java - 为 JAXB 转换的时间戳创建适配器

Question

我目前正在尝试将 JAXB 库用于 XML 到 POJO 的转换。我有一个类如下:

class Student {

 String name;
 Integer id;
 Date dateOfBirth;
 @XmlJavaTypeAdapter(TimeDateAdapter.class)
 Timestamp admitTime;

 //constructor and getter setters

}

现在我想通过 XML 输入这些字段。所以我重现了类似 xml 的东西:

  <student>
    <name>Student 1</name>
    <id>123</id>
    <dob>29-02-1991</dob>
    <admitTime>231441321413</admitTime>
  </student>

所以，正如您可能知道的那样，它会抛出一个错误，指出它无法转换 Timestamp，因为 Timestamp 类中没有无参数构造函数。所以我将不得不创建一个适配器。所以，我想知道是否有一种方法可以为日期、时间戳和日历创建通用适配器，以便可以根据实现对它们进行解码和编码？

编辑:我创建了一个适配器，用于将我的 java.sql.Timestamp 对象从 xml 编码和解码。这是代码:

导入java.sql.Timestamp;

导入javax.xml.bind.annotation.adapters.XmlAdapter;

public class TimeDateAdapter extends XmlAdapter<String, Timestamp>{

    @Override
    public String marshal(Timestamp v) throws Exception {
        return v.toString();
    }

    @Override
    public Timestamp unmarshal(String v) throws Exception {
        return new Timestamp(Long.parseLong(v));
    }

}

它给我以下错误:

Exception in thread "main" com.sun.xml.bind.v2.runtime.IllegalAnnotationsException: 3 counts of IllegalAnnotationExceptions
There are two properties named "publishDate" 
    this problem is related to the following location:
        at public java.sql.Timestamp Book.getPublishDate()
        at Book
    this problem is related to the following location:
        at private java.sql.Timestamp Book.publishDate
        at Book
java.sql.Timestamp does not have a no-arg default constructor.
    this problem is related to the following location:
        at java.sql.Timestamp
        at public java.sql.Timestamp Book.getPublishDate()
        at Book
Class has two properties of the same name "publishDate"
    this problem is related to the following location:
        at public java.sql.Timestamp Book.getPublishDate()
        at Book
    this problem is related to the following location:
        at private java.sql.Timestamp Book.publishDate
        at Book

    at com.sun.xml.bind.v2.runtime.IllegalAnnotationsException$Builder.check(IllegalAnnotationsException.java:102)
    at com.sun.xml.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:472)
    at com.sun.xml.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:302)
    at com.sun.xml.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1140)
    at com.sun.xml.bind.v2.ContextFactory.createContext(ContextFactory.java:154)
    at com.sun.xml.bind.v2.ContextFactory.createContext(ContextFactory.java:121)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:248)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:235)
    at javax.xml.bind.ContextFinder.find(ContextFinder.java:432)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:637)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584)
    at BookMain.main(BookMain.java:42)

Answer 1

JAXB (JSR-222) 实现默认支持 java.util.Date 和 java.util.Calendar，因此您不需要 XmlAdapter 为他们。 java.sql.Date、java.sql.Time 和 java.sql.Timestamp 等类需要 XmlAdapter。我会推荐单独的适配器，而不是尝试将它们组合成一个。

注意

XmlAdapter 可以在包级别指定。当这样做时，它适用于属于该包中域类的该类型的所有映射字段/属性。这可以大大减少您需要指定 @XmlJavaTypeAdapter 的次数。您可以在我的博客上阅读有关此方法的更多信息。

• http://blog.bdoughan.com/2012/02/jaxb-and-package-level-xmladapters.html

---

更新

There are two properties named "publishDate" 
    this problem is related to the following location:
        at public java.sql.Timestamp Book.getPublishDate()
        at Book
    this problem is related to the following location:
        at private java.sql.Timestamp Book.publishDate
        at Book

默认情况下，JAXB 将公共(public)属性(get/set 方法对)和带注释的字段视为已映射。这就是导致这部分异常的原因。您需要执行以下操作之一:

1. 注释 get 方法而不是字段。
2. 保留字段上的注释并在您的类上指定 @XmlAccessorType(XmlAccessType.FIELD)。

我在我的博客上写了更多关于这个的内容:

• http://blog.bdoughan.com/2011/06/using-jaxbs-xmlaccessortype-to.html