Re: How to implement this?

Lew <lew@lewscanon.nospam>
Mon, 06 Aug 2007 17:56:54 -0400
Chris wrote:

xz wrote:

I want all the classes write the runtime information into one common
file, let's say, log.
So I define a BufferedWriter log in one of the classes and make it
public static, as follows,


public class Tester {

                static String path = "/home/xi/Desktop/D2V/
                static FileWriter fwlog = new FileWriter(path +
                public static BufferedWriter log = new
                //the rest code

However, the constructor of FileWriter throws exception so it does not
-------------------- unreported exception; must be
caught or declared to be thrown
                static FileWriter fwlog = new FileWriter(path +
1 error

What can I do to handle this exception?

looks like I cannot either catch it here or put the "throws
IOException...." sentence after "public class Tester".

Try this:

public class Tester {
    private static BufferedWriter logger;

    public static BufferedWriter getLogger() throws IOException {
        if (logger==null) {
            logger = new BufferedWriter(whatever...);
        return logger;

In your code, call:

Tester.getLogger().write("some message");

Of if you want to avoid the call to if (logger==null) on every log
statement, create a static init() method and call that before the first
call to getLogger().

The latter likely avoids the threading complications of the unsynchronized
test-and-set idiom you presented. In a case like this there is no advantage
to lazy initialization.

If your Logger class is from log4j it is already thread safe, of course.

One more approach is a static initializer:

public class Tester
    private static final BufferedWriter logger;
      String path = "/home/xi/Desktop/D2V/validation/";
       logger = new BufferedWriter( new FileWriter(
                    new File( path, "log" )));
      catch ( IOException exc )
       String msg = "Cannot open log file \""+ path +"log\"";
       throw new IllegalStateException( msg, exc );

This is like using the static init() method without naming the method. The
body of the static initializer could be the body of a static initialization
method like initLogger().

public class Tester
    private static final BufferedWriter logger = initLogger();


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