No converter found for return value of type: class java.util.HashMap
SpringMVC 中使用 @ResponseBody 返回Json时，需要手动添加jackson依赖！Maven添加：

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.4.3</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.4.3</version>
</dependency>

“

不用maven也可以，springMVC-servlet.xml 配置如下

<!-- 启动Springmvc注解驱动 -->
    <mvc:annotation-driven/>
 <!-- 返回json 方法一 需要导入 fastjson.jar包 -->  
    <mvc:annotation-driven>
        <mvc:message-converters register-defaults="false">
            <!-- 避免IE执行AJAX时,返回JSON出现下载文件 -->
            <bean id="fastJsonHttpMessageConverter" class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
                <property name="supportedMediaTypes">
                    <list>
                        <!-- 这里顺序不能反，一定先写text/html,不然ie下出现下载提示 -->
                        <value>text/html;charset=UTF-8</value>
                        <value>application/json;charset=UTF-8</value>
                    </list>
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>
    
  
  <!-- 返回json 方法二 需要导入 jackson-annotations.jar,jackson-core.jar,jackson-databind.jar-->  
   <!--  <bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping" />
    <bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
        <property name="messageConverters">
            <list>
                <bean class="org.springframework.http.converter.StringHttpMessageConverter">
                    <property name="supportedMediaTypes">
                        <list>
                            <value>text/html; charset=UTF-8</value>
                            <value>application/json;charset=UTF-8</value>
                        </list>
                    </property>
                </bean>
                <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                    <property name="supportedMediaTypes">
                        <list>
                            <value>text/html; charset=UTF-8</value>
                            <value>application/json;charset=UTF-8</value>
                        </list>
                    </property>
                </bean>
            </list>
        </property>
    </bean> -->

controller代码：
@RequestMapping(value="/json")
@ResponseBody
public Object getJson(){
    Map<String, Object> map=new HashMap<String, Object>();
    map.put("fd", "郝鹏");
    return map;
}

可以返回map到前端了，如前端则ajax请求，返回数据如data.fd为郝鹏