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Py4j launch_gateway not connecting properly

I am trying to use py4j to open up a gateway that I can use to pass objects from java into python. When I try to open a gateway with the py4j function launch_gateway it does not seem to properly connect to my Java class. However, when I launch my java class in the command line and then connect to it in python using JavaGateway everything works as expected. I would like to be able to use the built in method as I am sure that I am not accounting for things that have already been considered in the design of py4j, but I'm just not sure what I'm doing wrong.
Let's say I wanted to create a gateway to the class sandbox.demo.solver.UtilityReporterEntryPoint.class. In the command line I can do this by executing the following:
java -cp /Users/grr/anaconda/share/py4j/py4j0.10.4.jar: sandbox.demo.solver.UtilityReporterEntryPoint py4j.GatewayServer
This launches as expected and I can use the methods in my class from within python after connecting to the gateway. So far so good.
My understanding of the py4j documentation would lead me to believe I should do the following to launch the gateway in python:
port = launch_gateway(classpath='sandbox.demo.solver.UtilityReporterEntryPoint')
params = GatewayParameters(port=port)
gateway= JavaGateway(gateway_parameters=params)
I get no errors when executing these three lines, but when I try to access my java class methods with gateway.entry_point.someMethod() it fails with the following error:
Py4JError: An error occurred while calling t.getReport. Trace:
py4j.Py4JException: Target Object ID does not exist for this gateway :t
at py4j.Gateway.invoke(Gateway.java:277)
at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
at py4j.commands.CallCommand.execute(CallCommand.java:79)
at py4j.GatewayConnection.run(GatewayConnection.java:214)
at java.lang.Thread.run(Thread.java:745)
Obviously something is not getting called correctly within launch_gateway or I am feeding it the wrong information.
In the py4j source code for launch_gateway you can see that given the inputs you provide and those constructed by the function, a command is constructed that eventually gets called by subprocess.Popen. So given the input passed to launch_gateway above the command passed into Popen would be:
command = ['java', '-classpath', '/Users/grr/anaconda/share/py4j/py4j0.10.4.jar:sandbox.demo.solver.UtilityReporterEntryPoint', 'py4j.GatewayServer', '0']
Passing this command to Popen returns the listening port as expected. However, connecting to this listening port still does not allow access to my class methods.
Finally, passing the command as a single string to Popen without the final argument ('0'), properly launches a gateway which again operates as expected. Having taken a glance at the Java source code for py4j.GatewayServer.class this makes no sense as the main method seems to indicate that the class should exit with status 1 if the length of arguments is 0.
At this point I'm kind of at a loss. I can hack my way into a workable solution, but as I said I'm sure that ignores important aspects of the gateway behavior and I don't like hacky solutions. I'd love to tag #Barthelemy in this one, but hopefully he reads this. Thanks in advance for any help.
EDIT
For now I have been able to work around this issue with the following steps.
Package entire project including all external dependencies into a single jar file magABM-all.jar, with 'Main-Class' set to UtilityReporterEntryPoint.
Include if...else block regarding presence of --die-on-exit exactly like it is in GatewayServer.java
Use subprocess.Popen to call the command to run the project jar.
UtilityReporterEntryPoint.java
public static void main(String[] args) throws IOException {
GatewayServer server = new GatewayServer(new UtilityReporterEntryPoint());
System.out.println("Gateway Server Started");
server.start();
if (args[0].equals("--die-on-exit")) {
try {
BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in, Charset.forName("UTF-8")));
stdin.readLine();
System.exit(0);
} catch (java.io.IOException e) {
System.exit(1);
}
}
}
app.py
def setup_gateway()
"""Launch a py4j gateway using UtilityReporterEntryPoint."""
process = subprocess.Popen('java -jar magABM-all.jar --die-on-exit', shell=True)
time.sleep(0.5)
gateway = JavaGateway()
return gateway
In this way I can still use gateway.shutdown if necessary and if the python process that starts the py4j gateway dies or is closed the gateway will be closed.
N.B I would by no means consider this a final solution as py4j was written by much smarter individuals with a clear purpose in mind and I am sure that there is a way to manage this exact workflow within the confines of py4j. This is just a stopgap solution.

