使用jaxb2实现序列化实体类时，如果类中存在泛型属性时，映射为List或者Set时会出现javax.xml.bind.JAXBException错误

解决办法：
使用一个包装类对List或者Set进行包装，如下：

@XmlRootElement(name = "test")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(propOrder = {"msg","num","code","list"})
public class ResultTest {

    @XmlElement
    private String msg;
    @XmlElement
    private Integer num;
    @XmlElement
    private Integer code;

    public Integer getNum() {
        return num;
    }

    public void setNum(Integer num) {
        this.num = num;
    }

    public Integer getCode() {
        return code;
    }

    public void setCode(Integer code) {
        this.code = code;
    }

    public String getMsg() {

        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    @XmlElementWrapper(name = "subjects")
    @XmlElement(name = "subject")
    private List<SubjectEntity> list;

    public List<SubjectEntity> getList() {
        return list;
    }

    public void setList(List<SubjectEntity> list) {
        this.list = list;
    }

    @Override
    public String toString() {
        return "ResultTest[" +
                "msg='" + msg + '\'' +
                ", num=" + num +
                ", code=" + code +
                ", list=" + list +
                ']';
    }
}       

通过使用ResultTest这个类将List< Subject >进行包装 ，然后替代泛型后进行序列化，可以成功将内容转为xml格式，泛型类如下：

@XmlRootElement
@XmlSeeAlso({SubjectEntity.class,SubjectList.class})
@XmlAccessorType(XmlAccessType.FIELD)
public class ResultUtil<T> {

    private String msg;

    private Integer num;

    private Integer code;

    @XmlElement(name = "data")
    private T data;

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public Integer getNum() {
        return num;
    }

    public void setNum(Integer num) {
        this.num = num;
    }

    public Integer getCode() {
        return code;
    }

    public void setCode(Integer code) {
        this.code = code;
    }

    @XmlTransient
    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }

    public ResultUtil(){
    }

    public ResultUtil(ResultCodeEnum resultCodeEnum){
        this.code = resultCodeEnum.getCode();
        this.msg = resultCodeEnum.getMsg();
    }

    public ResultUtil(ResultCodeEnum resultCodeEnum, Integer num){
        this.code = resultCodeEnum.getCode();
        this.msg = resultCodeEnum.getMsg();
        this.num = num;
    }

    public ResultUtil(ResultCodeEnum resultCodeEnum, Integer num, T data) {
        this.msg = resultCodeEnum.getMsg();
        this.num = num;
        this.code = resultCodeEnum.getCode();
        this.data = data;
    }

    public ResultUtil(ResultCodeEnum resultCodeEnum, T data){
        this.msg = resultCodeEnum.getMsg();
        this.code = resultCodeEnum.getCode();
        this.data = data;
    }

    @Override
    public String toString() {
        return "ResultUtil{" +
                "msg='" + msg + '\'' +
                ", num=" + num +
                ", code=" + code +
                '}';
    }
}

如果控制台出现javax.xml.bind.JAXBException: class 以及其任何超类对此上下文都是未知的。这个提示的话，则使用@XmlSeeAlso注解，将该类添加为所序列化实体类的子类即可解决这个问题。