Using Java to send PJL commands to HP 4515 Printer

I am trying to send Printer Job Language commands to a HP 4515 printer. However, the printer does not print anything. Below is my code. The printer is located remotely and I can only ask someone there to check if anything is printed out. Unfortunately nothing was printed out. Are the PJL commands not in good format? How can I get the job status using Java & PJL?

  socket = new Socket("192.168.1.101", 9100);
        out = new DataOutputStream(socket.getOutputStream());
        DataInputStream input = new DataInputStream(socket.getInputStream());


        final char ESC = 0x1b;
        final String UNESCAPED_UEL  = "%-12345X";
        String UEL = ESC + UNESCAPED_UEL;
        out.writeBytes(UEL); 
        out.writeBytes("@PJL\r\n");

        //out.writeBytes("@PJL SET MEDIASOURCE = TRAY2\r\n"); //I tried this line of code as well
        out.writeBytes("@PJL SET PAPER = LETTER\r\n");

        out.writeBytes("@PJL ENTER LANGUAGE = PDF\r\n");
        for(int i=0; i<copies; i++) {
            out.write(ps, 0, ps.length); //ps is of type byte[]. It contains the content of PostScript file
        }
        out.flush();

The printer's paper settings:

TRAY 1 SIZE 
TRAY 1 TYPE 
TRAY 2 SIZE LETTER
UNIT OF MEASURE 
X DIMENSION INCHES (5.83 - 8.5)
Y DIMENSION INCHES (8.27 - 14.0)
TRAY 2 TYPE

Solution

As noted here, it looks like you are missing the closing 'Universal Exit Language' command (UEL). It is required in PJL. It defines beginning and end of any PJL-based data stream.

E.g.:

socket = new Socket("192.168.1.101", 9100);
out = new DataOutputStream(socket.getOutputStream());
DataInputStream input = new DataInputStream(socket.getInputStream());


final char ESC = 0x1b;
final String UNESCAPED_UEL  = "%-12345X";
String UEL = ESC + UNESCAPED_UEL;
out.writeBytes(UEL); 
out.writeBytes("@PJL\r\n");
out.writeBytes("@PJL SET PAPER = LETTER\r\n");
out.writeBytes("@PJL ENTER LANGUAGE = PDF\r\n");
for(int i=0; i<copies; i++) {
    out.write(ps, 0, ps.length);
}
out.writeBytes(UEL); // <-- add this
out.flush();

I can't tell if there is something off with your PJL command syntax, but for reference this is working for me.