Re: [Py4j-users] Help Requested: error when accessing jvm for basic sample

[Barthelemy D. <ba...@cs...>]

Hi Sean,

The way Py4J works is that python code is executed in a Python 
interpreter and Java code is invoked by a Java Virtual Machine. Both the 
Python interpreter and the JVM must be started prior to using Py4J. In 
other words, Py4J won't start a JVM to execute code in a jar file.

To run the example, first, locate the py4j.jar and your jar and execute 
this command (using the right path):

java -cp path\to\py4j.jar;path\to\yourlib.jar \
py4j.examples.AdditionApplication

Then, open a python interpreter and try the example code, it should work.

You should also be able to access the code in your jar file.

Hope this helps,
Barthélémy

On 04/18/2011 08:43 PM, Sean Silvestri wrote:
> Hi Barthelemy,
> Interesting, I did not start any Java program. I must have
> misunderstood the premise of the module.
> My main goal is to simply call into a java jar file that I've
> registered e.g. the classpath.
>
> Since that was not working I just resorted to the basic sample on the
> web site using the .java.util.Random class (see below)
> I'm simply wanting to interface with a jar file in order to call the
> java methods.
> gateway = JavaGateway()                   # connect to the JVM
>>>> random = gateway.jvm.java.util.Random()   # create a java.util.Random instance
>>>> number1 = random.nextInt(10)              # call the Random.nextInt method
>>>> number2 = random.nextInt(10)
>>>> print(number1,number2)
> (2, 7)
>
> I had also turned off my firewall but still had gotten the error i had
> mentiond ( [Errno 10061] No connection could be made because the
> target machine actively refused it).
>
> What would be the steps to be able to call java code situated in a
> .jar file from a python script using py4j?
> many thanks,
> Sean
>
>
>
> On Mon, Apr 18, 2011 at 5:21 PM, Barthelemy Dagenais<ba...@cs...>  wrote:
>> Hi Sean,
>>
>> this error means that the python interpreter cannot connect to the jvm
>> either because:
>>
>> 1- The jvm is not yet started so nothing is listening on the default py4j
>> port.
>>
>> 2- You have a firewall blocking the port.
>>
>> You need to start the java program in the example and then, you can start
>> your python interpreter (not the other way around).
>>
>> If you don't have a firewall and if you started the Java program before
>> running the interpreter, we will need more information to help you (e.g.,
>> how did you start the Java program, what is the output of the "netstat"
>> command in a command prompt after starting the Java program, etc.).
>>
>> Barthélémy
>>
>> On Mon, April 18, 2011 8:07 pm, Sean Silvestri wrote:
>>> HI All,
>>> I'm just getting started with Py4J, basically just trying to call a
>>> jar. I'm having trouble with the basic sample however:
>>>
>>>
>>>>>> from py4j.java_gateway import JavaGateway gateway = JavaGateway()
>>>>>> # connect to the JVM
>>>>>> random = gateway.jvm.java.util.Random()   # create a
>>>>>> java.util.Random instance number1 = random.nextInt(10)
>>>>>> # call the Random.nextInt method
>>>>>> number2 = random.nextInt(10) print(number1,number2)
>>> (2, 7)
>>>
>>>>>> addition_app = gateway.entry_point        # get the
>>>>>> AdditionApplication instance
>>>>>> addition_app.addition(number1,number2)    # call the addition method
>>>>>>
>>> 9
>>>
>>>
>>> I keep getting the following error: [Errno 10061] No connection could
>>> be made because the target machine actively refused it
>>>
>>> I'm on python 2.71 for windows i have jre6 se installed have set path.
>>> cheers, Sean
>>>
>>>
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>>
>>
>>