JAXB解组XML类强制转换异常 [英] JAXB Unmarshalling XML Class Cast Exception

问题描述

我正在使用此 JAXB Collection Generics 来解组我的字符串xml并返回List类型。
这是我使用的方法。

I'm using this JAXB Collection Generics to unmarshall my string xml and return the List type. Here's the methods I used.

public static <T> List<T> unmarshalCollection(Class<T> cl, String s)
        throws JAXBException {
    return unmarshalCollection(cl, new StringReader(s));
}

public static <T> List<T> unmarshalCollection(Class<T> cl, Reader r)
        throws JAXBException {
    return unmarshalCollection(cl, new StreamSource(r));
}


private static <T> List<T> unmarshalCollection(Class<T> cl, Source s)
        throws JAXBException {
    JAXBContext ctx = JAXBContext.newInstance(JAXBCollection.class, cl);
    Unmarshaller u = ctx.createUnmarshaller();
    JAXBCollection<T> collection = u.unmarshal(s, JAXBCollection.class).getValue();
    return collection.getItems();
}

示例getter和setter：

Example getters and setters:

   @XmlRootElement(name = "person")
class Person{

    private String firstName;
    private String lastName;
    private String address;


    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;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Person [firstName ="+firstName+" , lastName = "+lastName+" , address = "+address+"]"; 
    }

}

主要类别：

public static void main(String[] args) throws JAXBException {
        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><person><firstName>Foo</firstName><lastName>Bar</lastName><address>U.S</address></person>";
        List<Person> p = unmarshalCollection(Person.class,xml);
        for(Person person : p ){
            System.out.println(person);
        }
    }

抛出异常

Exception in thread "main" java.lang.ClassCastException: org.apache.xerces.dom.ElementNSImpl cannot be cast to  com.Person
at com.JAXBUtil.main(JAXBUtil.java:62)

我做错了什么？任何想法？谢谢。

What did I do wrong? Any ideas?Thanks.

推荐答案

您的列表不是您期望的Person对象列表。由于java的泛型类型擦除，在尝试在循环中转换为person之前，您没有看到错误。

Your list is not a list of Person objects as you expect. Due to java's generic type erasure, you're not seeing the error until you try to cast to person in the loop.

尝试：

List<Person> p = unmarshalCollection(Person.class,xml);
for(Object person : p ){
   System.out.println(person.getClass());
}

参见 http://en.wikipedia.org/wiki/Generics_in_Java#Problems_with_type_erasure

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