_9) {
        return INT_0;
    }
    // [JACKSON-358]: we may want to allow them, after all...
    if (!isEnabled(Feature.ALLOW_NUMERIC_LEADING_ZEROS)) {
        reportInvalidNumber("Leading zeroes not allowed");
    }

    ...
}

使用的杰克逊库版本：2.9.4

Answer 1

只是给遇到该问题并正在寻找更新的工作解决方案的人的说明：

1. 在 maven 中导入最新版本的 fastxml jackson（截至今天为 2.11.0）：

   <dependency> <groupId>com.fasterxml.jackson.dataformat</groupId> <artifactId>jackson-dataformat-xml</artifactId> <version>2.11.0</version> </dependency>

2. 创建映射器对象：

   ObjectMapper objectMapper = new ObjectMapper();

3. 允许数字前导零（未弃用的版本）：

   objectMapper.enable(JsonReadFeature.ALLOW_LEADING_ZEROS_FOR_NUMBERS.mappedFeature());

使用过的进口：

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.core.json.JsonReadFeature;

请记住，这将修剪前导 0。如果你想保留它们，那么你的 json 值不应该是数字。

Answer 2

只需将以下属性放在您的 application.properties 文件中

spring.jackson.parser.allow-numeric-leading-zeros=true

如果没有设置默认，可以通过以下属性将jackson设置为默认转换器

spring.http.converters.preferred-json-mapper=jackson

Answer 3

MappingJackson2HttpMessageConverter 默认使用Jackson2ObjectMapperBuilder 类来构建ObjectMapper 类的新实例。要覆盖和使用容器中的ObjectMapper，我们需要覆盖JSON转换器：

import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;

import java.util.List;

@Configuration
public class JacksonMvcConfiguration extends WebMvcConfigurationSupport {

    @Autowired
    private ObjectMapper objectMapper;

    public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {
        MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
        converter.setObjectMapper(objectMapper);

        return converter;
    }

    @Override
    protected void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        converters.add(mappingJackson2HttpMessageConverter());
        super.configureMessageConverters(converters);
    }
}

见Customizing HttpMessageConverters with Spring Boot and Spring MVC。从现在开始，您应该能够解析带有前导零的数字了。

Answer 4

这很可能是由于ObjectMapper Spring 端点使用的配置不同于映射器被注入到字段中。 为什么这是我不能说的——也许 Spring 用户列表会有所帮助。