https://github.com/protocolbuffers/protobuf

https://github.com/protocolbuffers/protobuf/releases

https://github.com/protocolbuffers/protobuf/releases/tag/v2.5.0

wget https://github.com/protocolbuffers/protobuf/releases/download/v2.5.0/protobuf-2.5.0.tar.gz

./autogen.sh
./configure
make
make check
sudo make install

protoc --version
libprotoc 2.5.0

https://developers.google.com/protocol-buffers/docs/javatutorial

https://developers.google.com/protocol-buffers/docs/proto

https://github.com/protocolbuffers/protobuf/blob/v2.5.0/examples/addressbook.proto

protoc -I=./ --java_out=./ ./addressbook.proto # protoc -I=$SRC_DIR --java_out=$DST_DIR $SRC_DIR/addressbook.proto
或者
protoc --java_out=. addressbook.proto

tree -L 4
.
├── addressbook.proto
└── com
    └── example
        └── tutorial
            └── AddressBookProtos.java

syntax = "proto3";

https://github.com/protocolbuffers/protobuf/blob/main/examples/addressbook.proto

https://docs.confluent.io/platform/current/schema-registry/fundamentals/serdes-develop/serdes-protobuf.html

message HelloRequest {
  string name = 1; // 转换为json的时候，"name": ""
  optional string name1 = 2; // 转换为json的时候，将没有key
  google.protobuf.StringValue name2 = 3; // 转换为json的时候，"name2": null
}