java/11 : java.logging/java/util/logging/Level.java

Level
https://openjdk.java.net/
GPLv2 + Classpath Exception
/*
 * Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.util.logging;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Optional;
import java.util.ResourceBundle;
import java.util.function.Function;
import jdk.internal.loader.ClassLoaderValue;
import jdk.internal.misc.JavaUtilResourceBundleAccess;
import jdk.internal.misc.SharedSecrets;

The Level class defines a set of standard logging levels that
can be used to control logging output.  The logging Level objects
are ordered and are specified by ordered integers.  Enabling logging
at a given level also enables logging at all higher levels.

Clients should normally use the predefined Level constants such
as Level.SEVERE.

The levels in descending order are:

SEVERE (highest value)
WARNING
INFO
CONFIG
FINE
FINER
FINEST  (lowest value)

In addition there is a level OFF that can be used to turn
off logging, and a level ALL that can be used to enable
logging of all messages.

It is possible for third parties to define additional logging
levels by subclassing Level.  In such cases subclasses should
take care to chose unique integer level values and to ensure that
they maintain the Object uniqueness property across serialization
by defining a suitable readResolve method.
Since: 1.4/**
 * The Level class defines a set of standard logging levels that
 * can be used to control logging output.  The logging Level objects
 * are ordered and are specified by ordered integers.  Enabling logging
 * at a given level also enables logging at all higher levels.
 * <p>
 * Clients should normally use the predefined Level constants such
 * as Level.SEVERE.
 * <p>
 * The levels in descending order are:
 * <ul>
 * <li>SEVERE (highest value)
 * <li>WARNING
 * <li>INFO
 * <li>CONFIG
 * <li>FINE
 * <li>FINER
 * <li>FINEST  (lowest value)
 * </ul>
 * In addition there is a level OFF that can be used to turn
 * off logging, and a level ALL that can be used to enable
 * logging of all messages.
 * <p>
 * It is possible for third parties to define additional logging
 * levels by subclassing Level.  In such cases subclasses should
 * take care to chose unique integer level values and to ensure that
 * they maintain the Object uniqueness property across serialization
 * by defining a suitable readResolve method.
 *
 * @since 1.4
 */

public class Level implements java.io.Serializable {
    private static final String defaultBundle =
        "sun.util.logging.resources.logging";

    // Calling SharedSecrets.getJavaUtilResourceBundleAccess()
    // forces the initialization of ResourceBundle.class, which
    // can be too early if the VM has not finished booting yet.
    private static final class RbAccess {
        static final JavaUtilResourceBundleAccess RB_ACCESS =
            SharedSecrets.getJavaUtilResourceBundleAccess();
    }

    @serial  The non-localized name of the level./**
     * @serial  The non-localized name of the level.
     */
    private final String name;

    @serial  The integer value of the level./**
     * @serial  The integer value of the level.
     */
    private final int value;

    @serial The resource bundle name to be used in localizing the level name./**
     * @serial The resource bundle name to be used in localizing the level name.
     */
    private final String resourceBundleName;

    // localized level name
    private transient String localizedLevelName;
    private transient Locale cachedLocale;

    OFF is a special level that can be used to turn off logging.
This level is initialized to Integer.MAX_VALUE.
/**
     * OFF is a special level that can be used to turn off logging.
     * This level is initialized to <CODE>Integer.MAX_VALUE</CODE>.
     */
    public static final Level OFF = new Level("OFF",Integer.MAX_VALUE, defaultBundle);

    SEVERE is a message level indicating a serious failure.

In general SEVERE messages should describe events that are
of considerable importance and which will prevent normal
program execution.   They should be reasonably intelligible
to end users and to system administrators.
This level is initialized to 1000.
/**
     * SEVERE is a message level indicating a serious failure.
     * <p>
     * In general SEVERE messages should describe events that are
     * of considerable importance and which will prevent normal
     * program execution.   They should be reasonably intelligible
     * to end users and to system administrators.
     * This level is initialized to <CODE>1000</CODE>.
     */
    public static final Level SEVERE = new Level("SEVERE",1000, defaultBundle);

    WARNING is a message level indicating a potential problem.

