[GitHub] [pulsar] sijie opened a new pull request #3754: NullPointerException at using BytesSchema.of()

[GitBox <gi...@apache.org>]

sijie opened a new pull request #3754: NullPointerException at using BytesSchema.of()
URL: https://github.com/apache/pulsar/pull/3754
 
 
   Fixes #3734
   
   *Motivation*
   
   Exception occurred when using `BytesSchema.of()`
   
   ```
   Exception in thread "main" java.lang.ExceptionInInitializerError
   	at org.apache.pulsar.examples.simple.ProducerExample.main(ProducerExample.java:32)
   Caused by: java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
   	at org.apache.pulsar.client.internal.ReflectionUtils.catchExceptions(ReflectionUtils.java:36)
   	at org.apache.pulsar.client.internal.DefaultImplementation.newKeyValueSchema(DefaultImplementation.java:158)
   	at org.apache.pulsar.client.api.Schema.<clinit>(Schema.java:123)
   	... 1 more
   Caused by: java.lang.reflect.InvocationTargetException
   	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
   	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
   	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
   	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
   	at org.apache.pulsar.client.internal.DefaultImplementation.lambda$newKeyValueSchema$16(DefaultImplementation.java:160)
   	at org.apache.pulsar.client.internal.ReflectionUtils.catchExceptions(ReflectionUtils.java:34)
   	... 3 more
   Caused by: java.lang.NullPointerException
   	at org.apache.pulsar.client.impl.schema.KeyValueSchema.<init>(KeyValueSchema.java:68)
   	... 9 more
   ```
   
   The problem introduced because the weird class loading and reflection sequence.
   
   When accessing `BytesSchema`, `BytesSchema` will try to initialize `Schema`. When initializing Schema, it will attempts
   to initialize `KV_BYTES` using reflection, and initializing KV_BYTES requires `BytesSchema`. Hence it causes KV_BYTES not being
   initialized correctly.
   
   The change is to avoid this recrusive class loading.
   
   *Modifications*
   
   Make KV_BYTES as a method not a static field in `Schema`.
   
   *Verify this change*
   
   Add a test to reproduce the issue and verify it is fixed.
   
   ### Does this pull request potentially affect one of the following parts:
   
   *If `yes` was chosen, please highlight the changes*
   
     - Dependencies (does it add or upgrade a dependency): (no)
     - The public API: (*yes*) : we changed the type of `Schema#KV_BYTES` from a field to a method.
     - The schema: (*yes*)
     - The default values of configurations: (no)
     - The wire protocol: (no)
     - The rest endpoints: (no)
     - The admin cli options: (no)
     - Anything that affects deployment: (no)
   
   ### Documentation
   
     - Does this pull request introduce a new feature? (no)
     - If yes, how is the feature documented? (not applicable)
     - If a feature is not applicable for documentation, explain why?
     - If a feature is not documented yet in this PR, please create a followup issue for adding the documentation
   

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