com.dahuatech.hutool.core.builder.HashCodeBuilder Maven / Gradle / Ivy
package com.dahuatech.hutool.core.builder;
import com.dahuatech.hutool.core.lang.Assert;
import com.dahuatech.hutool.core.util.ArrayUtil;
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.Collection;
import java.util.HashSet;
import java.util.Set;
/**
* Assists in implementing {@link Object#hashCode()} methods.
*
* This class enables a good hashCode method to be built for any class. It follows
* the rules laid out in the book Effective Java by
* Joshua Bloch. Writing a good hashCode method is actually quite difficult. This class
* aims to simplify the process.
*
*
The following is the approach taken. When appending a data field, the current total is
* multiplied by the multiplier then a relevant value for that data type is added. For example, if
* the current hashCode is 17, and the multiplier is 37, then appending the integer 45 will create a
* hashcode of 674, namely 17 * 37 + 45.
*
*
All relevant fields from the object should be included in the hashCode method.
* Derived fields may be excluded. In general, any field used in the equals method must
* be used in the hashCode method.
*
*
To use this class write code as follows:
*
*
* public class Person {
* String name;
* int age;
* boolean smoker;
* ...
*
* public int hashCode() {
* // you pick a hard-coded, randomly chosen, non-zero, odd number
* // ideally different for each class
* return new HashCodeBuilder(17, 37).
* append(name).
* append(age).
* append(smoker).
* toHashCode();
* }
* }
*
*
* If required, the superclass hashCode() can be added using {@link #appendSuper}.
*
*
Alternatively, there is a method that uses reflection to determine the fields to test. Because
* these fields are usually private, the method, reflectionHashCode, uses
* AccessibleObject.setAccessible to change the visibility of the fields. This will fail
* under a security manager, unless the appropriate permissions are set up correctly. It is also
* slower than testing explicitly.
*
*
A typical invocation for this method would look like:
*
*
* public int hashCode() {
* return HashCodeBuilder.reflectionHashCode(this);
* }
*
*
* TODO 待整理 来自于Apache-Commons-Lang3
*
* @author looly，Apache-Commons
* @since 4.2.2
*/
public class HashCodeBuilder implements Builder {
private static final long serialVersionUID = 1L;
/** The default initial value to use in reflection hash code building. */
private static final int DEFAULT_INITIAL_VALUE = 17;
/** The default multipler value to use in reflection hash code building. */
private static final int DEFAULT_MULTIPLIER_VALUE = 37;
/**
* A registry of objects used by reflection methods to detect cyclical object references and avoid
* infinite loops.
*
* @since 2.3
*/
private static final ThreadLocal> REGISTRY = new ThreadLocal>();
/*
* NOTE: we cannot store the actual objects in a HashSet, as that would use the very hashCode()
* we are in the process of calculating.
*
* So we generate a one-to-one mapping from the original object to a new object.
*
* Now HashSet uses equals() to determine if two elements with the same hashcode really
* are equal, so we also need to ensure that the replacement objects are only equal
* if the original objects are identical.
*
* The original implementation (2.4 and before) used the System.indentityHashCode()
* method - however this is not guaranteed to generate unique ids (e.g. LANG-459)
*
* We now use the IDKey helper class (adapted from org.apache.axis.utils.IDKey)
* to disambiguate the duplicate ids.
*/
/** Constant to use in building the hashCode. */
private final int iConstant;
/** Running total of the hashCode. */
private int iTotal = 0;
/** Uses two hard coded choices for the constants needed to build a hashCode. */
public HashCodeBuilder() {
iConstant = 37;
iTotal = 17;
}
/**
* Two randomly chosen, odd numbers must be passed in. Ideally these should be different for each
* class, however this is not vital.
*
* Prime numbers are preferred, especially for the multiplier.
*
* @param initialOddNumber an odd number used as the initial value
* @param multiplierOddNumber an odd number used as the multiplier
* @throws IllegalArgumentException if the number is even
*/
public HashCodeBuilder(final int initialOddNumber, final int multiplierOddNumber) {
Assert.isTrue(initialOddNumber % 2 != 0, "HashCodeBuilder requires an odd initial value");
Assert.isTrue(multiplierOddNumber % 2 != 0, "HashCodeBuilder requires an odd multiplier");
iConstant = multiplierOddNumber;
iTotal = initialOddNumber;
}
/**
* Returns the registry of objects being traversed by the reflection methods in the current
* thread.