In general WARNING messages should describe events that will
be of interest to end users or system managers, or which
indicate potential problems.
This level is initialized to 900.
/**
     * WARNING is a message level indicating a potential problem.
     * <p>
     * In general WARNING messages should describe events that will
     * be of interest to end users or system managers, or which
     * indicate potential problems.
     * This level is initialized to <CODE>900</CODE>.
     */
    public static final Level WARNING = new Level("WARNING", 900, defaultBundle);

    INFO is a message level for informational messages.

Typically INFO messages will be written to the console
or its equivalent.  So the INFO level should only be
used for reasonably significant messages that will
make sense to end users and system administrators.
This level is initialized to 800.
/**
     * INFO is a message level for informational messages.
     * <p>
     * Typically INFO messages will be written to the console
     * or its equivalent.  So the INFO level should only be
     * used for reasonably significant messages that will
     * make sense to end users and system administrators.
     * This level is initialized to <CODE>800</CODE>.
     */
    public static final Level INFO = new Level("INFO", 800, defaultBundle);

    CONFIG is a message level for static configuration messages.

CONFIG messages are intended to provide a variety of static
configuration information, to assist in debugging problems
that may be associated with particular configurations.
For example, CONFIG message might include the CPU type,
the graphics depth, the GUI look-and-feel, etc.
This level is initialized to 700.
/**
     * CONFIG is a message level for static configuration messages.
     * <p>
     * CONFIG messages are intended to provide a variety of static
     * configuration information, to assist in debugging problems
     * that may be associated with particular configurations.
     * For example, CONFIG message might include the CPU type,
     * the graphics depth, the GUI look-and-feel, etc.
     * This level is initialized to <CODE>700</CODE>.
     */
    public static final Level CONFIG = new Level("CONFIG", 700, defaultBundle);

    FINE is a message level providing tracing information.

All of FINE, FINER, and FINEST are intended for relatively
detailed tracing.  The exact meaning of the three levels will
vary between subsystems, but in general, FINEST should be used
for the most voluminous detailed output, FINER for somewhat
less detailed output, and FINE for the  lowest volume (and
most important) messages.

In general the FINE level should be used for information
that will be broadly interesting to developers who do not have
a specialized interest in the specific subsystem.

FINE messages might include things like minor (recoverable)
failures.  Issues indicating potential performance problems
are also worth logging as FINE.
This level is initialized to 500.
/**
     * FINE is a message level providing tracing information.
     * <p>
     * All of FINE, FINER, and FINEST are intended for relatively
     * detailed tracing.  The exact meaning of the three levels will
     * vary between subsystems, but in general, FINEST should be used
     * for the most voluminous detailed output, FINER for somewhat
     * less detailed output, and FINE for the  lowest volume (and
     * most important) messages.
     * <p>
     * In general the FINE level should be used for information
     * that will be broadly interesting to developers who do not have
     * a specialized interest in the specific subsystem.
     * <p>
     * FINE messages might include things like minor (recoverable)
     * failures.  Issues indicating potential performance problems
     * are also worth logging as FINE.
     * This level is initialized to <CODE>500</CODE>.
     */
    public static final Level FINE = new Level("FINE", 500, defaultBundle);

    FINER indicates a fairly detailed tracing message.
By default logging calls for entering, returning, or throwing
an exception are traced at this level.
This level is initialized to 400.
/**
     * FINER indicates a fairly detailed tracing message.
     * By default logging calls for entering, returning, or throwing
     * an exception are traced at this level.
     * This level is initialized to <CODE>400</CODE>.
     */
    public static final Level FINER = new Level("FINER", 400, defaultBundle);

