How to enable 'ALLOW_NUMERIC_LEADING_ZEROS' feature to allow leading zeroes in JSON Request Body?

Question

As per JSON specification, I am aware that leading zeroes are not allowed in integers in JSON. But as per Jackson documentation, there is a property in Jackson library i.e.

Answer 1

MappingJackson2HttpMessageConverter by default uses Jackson2ObjectMapperBuilder class to build new instance of ObjectMapper class. To override and use ObjectMapper from container we need to override JSON converter:

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);
    }
}

See Customizing HttpMessageConverters with Spring Boot and Spring MVC. Since now you should be able to parse numbers with leading zeros.

Answer 2

Just a note for people that are having that issue and are looking for a newer working solution:

1. Import latest version of fasterxml jackson in maven (2.11.0 as of today):

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

2. Create the mapper object:

   ObjectMapper objectMapper = new ObjectMapper();

3. Allow the leading zeros for numbers (the not deprecated version):

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

used imports:

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

Keep in mind this will trim the leading 0s. If you want to keep them then your json value shouldn't be a numeric.

Answer 3

Simply put following property on your application.properties file

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

You can set jackson as default converter by following property if not set default

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

Answer 4

This is most likely due to ObjectMapper that Spring endpoint uses being configured different from mapper being injected into field. Why this is I can't say -- maybe Spring users list could help.