001 /** 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, software 013 * distributed under the License is distributed on an "AS IS" BASIS, 014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 015 * See the License for the specific language governing permissions and 016 * limitations under the License. 017 */ 018 019 package org.apache.hadoop.util; 020 021 import org.apache.hadoop.classification.InterfaceAudience; 022 import org.apache.hadoop.classification.InterfaceStability; 023 024 import com.google.common.collect.Interner; 025 import com.google.common.collect.Interners; 026 027 /** 028 * Provides equivalent behavior to String.intern() to optimize performance, 029 * whereby does not consume memory in the permanent generation. 030 */ 031 @InterfaceAudience.Public 032 @InterfaceStability.Stable 033 public class StringInterner { 034 035 /** 036 * Retains a strong reference to each string instance it has interned. 037 */ 038 private final static Interner<String> strongInterner; 039 040 /** 041 * Retains a weak reference to each string instance it has interned. 042 */ 043 private final static Interner<String> weakInterner; 044 045 046 047 static { 048 strongInterner = Interners.newStrongInterner(); 049 weakInterner = Interners.newWeakInterner(); 050 } 051 052 /** 053 * Interns and returns a reference to the representative instance 054 * for any of a collection of string instances that are equal to each other. 055 * Retains strong reference to the instance, 056 * thus preventing it from being garbage-collected. 057 * 058 * @param sample string instance to be interned 059 * @return strong reference to interned string instance 060 */ 061 public static String strongIntern(String sample) { 062 if (sample == null) { 063 return null; 064 } 065 return strongInterner.intern(sample); 066 } 067 068 /** 069 * Interns and returns a reference to the representative instance 070 * for any of a collection of string instances that are equal to each other. 071 * Retains weak reference to the instance, 072 * and so does not prevent it from being garbage-collected. 073 * 074 * @param sample string instance to be interned 075 * @return weak reference to interned string instance 076 */ 077 public static String weakIntern(String sample) { 078 if (sample == null) { 079 return null; 080 } 081 return weakInterner.intern(sample); 082 } 083 084 }