Java Examples: PipedWriter and PipedReader

Updated on March 11, 2018
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I am a software engineer. I have been working with C++, MFC, and .net technologies for 15 years. I like playing video games & reading books.

1. Introduction to PipedReader and PipedWriter

"PipedReader" class is used to read text stream of data and "PipedWriter" is used to write the Text Stream of Data. In Java, these PipedReaders and PipedWriters are used in pairs. Like Producer and Consumer situation, the Writer writes the Data at one end of the Pipe and Reader reads it at the other end. Usually the Reader and Writer operates asynchronously with the help of threads. In our example, we are not going to use threads for simplicity.

For Example, let us say we are writing an application which receives SMS (Short Message Text) from different mobile number with Request Code. The application searches the requested data in the in-house database and sends back the information to requested mobile number. In this case, two piped text streams can be used. One Pipe is for receiving the SMS and other one is for sending the SMS. The receiving and sending pipe can be constructed with PipedReader and PipedWriter. Let us consider only the Receiving Pipe. Here, the Writer reads the incoming message from GSM Modem (A hardware attached to the System) and writes to One end of the Pipe and Reader receives (Reads) the SMS message at the other end. The same goes while sending the message by switching the PipedReader and PipedWriter Ends.

The Data flow is in Single direction that is from Writer-End of the Pipe to Reader-End of the Pipe. OK, let us start out Example. Here, we are going to write stream of Text using PipedWriter and read the data written from the other end using PipedReader.

2. Create PipedReader and PipedWriter

First the required classes are imported from the "Java.io Package". The code for that is below:

//Sample 01: Package inclusion
import java.io.PipedReader;
import java.io.PipedWriter;
import java.io.IOException;

Next, we are creating PipedReader and PiperWriter objects and storing the references in ReaderEnd and WriterEnd Respectively. The PipedWriter is used to write the text content and PipedReader is used to read the text content from the pipe.

Once the objects are created, they are connected together to form the Pipe by making call to the method “connect()”. Note that both PipedReader and PipedWriter supports the connect method. When we call the connect() method on the PipedWriter object, we have to pass PipedReader as parameter. In our example, we are calling the connect on PipedReader object ReaderEnd. After the method call, we will be having PipedReader and PipedWriter forming a pipe connection with Writer at one end and Reader at another end. Below is the code:

//Sample 02: Create Piped Reader and Piped Writer
PipedReader ReaderEnd = new PipedReader();
PipedWriter WriterEnd = new PipedWriter();

//Sample 03: Connect the PipedReader and PipedWriter
ReaderEnd.connect(WriterEnd);

3. PipedWriter Writes and PiperReader Reads

Once we have Pipe is Connected with the Reader and Writer, we writing the Stream Of Text to the Pipe from one end by making use of WriterEnd instance. We are writing all the ASCII characters ranging from Uppercase ‘A’ to Lowercase ‘z’ to the Pipe by calling the “write()” method. Below is the code that writes text stream to the Pipe:

//Sample 04: Write the Character Stream at one end
for (int i = (int)('A'); i < ((int) ('z')) + 1; i++)
    WriterEnd.write((char) i );

The stream text written by the PipedWriter and at one end of the Pipe is read by the PipedReader on the other end by making use of the “read()” method. Note that the PipedReader object ReaderEnd reads the object in the same order in which it is written to the Pipe. For example, the writer wrote the letter ‘A’ first to the Pipe and the Reader reads that first. Below is the code:

//Sample 05: Read the Character from the Other End
for (int i = (int)('A'); i < ((int) ('z')) + 1; i++ ) {
    int chr = ReaderEnd.read();
    System.out.print((char) chr);
}

Now have a look at the depiction below:

Reading and Writing TextStream through PipedWriter and PipedReader
Reading and Writing TextStream through PipedWriter and PipedReader | Source

Below is the complete code example and its output:

//Sample 01: Package inclusion
import java.io.PipedReader;
import java.io.PipedWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        try
        {
            //Sample 02: Create Piped Reader and Piped Writer
            PipedReader ReaderEnd = new PipedReader();
            PipedWriter WriterEnd = new PipedWriter();

            //Sample 03: Connect the PipedReader and PipedWriter
            ReaderEnd.connect(WriterEnd);

        //Sample 04: Write the Character Stream at one end
        for (int i = (int)('A'); i < ((int) ('z')) + 1; i++)
            WriterEnd.write((char) i );

        //Sample 05: Read the Character from the Other End
        for (int i = (int)('A'); i < ((int) ('z')) + 1; i++ ) {
            int chr = ReaderEnd.read();
            System.out.print((char) chr);
        }

        } catch (IOException Ex)
        {
            System.out.println(Ex.getMessage());
        }
    }
}

The output of the above code below:


ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz

© 2018 sirama

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