How to implement this?

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xz - 06 Aug 2007 21:31 GMT

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".

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Chris - 06 Aug 2007 21:50 GMT

> I want all the classes write the runtime information into one common
> file, let's say, log.
[quoted text clipped - 30 lines]
> 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().

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xz - 06 Aug 2007 22:39 GMT

> > I want all the classes write the runtime information into one common
> > file, let's say, log.
[quoted text clipped - 52 lines]
> statement, create a static init() method and call that before the first
> call to getLogger().

Thanks. That works.

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Lew - 06 Aug 2007 22:56 GMT

>> I want all the classes write the runtime information into one common
>> file, let's say, log.
[quoted text clipped - 51 lines]
> 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();
...
}

Signature

Lew

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xz - 07 Aug 2007 06:23 GMT

> 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
[quoted text clipped - 28 lines]
> body of the static initializer could be the body of a static initialization
> method like initLogger().

This is more close to what I wanted originally.
Thank you!

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How to implement this?

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