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protobuf/java — reference target

Java is generated from the same ../schema/lwep.proto as Python and nanopb. It is not part of the live TCP tester; this is a smoke check that the schema produces a cross-language-compatible wire format.

Prerequisites

  • protoc on PATH
  • protobuf-java-<version>.jar matching your protoc (e.g. protoc 35.1 → protobuf-java-4.35.1.jar from Maven Central). Set $PB_JAR below. 
    curl -sSLO https://repo1.maven.org/maven2/com/google/protobuf/protobuf-java/4.35.1/protobuf-java-4.35.1.jar
  • a JDK (javac, java) — validated with Temurin JDK 17

On MSYS2, convert the jar path to Windows form for Java: PB_JAR=$(cygpath -w /path/to/protobuf-java-4.35.1.jar) (Java doesn't understand /c/... MSYS paths).

Generate

# from this folder
protoc --proto_path=..\schema --java_out=. ..\schema\lwep.proto
# -> ./lwep/Lwep.java  (git-ignored)

Compile + run

javac -cp "$PB_JAR" lwep/Lwep.java Example.java
java  -cp ".:$PB_JAR" Example          # Windows: use ';' instead of ':'
# -> writes sensor.bin

Verify cross-language interop

Decode the Java-produced bytes with the Python bindings:

import sys; sys.path.insert(0, "../python")
import lwep_pb2
m = lwep_pb2.SensorReading()
m.ParseFromString(open("sensor.bin", "rb").read())
print(m)          # should show id=4097, label="cabin-temp", value=23.5, ...

Matching output confirms Java and Python agree on the same neutral schema.