How can we configure the internal Jackson mapper when using RestTemplate?

The default RestTemplate constructor registers a set of HttpMessageConverters:

this.messageConverters.add(new ByteArrayHttpMessageConverter());this.messageConverters.add(new StringHttpMessageConverter());this.messageConverters.add(new ResourceHttpMessageConverter());this.messageConverters.add(new SourceHttpMessageConverter());this.messageConverters.add(new XmlAwareFormHttpMessageConverter());if (jaxb2Present) {    this.messageConverters.add(new Jaxb2RootElementHttpMessageConverter());}if (jacksonPresent) {    this.messageConverters.add(new MappingJacksonHttpMessageConverter());}if (romePresent) {    this.messageConverters.add(new AtomFeedHttpMessageConverter());    this.messageConverters.add(new RssChannelHttpMessageConverter());}

The MappingJacksonHttpMessageConverter in turns, creates ObjectMapper instance directly. You can either find this converter and replace ObjectMapper or register a new one before it. This should work:

@Beanpublic RestOperations restOperations() {    RestTemplate rest = new RestTemplate();    //this is crucial!    rest.getMessageConverters().add(0, mappingJacksonHttpMessageConverter());    return rest;}@Beanpublic MappingJacksonHttpMessageConverter mappingJacksonHttpMessageConverter() {    MappingJacksonHttpMessageConverter converter = new MappingJacksonHttpMessageConverter();    converter.setObjectMapper(myObjectMapper());    return converter;}@Beanpublic ObjectMapper myObjectMapper() {    //your custom ObjectMapper here}

In XML it is something along these lines:

<bean id="restOperations" class="org.springframework.web.client.RestTemplate">    <property name="messageConverters">        <util:list>            <bean class="org.springframework.http.converter.ByteArrayHttpMessageConverter"/>            <bean class="org.springframework.http.converter.StringHttpMessageConverter"/>            <bean class="org.springframework.http.converter.ResourceHttpMessageConverter"/>            <bean class="org.springframework.http.converter.xml.SourceHttpMessageConverter"/>            <bean class="org.springframework.http.converter.xml.XmlAwareFormHttpMessageConverter"/>            <bean class="org.springframework.http.converter.xml.Jaxb2RootElementHttpMessageConverter"/>            <bean class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">                <property name="objectMapper" ref="customObjectMapper"/>            </bean>        </util:list>    </property></bean><bean id="customObjectMapper" class="org.codehaus.jackson.map.ObjectMapper"/>

Note that the transition isn't really 1:1 - I have to explicitly create messageConverters list in XML while with @Configuration approach I could reference existing one and simply modify it. But this should work.

If you are not using Spring IOC, you can do something like this (Java 8):

ObjectMapper objectMapper = new ObjectMapper();// configure your ObjectMapper hereRestTemplate restTemplate = new RestTemplate();    MappingJackson2HttpMessageConverter messageConverter = new MappingJackson2HttpMessageConverter();messageConverter.setPrettyPrint(false);messageConverter.setObjectMapper(objectMapper);restTemplate.getMessageConverters().removeIf(m -> m.getClass().getName().equals(MappingJackson2HttpMessageConverter.class.getName()));restTemplate.getMessageConverters().add(messageConverter);

RestTemplate will initialize its default message converters. You should replace the MappingJackson2HttpMessageConverter with your own bean, which should use the object mapper you want to use. This worked for me:

@Beanpublic RestTemplate restTemplate() {    final RestTemplate restTemplate = new RestTemplate();    //find and replace Jackson message converter with our own    for (int i = 0; i < restTemplate.getMessageConverters().size(); i++) {        final HttpMessageConverter<?> httpMessageConverter = restTemplate.getMessageConverters().get(i);        if (httpMessageConverter instanceof MappingJackson2HttpMessageConverter){            restTemplate.getMessageConverters().set(i, mappingJackson2HttpMessageConverter());        }    }    return restTemplate;}@Beanpublic MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {    MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();    converter.setObjectMapper(myObjectMapper());    return converter;}@Beanpublic ObjectMapper myObjectMapper() {    // return your own object mapper}