Ben Chuanlong Du's Blog

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Call Java Code Using JPype from Python

Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

JPype is easy and intuitive to use. It is the most popular Java interface for Python currently.

import os
import sys
from pathlib import Path
import jpype


jpype.addClassPath("/path/to.jar")
jpype.startJVM()
print(jpype.java.lang.System.getProperty("java.class.path"))
import ...
obj = SomeClass(...)
obj.someMethod(...)
StaticClass.someMethod(...)


import pyarrow
import pyarrow.jvm
classpath = ":".join(str(jar.resolve()) for jar in Path().glob("*.jar"))
jpype.startJVM(jpype.getDefaultJVMPath(), f"-Djava.class.path={classpath}")
ra = jpype.JPackage("org").apache.arrow.memory.RootAllocator(sys.maxsize)
dm = jpype.JPackage("java").sql.DriverManager
connection = dm.getConnection("jdbc:hive2://hive.server.example.com:10000/default", "user_name", "password")
batch = jpype.JPackage("org").apache.arrow.adapter.jdbc.JdbcToArrow.sqlToArrow(
    connection, "SELECT * FROM some_table", ra
)
df = pyarrow.jvm.record_batch(batch).to_pandas()

Notice that you can import a Java class as usual after the following import.

import jpype.imports
  1. jpype.addClassPath must be called before starting the JVM. You can use the following statement to check that the correct dependency has been added.
    print(jpype.java.lang.System.getProperty("java.class.path"))

Passing Arguments Between Java and Python

https://stackoverflow.com/questions/13637614/jpype-passing-args-to-java

https://jpype.readthedocs.io/en/latest/quickguide.html#primitives

References

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