Okay, I finally got a minute to read all of these emails, and...
EVERYBODY FREEZE!
What if I could get you an extensible enum that required no interface
changes and no binary-incompatible changes at all? Sound too good to
be
true? I proposed this months ago (LOG4J2-41) and it got shot down
multiple
times, but as of now I've heard THREE people say "extensible enum" in
this
thread, so here it is, an extensible enum:
public abstract class Level implements Comparable<Level>,
Serializable {
public static final Level OFF;
public static final Level FATAL;
public static final Level ERROR;
public static final Level WARN;
public static final Level INFO;
public static final Level DEBUG;
public static final Level TRACE;
public static final Level ALL;
private static final long serialVersionUID = 0L;
private static final Hashtable<String, Level> map;
private static final TreeMap<Integer, Level> values;
private static final Object constructorLock;
static {
// static variables must be constructed in certain order
constructorLock = new Object();
map = new Hashtable<String, Level>();
values = new TreeMap<Integer, Level>();
OFF = new Level("OFF", 0) {};
FATAL = new Level("FATAL", 100) {};
ERROR = new Level("ERROR", 200) {};
WARN = new Level("WARN", 300) {};
INFO = new Level("INFO", 400) {};
DEBUG = new Level("DEBUG", 500) {};
TRACE = new Level("TRACE", 600) {};
ALL = new Level("ALL", Integer.MAX_VALUE) {};
}
private static int ordinals;
private final String name;
private final int intLevel;
private final int ordinal;
protected Level(String name, int intLevel) {
if(name == null || name.length() == 0)
throw new IllegalArgumentException("Illegal null Level
constant");
if(intLevel < 0)
throw new IllegalArgumentException("Illegal Level int less
than zero.");
synchronized (Level.constructorLock) {
if(Level.map.containsKey(name.toUpperCase()))
throw new IllegalArgumentException("Duplicate Level
constant [" + name + "].");
if(Level.values.containsKey(intLevel))
throw new IllegalArgumentException("Duplicate Level int
["
+ intLevel + "].");
this.name = name;
this.intLevel = intLevel;
this.ordinal = Level.ordinals++;
Level.map.put(name.toUpperCase(), this);
Level.values.put(intLevel, this);
}
}
public int intLevel() {
return this.intLevel;
}
public boolean isAtLeastAsSpecificAs(final Level level) {
return this.intLevel <= level.intLevel;
}
public boolean isAtLeastAsSpecificAs(final int level) {
return this.intLevel <= level;
}
public boolean lessOrEqual(final Level level) {
return this.intLevel <= level.intLevel;
}
public boolean lessOrEqual(final int level) {
return this.intLevel <= level;
}
@Override
@SuppressWarnings("CloneDoesntCallSuperClone")
public Level clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException();
}
@Override
public int compareTo(Level other) {
return intLevel < other.intLevel ? -1 : (intLevel >
other.intLevel
? 1 : 0);
}
@Override
public boolean equals(Object other) {
return other instanceof Level && other == this;
}
public Class<Level> getDeclaringClass() {
return Level.class;
}
@Override
public int hashCode() {
return this.name.hashCode();
}
public String name() {
return this.name;
}
public int ordinal() {
return this.ordinal;
}
@Override
public String toString() {
return this.name;
}
public static Level toLevel(String name) {
return Level.toLevel(name, Level.DEBUG);
}
public static Level toLevel(String name, Level defaultLevel) {
if(name == null)
return defaultLevel;
name = name.toUpperCase();
if(Level.map.containsKey(name))
return Level.map.get(name);
return defaultLevel;
}
public static Level[] values() {
return Level.values.values().toArray(new
Level[Level.values.size()]);
}
public static Level valueOf(String name) {
if(name == null)
throw new IllegalArgumentException("Unknown level constant
["
+ name + "].");
name = name.toUpperCase();
if(Level.map.containsKey(name))
return Level.map.get(name);
throw new IllegalArgumentException("Unknown level constant [" +
name + "].");
}
public static <T extends Enum<T>> T valueOf(Class<T> enumType,
String
name) {
return Enum.valueOf(enumType, name);
}
// for deserialization
protected final Object readResolve() throws ObjectStreamException {
return Level.valueOf(this.name);
}
}
Extending it is easy:
public final class ExtendedLevels {
public static final Level MY_LEVEL = new Level("MY_LEVEL", 250) {};
}
I still and have ALWAYS believed this was the best option. If we used
this
option, I would be fine with not adding any new Levels because I
could add
them myself.
