How to get protobuf for Java Object by given message type name and raw bytes?

Question

I have message type name in string and raw bytes. how to create java object by these meterials? b.proto

pakage foo;
message Bar {
 required int32 id = 1;
 required string name = 2;
}

TestMain.java

foo.Bar bar = foo.Bar.newBuilder()
.setId(1).setName("foobar").build();
byte[] rawbytes = bar.toByteArray();
String typeName = bar.getDescriptorForType().getFullName();

foo.Bar b = (foo.Bar) howTo(rawbyte, typeName);

Surely if you know that you need a foo.Bar at compile-time (your last line shows that twice), you can go the normal route of deserialization. Please give more details about what you're trying to do. — Jon Skeet
– Jon Skeet, Commented Apr 12, 2013 at 5:43
the howTo is a common function, I want it can also create other message object. like foo.Bar b = (foo.Bar) howTo(rawbyte, "foo.Bar"); foo.Boom bm = (foo.Boom) howTo(rawbyte, "foo.Boom"); — Leajon
– Leajon, Commented Apr 12, 2013 at 5:47
here is a C++ demo github.com/chenshuo/recipes/blob/master/protobuf/codec.h#L35 — Leajon
– Leajon, Commented Apr 12, 2013 at 5:49
How is there any benefit in using howTo over using: foo.Boom bm = foo.Boom.parseFrom(rawBytes)? If you were trying to then use this just as a generic message that would make more sense, but if you know at compile-time what type you need, it just seems pointless. — Jon Skeet
– Jon Skeet, Commented Apr 12, 2013 at 5:53

Jon Skeet · Accepted Answer · 2013-04-12 05:58:01Z

6

As I've said in my comments, it seems completely pointless to me, but you can easily just use reflection:

public static Object parseDynamic(String type, byte[] bytes) {
    try {
        Class<?> clazz = Class.forName(type);
        Method method = clazz.getDeclaredMethod("parseFrom", byte[].class);
        return method.invoke(null, bytes);
    } catch (NoSuchMethodException e) {
        throw new IllegalArgumentException("Non-message type", e);
    } catch (IllegalAccessException e) {
        throw new IllegalArgumentException("Non-message type", e);
    } catch (InvocationTargetException e) {
        // TODO: Work out what exactly you want to do.
        throw new IllegalArgumentException("Bad data?", e);
    }
}

answered Apr 12, 2013 at 5:58

Jon Skeet

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