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Tip of the Day
Language: Java
Expertise: Intermediate
Apr 6, 1999

A Basic Output Stream Wrapper Class

When writing a program, you often need flexibility in where the trace/log output of the program is supposed to go. It could go to standard output, a log file, or even to a socket. This simple utility class wraps an output stream and allows the program to specify the output stream at the beginning.
 
1.     public class MyOutputStream {
2. 
3.       PrintWriter out_ = null;
4. 
5.       public MyOutputStream (OutputStream out) {
6.         out_ = new PrintWriter(out);
7.       }
8. 
9.       public void println (String str) {
10.      out_.println(str);
11.      flush();
12.    }
13. }
The class MyOutStream wraps an OutputStream class. It has a single variable out_, which is used for writing out all the print statements. A single method println() is declared for printing out a single line on the default output device. Note that the println() method also includes a flush() call so that the contents are flushed out as soon as they are written. This would be the desired behavior for a tracing utility. This code illustrates how MyOutputStream may be used:
 
1. MyOutputStream sysOut = new MyOutputStream(System.out);
2. sysOut.println("This is going to System.out");
3.
4. FileOutputStream fos = new FileOutputStream("myfile");
5. MyOutputStream sysOut = new MyOutputStream(fos);
6. sysOut.println("This is going to myFile");
On Line 1, an object of type MyOutputStream is instantiated by passing in System.out to the constructor. This object (sysOut) is used on Line 2 to print out a string. On Lines 4 and 5, a FileOutputStream is wrapped by MyOutputStream. On Line 6, sysOut is used to print out the string. The advantage of this wrapper class is that you would just have to change one line in your code to change the target of the output. If you had System.out calls scattered in your code, you would have to change each instance in order to redirect the output to another output stream.
Ajit Sagar
 
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