Summary: This is an abstraction for working with custom Comparators implemented in native C++ code from Java. Native code must directly extend `rocksdb::Comparator`. When the native code comparator is compiled into the RocksDB codebase, you can then create a Java Class, and JNI stub to wrap it. Useful if the C++/JNI barrier overhead is too much for your applications comparator performance. An example is provided in `java/rocksjni/native_comparator_wrapper_test.cc` and `java/src/main/java/org/rocksdb/NativeComparatorWrapperTest.java`. Closes https://github.com/facebook/rocksdb/pull/3334 Differential Revision: D7172605 Pulled By: miasantreble fbshipit-source-id: e24b7eb267a3bcb6afa214e0379a1d5e8a2ceabemain
Adam Retter
6 years ago
committed by
Facebook Github Bot
parent
e476d0e252
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#include <jni.h> |
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#include <string> |
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#include "rocksdb/comparator.h" |
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#include "rocksdb/slice.h" |
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#include "include/org_rocksdb_NativeComparatorWrapperTest_NativeStringComparatorWrapper.h" |
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namespace rocksdb { |
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class NativeComparatorWrapperTestStringComparator |
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: public Comparator { |
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const char* Name() const { |
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return "NativeComparatorWrapperTestStringComparator"; |
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} |
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int Compare( |
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const Slice& a, const Slice& b) const { |
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return a.ToString().compare(b.ToString()); |
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} |
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void FindShortestSeparator( |
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std::string* start, const Slice& limit) const { |
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return; |
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} |
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void FindShortSuccessor( |
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std::string* key) const { |
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return; |
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} |
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}; |
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} // end of rocksdb namespace
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/*
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* Class: org_rocksdb_NativeComparatorWrapperTest_NativeStringComparatorWrapper |
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* Method: newStringComparator |
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* Signature: ()J |
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*/ |
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jlong Java_org_rocksdb_NativeComparatorWrapperTest_00024NativeStringComparatorWrapper_newStringComparator( |
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JNIEnv* env , jobject jobj) { |
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auto* comparator = |
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new rocksdb::NativeComparatorWrapperTestStringComparator(); |
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return reinterpret_cast<jlong>(comparator); |
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} |
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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package org.rocksdb; |
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enum ComparatorType { |
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JAVA_COMPARATOR((byte)0x0), |
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JAVA_DIRECT_COMPARATOR((byte)0x1), |
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JAVA_NATIVE_COMPARATOR_WRAPPER((byte)0x2); |
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private final byte value; |
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ComparatorType(final byte value) { |
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this.value = value; |
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} |
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/** |
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* <p>Returns the byte value of the enumerations value.</p> |
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* |
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* @return byte representation |
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*/ |
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byte getValue() { |
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return value; |
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} |
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/** |
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* <p>Get the ComparatorType enumeration value by |
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* passing the byte identifier to this method.</p> |
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* |
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* @param byteIdentifier of ComparatorType. |
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* |
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* @return ComparatorType instance. |
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* |
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* @throws IllegalArgumentException if the comparator type for the byteIdentifier |
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* cannot be found |
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*/ |
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static ComparatorType getComparatorType(final byte byteIdentifier) { |
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for (final ComparatorType comparatorType : ComparatorType.values()) { |
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if (comparatorType.getValue() == byteIdentifier) { |
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return comparatorType; |
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} |
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} |
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throw new IllegalArgumentException( |
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"Illegal value provided for ComparatorType."); |
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} |
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} |
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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package org.rocksdb; |
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/** |
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* A simple abstraction to allow a Java class to wrap a custom comparator |
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* implemented in C++. |
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* |
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* The native comparator must directly extend rocksdb::Comparator. |
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*/ |
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public abstract class NativeComparatorWrapper |
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extends AbstractComparator<Slice> { |
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@Override |
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final ComparatorType getComparatorType() { |
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return ComparatorType.JAVA_NATIVE_COMPARATOR_WRAPPER; |
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} |
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@Override |
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public final String name() { |
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throw new IllegalStateException("This should not be called. " + |
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"Implementation is in Native code"); |
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} |
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@Override |
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public final int compare(final Slice s1, final Slice s2) { |
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throw new IllegalStateException("This should not be called. " + |
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"Implementation is in Native code"); |
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} |
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@Override |
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public final String findShortestSeparator(final String start, final Slice limit) { |
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throw new IllegalStateException("This should not be called. " + |
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"Implementation is in Native code"); |
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} |
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@Override |
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public final String findShortSuccessor(final String key) { |
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throw new IllegalStateException("This should not be called. " + |
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"Implementation is in Native code"); |
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} |
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/** |
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* We override {@link RocksCallbackObject#disposeInternal()} |
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* as disposing of a native rocksd::Comparator extension requires |
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* a slightly different approach as it is not really a RocksCallbackObject |
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*/ |
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@Override |
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protected void disposeInternal() { |
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disposeInternal(nativeHandle_); |
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} |
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private native void disposeInternal(final long handle); |
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} |
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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package org.rocksdb; |
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import org.junit.Rule; |
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import org.junit.Test; |
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import org.junit.rules.TemporaryFolder; |
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import java.util.*; |
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import java.util.Comparator; |
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import static org.junit.Assert.assertEquals; |
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public class NativeComparatorWrapperTest { |
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@Rule |
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public TemporaryFolder dbFolder = new TemporaryFolder(); |
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private static final Random random = new Random(); |
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@Test |
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public void rountrip() throws RocksDBException { |
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final String dbPath = dbFolder.getRoot().getAbsolutePath(); |
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final int ITERATIONS = 1_000; |
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final String[] storedKeys = new String[ITERATIONS]; |
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try (final NativeStringComparatorWrapper comparator = new NativeStringComparatorWrapper(); |
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final Options opt = new Options() |
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.setCreateIfMissing(true) |
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.setComparator(comparator)) { |
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// store random integer keys
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try (final RocksDB db = RocksDB.open(opt, dbPath)) { |
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for (int i = 0; i < ITERATIONS; i++) { |
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final String strKey = randomString(); |
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final byte key[] = strKey.getBytes(); |
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// does key already exist (avoid duplicates)
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if (i > 0 && db.get(key) != null) { |
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i--; // generate a different key
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} else { |
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db.put(key, "value".getBytes()); |
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storedKeys[i] = strKey; |
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} |
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} |
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} |
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// sort the stored keys into ascending alpha-numeric order
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Arrays.sort(storedKeys, new Comparator<String>() { |
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@Override |
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public int compare(final String o1, final String o2) { |
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return o1.compareTo(o2); |
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} |
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}); |
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// re-open db and read from start to end
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// string keys should be in ascending
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// order
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try (final RocksDB db = RocksDB.open(opt, dbPath); |
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final RocksIterator it = db.newIterator()) { |
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int count = 0; |
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for (it.seekToFirst(); it.isValid(); it.next()) { |
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final String strKey = new String(it.key()); |
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assertEquals(storedKeys[count++], strKey); |
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} |
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} |
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} |
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} |
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private String randomString() { |
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final char[] chars = new char[12]; |
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for(int i = 0; i < 12; i++) { |
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final int letterCode = random.nextInt(24); |
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final char letter = (char) (((int) 'a') + letterCode); |
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chars[i] = letter; |
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} |
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return String.copyValueOf(chars); |
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} |
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public static class NativeStringComparatorWrapper |
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extends NativeComparatorWrapper { |
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@Override |
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protected long initializeNative(final long... nativeParameterHandles) { |
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return newStringComparator(); |
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} |
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private native long newStringComparator(); |
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} |
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} |
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