json解析出现：java.lang.ClassCastException: net.sf.ezmorph.bean.MorphDynaBean cannot be cast to XXX

一、出错原因

当我们利用json解析中的toBean方法时，如果它的属性里面包含复杂对象，那么在我们调用这个复杂对象时就会出现这个错误：java.lang.ClassCastException: net.sf.ezmorph.bean.MorphDynaBean cannot be cast to XXX

二、出错场景

student类，里面有姓名、性别和年龄三个属性和它们对应的get、set方法：

public class Student {

    private String stuName;
    private String sex;
    private Integer age;

    public String getStuName() {
        return stuName;
    }

    public void setStuName(String stuName) {
        this.stuName = stuName;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

}

Teacher类，里面有教师姓名、Student、list集合的Student、map集合的Student

public class Teacher {

    private String teaName;
    private Student stu;
    private List<Student> stuList;
    private Map<String, Student> stuMap;

    public String getTeaName() {
        return teaName;
    }

    public void setTeaName(String teaName) {
        this.teaName = teaName;
    }

    public Student getStu() {
        return stu;
    }

    public void setStu(Student stu) {
        this.stu = stu;
    }

    public List<Student> getStuList() {
        return stuList;
    }

    public void setStuList(List<Student> stuList) {
        this.stuList = stuList;
    }

    public Map<String, Student> getStuMap() {
        return stuMap;
    }

    public void setStuMap(Map<String, Student> stuMap) {
        this.stuMap = stuMap;
    }
}

测试用的json字符串

{
    "teaName":"老王",
    "stu":{
        "stuName":"张三",
        "sex":"男",
        "age":18
    },
    "stuList":[
        {
            "stuName":"李四",
            "sex":"男",
            "age":18
        },
        {
            "stuName":"王五",
            "sex":"男",
            "age":18
        }
    ],
    "stuMap":{
        "小明":{
            "stuName":"小明",
            "sex":"男",
            "age":18
        },
        "小红":{
            "stuName":"小红",
            "sex":"nü",
            "age":18
        }
    }
}

测试用例，其中的jsonStr使用上面的json字符串：

public class JsonParsingTest {
    
    private final static String jsonStr = "";
    
    public static void main(String[] args) {
        JSONObject jsonObj  = JSONObject.fromObject(jsonStr);
        Teacher teacher = (Teacher)JSONObject.toBean(jsonObj, Teacher.class);
        testStu(teacher.getStu());
        testListStu(teacher.getStuList());
        testMapStu(teacher.getStuMap());
    }
    
    private static void testStu(Student stu) {//正常运行
        System.out.println(stu.getStuName());
    }
    
    private static void testListStu(List<Student> stuList) {//出现ClassCastException异常
        for(Student stu : stuList) {
            System.out.println(stu.getStuName());
        }
    }
    
    private static void testMapStu(Map<String, Student> stuMap) {//出现ClassCastException
        for(String key : stuMap.keySet()) {
            Student stu = stuMap.get(key);
            System.out.println(stu.getStuName());
        }
    }

}

三、解决方案

一、json转化为带有list集合的复杂对象时出现的ClassCastException异常的解决方案

1. 新建一个map对象
2. 以list集合的名称作为key，list集合里面的对象的Class作为value存入到map对象里面
3. 在将json对象转化为javaBean对象时将新建的map作为最后一个参数传入到toBean方法里面

示例代码如下：

Map<String, Class<?>> classMap = new HashMap<String, Class<?>>();
classMap.put("stuList", Student.class);
Teacher teacher = (Teacher)JSONObject.toBean(jsonObj, Teacher.class, classMap);

二、json转化为带有map集合的复杂对象时出现的ClassCastException异常的解决方案

ps.将json对象转为包含复杂map集合的对象比较困难，需要具体情况具体分析，以下是我的解决思路：

1. 通过json对象的getJSONObject方法获得需要被转化为map集合的json对象
2. 建立一个方法parseJSON2Map，将上一步获得的json对象转为map对象
3. 将第二步转化好的map对象set进最开始转化好的javaBean对象中

示例代码如下：

JSONObject jsonObj  = JSONObject.fromObject(jsonStr);
Teacher teacher = (Teacher)JSONObject.toBean(jsonObj, Teacher.class);
Map<String, Student> stuMap = parseJSON2Map(jsonObj.getJSONObject("stuMap"));
teacher.setStuMap(stuMap);

将json对象转为map对象方法代码：

Map<String, Student> parseJSON2Map(JSONObject json) {
    Map<String, Student> tables = new HashMap<String, Student>();
    Map<String, Class<?>> classMap = new HashMap<String, Class<?>>();
    for(Object key: json.keySet()) {
        JSONObject value = json.getJSONObject(key.toString());
        Student table = (Student)JSONObject.toBean(value, Student.class, classMap);
        tables.put(key.toString(), table);
    }
    return tables;
}