There are a few issues:
The classpath parameter in launch_gateway should be a directory or a jar file, not a class name. For example, if you want to include additional Java libraries, you would add them to the classpath parameter.
The error you receive when you call gateway.entry_point.someMethod() means that you have no entry point. When you call launch_gateway, the JVM is started with GatewayServer.main, which launches a GatewayServer with no entry point: GatewayServer server = new GatewayServer(null, port). It is not possible currently to use launch_gateway and specify an entry point.
When you start the JVM with java -cp /Users/grr/anaconda/share/py4j/py4j0.10.4.jar: sandbox.demo.solver.UtilityReporterEntryPoint py4j.GatewayServer I believe the JVM uses UtilityReporterEntryPoint as the main class. Although you did not provide the code, I assume that this class has a main method and that it launches a GatewayServer with an instance of UtilityReporterEntryPoint as the entry point. Note that there is a whitespace between the colon and the class name so UtilityReporterEntryPoint is seen as the main class and not as being part of the classpath.

Calling methods between groovy scripts with correct parameters

I just started learning about groovy and trying to transpose my java code to groovy scripts. Usually java allows you have a class with only methods that you can call from other classes. I wanted to translate that to groovy. I have in one file - lets call it File1- a method like this:
def retrieveData(String name){
// do something
}
and in the second file, File2, I call File1 like this:
def file1Class = this.class.classLoader.parseClass(new File("../File1.groovy"))
and then try to call the method in File1 like this:
def data = file1Class.retrieveData("String")
but it keeps giving me this error - MissingMethodException:
groovy.lang.MissingMethodException: No signature of method: static File1.retrieveData() is applicable for argument types: (java.lang.String) values: [String] Possible solutions: retrieveData(java.lang.String)
so it does recognize that I am sending in the correct number of parameters and even the correct object, but it isn't running the method as it should?
Is there something I am missing? I tried to remove the object definition from the method - in other words - like this:
def retrieveData(name){
// do something
}
but that didn't work either. I am clueless about what the next step would be. Can anyone please help push me in the right direction? I would greatly appreciate it.

See the answer provided in this StackOverflow reponse.
Use the GroovyScriptEngine class. What does the GroovyScriptEngine do? From the docs:
Specific script engine able to reload modified scripts as well as
dealing properly with dependent scripts.
See the example below.
def script = new GroovyScriptEngine( '.' ).with {
loadScriptByName( '..\File1.groovy' )
}
this.metaClass.mixin script
retrieveData()
Note how we use the loadScriptByNamemethod to
Get the class of the scriptName in question, so that you can
instantiate Groovy objects with caching and reloading.
This will allow you to access Groovy objects from files however you please.

How do I evaluate a Groovy string within a script?

I'm essentially trying to create a CLI with Groovy. I have a whole JavaFX GUI set up in Java and I want to be able to type in groovy script to run different functions inside a groovy script.
For example, say I have this script:
void meow() {
println "walrus"
}
I want to be able to type in "meow();" and press enter and evaluate it using the script as a reference.
I've tried using
shell.evaluate(inputStr, "src/Server/Scripting/CommandLineScript.groovy");
but to no avail; it just comes up with the error:
groovy.lang.MissingMethodException: No signature of method: CommandLineScript.meow() is applicable for argument types: () values: []
I can call other standard functions, such as:
shell.evaluate("println 'Hello World!';");
but I just can't run my own methods... How to solve it?

The following worked for me.
evaluate(new File("/Users/jellin/meow.groovy"))
I did change the meow.groovy file to execute the method within the file.
void meow() {
println "walrus"
}
meow()
One issue is I don't see a way to pass a parameter to the calling script.
I have used the following before, you can pass parameters as part of the binding.
String script = "full path to the script"
GroovyScriptEngine gse = new GroovyScriptEngine()
Binding binding = new Binding();
Object result = gse.run(script, binding)
Also, you might be able to simply reference the other scripts as classes and execute the run method on them.
There is also an AST transformation that can be used to have scripts extend a base script.
See here for more info
http://mrhaki.blogspot.com/2014/05/groovy-goodness-basescript-with.html

Thanks for your time guys; after a little more searching (always after posting a question do I find the answer in research >,<), I found that you can set a base class for the GroovyShell... I did it this way:
ClassLoader parent = getClass().getClassLoader();
GroovyClassLoader loader = new GroovyClassLoader(parent);
loader.addClasspath("src/ScriptLoc/");
binding = new Binding();
CompilerConfiguration compConfig = new CompilerConfiguration();
compConfig.setScriptBaseClass("ScriptName");
shell = new GroovyShell(loader, binding, compConfig);
I thought there would be a way to do it, and there it is... Now whenever I need to evaluate a script from the text box, I can just evaluate it and it evaluates it in the context of the base script.

