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[Update] remove hashCode, add nano & secure

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@hangga 2023-11-19 13:43:34 +07:00
commit 7bc08e8e74
2 changed files with 52 additions and 40 deletions
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35
core-java-modules/core-java-uuid/src/main/java/com/baeldung/uuid/UUIDPositiveLongGenerator.java
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@ -1,6 +1,7 @@
package com.baeldung.uuid;
import java.nio.ByteBuffer;
import java.security.SecureRandom;
import java.util.UUID;
/**
@ -16,10 +17,6 @@ public class UUIDPositiveLongGenerator {
return Math.abs(UUID.randomUUID().getMostSignificantBits());
}
public long getHashCode() {
return Math.abs(UUID.randomUUID().toString().hashCode());
}
public long combineByteBuffer() {
UUID uuid = UUID.randomUUID();
ByteBuffer bb = ByteBuffer.wrap(new byte[16]);
@ -30,9 +27,10 @@ public class UUIDPositiveLongGenerator {
}
public long combineBitwise() {
UUID uniqueUUID;
uniqueUUID = UUID.randomUUID();
return Math.abs((uniqueUUID.getMostSignificantBits() << 32) | (uniqueUUID.getLeastSignificantBits() & 0xFFFFFFFFL));
UUID uniqueUUID = UUID.randomUUID();
long mostSignificantBits = uniqueUUID.getMostSignificantBits();
long leastSignificantBits = uniqueUUID.getLeastSignificantBits();
return Math.abs((mostSignificantBits << 32) | (leastSignificantBits & 0xFFFFFFFFL));
}
public long combineDirect() {
@ -59,4 +57,27 @@ public class UUIDPositiveLongGenerator {
}
return Math.abs(result);
}
public long combineWithSecureRandom() {
UUID uniqueUUID = UUID.randomUUID();
SecureRandom secureRandom = new SecureRandom();
long randomBits = secureRandom.nextLong();
long mostSignificantBits = uniqueUUID.getMostSignificantBits() ^ randomBits;
long leastSignificantBits = uniqueUUID.getLeastSignificantBits();
return Math.abs((mostSignificantBits << 32) | (leastSignificantBits & 0xFFFFFFFFL));
}
public long combineWithNanoTime() {
UUID uniqueUUID = UUID.randomUUID();
long nanoTime = System.nanoTime();
long mostSignificantBits = uniqueUUID.getMostSignificantBits() ^ nanoTime;
long leastSignificantBits = uniqueUUID.getLeastSignificantBits();
return Math.abs((mostSignificantBits << 32) | (leastSignificantBits & 0xFFFFFFFFL));
}
}

57
core-java-modules/core-java-uuid/src/test/java/com/baeldung/uuid/UUIDPositiveLongGeneratorUnitTest.java
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@ -1,52 +1,43 @@
package com.baeldung.uuid;
import org.junit.jupiter.api.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.lang.reflect.Method;
import java.text.DecimalFormat;
import java.util.HashSet;
import java.util.Set;
import static org.assertj.core.api.Assertions.assertThat;
public class UUIDPositiveLongGeneratorUnitTest {
private final static int NUMBER_OF_CHECKS = 1000000;
private final static double COLLISION_THRESHOLD = 0.001;
private final UUIDPositiveLongGenerator uuidLongGenerator = new UUIDPositiveLongGenerator();
private final Logger logger = LoggerFactory.getLogger(UUIDPositiveLongGeneratorUnitTest.class);
private final Set<Long> uniqueValues = new HashSet<>();
@Test
void whenForeachGenerateLongValue_thenCollisionsCheck() throws Exception {
printTableHeader();
void whenForeachMethods_thenRetryWhileNotUnique() throws Exception {
for (Method method : uuidLongGenerator.getClass().getDeclaredMethods()) {
collisionCheck(method);
}
}
private void printTableHeader() {
logger.info(String.format("%-30s %-15s %-15s", "Approach(method name)", "collisions", "probability"));
logger.info("-----------------------------------------------------------------------");
}
private void printOutput(String method, int collisionsCount, double collisionsProbability) {
DecimalFormat decimalFormat = new DecimalFormat("#.#####");
logger.info(String.format("%-30s %-15s %-15s", method, collisionsCount, decimalFormat.format(collisionsProbability)));
}
private void collisionCheck(Method method) throws Exception {
Set<Long> uniqueValues = new HashSet<>();
int collisions = 0;
for (int i = 0; i < NUMBER_OF_CHECKS; i++) {
long uniqueValue = (long) method.invoke(uuidLongGenerator);
long uniqueValue;
do uniqueValue = (long) method.invoke(uuidLongGenerator); while (!isUnique(uniqueValue));
assertThat(uniqueValue).isPositive();
if (!uniqueValues.add(uniqueValue)) {
collisions++;
}
}
double collisionsProbability = (double) collisions / NUMBER_OF_CHECKS;
printOutput(method.getName(), collisions, collisionsProbability);
assertThat(collisionsProbability).isLessThan(COLLISION_THRESHOLD);
}
@Test
void whenGivenLongValue_thenCheckUniqueness() {
long uniqueValue = generateUniqueLong();
assertThat(uniqueValue).isPositive();
}
private long generateUniqueLong() {
long uniqueValue;
do uniqueValue = uuidLongGenerator.combineBitwise(); while (!isUnique(uniqueValue));
return uniqueValue;
}
private boolean isUnique(long value) {
// Implement uniqueness checking logic, for example, by checking in the database
return uniqueValues.add(value);
}
}