hadoop StringInterner 源码
haddop StringInterner 代码
文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/StringInterner.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.hadoop.util;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.thirdparty.com.google.common.collect.Interner;
import org.apache.hadoop.thirdparty.com.google.common.collect.Interners;
/**
* Provides string interning utility methods. For weak interning,
* we use the standard String.intern() call, that performs very well
* (no problems with PermGen overflowing, etc.) starting from JDK 7.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class StringInterner {
/**
* Retains a strong reference to each string instance it has interned.
*/
private final static Interner<String> STRONG_INTERNER =
Interners.newStrongInterner();
/**
* Interns and returns a reference to the representative instance
* for any of a collection of string instances that are equal to each other.
* Retains strong reference to the instance,
* thus preventing it from being garbage-collected.
*
* @param sample string instance to be interned
* @return strong reference to interned string instance
*/
public static String strongIntern(String sample) {
if (sample == null) {
return null;
}
return STRONG_INTERNER.intern(sample);
}
/**
* Interns and returns a reference to the representative instance
* for any of a collection of string instances that are equal to each other.
* Retains weak reference to the instance,
* and so does not prevent it from being garbage-collected.
*
* @param sample string instance to be interned
* @return weak reference to interned string instance
*/
public static String weakIntern(String sample) {
if (sample == null) {
return null;
}
return sample.intern();
}
/**
* Interns all the strings in the given array in place,
* returning the same array.
*
* @param strings strings.
* @return internStringsInArray.
*/
public static String[] internStringsInArray(String[] strings) {
for (int i = 0; i < strings.length; i++) {
strings[i] = weakIntern(strings[i]);
}
return strings;
}
}
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