如何使用JAXBContext將Singleton對象保存到XML文件？

Question

我期待使用JAXBContext將Singleton對象保存到XML文件。 有問題的對象叫做Player，它擴展了一個抽象類Entity。 實體也擴展了Thread。 由於Player是一個Singleton對象，因此它的構造函數是私有的，並且從類外部無法訪問。 我該怎么做呢？

以下是我用來保存播放器的代碼：

public static void savePlayer() throws JAXBException {
        JAXBContext context = JAXBContext.newInstance(Player.class);
        Marshaller m = context.createMarshaller();
        m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        OutputStream os = null;
        try {
            os = new FileOutputStream(StringConstants.PLAYER_SAVE_FILE);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        m.marshal(Player.getInstance(), os);
    }

在這里再次讀出它的代碼：

public static Player readPlayer() throws JAXBException {
        JAXBContext context = JAXBContext.newInstance(Player.class);
        Unmarshaller u = context.createUnmarshaller();
        File f = new File(StringConstants.PLAYER_SAVE_FILE);
        return (Player) u.unmarshal(f);
    }

在Entity和Player這兩個類中我使用了以下anotation：

@XmlRootElement

Richt在課程開始之上。

這是我得到的錯誤輸出：

com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 1 counts of IllegalAnnotationExceptions
java.lang.Thread$UncaughtExceptionHandler is an interface, and JAXB can't handle interfaces.
    this problem is related to the following location:
        at java.lang.Thread$UncaughtExceptionHandler
        at public java.lang.Thread$UncaughtExceptionHandler java.lang.Thread.getUncaughtExceptionHandler()
        at java.lang.Thread
        at model.entities.Entity
        at model.entities.Player

    at com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException$Builder.check(IllegalAnnotationsException.java:91)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:445)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:277)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:124)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1123)
    at com.sun.xml.internal.bind.v2.ContextFactory.createContext(ContextFactory.java:147)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:247)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:234)
    at javax.xml.bind.ContextFinder.find(ContextFinder.java:462)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:641)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584)
    at model.io.SaveWriter.savePlayer(SaveWriter.java:20)
    at tests.SaveTest.main(SaveTest.java:17)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 1 counts of IllegalAnnotationExceptions
java.lang.Thread$UncaughtExceptionHandler is an interface, and JAXB can't handle interfaces.
    this problem is related to the following location:
        at java.lang.Thread$UncaughtExceptionHandler
        at public java.lang.Thread$UncaughtExceptionHandler java.lang.Thread.getUncaughtExceptionHandler()
        at java.lang.Thread
        at model.entities.Entity
        at model.entities.Player

    at com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException$Builder.check(IllegalAnnotationsException.java:91)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:445)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:277)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:124)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1123)
    at com.sun.xml.internal.bind.v2.ContextFactory.createContext(ContextFactory.java:147)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:247)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:234)
    at javax.xml.bind.ContextFinder.find(ContextFinder.java:462)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:641)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584)
    at model.io.SaveReader.readPlayer(SaveReader.java:18)
    at tests.SaveTest.main(SaveTest.java:23)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)

Answer 1

最后我發現了這個問題。 正如問題中所解釋的那樣，類Player擴展了類Entity。 類Entity擴展了公共Thread類 。 顯然，JAXBContext無法為Thread對象正確實例化。 我通過讓類Entity實現Runnable接口來解決這個問題，這讓我沒有任何錯誤。