Protocol buffer `ParseFromString` in Java for pars

问题:

Is ParseFromString available in Java for protocol buffers?

The C++ version has it: here

回答1:

Here is the implementation of ParseFromString (note that TextFormat::ParseFromString simply calls TextFormat::Parser::ParseFromString on a new Parser object):

bool TextFormat::Parser::Parse(io::ZeroCopyInputStream* input,
                               Message* output) {
  output->Clear();
  return Merge(input, output);
}

bool TextFormat::Parser::ParseFromString(const string& input,
                                         Message* output) {
  io::ArrayInputStream input_stream(input.data(), input.size());
  return Parse(&input_stream, output);
}

You can see that Parse simply clears the message, then calls Merge. Although the Java implementation of Protocol Buffers doesn't have a Parse method, you can easily implement it:

public static void parseFromString(CharSequence input, ExtensionRegistry extensionRegistry, Message.Builder builder) throws ParseException {
    builder.clear();
    TextFormat.merge(input, extensionRegistry, builder);
}

回答2:

For a message A, method TextFormat.getParser().merge(str, builder); does it. E.g.:

    AOuterClass.A.Builder buildA = AOuterClass.A.newBuilder();
    buildA.setName("Abra Kadabra");
    buildA.addPrices(3.14);
    buildA.addPrices(3.141592);
    AOuterClass.A aaa = buildA.build();

    String str = aaa.toString();

    AOuterClass.A.Builder builder = AOuterClass.A.newBuilder();
    ///////////////////////////////////////////
    TextFormat.getParser().merge(str, builder);

    System.out.println(builder.build().equals(aaa));  //true

Tested with proto3.