    FINEST indicates a highly detailed tracing message.
This level is initialized to 300.
/**
     * FINEST indicates a highly detailed tracing message.
     * This level is initialized to <CODE>300</CODE>.
     */
    public static final Level FINEST = new Level("FINEST", 300, defaultBundle);

    ALL indicates that all messages should be logged.
This level is initialized to Integer.MIN_VALUE.
/**
     * ALL indicates that all messages should be logged.
     * This level is initialized to <CODE>Integer.MIN_VALUE</CODE>.
     */
    public static final Level ALL = new Level("ALL", Integer.MIN_VALUE, defaultBundle);

    private static final Level[] standardLevels = {
        OFF, SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST, ALL
    };

    Create a named Level with a given integer value.

Note that this constructor is "protected" to allow subclassing.
In general clients of logging should use one of the constant Level
objects such as SEVERE or FINEST.  However, if clients need to
add new logging levels, they may subclass Level and define new
constants.
Params: name –  the name of the Level, for example "SEVERE".
value – an integer value for the level.
Throws: NullPointerException – if the name is null/**
     * Create a named Level with a given integer value.
     * <p>
     * Note that this constructor is "protected" to allow subclassing.
     * In general clients of logging should use one of the constant Level
     * objects such as SEVERE or FINEST.  However, if clients need to
     * add new logging levels, they may subclass Level and define new
     * constants.
     * @param name  the name of the Level, for example "SEVERE".
     * @param value an integer value for the level.
     * @throws NullPointerException if the name is null
     */
    protected Level(String name, int value) {
        this(name, value, null);
    }

    Create a named Level with a given integer value and a
given localization resource name.
Params: name –  the name of the Level, for example "SEVERE".
value – an integer value for the level.
resourceBundleName – name of a resource bundle to use in
   localizing the given name. If the resourceBundleName is null
   or an empty string, it is ignored.
Throws: NullPointerException – if the name is null/**
     * Create a named Level with a given integer value and a
     * given localization resource name.
     *
     * @param name  the name of the Level, for example "SEVERE".
     * @param value an integer value for the level.
     * @param resourceBundleName name of a resource bundle to use in
     *    localizing the given name. If the resourceBundleName is null
     *    or an empty string, it is ignored.
     * @throws NullPointerException if the name is null
     */
    protected Level(String name, int value, String resourceBundleName) {
        this(name, value, resourceBundleName, true);
    }

    // private constructor to specify whether this instance should be added
    // to the KnownLevel list from which Level.parse method does its look up
    private Level(String name, int value, String resourceBundleName, boolean visible) {
        if (name == null) {
            throw new NullPointerException();
        }
        this.name = name;
        this.value = value;
        this.resourceBundleName = resourceBundleName;
        this.localizedLevelName = resourceBundleName == null ? name : null;
        this.cachedLocale = null;
        if (visible) {
            KnownLevel.add(this);
        }
    }

    Return the level's localization resource bundle name, or
null if no localization bundle is defined.
Returns: localization resource bundle name/**
     * Return the level's localization resource bundle name, or
     * null if no localization bundle is defined.
     *
     * @return localization resource bundle name
     */
    public String getResourceBundleName() {
        return resourceBundleName;
    }

    Return the non-localized string name of the Level.
Returns: non-localized name/**
     * Return the non-localized string name of the Level.
     *
     * @return non-localized name
     */
    public String getName() {
        return name;
    }

    Return the localized string name of the Level, for
the current default locale.