Using Java class in Matlab

I've been struggling with this problem for two days now and no resource I've found have been able to solve it.
I am trying to call a java class (added the link at the bottom) from Matlab (version 7.13.0.564 (R2011b)). I've compiled the java class using java 1.6 into a .class file and also added the path to the folder where the file is situated using javaaddpath (I've of course checked that the path is correct in the list of dynamic paths). However, when I try to call the class from Matlab using javaMethod('main','PerlinNoiseGenerator','') I get the error:
"No class PerlinNoiseGenerator can be located on Java class path"
I would be extremely grateful if someone with experience in calling java from Matlab could put together a short tut on how to do this. I am probably going to distribute my code so I kinda need to set the java path dynamically and from what I've read it really should be possible although I've seen post that indicate that it could be the cause of the problem.
http://svn.j3d.org/code/tags/Xj3D-M10/src/java/org/j3d/texture/procedural/PerlinNoiseGenerator.java

Usually I create jar files that contain java classes. I also had problems loading individual java classes before. In your case I did the following on xubuntu 13.04 x64 and Matlab 2013a x64 to load your particular class:
Compile it using java 6 (not the default 7) with option -d . to create a set of package folders, as your class defines a package org/j3d/texture/proecedural/ etc:
/usr/lib/jvm/java-6-openjdk-amd64/bin/javac -d . PerlinNoiseGenerator.java
This will compile the class and make in the current director (thus .) the set of package folders.
Make jar file containing your class again using jar from java 6. I named it javaNoise.jar:
/usr/lib/jvm/java-6-openjdk-amd64/bin/jar cf javaNoise.jar ./org/j3d/texture/procedural/PerlinNoiseGenerator.class
In Matlab, in the directory where javaNoise.jar is:
javaaddpath('./javaNoise.jar');
Create object of your java class:
png=org.j3d.texture.procedural.PerlinNoiseGenerator()
% results in: png = org.j3d.texture.procedural.PerlinNoiseGenerator#3982a033
To test it, I just generated some 1D noise:
png.noise1(1.2)
ans = -0.0960
Hope this helps.
P.S.
javaMethod('main','PerlinNoiseGenerator','') wont work because this class has no main method:-).

Your notation to the compiler of the constructor is a polymorphic class meaning "use appropriate constructor that is called at runtime".
public PerlinNoiseGenerator()
public PerlinNoiseGenerator(int seed)
The first form with no argument can be called but is irrelevent because the line with this(DEFAULT_SEED) attempts to call itself but only one constructor is allowed used
Second constructor has int for an argument but requires being loaded by an already loaded class.
Use the first version and change the case sensitive name of the one with the argument and remove this(DEFAULT_SEED) from it replace with the method name(the one you changed from a constructor that has the argument).
e.g. public perlinNoiseGenerator(int seed)
note: by convention java code method names start with a lower-case letter.
A final note, java arguments from the command line come in as "String" data type through the "main" method, a starter method for applications (gui or command prompt).
The first argument on the main method argument is the first commandline argument.
public static void main(String[] Args){
new PerlinNoiseGenerator(Args); // recursive class call
}//end main method
int[] args; // global
public PerlinNoiseGenerator(String[] Args){
int arglength=Args.length();
args = new int[arglength];
for(int cnt=0;cnt<arglength;cnt++){
Args[cnt].trim();
args[cnt]=new Integer(Args[cnt]).intValue();
}//enfor
perlinNoiseGenerator(args[0]); // call method
}//end constructor

how to pass java output as a matlab variable?

I have written a Java program which is invoked using system() function, thus it runs on the command window of Matlab. Now I want to know if there's another way to run a Java program other than running it on command window? Can it be run on any user made GUI in Matlab? Another problem is, I want to know if my program has some string value as output, which is generally displayed on command window, how can i store it in variable in Matlab?
Hope to hear from you very soon.

The Hello World solution by The MathWorks provides some insights on how to run a simple 'Hello World' java application inside MATLAB. You may change the Java code a bit, in order to have a method that returns a String.
public class HelloWorld
{
public String hello()
{
String helloWorld = "Hello World!";
return helloWorld;
}
}
Once this simple class is compiled and on the MATLAB JVM classpath create an instance and invoke the method with the following two commands.
o = HelloWorld
output = o.hello;
The String returned by the HelloWorld instance is assigned to the MATLAB variable output.
There is no need for a system command with Java code in MATLAB. You have direct access to the JVM from inside MATLAB. For an application with a complex GUI, break out to Java.
Undocumented Java is a valuable source on MATLAB, Java and GUIs.

Yes the classpath set is correct.
I modified the code, using it without main..
class HelloWorld
{
public String Hello()
{
String helloWorld="Hello World!";
return helloWorld;
}
}
Now, as per guided i try to create instance obj in Matlab, with following command:
o = HelloWorld;
Here I get following err:
??? No constructor 'HelloWorld' with
matching signature found.
The next command indicated it this:
output = o.hello;
which wouldnt work unless instance is created.