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A set of platform constants (e.g. errno values)
/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package jnr.constants;
import java.lang.reflect.Field;
import java.net.URL;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* Provides forward and reverse lookup for platform constants
*/
public class ConstantSet extends AbstractSet {
private final Map nameToConstant;
private final Map valueToConstant;
private final Set constants;
private final Class enumClass;
private volatile Long minValue;
private volatile Long maxValue;
private static final ConcurrentMap constantSets
= new ConcurrentHashMap();
private static final Object lock = new Object();
private static final ClassLoader LOADER;
static {
ClassLoader _loader = ConstantSet.class.getClassLoader();
if (_loader != null) {
LOADER = _loader;
} else {
LOADER = ClassLoader.getSystemClassLoader();
}
}
/**
* Gets a ConstantSet
*
* @param name The name of the constant set to get.
* @return A ConstantSet.
*/
public static ConstantSet getConstantSet(String name) {
ConstantSet constants = constantSets.get(name);
return constants != null ? constants : loadConstantSet(name);
}
private static ConstantSet loadConstantSet(String name) {
synchronized (lock) {
ConstantSet constants = constantSets.get(name);
if (constants == null) {
Class enumClass = getEnumClass(name);
if (enumClass == null) {
return null;
}
if (!Constant.class.isAssignableFrom(enumClass)) {
throw new ClassCastException("class for " + name
+ " does not implement Constant interface");
}
constantSets.put(name, constants = new ConstantSet(enumClass));
}
return constants;
}
}
/**
* Gets the {@link Enum} class for the constant name space.
*
* @param name The name of the constants to locate.
* @return A Class.
*/
@SuppressWarnings("unchecked")
private static final Class getEnumClass(String name) {
String[] prefixes = Platform.getPlatform().getPackagePrefixes();
for (String prefix : prefixes) {
String fullName = prefix + "." + name;
// Reduce exceptions on boot by trying to find the class as a resource first
String path = fullName.replace('.', '/') + ".class";
URL resource = LOADER.getResource(path);
if (resource != null) {
try {
return (Class) Class.forName(fullName).asSubclass(Enum.class);
} catch (ClassNotFoundException ex) {
}
}
}
return null;
}
/**
* Creates a new instance of ConstantSet
*
* @param enumClass The Enum subclass to load constants from.
*/
@SuppressWarnings("unchecked")
private ConstantSet(Class enumClass) {
this.enumClass = enumClass;
this.constants = EnumSet.allOf(enumClass);
Map names = new HashMap();
Map values = new HashMap();
for (Enum e : constants) {
if (e instanceof Constant) {
Constant c = (Constant) e;
names.put(e.name(), c);
values.put(c.longValue(), c);
}
}
nameToConstant = Collections.unmodifiableMap(names);
valueToConstant = Collections.unmodifiableMap(values);
}
/**
* Gets the constant for a name.
*
* @param name The name of the system constant (e.g. "EINVAL").
* @return A {@link Constant} instance.
*/
public final Constant getConstant(String name) {
return nameToConstant.get(name);
}
/**
* Gets the constant for a value.
*
* @param value A system constant value.
* @return A {@link Constant} instance.
*/
public Constant getConstant(long value) {
return valueToConstant.get(value);
}
/**
* Gets the integer value of a platform constant.
*
* @param name The name of the platform constant to look up (e.g. "EINVAL").
* @return The integer value of the constant.
*/
public long getValue(String name) {
Constant c = getConstant(name);
return c != null ? c.longValue() : 0;
}
/**
* Gets the name of a platform constant value.
*
* @param value The integer value to look up.
* @return The name of the constant.
*/
public String getName(int value) {
Constant c = getConstant(value);
return c != null ? c.name() : "unknown";
}
private Long getLongField(String name, long defaultValue) {
try {
Field f = enumClass.getField(name);
return (Long) f.get(enumClass);
} catch (NoSuchFieldException ex) {
return defaultValue;
} catch (RuntimeException ex) {
throw ex;
} catch (Exception ex) {
throw new RuntimeException(ex);
}
}
/**
* Returns the minimum value in this ConstantSet
* @return a long value
*/
public long minValue() {
if (minValue == null) {
minValue = getLongField("MIN_VALUE", Integer.MIN_VALUE);
}
return minValue.intValue();
}
/**
* Returns the maximum value in this ConstantSet
* @return a long value
*/
public long maxValue() {
if (maxValue == null) {
maxValue = getLongField("MAX_VALUE", Integer.MAX_VALUE);
}
return maxValue.intValue();
}
private final class ConstantIterator implements Iterator {
private final Iterator it;
private Constant next = null;
ConstantIterator(Collection constants) {
this.it = constants.iterator();
next = it.hasNext() ? (Constant) it.next() : null;
}
public boolean hasNext() {
return next != null && !next.name().equals("__UNKNOWN_CONSTANT__");
}
public void remove() {
throw new UnsupportedOperationException();
}
public Constant next() {
Constant prev = next;
next = it.hasNext() ? (Constant) it.next() : null;
return prev;
}
}
@Override
public Iterator iterator() {
return new ConstantIterator(constants);
}
@Override
public int size() {
return constants.size();
}
@Override
public boolean contains(Object o) {
return o != null && o.getClass().equals(enumClass);
}
}