If no localization information is available, the
non-localized name is returned.
Returns: localized name/**
     * Return the localized string name of the Level, for
     * the current default locale.
     * <p>
     * If no localization information is available, the
     * non-localized name is returned.
     *
     * @return localized name
     */
    public String getLocalizedName() {
        return getLocalizedLevelName();
    }

    // package-private getLevelName() is used by the implementation
    // instead of getName() to avoid calling the subclass's version
    final String getLevelName() {
        return this.name;
    }

    private String computeLocalizedLevelName(Locale newLocale) {
        // Resource bundle should be loaded from the defining module
        // or its defining class loader, if it's unnamed module,
        // of this Level instance that can be a custom Level subclass;
        Module module = this.getClass().getModule();
        ResourceBundle rb = RbAccess.RB_ACCESS.getBundle(resourceBundleName,
                newLocale, module);

        final String localizedName = rb.getString(name);
        final boolean isDefaultBundle = defaultBundle.equals(resourceBundleName);
        if (!isDefaultBundle) return localizedName;

        // This is a trick to determine whether the name has been translated
        // or not. If it has not been translated, we need to use Locale.ROOT
        // when calling toUpperCase().
        final Locale rbLocale = rb.getLocale();
        final Locale locale =
                Locale.ROOT.equals(rbLocale)
                || name.equals(localizedName.toUpperCase(Locale.ROOT))
                ? Locale.ROOT : rbLocale;

        // ALL CAPS in a resource bundle's message indicates no translation
        // needed per Oracle translation guideline.  To workaround this
        // in Oracle JDK implementation, convert the localized level name
        // to uppercase for compatibility reason.
        return Locale.ROOT.equals(locale) ? name : localizedName.toUpperCase(locale);
    }

    // Avoid looking up the localizedLevelName twice if we already
    // have it.
    final String getCachedLocalizedLevelName() {

        if (localizedLevelName != null) {
            if (cachedLocale != null) {
                if (cachedLocale.equals(Locale.getDefault())) {
                    // OK: our cached value was looked up with the same
                    //     locale. We can use it.
                    return localizedLevelName;
                }
            }
        }

        if (resourceBundleName == null) {
            // No resource bundle: just use the name.
            return name;
        }

        // We need to compute the localized name.
        // Either because it's the first time, or because our cached
        // value is for a different locale. Just return null.
        return null;
    }

    final synchronized String getLocalizedLevelName() {

        // See if we have a cached localized name
        final String cachedLocalizedName = getCachedLocalizedLevelName();
        if (cachedLocalizedName != null) {
            return cachedLocalizedName;
        }

        // No cached localized name or cache invalid.
        // Need to compute the localized name.
        final Locale newLocale = Locale.getDefault();
        try {
            localizedLevelName = computeLocalizedLevelName(newLocale);
        } catch (Exception ex) {
            localizedLevelName = name;
        }
        cachedLocale = newLocale;
        return localizedLevelName;
    }

    // Returns a mirrored Level object that matches the given name as
    // specified in the Level.parse method.  Returns null if not found.
    //
    // It returns the same Level object as the one returned by Level.parse
    // method if the given name is a non-localized name or integer.
    //
    // If the name is a localized name, findLevel and parse method may
    // return a different level value if there is a custom Level subclass
    // that overrides Level.getLocalizedName() to return a different string
    // than what's returned by the default implementation.
    //
    static Level findLevel(String name) {
        if (name == null) {
            throw new NullPointerException();
        }

        Optional<Level> level;

        // Look for a known Level with the given non-localized name.
        level = KnownLevel.findByName(name, KnownLevel::mirrored);
        if (level.isPresent()) {
            return level.get();
        }

        // Now, check if the given name is an integer.  If so,
        // first look for a Level with the given value and then
        // if necessary create one.
        try {
            int x = Integer.parseInt(name);
            level = KnownLevel.findByValue(x, KnownLevel::mirrored);
            if (level.isPresent()) {
                return level.get();
            }
            // add new Level
            Level levelObject = new Level(name, x);
            // There's no need to use a reachability fence here because
            // KnownLevel keeps a strong reference on the level when
            // level.getClass() == Level.class.
            return KnownLevel.findByValue(x, KnownLevel::mirrored).get();
        } catch (NumberFormatException ex) {
            // Not an integer.
            // Drop through.
        }

        level = KnownLevel.findByLocalizedLevelName(name,
                KnownLevel::mirrored);
        if (level.isPresent()) {
            return level.get();
        }

        return null;
    }

    Returns a string representation of this Level.
Returns: the non-localized name of the Level, for example "INFO"./**
     * Returns a string representation of this Level.
     *
     * @return the non-localized name of the Level, for example "INFO".
     */
    @Override
    public final String toString() {
        return name;
    }

