无法读取用C ++序列化的Java数据

Question

I have a Java client connected via socket to a C++ server.

The C++ server sends back to the client serialized objects.

However serialization works differently for Java and C++, so I cannot read the objects in that way:

objectInputStream.readObject();

This forces me to read each single value of the object manually:

byte[] buffer = read(FOUR_BYTES);
int flag = convertBufferToInt(buffer);

byte[] buffer = read(FOUR_BYTES);
float price = convertBufferToFloat(buffer);

// More stuff

myObject.setFlag(flag);
myObject.setPrice(price);

// More stuff

That's very hard to maintain. Isn't there an easier way to fill in my object with data?

Answer 1

Yes there is (are). You have 2 options using only the standard library:

Using the DataInputStream class

Check out the DataInputStream class. It has methods to read values of primitive types like readByte() , readInt() , readLong() , readFloat() , readChar() , readUTF() (for reading UTF-8 encoded String ) etc.

So your code becomes as simple as:

// Obtain InputStream from Socket:
InputStream is = ...;
// Create DataInputStream:
DataInputStream dis = new DataInputStream(is);

myObject.setFlag(dis.readInt());
myObject.setPrice(dis.readFloat());

Using the ByteBuffer class

For this you have to read first the whole data into a byte array. Once you've done that, you can create a ByteBuffer using the ByteBuffer.wrap(byte[] array) method. The ByteBuffer class also supports reading primitive types just like the DataInputStream class.

The good thing about ByteBuffer that it supports changing the byte order (the order how the low and high bytes of a multi-byte value like int are read/written): ByteBuffer.order(ByteOrder bo) . This is very useful if you're communicating with systems which use a differnet byte order (which might apply in your case).

Example using ByteBuffer :

// Read all your input data:
byte[] data = ...;
// Create ByteBuffer:
ByteBuffer bb = ByteBuffer.wrap(data);

myObject.setFlag(bb.getInt());
myObject.setPrice(bb.getFloat());

Answer 2

To solve this in general you would need to write a C++ parser for objects serialized in Java. This is no small task.

Rather, I would recommend that you find some serialization format that is easy to parse and share between your Java and C++ programs. Preferably a format where there exists Java as well as C++ libraries for the serialization/deserialization. JSON or Google Protocol Buffers are obvious candidates.