/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.juli;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;
Cache structure for SimpleDateFormat formatted timestamps based on
seconds.
Millisecond formatting using S is not supported. You should add the
millisecond information after getting back the second formatting.
The cache consists of entries for a consecutive range of
seconds. The length of the range is configurable. It is
implemented based on a cyclic buffer. New entries shift the range.
The cache is not threadsafe. It can be used without synchronization
via thread local instances, or with synchronization as a global cache.
The cache can be created with a parent cache to build a cache hierarchy.
Access to the parent cache is threadsafe.
/**
* <p>Cache structure for SimpleDateFormat formatted timestamps based on
* seconds.</p>
*
* <p>Millisecond formatting using S is not supported. You should add the
* millisecond information after getting back the second formatting.</p>
*
* <p>The cache consists of entries for a consecutive range of
* seconds. The length of the range is configurable. It is
* implemented based on a cyclic buffer. New entries shift the range.</p>
*
* <p>The cache is not threadsafe. It can be used without synchronization
* via thread local instances, or with synchronization as a global cache.</p>
*
* <p>The cache can be created with a parent cache to build a cache hierarchy.
* Access to the parent cache is threadsafe.</p>
*/
public class DateFormatCache {
private static final String msecPattern = "#";
/* Timestamp format */
private final String format;
/* Number of cached entries */
private final int cacheSize;
private final Cache cache;
Replace the millisecond formatting character 'S' by
some dummy characters in order to make the resulting
formatted time stamps cacheable. Our consumer might
choose to replace the dummy chars with the actual
milliseconds because that's relatively cheap.
/**
* Replace the millisecond formatting character 'S' by
* some dummy characters in order to make the resulting
* formatted time stamps cacheable. Our consumer might
* choose to replace the dummy chars with the actual
* milliseconds because that's relatively cheap.
*/
private String tidyFormat(String format) {
boolean escape = false;
StringBuilder result = new StringBuilder();
int len = format.length();
char x;
for (int i = 0; i < len; i++) {
x = format.charAt(i);
if (escape || x != 'S') {
result.append(x);
} else {
result.append(msecPattern);
}
if (x == '\'') {
escape = !escape;
}
}
return result.toString();
}
public DateFormatCache(int size, String format, DateFormatCache parent) {
cacheSize = size;
this.format = tidyFormat(format);
Cache parentCache = null;
if (parent != null) {
synchronized(parent) {
parentCache = parent.cache;
}
}
cache = new Cache(parentCache);
}
public String getFormat(long time) {
return cache.getFormat(time);
}
public String getTimeFormat() {
return format;
}
private class Cache {
/* Second formatted in most recent invocation */
private long previousSeconds = Long.MIN_VALUE;
/* Formatted timestamp generated in most recent invocation */
private String previousFormat = "";
/* First second contained in cache */
private long first = Long.MIN_VALUE;
/* Last second contained in cache */
private long last = Long.MIN_VALUE;
/* Index of "first" in the cyclic cache */
private int offset = 0;
/* Helper object to be able to call SimpleDateFormat.format(). */
private final Date currentDate = new Date();
private String cache[];
private SimpleDateFormat formatter;
private Cache parent = null;
private Cache(Cache parent) {
cache = new String[cacheSize];
formatter = new SimpleDateFormat(format, Locale.US);
formatter.setTimeZone(TimeZone.getDefault());
this.parent = parent;
}
private String getFormat(long time) {
long seconds = time / 1000;
/* First step: if we have seen this timestamp
during the previous call, return the previous value. */
if (seconds == previousSeconds) {
return previousFormat;
}
/* Second step: Try to locate in cache */
previousSeconds = seconds;
int index = (offset + (int)(seconds - first)) % cacheSize;
if (index < 0) {
index += cacheSize;
}
if (seconds >= first && seconds <= last) {
if (cache[index] != null) {
/* Found, so remember for next call and return.*/
previousFormat = cache[index];
return previousFormat;
}
/* Third step: not found in cache, adjust cache and add item */
} else if (seconds >= last + cacheSize || seconds <= first - cacheSize) {
first = seconds;
last = first + cacheSize - 1;
index = 0;
offset = 0;
for (int i = 1; i < cacheSize; i++) {
cache[i] = null;
}
} else if (seconds > last) {
for (int i = 1; i < seconds - last; i++) {
cache[(index + cacheSize - i) % cacheSize] = null;
}
first = seconds - (cacheSize - 1);
last = seconds;
offset = (index + 1) % cacheSize;
} else if (seconds < first) {
for (int i = 1; i < first - seconds; i++) {
cache[(index + i) % cacheSize] = null;
}
first = seconds;
last = seconds + (cacheSize - 1);
offset = index;
}
/* Last step: format new timestamp either using
* parent cache or locally. */
if (parent != null) {
synchronized(parent) {
previousFormat = parent.getFormat(time);
}
} else {
currentDate.setTime(time);
previousFormat = formatter.format(currentDate);
}
cache[index] = previousFormat;
return previousFormat;
}
}
}