springMVC利用FastJson接口返回json数据相关配置详解

```
 <!-- 启用默认配置 -->
  <mvc:annotation-driven>
    <mvc:message-converters register-defaults="true">
      <!-- 配置Fastjson支持 -->
      <bean class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
        <property name="supportedMediaTypes">
          <list>
            <value>text/html;charset=UTF-8</value>
            <value>application/json</value>
          </list>
        </property>
        <property name="features">
          <list>
            <value>WriteMapNullValue</value>
            <value>QuoteFieldNames</value>
          </list>
        </property>
      </bean>
    </mvc:message-converters>
  </mvc:annotation-driven>

<dependency>
  <groupId>com.alibaba</groupId>
  <artifactId>fastjson</artifactId>
  <version>1.2.7</version>
</dependency>

Map < String , Object > jsonMap = new HashMap< String , Object>();
jsonMap.put("a",1);
jsonMap.put("b","");
jsonMap.put("c",null);
jsonMap.put("d","zhenghuasheng");

String str = JSONObject.toJSONString(jsonMap);
System.out.println(str);
//输出结果:{"a":1,"b":"",d:"zhenghuasheng"}

      <!-- 输出key时是否使用双引号 -->
      <value>QuoteFieldNames</value>
      <!-- 是否输出值为null的字段 -->
      <!-- <value>WriteMapNullValue</value> -->
      <!-- 数值字段如果为null,输出为0,而非null -->
      <value>WriteNullNumberAsZero</value>
      <!-- List字段如果为null,输出为[],而非null -->
      <value>WriteNullListAsEmpty</value>
      <!-- 字符类型字段如果为null,输出为"",而非null -->
      <value>WriteNullStringAsEmpty</value>
      <!-- Boolean字段如果为null,输出为false,而非null -->
      <value>WriteNullBooleanAsFalse</value>
      <!-- null String不输出 -->
      <value>WriteNullStringAsEmpty</value>
      <!-- null String也要输出 -->
      <!-- <value>WriteMapNullValue</value> -->

      <!-- Date的日期转换器 -->
      <value>WriteDateUseDateFormat</value>
    </list>