cache读写问题【一道考试题】

"0","realName":"张小明","schoolId":13068,"schoolName":"四五二小学",
"teachClasses":[{"className":"三年级3班","classRole":"0","croName":"小学","croid":3,"gradeId":6,"gradeName":"三年级","id":31105,"[b]teachSubjects[/b]":[{"id":4,"subjectName":"数学"}]},
{"className":"四年级4班","classRole":"1","croName":"小学","croid":3,"gradeId":7,"gradeName":"四年级","id":31106}],"uid":1003147629,"uuid":"T0000001003147629"}
因为这个JSON串中teachClasses也是一个JSON串，所以需要做2次解析，但是在这个teachClasses字符串中，teachSubjects有可能不存在，那么我在使用JSON INPUT工具解析