深入理解fastjson

fastjosn在遍历输出是默认是无序的因为这样是最快的
但是如果想保持有序，fastjson也提供了解决办法
就是加一个参数Feature.OrderedField
实例如下

val text: String = JSON.toJSONString(JSON.parseObject(str,Feature.OrderedField),
SerializerFeature.WriteNullListAsEmpty,
SerializerFeature.WriteNullStringAsEmpty,
SerializerFeature.WriteNullNumberAsZero,
SerializerFeature.WriteNullBooleanAsFalse,
SerializerFeature.WriteMapNullValue,
SerializerFeature.PrettyFormat)

跟踪fastjson源码，在com.alibaba.fastjson.parser.DefaultJSONParser 类中475行发现：
原因是：在fastjson会进行Feature.OrderField的判断

else if (ch == '{') { // 减少嵌套，兼容android

lexer.nextToken();

final boolean parentIsArray = fieldName != null && fieldName.getClass() == Integer.class;

<span style="color: #ff0000;"><strong>JSONObject input = new JSONObject(lexer.isEnabled(Feature.OrderedField)</strong></span>);
``