Java中的泛型Parsing [英] Generic Parsing of PB in java

问题描述

是否可以在Java中以通用方式解析protobuf？

Is it possible to parse protobuf in a generic fashion in Java?

我查看了GeneratedMessage，找不到将任何PB字节缓冲区解析为GeneratedMessage的方法。

I have looked into GeneratedMessage and could not find a way to parse any PB byte buffer into a GeneratedMessage.

基本上，我试图将PB字节缓冲区解析为GeneratedMessage，然后我会使用反射来检测其中的字段。

Essentially, I am trying to parse a PB byte buffer into GeneratedMessage and then I would use reflection to detect fields inside it.

推荐答案

首先，在不知道架构的情况下，无法解析PB数据。模式最初来自.proto文件，通常嵌入在 protoc 生成的代码中。但是，您也可以告诉 protoc 以Java Protobuf库可用的格式存储架构：

First of all, you can't parse PB data without knowing the schema. The schema originally comes from a ".proto" file and is typically embedded in the code generated by protoc. However, you can also tell protoc to store the schema in a format that's usable by the Java Protobuf library:

protoc --descriptor_set_out=mymessages.desc mymessages.proto

然后将它加载到Java代码中：

Then load it in your Java code:

FileInputStream fin = new FileInputStream("mymessages.desc");
Descriptors.FileDescriptorSet set =
  Descriptors.FileDescriptorSet.parseFrom(fin);
Descriptors.Descriptor md = set.getFile(0).getMessageType(0);

获得消息的架构后（ Descriptor.Descriptor ）解析消息很简单：

Once you have the schema for a message (Descriptor.Descriptor) parsing a message is easy:

byte[] data = ...;
DynamicMessage m = DynamicMessage.parseFrom(md, data);

DynamicMessage 有一个反光的API可以让你浏览字段。

DynamicMessage has a reflective API that lets you look through the fields.

凌乱的部分是调用 protoc 工具来转换.proto将文件转换为可用格式。 C ++ Protobuf库有一种直接加载.proto文件的方法，但不幸的是Java Protobuf库没有。

The messy part is calling out to the protoc tool to convert the ".proto" file into a usable format. The C++ Protobuf library has a way to load ".proto" files directly, but unfortunately the Java Protobuf library does not.

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