How to execute a python script in Spring Boot with GraalVM?

Question

I'm struggling executing a python script in a Spring Boot application with GraalVM. The code works without Spring Boot in a simple library. The problem is that there are no members found and pystacCreatorClass is null.

The context seems to be ok, since I'm able to execute some python code (see context.eval("python", "print(\"Hello World\")");).

Are there any debug options?

I'm using Spring Boot 2.6.13 and GraalVM 22.3.0.

    @GetMapping("/foo")
    public String foo() {
        
        String PYTHON = "python";
        String VENV_EXECUTABLE = MainController.class.getClassLoader().getResource(Paths.get("venv", "bin", "graalpy").toString()).getPath();
        String SOURCE_FILE_NAME = "staccreator.py";
                
        Context context = Context.newBuilder(PYTHON).
                allowAllAccess(true).
                option("python.Executable", VENV_EXECUTABLE).
                option("python.ForceImportSite", "true").
                build();
        
        context.eval("python", "print(\"Hello World\")");
        
        InputStreamReader code = new InputStreamReader(MainController.class.getClassLoader().getResourceAsStream(SOURCE_FILE_NAME));               
        Source source;
        try {
            source = Source.newBuilder(PYTHON, code, SOURCE_FILE_NAME).build();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        
        System.out.println(source);
        
        context.eval(source);
              
        Set<String> keys = context.getPolyglotBindings().getMemberKeys();
        System.out.println(keys.size());
  
        Value pystacCreatorClass = context.getPolyglotBindings().getMember("StacCreator");
        Value pystacCreator = pystacCreatorClass.newInstance();
        
        StacCreator stacCreator = pystacCreator.as(StacCreator.class);
        // stacCreator do something

        context.close(); 
        return "foo";
    }

import polyglot
import os

class StacCreator:
    def create(self, collection_file_path):
        print("Hello from Python.")

Error message:

2022-10-31 08:58:01.139 ERROR 9668 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException: Cannot invoke "org.graalvm.polyglot.Value.newInstance(Object[])" because "pystacCreatorClass" is null] with root cause

java.lang.NullPointerException: Cannot invoke "org.graalvm.polyglot.Value.newInstance(Object[])" because "pystacCreatorClass" is null
    at com.example.staccreator.MainController.foo(MainController.java:61) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:568) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.23.jar:5.3.23]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150) ~[spring-web-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1071) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:964) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:670) ~[tomcat-embed-core-9.0.68.jar:4.0.FR]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:779) ~[tomcat-embed-core-9.0.68.jar:4.0.FR]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.68.jar:9.0.68]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.23.jar:5.3.23]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.23.jar:5.3.23]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.23.jar:5.3.23]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1789) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.68.jar:9.0.68]
    at java.base/java.lang.Thread.run(Thread.java:833) ~[na:na]

can you share error log please. – muhammed ozbilici Oct 30 '22 at 19:12 — muhammed ozbilici, Oct 30 '22 at 19:12
I updated the questions with the error message. – Stefan Ziegler Oct 31 '22 at 07:59 — Stefan Ziegler, Oct 31 '22 at 07:59

score 0 · Accepted Answer · answered Nov 01 '22 at 07:01

If you use "polyglot bindings" you need to first explicitly export the symbol on the Python side, by using:

import polyglot
polyglot.export_value("my_identifier", StacCreator)

then on the Java side, you'd access this by:

context.getPolyglotBindings().getMember("my_identifier")

Polyglot bindings are shared among all the languages loaded in the context.

You can also use language bindings, which do not require explicit export step:

context.getBindings("python").getMember("StacCreator")

Thanks. I _thought_ it works without Spring Boot. But I stripped down the python code for the Spring Boot variant and did also delete the export_value() line. — Stefan Ziegler, Nov 01 '22 at 16:57

How to execute a python script in Spring Boot with GraalVM?

1 Answers1