Java對象的XML序列化和反序列化 - (2)

前一篇文章裡寫了如何用XMLEncoder和XMLDecoder序列化和反序列化符合JavaBeans規範的對象。那麼，如果待序列化的對象不符合JavaBeans規範，比如一個純資料對象，那會是什麼後果？

下面是一個純資料對象的代碼：

public class PureDataObject
{
   public PureDataObject()
   {
   }

   public PureDataObject(int id, String name, double value, boolean valid)
   {
      this.id = id;
      this.name = name;
      this.value = value;
      this.valid = valid;
   }

   public int id;
   public String name;
   public double value;
   public boolean valid;

}
           

下面是示範代碼：

import java.beans.XMLDecoder;
import java.beans.XMLEncoder;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class XmlSerialize
{
   public XmlSerialize()
   {
   }

   public void serializeSingleObject(OutputStream os, Object obj)       // 序列化單個java對象
   {
      // XMLEncoder xe = new XMLEncoder(os);
      XMLEncoder xe = new XMLEncoder(os, "GBK", true, 0);     // 僅用于Java SE 7
      xe.writeObject(obj);    // 序列化成XML字元串
      xe.close();
   }

   public Object deserializeSingleObject(InputStream is)       // 反序列化單個Java對象
   {
      XMLDecoder xd = new XMLDecoder(is);
      Object obj = xd.readObject();       // 從XML序列中解碼為Java對象
      xd.close();
      return obj;
   }

   public void runPureDataObject()     // 無法正常序列化純資料對象。
   {
      File xmlFile = new File("data.xml");

      PureDataObject pdo4Out = new PureDataObject();
      pdo4Out.id = 1;
      pdo4Out.name = "Hello, World !";
      pdo4Out.value = 1.414;
      pdo4Out.valid = true;

      try
      {
         FileOutputStream ofs = new FileOutputStream(xmlFile);       // 建立檔案輸出流對象
         serializeSingleObject(ofs, pdo4Out);
         ofs.close();
      } catch (FileNotFoundException e)
      {
         e.printStackTrace();
      } catch (IOException e)
      {
         e.printStackTrace();
      }

      try
      {
         FileInputStream ifs = new FileInputStream(xmlFile);
         PureDataObject pdo4In = (PureDataObject)deserializeSingleObject(ifs);
         System.out.println("id: " + pdo4In.id);
         System.out.println("name: " + pdo4In.name);
         System.out.println("value: " + pdo4In.value);
         System.out.println("valid: " + pdo4In.valid);
      } catch (FileNotFoundException e)
      {
         e.printStackTrace();
      }
   }

   public static void main(String[] args)
   {
      XmlSerialize xs = new XmlSerialize();
      xs.runSingleObject();
      xs.runMultipleObject();
      xs.runPureDataObject();
   }

}
           

以下是生成的XML檔案：

<?xml version="1.0" encoding="GBK"?>
<java version="1.7.0" class="java.beans.XMLDecoder">
 <object class="PureDataObject" id="PureDataObject0">
  <void class="PureDataObject" method="getField">
   <string>id</string>
   <void method="set">
    <object idref="PureDataObject0">
     <void class="PureDataObject" method="getField">
      <string>name</string>
      <void method="set">
       <object idref="PureDataObject0">
        <void class="PureDataObject" method="getField">
         <string>value</string>
         <void method="set">
          <object idref="PureDataObject0">
           <void class="PureDataObject" method="getField">
            <string>valid</string>
            <void method="set">
             <object idref="PureDataObject0"/>
             <boolean>true</boolean>
            </void>
           </void>
          </object>
          <double>1.414</double>
         </void>
        </void>
       </object>
       <string>Hello, World !</string>
      </void>
     </void>
    </object>
    <int>1</int>
   </void>
  </void>
 </object>
</java> 
           

再看看反序列化之後螢幕上輸出的結果：

id: 1
name: Hello, World !
value: 1.414
valid: true
           

可以看到，仍舊能夠正常地執行XML序列化和反序列化。不過，序列化之後生成的XML檔案，看上去實在是一團亂麻。