求大神指点：SpringMVC使用了jackson-dataformat-xml包之后，无法返回JSON

原本使用@ResponseBody返回json数据，但由于需要使用jackson-dataformat-xml包（该包还依赖jackson-module-jaxb-annotations），结果所有response都变成了xml。只要去掉这2个包，就正常了。

看了一下RequestMappingHandlerAdapter源码

以下是默认的构造函数，添加了几个默认的converter

public RequestMappingHandlerAdapter() {
		StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
		stringHttpMessageConverter.setWriteAcceptCharset(false);  // see SPR-7316

		this.messageConverters = new ArrayList<HttpMessageConverter<?>>(4);
		this.messageConverters.add(new ByteArrayHttpMessageConverter());
		this.messageConverters.add(stringHttpMessageConverter);
		this.messageConverters.add(new SourceHttpMessageConverter<Source>());
		this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());
	}

最后一行内部如下：根据项目情况，jaxb2Present==true,jackson2Present=true,jackson2XmlPresent=true,gsonPresent=false

public AllEncompassingFormHttpMessageConverter() {
		addPartConverter(new SourceHttpMessageConverter<Source>());

		if (jaxb2Present && !jackson2Present) {
			addPartConverter(new Jaxb2RootElementHttpMessageConverter());
		}

		if (jackson2Present) {
			addPartConverter(new MappingJackson2HttpMessageConverter());
		}
		else if (gsonPresent) {
			addPartConverter(new GsonHttpMessageConverter());
		}

		if (jackson2XmlPresent) {
			addPartConverter(new MappingJackson2XmlHttpMessageConverter());
		}
	}

所以，看样子是MappingJackson2HttpMessageConverter和MappingJackson2XmlHttpMessageConverter同时都有了。但怎么能禁止xml视图，只返回json呢？

以下是spring配置文件中的内容

<annotation-driven/>

<beans:bean
            class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
        <beans:property name="messageConverters">
            <beans:list>
                <beans:bean
                        class="org.springframework.http.converter.ByteArrayHttpMessageConverter"/>
                <beans:bean
                        class="org.springframework.http.converter.ResourceHttpMessageConverter"/>
                <beans:bean
                        class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                    <beans:property name="objectMapper">
                        <beans:bean class="com.fasterxml.jackson.databind.ObjectMapper">
                            <beans:property name="dateFormat">
                                <beans:bean class="java.text.SimpleDateFormat">
                                    <beans:constructor-arg type="java.lang.String" value="yyyy-MM-dd HH🇲🇲ss"/>
                                </beans:bean>
                            </beans:property>
                        </beans:bean>
                    </beans:property>
                    <beans:property name="supportedMediaTypes">
                        <beans:list>
                            <beans:value>application/json;charset=UTF-8</beans:value>
                        </beans:list>
                    </beans:property>
                </beans:bean>
                <beans:bean
                        class="org.springframework.http.converter.StringHttpMessageConverter">
                    <beans:constructor-arg value="UTF-8"></beans:constructor-arg>
                    <beans:property name="supportedMediaTypes">
                        <beans:list>
                            <beans:value>text/plain;charset=UTF-8</beans:value>
                        </beans:list>
                    </beans:property>
                </beans:bean>
            </beans:list>
        </beans:property>
    </beans:bean>