如java类为
public class Person {
private String firstName;
private String lastName;
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}

}

jsonstr 为:{
"FirstName": "John",
"lastName": "Peter"
}

Person person=JSON.parseObject(jsonstr , Person.class);

现想将FirstName字段(首字母大写)忽略掉，使person中的firstName属性为null，经测试发现不管为json中的首字母是否大写都可以转化到person中，怎样才能过滤掉该字段啊？