Java class not found when deserializing with ObjectInputStream

[TovlyDeutsch]

I'm using the Stanford Parser with pyjnius. Using the autoclass function of pyjnius, I can use the java classes from the parser. However, when I try to deserialize something that uses those classes, I get a ClassNotFoundException. How could I ensure that the jvm has access to the the class when deserializing (calling readObject)?

This works fine

ArrayList = autoclass('java.util.ArrayList')
ScoredObject = autoclass('edu.stanford.nlp.util.ScoredObject')
sensTrees = ArrayList()
sensTrees.add(ScoredObject(ArrayList(), 5))
outFile = FileOutputStream('javaParses.ser')
oos = ObjectOutputStream(outFile)
oos.writeObject(sensTrees)

But this throws the error below

inFile = FileInputStream('javaParses.ser')
ois = ObjectInputStream(inFile)
Docs = ois.readObject() // this line throws the error

Error

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\we890\seniorThesis\parseDocs.py", line 75, in test
    Docs = ois.readObject()
  File "jnius\jnius_export_class.pxi", line 766, in jnius.JavaMethod.__call__
  File "jnius\jnius_export_class.pxi", line 843, in jnius.JavaMethod.call_method
  File "jnius\jnius_utils.pxi", line 91, in jnius.check_exception
jnius.JavaException: JVM exception occurred: edu.stanford.nlp.util.ScoredObject

Older Error (I think from a different jdk and pyjinius version)

java.lang.ClassNotFoundException: edu.stanford.nlp.util.ScoredObject

[tueda]

I hit the same issue. To reproduce it, a concrete example with Guava is here:

import jnius_config
jnius_config.set_classpath('guava-28.2-jre.jar')
from jnius import autoclass

Stats = autoclass('com.google.common.math.Stats')

ByteArrayOutputStream = autoclass('java.io.ByteArrayOutputStream')
ObjectOutputStream = autoclass('java.io.ObjectOutputStream')
ByteArrayInputStream = autoclass('java.io.ByteArrayInputStream')
ObjectInputStream = autoclass('java.io.ObjectInputStream')

a = Stats.of(1, 2, 3)

# Of course, it works.
# print(a.toString())
# print()

b_out = ByteArrayOutputStream()
o_out = ObjectOutputStream(b_out)
o_out.writeObject(a)
b_array = b_out.toByteArray()

b_in = ByteArrayInputStream(b_array)
o_in = ObjectInputStream(b_in)

try:
    b = o_in.readObject()
except Exception as e:
    print(e)
    print()
    print(e.classname)
    print()
    print(e.innermessage)
    print()
    for x in e.stacktrace:
        print(x)

JVM exception occurred: com.google.common.math.Stats

java.lang.ClassNotFoundException

com.google.common.math.Stats

java.lang.ClassNotFoundException: com.google.common.math.Stats
java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583)
java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
java.base/java.lang.Class.forName0(Native Method)
java.base/java.lang.Class.forName(Class.java:398)
java.base/java.io.ObjectInputStream.resolveClass(ObjectInputStream.java:693)
java.base/java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1886)
java.base/java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1772)
java.base/java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
java.base/java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1594)
java.base/java.io.ObjectInputStream.readObject(ObjectInputStream.java:430)

where I used

Python 3.7.6
pyjnius 1.2.1
openjdk 11.0.4 2019-07-16

[tueda]

Somehow the system class loader and the context class loader, which can be found by

print(autoclass('java.lang.ClassLoader').getSystemClassLoader())
print(autoclass('java.lang.Thread').currentThread().getContextClassLoader())

is not used for ObjectInputStream:

print(o_in.getClass().getClassLoader())

(The last one becomes None.)

I am still not sure why it happens with Pyjnius, but then JDK-4340158 is relevant, and a workaround would be creating a custom class extending ObjectInputStream: https://stackoverflow.com/a/12180547. I also found that it was an issue in Scala, scala/bug#9237.