    Get the integer value for this level.  This integer value
can be used for efficient ordering comparisons between
Level objects.
Returns: the integer value for this level./**
     * Get the integer value for this level.  This integer value
     * can be used for efficient ordering comparisons between
     * Level objects.
     * @return the integer value for this level.
     */
    public final int intValue() {
        return value;
    }

    private static final long serialVersionUID = -8176160795706313070L;

    // Serialization magic to prevent "doppelgangers".
    // This is a performance optimization.
    private Object readResolve() {
        Optional<Level> level = KnownLevel.matches(this);
        if (level.isPresent()) {
            return level.get();
        }
        // Woops.  Whoever sent us this object knows
        // about a new log level.  Add it to our list.
        return new Level(this.name, this.value, this.resourceBundleName);
    }

    Parse a level name string into a Level.

The argument string may consist of either a level name
or an integer value.

For example:

     "SEVERE"
     "1000"

Params: name –   string to be parsed
Throws: NullPointerException – if the name is null
IllegalArgumentException – if the value is not valid.
Valid values are integers between Integer.MIN_VALUE
and Integer.MAX_VALUE, and all known level names.
Known names are the levels defined by this class (e.g., FINE,
FINER, FINEST), or created by this class with
appropriate package access, or new levels defined or created
by subclasses.
Returns: The parsed value. Passing an integer that corresponds to a known name
(e.g., 700) will return the associated name (e.g., CONFIG).
Passing an integer that does not (e.g., 1) will return a new level name
initialized to that value./**
     * Parse a level name string into a Level.
     * <p>
     * The argument string may consist of either a level name
     * or an integer value.
     * <p>
     * For example:
     * <ul>
     * <li>     "SEVERE"
     * <li>     "1000"
     * </ul>
     *
     * @param  name   string to be parsed
     * @throws NullPointerException if the name is null
     * @throws IllegalArgumentException if the value is not valid.
     * Valid values are integers between <CODE>Integer.MIN_VALUE</CODE>
     * and <CODE>Integer.MAX_VALUE</CODE>, and all known level names.
     * Known names are the levels defined by this class (e.g., <CODE>FINE</CODE>,
     * <CODE>FINER</CODE>, <CODE>FINEST</CODE>), or created by this class with
     * appropriate package access, or new levels defined or created
     * by subclasses.
     *
     * @return The parsed value. Passing an integer that corresponds to a known name
     * (e.g., 700) will return the associated name (e.g., <CODE>CONFIG</CODE>).
     * Passing an integer that does not (e.g., 1) will return a new level name
     * initialized to that value.
     */
    public static synchronized Level parse(String name) throws IllegalArgumentException {
        // Check that name is not null.
        name.length();

        Optional<Level> level;

        // Look for a known Level with the given non-localized name.
        level = KnownLevel.findByName(name, KnownLevel::referent);
        if (level.isPresent()) {
            return level.get();
        }

        // Now, check if the given name is an integer.  If so,
        // first look for a Level with the given value and then
        // if necessary create one.
        try {
            int x = Integer.parseInt(name);
            level = KnownLevel.findByValue(x, KnownLevel::referent);
            if (level.isPresent()) {
                return level.get();
            }
            // add new Level.
            Level levelObject = new Level(name, x);
            // There's no need to use a reachability fence here because
            // KnownLevel keeps a strong reference on the level when
            // level.getClass() == Level.class.
            return KnownLevel.findByValue(x, KnownLevel::referent).get();
        } catch (NumberFormatException ex) {
            // Not an integer.
            // Drop through.
        }

