Re: RPC - Silent failure using LinkedHashMap

Ok taken a look at LinkedHashMap and HashMap emulations of GWT reveals that:

1.) LinkedHashMap extends HashMap but does not override HashMap.clone();

https://gwt.googlesource.com/gwt/+/releases/2.5/user/super/com/google/gwt/emul/java/util/LinkedHashMap.java

2.) HashMap.clone() returns a new HashMap instance.

https://gwt.googlesource.com/gwt/+/releases/2.5/user/super/com/google/gwt/emul/java/util/HashMap.java

This means when you call LinkedHashMap.clone() you only receive a HashMap that can't be cast to LinkedHashMap. Thats why you have a ClassCastException and thats why the exception disappears when you cast it to HashMap. In DevMode it works because in DevMode the ordinary JRE classes are used. For web mode GWT provides different (JS based) implementations (the links above).

Although I am not sure if GWT's JRE emulation respects inheritance it clearly states that HashMap.clone() is emulated while LinkedHashMap.clone() is not (https://developers.google.com/web-toolkit/doc/latest/RefJreEmulation#Package_java_util) although its a sub class. A similar situation exists with java.util.Vector and java.util.Stack. Stack extends Vector but in this case the JRE emulation page says that Stack.clone() and Vector.clone() are emulated.

But in general I would say that its a bug in the LinkedHashMap emulation. It should override HashMap.clone() to return a LinkedHashMap instead. Its too easy to hit this issue.

-- J.

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