无法将INetAddress编码为xml

Question

I'm trying to encode an object that has a member of type INetAddress to xml using the java.beans.XMLEncoder class. Unfortunately, I get the following exception:

java.lang.IllegalAccessException: Class sun.reflect.misc.Trampoline can not access a member of class java.net.Inet4Address with modifiers ""

Here is my code:

public class INetAddressFoo {

   private InetAddress addr;

   public INetAddressFoo() {
   }

   public InetAddress getAddr() {
      return addr;
   }

   public void setAddr(InetAddress addr) {
     this.addr = addr;
   }
}

---

public class Test{

    public static void main() throws Exception  {
        INetAddressFoo foo = new INetAddressFoo();
        InetAddress addr = InetAddress.getByName("localhost");
        foo.setAddr(addr);
        File file = new File("inet.xml");

        XMLEncoder encoder = null;

       try {
          encoder = new XMLEncoder(new BufferedOutputStream(new FileOutputStream(file)));
          encoder.writeObject(t);
       } finally {
          if (encoder != null) {
             encoder.close();
          }
       }
    }

}

Answer 1

The javadoc for XmlEncoder says:

The XMLEncoder class is a complementary alternative to the ObjectOutputStream and can used to generate a textual representation of a JavaBean [...]

(their emphasis)

Inet4Address is not a JavaBean, and therefore is not suitable for serializing in this way.

You'll have to use a different mechanism to achieve what you're trying to do. The JAXB framework, included as part of java6 and above , is a more robust and general XML serialization framework.

Answer 2

You just need to install a persistence delegate for the Inet4Address class. Adapted from an example in Chapter 8 of Core Java Vol. 2 :

e.setPersistenceDelegate(Inet4Address.class, new DefaultPersistenceDelegate() {
    @Override
    protected Expression instantiate(Object oldInstance, Encoder out) {
        InetAddress old = (InetAddress) oldInstance;
        return new Expression(oldInstance, InetAddress.class, "getByAddress",
            new Object[]{old.getAddress()});
    }
});