Nick
On Jan 22, 2014, at 7:04 PM, Remko Popma wrote:
This is only a problem for webapps, right?
Putting log4j jars in WEB-INF/lib avoids that problem (different
class
loader).
Apps that really want to share log4j jars with other apps would need
to
play nice. Such apps would do well to use a naming convention like
Gary
suggests.
Otherwise, the last to register would overwrite any previous level
with
the same name. (Should probably emit a StatusLogger warning.)
Same intLevel for different names should not be a problem.
On Thursday, January 23, 2014, Gary Gregory <[email protected]>
wrote:
Playing devils advocate:
What happens when different apps register levels with the same name
and
different intLevels?
What happens when different apps register levels with the same
intLevel
and different names?
Should there be a convention that custom level names be FQNs?
Gary
On Wed, Jan 22, 2014 at 10:05 PM, Paul Benedict
<[email protected]>
wrote:
As Gary wanted, a new thread....
First, each enum needs an inherit strength. This would be part of
the
interface. Forgive me if the word "strength" is wrong; but it's the
100,
200, 300, etc. number that triggers the log level. So make sure the
interface contains the intLevel() method.
Second, we need to know the name, right? The name probably requires
a
new method since it can't be extracted from the enum anymore.
public interface Level {
int intLevel();
String name();
}
PS: The intStrength() name seems hackish. What about strength() or
treshold()?
Third, the registration can be done manually by providing a static
method (as your did Remko) that the client needs to invoke, or you
could
have a class-path scanning mechanism. For the latter, you could
introduce a
new annotation to be placed on the enum class.
@CustomLevels
public enum MyCustomEnums {
}
Paul
On Wed, Jan 22, 2014 at 8:52 PM, Remko Popma <[email protected]>
wrote:
Paul, can you give a bit more detail?
I tried this: copy the current Level enum to a new enum called
"Levels"
in the same package (other name would be fine too). Then change Level
to an
interface (removing the constants and static methods, keeping only
the
non-static methods). Finally make the Levels enum implement the Level
interface.
After this, we need to do a find+replace for the references to
Level.CONSTANT to Levels.CONSTANT and Level.staticMethod() to
Levels.staticMethod().
Finally, the interesting part: how do users add or register their
custom
levels and how do we enable the Levels.staticLookupMethod(String,
Level) to
recognize these custom levels?
On Thursday, January 23, 2014, Paul Benedict <[email protected]>
wrote:
Agreed. This is not an engineering per se, but really more about if
the
feature set makes sense.
Well if you guys ever look into the interface idea, you'll give
log4j
the feature of getting enums to represent custom levels. That's
pretty
cool, IMO. I don't know if any other logging framework has that and
that
would probably get some positive attention. It shouldn't be so hard
to do a
find+replace on the code that accepts Level and replace it with
another
name. Yes, there will be some minor refactoring that goes with it,
but
hard? It shouldn't be.
A name I propose for the interface is LevelDefinition.
Paul
On Wed, Jan 22, 2014 at 6:48 PM, Gary Gregory
<[email protected]>
wrote:
Hi, I do not see this as an engineering problem but more a feature
set
definition issue. So while there may be lots of more or less
internally
complicated ways of solving this with interfaces, makers and
whatnots, the
built in levels are the most user friendly.
I have have lots of buttons, knobs and settings on my sound system
that
I do not use, just like I do not use all the methods in all the
classes in
the JRE...
Gary
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E-Mail: garydgre
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