        // Finally, look for a known level with the given localized name,
        // in the current default locale.
        // This is relatively expensive, but not excessively so.
        level = KnownLevel.findByLocalizedLevelName(name, KnownLevel::referent);
        if (level .isPresent()) {
            return level.get();
        }

        // OK, we've tried everything and failed
        throw new IllegalArgumentException("Bad level \"" + name + "\"");
    }

    Compare two objects for value equality.
Returns: true if and only if the two objects have the same level value./**
     * Compare two objects for value equality.
     * @return true if and only if the two objects have the same level value.
     */
    @Override
    public boolean equals(Object ox) {
        try {
            Level lx = (Level)ox;
            return (lx.value == this.value);
        } catch (Exception ex) {
            return false;
        }
    }

    Generate a hashcode.
Returns: a hashcode based on the level value/**
     * Generate a hashcode.
     * @return a hashcode based on the level value
     */
    @Override
    public int hashCode() {
        return this.value;
    }

    // KnownLevel class maintains the global list of all known levels.
    // The API allows multiple custom Level instances of the same name/value
    // be created. This class provides convenient methods to find a level
    // by a given name, by a given value, or by a given localized name.
    //
    // KnownLevel wraps the following Level objects:
    // 1. levelObject:   standard Level object or custom Level object
    // 2. mirroredLevel: Level object representing the level specified in the
    //                   logging configuration.
    //
    // Level.getName, Level.getLocalizedName, Level.getResourceBundleName methods
    // are non-final but the name and resource bundle name are parameters to
    // the Level constructor.  Use the mirroredLevel object instead of the
    // levelObject to prevent the logging framework to execute foreign code
    // implemented by untrusted Level subclass.
    //
    // Implementation Notes:
    // If Level.getName, Level.getLocalizedName, Level.getResourceBundleName methods
    // were final, the following KnownLevel implementation can be removed.
    // Future API change should take this into consideration.
    static final class KnownLevel extends WeakReference<Level> {
        private static Map<String, List<KnownLevel>> nameToLevels = new HashMap<>();
        private static Map<Integer, List<KnownLevel>> intToLevels = new HashMap<>();
        private static final ReferenceQueue<Level> QUEUE = new ReferenceQueue<>();

        // CUSTOM_LEVEL_CLV is used to register custom level instances with
        // their defining class loader, so that they are garbage collected
        // if and only if their class loader is no longer strongly
        // referenced.
        private static final ClassLoaderValue<List<Level>> CUSTOM_LEVEL_CLV =
                    new ClassLoaderValue<>();

        final Level mirroredLevel;   // mirror of the custom Level
        KnownLevel(Level l) {
            super(l, QUEUE);
            if (l.getClass() == Level.class) {
                this.mirroredLevel = l;
            } else {
                // this mirrored level object is hidden
                this.mirroredLevel = new Level(l.name, l.value,
                        l.resourceBundleName, false);
            }
        }

        Optional<Level> mirrored() {
            return Optional.of(mirroredLevel);
        }

        Optional<Level> referent() {
            return Optional.ofNullable(get());
        }

        private void remove() {
            Optional.ofNullable(nameToLevels.get(mirroredLevel.name))
                    .ifPresent((x) -> x.remove(this));
            Optional.ofNullable(intToLevels.get(mirroredLevel.value))
                    .ifPresent((x) -> x.remove(this));
        }

