如何使用JAXBContext將單例對象保存到XML文件？

我正在尋找使用JAXBContext將單例對象保存到XML文件。所討論的Object被稱爲Player，它正在擴展抽象類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，並且不能從類外部訪問。我該如何正確地做到這一點？如何使用JAXBContext將單例對象保存到XML文件？

下面是一段代碼，我用它來保存播放器：

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); 
    }

而且這裏的一段代碼來再讀一遍：

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); 
    }

在這兩個類別的實體和球員，我使用以下加註：

@XmlRootElement

Richt以上類的開始。

以下是錯誤輸出，我得到：

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)

來源

2015-02-23 Thibstars

您是否在Player類設置器中使用@XmlElement註釋？你需要標記你想要的東西。你可以在本教程中找到更多內容：http://www.java2blog.com/2013/02/jaxb-tutorial.html – RichardK 2015-02-23 14:54:16

到目前爲止，我沒有像Player類目前沒有setter（除了Entity中的那些它延伸的類）。我認爲這個問題是JAXBContext的實例化。 Player和Entity類都沒有公共構造函數。我嘗試應用您提到的註釋，但這並沒有改變錯誤日誌中的任何內容。 – Thibstars 2015-02-23 15:56:39

最後我找到了這個問題。正如問題中所解釋的，Player類擴展了類實體。 類實體擴展了常見的Thread類。顯然JAXBContext不能正確實例化一個線程對象。我通過讓類實體實現了接口Runnable來解決這個問題，什麼讓我沒有更多的錯誤。

來源

2015-02-23 16:09:12 Thibstars

如何使用JAXBContext將單例對象保存到XML文件？

回答

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