使用RestTemplate时如何配置内部Jackson映射器？

我想更新Spring RestTemplate所使用的jackson映射器的SerializationConfig.Feature ...属性，任何想法都知道如何获得它或在哪里可以/应该对其进行配置。

默认RestTemplate构造函数注册一组HttpMessageConverter：

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());
}

该MappingJacksonHttpMessageConverter轮流，造成ObjectMapper直接实例。您可以找到该转换器并替换ObjectMapper或注册一个新的转换器。这应该工作：

@Bean
public RestOperations restOperations() {
    RestTemplate rest = new RestTemplate();
    //this is crucial!
    rest.getMessageConverters().add(0, mappingJacksonHttpMessageConverter());
    return rest;
}

@Bean
public MappingJacksonHttpMessageConverter mappingJacksonHttpMessageConverter() {
    MappingJacksonHttpMessageConverter converter = new MappingJacksonHttpMessageConverter();
    converter.setObjectMapper(myObjectMapper());
    return converter;
}

@Bean
public ObjectMapper myObjectMapper() {
    //your custom ObjectMapper here
}

在XML中，遵循以下原则：

<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"/>

请注意，转换并不是真正的1：1-我必须以messageConvertersXML显式创建列表，而采用@Configuration这种方法，我可以引用现有列表并简单地对其进行修改。但这应该可行。

如果您不使用Spring IOC，则可以执行以下操作（Java 8）：

ObjectMapper objectMapper = new ObjectMapper();
// configure your ObjectMapper here

RestTemplate 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将初始化其默认消息转换器。您应该用MappingJackson2HttpMessageConverter自己的bean替换，后者应使用要使用的对象映射器。这为我工作：

@Bean
public 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;
}

@Bean
public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {
    MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
    converter.setObjectMapper(myObjectMapper());
    return converter;
}

@Bean
public ObjectMapper myObjectMapper() {
    // return your own object mapper
}

要完成其他答案：如果你ObjectMapper只是注册了杰克逊Module定制的串行/解串器，你可能想直接在现有注册模块ObjectMapper从RestTemplate的默认MappingJackson2HttpMessageConverter如下（例如无DI但同样适用，如果使用DI）：

    SimpleModule module = new SimpleModule();
    module.addSerializer(...);
    module.addDeserializer(...);

    MappingJackson2HttpMessageConverter messageConverter = restTemplate.getMessageConverters().stream()
                    .filter(MappingJackson2HttpMessageConverter.class::isInstance)
                    .map(MappingJackson2HttpMessageConverter.class::cast)
                    .findFirst().orElseThrow( () -> new RuntimeException("MappingJackson2HttpMessageConverter not found"));
    messageConverter.getObjectMapper().registerModule(module);

这样您就可以完成原始文件的配置ObjectMapper（如Spring的那样Jackson2ObjectMapperBuilder），而不是替换它。

使用Spring Boot，它很简单：

RestTemplate template = new RestTemplateBuilder()
                            .additionalMessageConverters(new MappingJackson2HttpMessageConverter(objectMapper))
                            .build()

（使用Spring Boot 2.2.1进行测试）