Re: [Py4j-users] Exception when printing a returned List<String> object

[Barthelemy D. <bar...@in...>]

Hi,

When printing the list, Py4J retrieves an Iterator and wraps it with
py4j.java_collections.JavaIterator. It then cycles through the list
with the iterator. JavaIterator should catch the
NoSuchElementException and raise instead a StopIteration. Because it
does not, I suspect something is messing with the automated wrapping
of collections.

could you do:

iter = ret.iterator()
print(type(iter))

This should print something like <class 'py4j.java_collections.JavaIterator'>

Thanks,
Barthelemy

On Tue, Dec 23, 2014 at 6:10 AM,  <hg...@it...> wrote:
> Hi,
>
>
> The method in my gateway server will return a List<String> object. When I
> access it in my python client code, the server has exception and then
> closed. The following is part of the exceptions
>
>
>
>
> ▒Q▒G▒▒ 23, 2014 5:18:14 ▒U▒▒ py4j.reflection.MethodInvoker invoke
> ĵ▒i: Exception occurred in client code.
> java.lang.reflect.InvocationTargetException
>         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 py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:231)
>         at
> py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:379)
>         at py4j.Gateway.invoke(Gateway.java:259)
>         at
> py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:133)
>         at py4j.commands.CallCommand.execute(CallCommand.java:79)
>         at py4j.GatewayConnection.run(GatewayConnection.java:207)
>         at java.lang.Thread.run(Thread.java:745)
> Caused by: java.util.NoSuchElementException
>         at java.util.AbstractList$Itr.next(AbstractList.java:364)
>         ... 11 more
>
> What I do in client code is the following:
>
>>>>ret = gateway.entry_point.getMyStringList(inputStr)    # it's ok to run
>>>> this line
>>>>print ret       # when running to this line, the server raised exception
>
>
> Below is the method in server side:
>
> public List<String> getMyStringList(String input) throws IOException {
>     List<String> strList = new ArrayList<String>();
>     strList = segmenter.segmentString(input);    //  this is some 3rd party
> API for string tokenization and has been tested OK in console, the return
> object is List<String>
>
>     return strList;
> }
>
> It's OK to access "ret" using indices and len(), but when I just type "ret"
> or "print ret", then it would display the content of "ret", but then the
> server poped Exception and stopped. What would be the problemt? Thanks for
> any help!
>
>
>
> Frank Yang
>
>
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