序列化期间没有有效的构造函数 [英] No valid constructor during serialization
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问题描述
在将扩展程序加载到程序中时遇到了一个主要问题。我得到一个例外，因为没有有效的构造函数。
I have a major problem during loading the extension into the program. I get an exception as there is no valid constructor.
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) {
}
}
}
推荐答案
类 Dydaktyk 应该有一个可访问的（公共的或受保护的）no-args构造函数，所以序列化反射机制可以创建类的实例：
The class Dydaktyk should have an accessible (public or protected) no-args constructor so that the serialization reflection mechanism can create an instance of the class:
public Dydaktyk() {
...
}
来自 docs
在反序列化期间，不可序列化的类将使用该类的public或protected no-arg构造函数进行初始化。必须可以对可序列化的子类访问no-arg构造函数。可序列化子类的字段将从流中恢复。
During deserialization, the fields of non-serializable classes will be initialized using the public or protected no-arg constructor of the class. A no-arg constructor must be accessible to the subclass that is serializable. The fields of serializable subclasses will be restored from the stream.
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