In this Java project I'm working on for university, I have a situation where I am currently sending strings through the network successfully using
streamOut = ObjectOutputStream
streamIn = ObjectInputStream
streamOut.writeUTF(msgs.peek());
where msgs is a linked blocking queue, receiving it with
String in = streamIn.readUTF();
however, I would like to use an ObjectInputStream and an ObjectOutputStream. I have initialized them both in the constructor and I flush the ObjectOutputStream after constructing it, I read somewhere you have to do this.
I want to send both Strings and another Object type, call it gameWorld over the network (don't care about efficiency at this point).. however when I do
streamOut.writeObject("mad cuz i'm bad");
Object in = streamIn.readObject();
if(in instanceof String) String inS = (String) in;
it doesn't pick anything up when I send strings over... my friend is working on the same project and he passes around only 1 type of object, one of the subclasses of this object is essentially a string and his version works fine, but he makes a new stream in every iteration of his thread's run loop.
Do I need to do something with the stream to receive different objects which don't have a common ancestor other than Object, do I need to make a new stream every iteration of the run loop or is there just something else completely that I'm missing and the information I've provided isn't sufficient to tell whats wrong?
There is a significant difference between writing a String into the stream as primitive data or as an Object. A String instance written by writeObject is written into the stream as a String initially. Future writeObject() calls write references to the string into the stream.
For Example
ByteArrayOutputStream baos1=new ByteArrayOutputStream();
oos1=new ObjectOutputStream(baos1);
baos2=new ByteArrayOutputStream();
ObjectOutputStream oos2=new ObjectOutputStream(baos2);
String testString="First";
oos1.writeObject(testString);
oos2.writeUTF(testString);
testString="Second";
oos1.writeObject(testString);
oos2.writeUTF(testString);
testString="Third";
oos1.writeObject(testString);
oos2.writeUTF(testString);
oos1.flush();
oos2.flush();
byte[] byteArray1=baos1.toByteArray();
byte[] byteArray2=baos2.toByteArray();
Dump last two arrays you will get result like:
writeObject i.e. byteArray1
Binary: -84 -19 0 5 116 0 5 70 105 114 115 116 116 0 6 83 101 99 111 110 100 116 0 5 84 104 105 114 100
ASCII: -T - t F i r s t t S e c o n d t T h i r d
writeUTF i.e. byteArray2
Binary: -84 -19 0 5 119 22 0 5 70 105 114 115 116 0 6 83 101 99 111 110 100 0 5 84 104 105 114 100
ASCII: -T - w F i r s t S e c o n d T h i r d
Conclusion: In case of writeObject an extra data (here t)to be streamed whereas in case of writeUTF only the string data to be streamed.
For more: http://docs.oracle.com/javase/7/docs/api/java/io/ObjectOutputStream.html#writeUTF(java.lang.String)