Re: How to implement this?
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,
import java.io.BufferedWriter;
import java.io.FileWriter;
public class Tester {
static String path = "/home/xi/Desktop/D2V/
validation/";
static FileWriter fwlog = new FileWriter(path +
"log");
public static BufferedWriter log = new
BufferedWriter(fwlog);
//the rest code
}
However, the constructor of FileWriter throws exception so it does not
compile:
--------------------
Tester.java:11: unreported exception java.io.IOException; must be
caught or declared to be thrown
static FileWriter fwlog = new FileWriter(path +
"log");
^
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;
static
{
String path = "/home/xi/Desktop/D2V/validation/";
try
{
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();
....
}
--
Lew