java - Java 的 XMLEncoder 可以序列化具有不可序列化字段的对象吗？

Question

我对书中甚至在这里找到的所有观点感到非常困惑，所以请耐心等待!

Clay Richardson 的 Professional Java JDK 6 中指出

you will notice that MyBean does not implement Serializable. XMLEncoder/Decoder does not require classes it serializes to implement Serializable.

还有那个

the XMLEncoder/Decoder API serializes object instances without any knowledge of their private data members. It serializes based upon the object’s methods, its JavaBean properties, exposed through the JavaBeans convention > of getters and setters (getXXX and setXXX).

这是否意味着 XMLEncoder 可以序列化不可序列化的对象，例如 javafx.scence.color(如果它是 JavaBean 内的字段)？好吧，我尝试创建一个 JavaBean 并遵循有关命名和默认无参数构造函数的所有规定约定，如下所示

import javafx.geometry.Point2D;
import javafx.scene.paint.Color;
import java.io.Serializable;
import java.util.Map;

public class PCircle extends Shape implements Serializable {

    private Point2D position;
    private Map<String, Double> properties;
    private Color backColor;
    private Color strokeColor;

    public void setPosition(Point2D position) { this.position = position; }
    public Point2D getPosition() { return this.position; }


    public void setProperties(Map<String, Double> properties) { this.properties = properties; }
    public Map<String, Double> getProperties() { return this.properties; }


    public void setBackColor(Color color) { this.backColor = color; }
    public Color getBackColor() { return this.backColor; }

    public void setStrokeColor(Color color) { this.strokeColor = color; }
    public Color getStrokeColor() { return this.strokeColor; }

} 

其中Shape是一个实现IShape接口(interface)的抽象类，如下所示

import javafx.geometry.Point2D;
import javafx.scene.paint.Color;
import java.util.Map;

public interface IShape {

    void setPosition(Point2D position);
    Point2D getPosition();

    void setProperties(Map<String, Double> properties);
    Map<String, Double> getProperties();

    void setBackColor(Color color);
    Color getBackColor();

    void setStrokeColor(Color color);
    Color getStrokeColor();

}

public abstract class Shape implements IShape {

    abstract public void setPosition(Point2D position);
    abstract public Point2D getPosition();


    abstract public void setProperties(Map<String, Double> properties);
    abstract public Map<String, Double> getProperties();

    abstract public void setBackColor(Color color);
    abstract public Color getBackColor();

    abstract public void setStrokeColor(Color color);
    abstract public Color getStrokeColor();

}

现在如果我运行这个主要方法来测试

import javafx.geometry.Point2D;
import javafx.scene.paint.Color;
import java.beans.XMLEncoder;
import java.io.FileOutputStream;
import java.util.HashMap;

public class Main {

    public static void main(String[] args) {

        HashMap<String, Double> properties = new HashMap<>();
        properties.put("First Property", 20.5);

        PCircle circle = new PCircle();

        circle.setPosition(new Point2D(20, 30));
        circle.setProperties(properties);
        circle.setBackColor(Color.BLACK);
        circle.setStrokeColor(Color.RED);

        try {
            FileOutputStream fos = new FileOutputStream("output.xml");
            XMLEncoder encoder = new XMLEncoder(fos);
            encoder.writeObject(circle);
            encoder.close();
            fos.close();
        } catch (Exception ex) {
            System.out.println("Exception! " + ex.getMessage());
        }

    }
}

我收到此错误

java.lang.InstantiationException: javafx.scene.paint.Color
Continuing ...
java.lang.RuntimeException: failed to evaluate: <unbound>=Class.new();
Continuing ...
java.lang.InstantiationException: javafx.scene.paint.Color
Continuing ...
java.lang.RuntimeException: failed to evaluate: <unbound>=Class.new();
Continuing ...
java.lang.InstantiationException: javafx.scene.paint.Color
Continuing ...
java.lang.RuntimeException: failed to evaluate: <unbound>=Class.new();
Continuing ...
java.lang.InstantiationException: javafx.scene.paint.Color
Continuing ...
java.lang.RuntimeException: failed to evaluate: <unbound>=Class.new();
Continuing ...

有趣的是，如果我使用可序列化的类，例如 java.awt.Color，代码可以正常工作并生成 XML。但是，即使明确指出 JavaBean 不需要实现 Serialized 接口(interface)，这又有什么关系呢？

Answer 1

Doesn't that mean that XMLEncoder can serialize non-serializable objects such as a javafx.scene.[paint.]color if it is a field inside a JavaBean?

没有。这意味着它可以序列化不可序列化的对象，例如 javafx.scene.paint.color 如果它们也遵守 JavaBeans 约定，并且提供它们的对象值属性以此类推，直到关闭。

在本例中，javafx.scene.paint.color 没有无参数构造函数。 java.awt.Color 之所以有效，是因为它遵守 JavaBeans 约定，而不是因为它是Serialized。