PrintWriter and OutputStream for a simple client server socket program

Question

I was following this tutorial (dateserver) on Socket programming in Java:

http://cs.lmu.edu/~ray/notes/javanetexamples/

This is the piece of code i don't understand:

try {
       PrintWriter out =
       new PrintWriter(socket.getOutputStream(), true);
       out.println(new Date().toString());
                } 

What is PrintWriter doing here? why we need to set the parameter to 'true?' i guess first we enable outputstream for the socket (by making it true ) and then with the out.println we send date as outputstream, is my assumption right?

Answer 1

What is PrintWriter doing here? why we need to set the parameter to 'true?' i guess first we enable outputstream for the socket (by making it true) and then with the out.println we send date as outputstream, is my assumption right?

Your assumption is wrong. Read more about it below.

new PrintWriter(socket.getOutputStream(), true);

What JavaDoc of PrintWriter states:

Creates a new PrintWriter from an existing OutputStream . This convenience constructor creates the necessary intermediate OutputStreamWriter , which will convert characters into bytes using the default character encoding.

1. Here PrintWriter stream is connected to the client/server's output stream it means any data written by print writer will sent to client/server.

2. Here true means Auto-flush the data from the output buffer once new line methods are called such as println() , printf() , or format() or any newline character ('\\n') is found in the string. In that case you don't need to call flush() method manually.

Answer 2

From the Javadocs, the PrintWriter class "prints formatted representations of objects to a text-output stream". In this case it is printing the date to the output stream attached to the socket.

true in the constructor means subsequent call to out.println(new Date().toString()) will automatically flush the buffer of the output stream, meaning it will force the string to be written to the stream, instead of storing the string in a temporary buffer.

Answer 3

创建PrintWriter对象以写入OutputStream对象，true用于刷新流，请在以下API中检查构造函数： http : //docs.oracle.com/javase/7/docs/api/java/io/ PrintWriter.html