*
* @return Set the registry of objects being traversed
* @since 2.3
*/
private static Set getRegistry() {
return REGISTRY.get();
}
/**
* Returns true if the registry contains the given object. Used by the reflection
* methods to avoid infinite loops.
*
* @param value The object to lookup in the registry.
* @return boolean true if the registry contains the given object.
* @since 2.3
*/
private static boolean isRegistered(final Object value) {
final Set registry = getRegistry();
return registry != null && registry.contains(new IDKey(value));
}
/**
* Appends the fields and values defined by the given object of the given Class.
*
* @param object the object to append details of
* @param clazz the class to append details of
* @param builder the builder to append to
* @param useTransients whether to use transient fields
* @param excludeFields Collection of String field names to exclude from use in calculation of
* hash code
*/
private static void reflectionAppend(
final Object object,
final Class clazz,
final HashCodeBuilder builder,
final boolean useTransients,
final String[] excludeFields) {
if (isRegistered(object)) {
return;
}
try {
register(object);
final Field[] fields = clazz.getDeclaredFields();
AccessibleObject.setAccessible(fields, true);
for (final Field field : fields) {
if (false == ArrayUtil.contains(excludeFields, field.getName())
&& (field.getName().indexOf('$') == -1)
&& (useTransients || !Modifier.isTransient(field.getModifiers()))
&& (!Modifier.isStatic(field.getModifiers()))) {
try {
final Object fieldValue = field.get(object);
builder.append(fieldValue);
} catch (final IllegalAccessException e) {
// this can't happen. Would get a Security exception instead
// throw a runtime exception in case the impossible happens.
throw new InternalError("Unexpected IllegalAccessException");
}
}
}
} finally {
unregister(object);
}
}
/**
* Uses reflection to build a valid hash code from the fields of {@code object}.
*
* It uses AccessibleObject.setAccessible to gain access to private fields. This
* means that it will throw a security exception if run under a security manager, if the
* permissions are not set up correctly. It is also not as efficient as testing explicitly.
*
*
Transient members will be not be used, as they are likely derived fields, and not part of
* the value of the Object.
*
*
Static fields will not be tested. Superclass fields will be included.
*
*
Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be
* different for each class, however this is not vital. Prime numbers are preferred, especially
* for the multiplier.
*
* @param initialNonZeroOddNumber a non-zero, odd number used as the initial value. This will be
* the returned value if no fields are found to include in the hash code
* @param multiplierNonZeroOddNumber a non-zero, odd number used as the multiplier
* @param object the Object to create a hashCode for
* @return int hash code
* @throws IllegalArgumentException if the Object is null
* @throws IllegalArgumentException if the number is zero or even
*/
public static int reflectionHashCode(
final int initialNonZeroOddNumber,
final int multiplierNonZeroOddNumber,
final Object object) {
return reflectionHashCode(
initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, false, null);
}
// -------------------------------------------------------------------------
/**
* Uses reflection to build a valid hash code from the fields of {@code object}.
*
*
It uses AccessibleObject.setAccessible to gain access to private fields. This
* means that it will throw a security exception if run under a security manager, if the
* permissions are not set up correctly. It is also not as efficient as testing explicitly.
*
*
If the TestTransients parameter is set to true, transient members will be
* tested, otherwise they are ignored, as they are likely derived fields, and not part of the
* value of the Object.
*
*
Static fields will not be tested. Superclass fields will be included.
*
*
Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be
* different for each class, however this is not vital. Prime numbers are preferred, especially
* for the multiplier.
*
* @param initialNonZeroOddNumber a non-zero, odd number used as the initial value. This will be
* the returned value if no fields are found to include in the hash code
* @param multiplierNonZeroOddNumber a non-zero, odd number used as the multiplier
* @param object the Object to create a hashCode for
* @param testTransients whether to include transient fields
* @return int hash code
* @throws IllegalArgumentException if the Object is null
* @throws IllegalArgumentException if the number is zero or even
*/
public static int reflectionHashCode(
final int initialNonZeroOddNumber,
final int multiplierNonZeroOddNumber,
final Object object,
final boolean testTransients) {
return reflectionHashCode(
initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, testTransients, null);
}
/**
* Uses reflection to build a valid hash code from the fields of {@code object}.
*
*
It uses AccessibleObject.setAccessible to gain access to private fields. This
* means that it will throw a security exception if run under a security manager, if the
* permissions are not set up correctly. It is also not as efficient as testing explicitly.
*
*
If the TestTransients parameter is set to true, transient members will be
* tested, otherwise they are ignored, as they are likely derived fields, and not part of the
* value of the Object.
