Transferring data in Java using streams

Question

I have been reading the Java Tutorials on I/O in an attempt to understand stream and their proper usage. Say I have two devices that are connected, and an InputStream and OutputStream on both devices. How do I transfer data between the two?

For example, if I wanted to one device to send a bunch of words to the other device, which would then print them to the screen. How would that work?

public class Device1 {
    // assuming connectedDevice is something
    String[] words = new String()[]{"foo", "bar", "baz"};
    OutputStream os = connectedDevice.getOutputStream();
    InputStream is = connectedDevice.getInputStream();
    /*
        How to write to output stream?
    */
}

public class Device2 {
    // assuming connectedDevice is something
    ArrayList<String> words = new ArrayList<String>();
    OutputStream os = connectedDevice.getOutputStream();
    InputStream is = connectedDevice.getInputStream();
    /*
        How can I somehow get the words using `read()` and `put()`
        them into the ArrayList for use?
    */
}

Maybe I'm doing all of this wrong. Thanks in advance for any help in understanding.

How are the words delimited? By spaces? Do more than one space matter? — Garrett Hall
– Garrett Hall, Commented Jul 9, 2012 at 16:44
@assylias I imagine two completely separate devices (e.g. an Android device and a Desktop). — Whymarrh
– Whymarrh, Commented Jul 9, 2012 at 16:47
@Whymarrh in that case erickson's answer is one (fairly low level in the case of TCP) solution. — assylias
– assylias, Commented Jul 9, 2012 at 16:48
@GarrettHall when the words are being received, I would expect maybe separate items in the ArrayList. — Whymarrh
– Whymarrh, Commented Jul 9, 2012 at 16:48

erickson · Accepted Answer · 2012-07-09 16:44:00Z

2

It depends on how the devices are connected. For example, they might connect via TCP, or via a shared file system.

If you want to focus on streams, create an application that uses the file system. Then, use FileOutputStream and FileInputStream to understand the stream APIs.

If your focus is on networking, you'll want to study the networking tutorial too.

answered Jul 9, 2012 at 16:44

erickson

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Keith Randall · Accepted Answer · 2012-07-09 16:50:15Z

1

If you just want to send characters, wrap your streams using an OutputStreamWriter on the writing side and an InputStreamReader on the reading side. You can write whole strings, then read one character at a time and print it. If you need to be really careful you should pick a fixed character encoding for both.

If you want to send whole simple objects like Strings, you can use DataOutputStream/DataInputStream. (For strings, use the UTF methods.)

If you want to get more complicated, you'll need to do serialization/deserialization of objects using ObjectOutputStream and ObjectInputStream.

answered Jul 9, 2012 at 16:50

Keith Randall

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