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products/sources/formale Sprachen/Java/Tomcat/java/org/apache/juli/ (Apache Software Stiftung Version 2.4.65^©) Datei vom 10.10.2023 mit Größe 6 kB

Quelle DateFormatCache.java Sprache: JAVA

/*
* 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.
* 
*/
public class DateFormatCache {

 public static final char MSEC_PATTERN = '#';

 /* 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.
 */
 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(MSEC_PATTERN);
 }
 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;
 }
 }
}

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