*
*
Static fields will not be included. Superclass fields will be included up to and including
* the specified superclass. A null superclass is treated as java.lang.Object.
*
*
Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be
* different for each class, however this is not vital. Prime numbers are preferred, especially
* for the multiplier.
*
* @param the type of the object involved
* @param initialNonZeroOddNumber a non-zero, odd number used as the initial value. This will be
* the returned value if no fields are found to include in the hash code
* @param multiplierNonZeroOddNumber a non-zero, odd number used as the multiplier
* @param object the Object to create a hashCode for
* @param testTransients whether to include transient fields
* @param reflectUpToClass the superclass to reflect up to (inclusive), may be null
* @param excludeFields array of field names to exclude from use in calculation of hash code
* @return int hash code
* @throws IllegalArgumentException if the Object is null
* @throws IllegalArgumentException if the number is zero or even
* @since 2.0
*/
public static int reflectionHashCode(
final int initialNonZeroOddNumber,
final int multiplierNonZeroOddNumber,
final T object,
final boolean testTransients,
final Class reflectUpToClass,
final String... excludeFields) {
if (object == null) {
throw new IllegalArgumentException("The object to build a hash code for must not be null");
}
final HashCodeBuilder builder =
new HashCodeBuilder(initialNonZeroOddNumber, multiplierNonZeroOddNumber);
Class clazz = object.getClass();
reflectionAppend(object, clazz, builder, testTransients, excludeFields);
while (clazz.getSuperclass() != null && clazz != reflectUpToClass) {
clazz = clazz.getSuperclass();
reflectionAppend(object, clazz, builder, testTransients, excludeFields);
}
return builder.toHashCode();
}
/**
* Uses reflection to build a valid hash code from the fields of {@code object}.
*
* This constructor uses two hard coded choices for the constants needed to build a hash code.
*
*
It uses AccessibleObject.setAccessible to gain access to private fields. This
* means that it will throw a security exception if run under a security manager, if the
* permissions are not set up correctly. It is also not as efficient as testing explicitly.
*
*
If the TestTransients parameter is set to true, transient members will be
* tested, otherwise they are ignored, as they are likely derived fields, and not part of the
* value of the Object.
*
*
Static fields will not be tested. Superclass fields will be included. If no fields are found
* to include in the hash code, the result of this method will be constant.
*
* @param object the Object to create a hashCode for
* @param testTransients whether to include transient fields
* @return int hash code
* @throws IllegalArgumentException if the object is null
*/
public static int reflectionHashCode(final Object object, final boolean testTransients) {
return reflectionHashCode(
DEFAULT_INITIAL_VALUE, DEFAULT_MULTIPLIER_VALUE, object, testTransients, null);
}
/**
* Uses reflection to build a valid hash code from the fields of {@code object}.
*
*
This constructor uses two hard coded choices for the constants needed to build a hash code.
*
*
It uses AccessibleObject.setAccessible to gain access to private fields. This
* means that it will throw a security exception if run under a security manager, if the
* permissions are not set up correctly. It is also not as efficient as testing explicitly.
*
*
Transient members will be not be used, as they are likely derived fields, and not part of
* the value of the Object.
*
*
Static fields will not be tested. Superclass fields will be included. If no fields are found
* to include in the hash code, the result of this method will be constant.
*
* @param object the Object to create a hashCode for
* @param excludeFields Collection of String field names to exclude from use in calculation of
* hash code
* @return int hash code
* @throws IllegalArgumentException if the object is null
*/
public static int reflectionHashCode(
final Object object, final Collection excludeFields) {
return reflectionHashCode(object, ArrayUtil.toArray(excludeFields, String.class));
}
/**
* Uses reflection to build a valid hash code from the fields of {@code object}.
*
* This constructor uses two hard coded choices for the constants needed to build a hash code.
*
*
It uses AccessibleObject.setAccessible to gain access to private fields. This
* means that it will throw a security exception if run under a security manager, if the
* permissions are not set up correctly. It is also not as efficient as testing explicitly.
*
*
Transient members will be not be used, as they are likely derived fields, and not part of
* the value of the Object.
*
*
Static fields will not be tested. Superclass fields will be included. If no fields are found
* to include in the hash code, the result of this method will be constant.
*
* @param object the Object to create a hashCode for
* @param excludeFields array of field names to exclude from use in calculation of hash code
* @return int hash code
* @throws IllegalArgumentException if the object is null
*/
public static int reflectionHashCode(final Object object, final String... excludeFields) {
return reflectionHashCode(
DEFAULT_INITIAL_VALUE, DEFAULT_MULTIPLIER_VALUE, object, false, null, excludeFields);
}
/**
* Registers the given object. Used by the reflection methods to avoid infinite loops.
