com.groupbyinc.common.jackson.databind.util.CompactStringObjectMap Maven / Gradle / Ivy
package com.fasterxml.jackson.databind.util;
import java.util.*;
/**
* Specialized lookup class that implements functionality similar to
* {@link java.util.Map}, but for special case of key always being
* {@link java.lang.String} and using more compact (and memory-access
* friendly) hashing scheme. Assumption is also that keys are typically
* intern()ed.
*
* Generics are not used to avoid bridge methods and since these maps
* are not exposed as part of external API.
*
* @since 2.6
*/
public final class CompactStringObjectMap
implements java.io.Serializable // since 2.6.2
{
private static final long serialVersionUID = 1L;
/**
* Shared instance that can be used when there are no contents to Map.
*/
private final static CompactStringObjectMap EMPTY = new CompactStringObjectMap(1, 0,
new Object[4]);
private final int _hashMask, _spillCount;
private final Object[] _hashArea;
private CompactStringObjectMap(int hashMask, int spillCount, Object[] hashArea)
{
_hashMask = hashMask;
_spillCount = spillCount;
_hashArea = hashArea;
}
public static CompactStringObjectMap construct(Map all)
{
if (all.isEmpty()) { // can this happen?
return EMPTY;
}
// First: calculate size of primary hash area
final int size = findSize(all.size());
final int mask = size-1;
// and allocate enough to contain primary/secondary, expand for spillovers as need be
int alloc = (size + (size>>1)) * 2;
Object[] hashArea = new Object[alloc];
int spillCount = 0;
for (Map.Entry entry : all.entrySet()) {
String key = entry.getKey();
int slot = key.hashCode() & mask;
int ix = slot+slot;
// primary slot not free?
if (hashArea[ix] != null) {
// secondary?
ix = (size + (slot >> 1)) << 1;
if (hashArea[ix] != null) {
// ok, spill over.
ix = ((size + (size >> 1) ) << 1) + spillCount;
spillCount += 2;
if (ix >= hashArea.length) {
hashArea = Arrays.copyOf(hashArea, hashArea.length + 4);
}
}
}
hashArea[ix] = key;
hashArea[ix+1] = entry.getValue();
}
return new CompactStringObjectMap(mask, spillCount, hashArea);
}
private final static int findSize(int size)
{
if (size <= 5) {
return 8;
}
if (size <= 12) {
return 16;
}
int needed = size + (size >> 2); // at most 80% full
int result = 32;
while (result < needed) {
result += result;
}
return result;
}
public Object find(String key) {
int slot = key.hashCode() & _hashMask;
int ix = (slot<<1);
Object match = _hashArea[ix];
if ((match == key) || key.equals(match)) {
return _hashArea[ix+1];
}
return _find2(key, slot, match);
}
private final Object _find2(String key, int slot, Object match)
{
if (match == null) {
return null;
}
int hashSize = _hashMask+1;
int ix = hashSize + (slot>>1) << 1;
match = _hashArea[ix];
if (key.equals(match)) {
return _hashArea[ix+1];
}
if (match != null) { // _findFromSpill(...)
int i = (hashSize + (hashSize>>1)) << 1;
for (int end = i + _spillCount; i < end; i += 2) {
match = _hashArea[i];
if ((match == key) || key.equals(match)) {
return _hashArea[i+1];
}
}
}
return null;
}
/**
* @since 2.9
*/
public Object findCaseInsensitive(String key) {
for (int i = 0, end = _hashArea.length; i < end; i += 2) {
Object k2 = _hashArea[i];
if (k2 != null) {
String s = (String) k2;
if (s.equalsIgnoreCase(key)) {
return _hashArea[i+1];
}
}
}
return null;
}
public List keys() {
final int end = _hashArea.length;
List keys = new ArrayList(end >> 2);
for (int i = 0; i < end; i += 2) {
Object key = _hashArea[i];
if (key != null) {
keys.add((String) key);
}
}
return keys;
}
}