JSON字符串转换object错误：MorphDynaBean cannot be cast to com.softright.bean.TestBean

public class JsonConvertorDemo { 

public static void main(String[] args) { 
B b1 = new B("b1"); 
Map bMap = new HashMap(); 
bMap.put("key1", b1); 
A a1 = new A(bMap); 

JSONObject jsonObject = JSONObject.fromObject(a1); 
String json = jsonObject.toString(); 
jsonObject = JSONObject.fromObject(json); 

Map classMap = new HashMap(); 
classMap.put("bMap", Map.class); 
a1 = (A) JSONObject.toBean(jsonObject, A.class, classMap); 

bMap = a1.getbMap(); 
System.out.println(bMap.get("key1").getB1()); 
} 
} 

public class A { 
private Map bMap = new HashMap(); 
public A() {} 
public A(Map bMap) { 
this.bMap = bMap; 
} 
public Map getbMap() { 
return bMap; 
} 
public void setbMap(Map bMap) { 
this.bMap = bMap; 
} 
} 

public class B { 
private String b1; 
public B() {} 
public B(String b1) { 
this.b1 = b1; 
} 
public String getB1() { 
return b1; 
} 
public void setB1(String b1) { 
this.b1 = b1; 
} 
}