GWT編譯期間的NPE

Question

以下NPE在GWT編譯期間出現。這是在編譯器本身，而不是在應用程序代碼：

[ERROR] Exception in thread "pool-1-thread-96" java.lang.NullPointerException 
[ERROR]  at com.google.gwt.dev.util.DiskCache.transferToStream(DiskCache.java:185) 
[ERROR]  at com.google.gwt.dev.util.DiskCacheToken.writeObject(DiskCacheToken.java:73) 
[ERROR]  at sun.reflect.GeneratedMethodAccessor29.invoke(Unknown Source) 
[ERROR]  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
[ERROR]  at java.lang.reflect.Method.invoke(Method.java:498) 
[ERROR]  at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:1028) 
[ERROR]  at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496) 
[ERROR]  at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432) 
[ERROR]  at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178) 
[ERROR]  at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548) 
[ERROR]  at java.io.ObjectOutputStream.defaultWriteObject(ObjectOutputStream.java:441) 
[ERROR]  at com.google.gwt.dev.javac.CachedCompilationUnit.writeObject(CachedCompilationUnit.java:222) 
[ERROR]  at sun.reflect.GeneratedMethodAccessor33.invoke(Unknown Source) 
[ERROR]  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
[ERROR]  at java.lang.reflect.Method.invoke(Method.java:498) 
[ERROR]  at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:1028) 
[ERROR]  at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496) 
[ERROR]  at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432) 
[ERROR]  at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178) 
[ERROR]  at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348) 
[ERROR]  at com.google.gwt.dev.javac.PersistentUnitCache$6.run(PersistentUnitCache.java:492) 
[ERROR]  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) 
[ERROR]  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) 
[ERROR]  at java.lang.Thread.run(Thread.java:745) 

GWT版本2.6.1

Answer 1

當不是所有共享類（在服務器和客戶端同時使用）實現Serializable接口此錯誤通常發生。