5

在将扩展加载到程序中时，我遇到了一个主要问题。我得到一个异常，因为没有有效的构造函数。

问题在于： 

 ekstensja =  (ArrayList<Dydaktyk>) ois.readObject();

我得到类似的东西：

java.io.InvalidClassException: Dydaktyk; no valid constructor
    at java.io.ObjectStreamClass$ExceptionInfo.newInvalidClassException(Unknown Source)
    at java.io.ObjectStreamClass.checkDeserialize(Unknown Source)
    at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.readObject(Unknown Source)
    at java.util.ArrayList.readObject(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at java.io.ObjectStreamClass.invokeReadObject(Unknown Source)
    at java.io.ObjectInputStream.readSerialData(Unknown Source)
    at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.readObject(Unknown Source)
    at Dydaktyk.wczytajEkstensje(Dydaktyk.java:81)
    at Dydaktyk.<clinit>(Dydaktyk.java:69)
    at java.io.ObjectStreamClass.hasStaticInitializer(Native Method)
    at java.io.ObjectStreamClass.computeDefaultSUID(Unknown Source)
    at java.io.ObjectStreamClass.access$100(Unknown Source)
    at java.io.ObjectStreamClass$1.run(Unknown Source)
    at java.io.ObjectStreamClass$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.io.ObjectStreamClass.getSerialVersionUID(Unknown Source)
    at java.io.ObjectStreamClass.initNonProxy(Unknown Source)
    at java.io.ObjectInputStream.readNonProxyDesc(Unknown Source)
    at java.io.ObjectInputStream.readClassDesc(Unknown Source)
    at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.defaultReadFields(Unknown Source)
    at java.io.ObjectInputStream.readSerialData(Unknown Source)
    at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.readObject(Unknown Source)
    at java.util.ArrayList.readObject(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at java.io.ObjectStreamClass.invokeReadObject(Unknown Source)
    at java.io.ObjectInputStream.readSerialData(Unknown Source)
    at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.defaultReadFields(Unknown Source)
    at java.io.ObjectInputStream.readSerialData(Unknown Source)
    at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.readObject(Unknown Source)
    at java.util.ArrayList.readObject(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at java.io.ObjectStreamClass.invokeReadObject(Unknown Source)
    at java.io.ObjectInputStream.readSerialData(Unknown Source)
    at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.readObject(Unknown Source)
    at Przedmiot.wczytajEkstensje(Przedmiot.java:99)
    at Przedmiot.<clinit>(Przedmiot.java:87)
    at GUI.main(GUI.java:100)

static {
    wczytajEkstensje(); // load Extension
}

public static void wczytajEkstensje() {// load extension
    FileInputStream fis = null;
    ObjectInputStream ois = null;
    try {
        fis = new FileInputStream("dydaktyk.ser");
        ois = new ObjectInputStream(fis);
        // here is the problem
        ekstensja =  (ArrayList<Dydaktyk>) ois.readObject();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } finally {
        try {
            if (ois != null) {
                ois.close();
            }
        } catch (IOException e) {
        }
        try {
            if (fis != null) {
                fis.close();
            }
        } catch (IOException e) {
        }
    }
}

public static void zapiszEkstensje() {// save extension
    FileOutputStream fos = null;
    ObjectOutputStream oos = null;
    try {
        fos = new FileOutputStream("dydaktyk.ser");
        oos = new ObjectOutputStream(fos);

        oos.writeObject(ekstensja); // serialization
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (oos != null) {
                oos.close();
            }
        } catch (IOException e) {
        }
        try {
            if (fos != null) {
                fos.close();
            }
        } catch (IOException e) {
        }
    }
}
4

2 回答 2

10

该类Dydaktyk应该有一个可访问的（公共或受保护的）无参数构造函数，以便序列化反射机制可以创建该类的实例：

public Dydaktyk() { 
  ...
}

从文档

在反序列化过程中，不可序列化类的字段将使用类的公共或受保护的无参数构造函数进行初始化。可序列化的子类必须可以访问无参数构造函数。可序列化子类的字段将从流中恢复。

于 2013-06-17T17:54:17.910 回答
3

如 Oracle 站点中关于Serialization接口的指定：

在反序列化过程中，不可序列化类的字段将使用类的公共或受保护的无参数构造函数进行初始化。可序列化的子类必须可以访问无参数构造函数。可序列化子类的字段将从流中恢复。

我猜这Dydaktyk是某个类的子类。并且您已经在其中定义parametric constructor了superclass并且没有parameter-less constructor在其中定义 a 。并且编译器没有为此插入默认构造函数superclass。所以，你也应该parameter-less constructor在你的超类中定义一个。

于 2013-06-17T18:14:35.267 回答