        // Remove all stale KnownLevel instances
        static synchronized void purge() {
            Reference<? extends Level> ref;
            while ((ref = QUEUE.poll()) != null) {
                if (ref instanceof KnownLevel) {
                    ((KnownLevel)ref).remove();
                }
            }
        }

        private static void registerWithClassLoader(Level customLevel) {
            PrivilegedAction<ClassLoader> pa =
                  () -> customLevel.getClass().getClassLoader();
            PrivilegedAction<String> pn =  customLevel.getClass()::getName;
            final String name = AccessController.doPrivileged(pn);
            final ClassLoader cl = AccessController.doPrivileged(pa);
            CUSTOM_LEVEL_CLV.computeIfAbsent(cl, (c, v) -> new ArrayList<>())
                .add(customLevel);
        }

        static synchronized void add(Level l) {
            purge();
            // the mirroredLevel object is always added to the list
            // before the custom Level instance
            KnownLevel o = new KnownLevel(l);
            List<KnownLevel> list = nameToLevels.get(l.name);
            if (list == null) {
                list = new ArrayList<>();
                nameToLevels.put(l.name, list);
            }
            list.add(o);

            list = intToLevels.get(l.value);
            if (list == null) {
                list = new ArrayList<>();
                intToLevels.put(l.value, list);
            }
            list.add(o);

            // keep the custom level reachable from its class loader
            // This will ensure that custom level values are not GC'ed
            // until there class loader is GC'ed.
            if (o.mirroredLevel != l) {
                registerWithClassLoader(l);
            }

        }

        // Returns a KnownLevel with the given non-localized name.
        static synchronized Optional<Level> findByName(String name,
                Function<KnownLevel, Optional<Level>> selector) {
            purge();
            return nameToLevels.getOrDefault(name, Collections.emptyList())
                        .stream()
                        .map(selector)
                        .flatMap(Optional::stream)
                        .findFirst();
        }

        // Returns a KnownLevel with the given value.
        static synchronized Optional<Level> findByValue(int value,
                Function<KnownLevel, Optional<Level>> selector) {
            purge();
            return intToLevels.getOrDefault(value, Collections.emptyList())
                        .stream()
                        .map(selector)
                        .flatMap(Optional::stream)
                        .findFirst();
        }

        // Returns a KnownLevel with the given localized name matching
        // by calling the Level.getLocalizedLevelName() method (i.e. found
        // from the resourceBundle associated with the Level object).
        // This method does not call Level.getLocalizedName() that may
        // be overridden in a subclass implementation
        static synchronized Optional<Level> findByLocalizedLevelName(String name,
                Function<KnownLevel, Optional<Level>> selector) {
            purge();
            return nameToLevels.values().stream()
                         .flatMap(List::stream)
                         .map(selector)
                         .flatMap(Optional::stream)
                         .filter(l -> name.equals(l.getLocalizedLevelName()))
                         .findFirst();
        }

        static synchronized Optional<Level> matches(Level l) {
            purge();
            List<KnownLevel> list = nameToLevels.get(l.name);
            if (list != null) {
                for (KnownLevel ref : list) {
                    Level levelObject = ref.get();
                    if (levelObject == null) continue;
                    Level other = ref.mirroredLevel;
                    Class<? extends Level> type = levelObject.getClass();
                    if (l.value == other.value &&
                           (l.resourceBundleName == other.resourceBundleName ||
                               (l.resourceBundleName != null &&
                                l.resourceBundleName.equals(other.resourceBundleName)))) {
                        if (type == l.getClass()) {
                            return Optional.of(levelObject);
                        }
                    }
                }
            }
            return Optional.empty();
        }
    }

}
Params:	name – the name of the Level, for example "SEVERE". value – an integer value for the level.
Throws:	NullPointerException – if the name is null
Params:	name – string to be parsed
Throws:	NullPointerException – if the name is null IllegalArgumentException – if the value is not valid. Valid values are integers between `Integer.MIN_VALUE` and `Integer.MAX_VALUE`, and all known level names. Known names are the levels defined by this class (e.g., `FINE`, `FINER`, `FINEST`), or created by this class with appropriate package access, or new levels defined or created by subclasses.
Returns:	The parsed value. Passing an integer that corresponds to a known name (e.g., 700) will return the associated name (e.g., `CONFIG`). Passing an integer that does not (e.g., 1) will return a new level name initialized to that value.
/

java/ 11/ java.logging/java/util/logging/Level.java
