Debug GWT RPC Payloads With VM Arguments

• 2/5/2011
• One-minute read

GWT RPC serialises Java objects into a compact wire format. When requests fail or exceed the 1 MB default size, you need visibility into the payload to understand which fields misbehave.

Enable Payload Logging

Add the following VM argument to your DevMode or application server startup script:

-Dgwt.rpc.dumpPayload=true

The flag instructs GWT to write each encoded request and response to the log directory (defaults to your working directory). Pair it with -Dgwt.rpc.dumpPayload.limit=10240 to control how many bytes are captured per message.

Troubleshooting Tips

• Obfuscation or compression may still hide field names; enable the pretty flag in your logging formatter if available.
• When payloads contain unexpected nulls, confirm the affected DTO implements IsSerializable or has a zero-arg constructor.
• For production incidents, disable the flag immediately after diagnosis to avoid logging sensitive data.

Further Reading

• GWT RPC Serialization Documentation
• GWT Logging Configuration Guide