*
* @param value The object to register.
*/
static void register(final Object value) {
synchronized (HashCodeBuilder.class) {
if (getRegistry() == null) {
REGISTRY.set(new HashSet());
}
}
getRegistry().add(new IDKey(value));
}
/**
* Unregisters the given object.
*
* Used by the reflection methods to avoid infinite loops.
*
* @param value The object to unregister.
* @since 2.3
*/
static void unregister(final Object value) {
Set registry = getRegistry();
if (registry != null) {
registry.remove(new IDKey(value));
synchronized (HashCodeBuilder.class) {
// read again
registry = getRegistry();
if (registry != null && registry.isEmpty()) {
REGISTRY.remove();
}
}
}
}
/**
* Append a hashCode for a boolean.
*
* This adds 1 when true, and 0 when false to the hashCode
* .
*
*
This is in contrast to the standard java.lang.Boolean.hashCode handling, which
* computes a hashCode value of 1231 for java.lang.Boolean
* instances that represent true or 1237 for java.lang.Boolean
* instances that represent false.
*
*
This is in accordance with the Effective Java design.
*
* @param value the boolean to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final boolean value) {
iTotal = iTotal * iConstant + (value ? 0 : 1);
return this;
}
/**
* Append a hashCode for a boolean array.
*
* @param array the array to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final boolean[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final boolean element : array) {
append(element);
}
}
return this;
}
// -------------------------------------------------------------------------
/**
* Append a hashCode for a byte.
*
* @param value the byte to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final byte value) {
iTotal = iTotal * iConstant + value;
return this;
}
// -------------------------------------------------------------------------
/**
* Append a hashCode for a byte array.
*
* @param array the array to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final byte[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final byte element : array) {
append(element);
}
}
return this;
}
/**
* Append a hashCode for a char.
*
* @param value the char to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final char value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a hashCode for a char array.
*
* @param array the array to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final char[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final char element : array) {
append(element);
}
}
return this;
}
/**
* Append a hashCode for a double.
*
* @param value the double to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final double value) {
return append(Double.doubleToLongBits(value));
}
/**
* Append a hashCode for a double array.
*
* @param array the array to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final double[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final double element : array) {
append(element);
}
}
return this;
}
/**
* Append a hashCode for a float.
*
* @param value the float to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final float value) {
iTotal = iTotal * iConstant + Float.floatToIntBits(value);
return this;
}
/**
* Append a hashCode for a float array.
*
* @param array the array to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final float[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final float element : array) {
append(element);
}
}
return this;
}
/**
* Append a hashCode for an int.
*
* @param value the int to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final int value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a hashCode for an int array.
*
* @param array the array to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final int[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final int element : array) {
append(element);
}
}
return this;
}
/**
* Append a hashCode for a long.
*
* @param value the long to add to the hashCode
* @return this
*/
// NOTE: This method uses >> and not >>> as Effective Java and
// Long.hashCode do. Ideally we should switch to >>> at
// some stage. There are backwards compat issues, so
// that will have to wait for the time being. cf LANG-342.
public HashCodeBuilder append(final long value) {
iTotal = iTotal * iConstant + ((int) (value ^ (value >> 32)));
return this;
}
/**
* Append a hashCode for a long array.
*
* @param array the array to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final long[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final long element : array) {
append(element);
}
}
return this;
}
/**
* Append a hashCode for an Object.
*
* @param object the Object to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final Object object) {
if (object == null) {
iTotal = iTotal * iConstant;
} else {
if (object.getClass().isArray()) {
// 'Switch' on type of array, to dispatch to the correct handler
// This handles multi dimensional arrays
if (object instanceof long[]) {
append((long[]) object);
} else if (object instanceof int[]) {
append((int[]) object);
} else if (object instanceof short[]) {
append((short[]) object);
} else if (object instanceof char[]) {
append((char[]) object);
} else if (object instanceof byte[]) {
append((byte[]) object);
} else if (object instanceof double[]) {
append((double[]) object);
} else if (object instanceof float[]) {
append((float[]) object);
} else if (object instanceof boolean[]) {
append((boolean[]) object);
} else {
// Not an array of primitives
append((Object[]) object);
}
} else {
iTotal = iTotal * iConstant + object.hashCode();
}
}
return this;
}
/**
* Append a hashCode for an Object array.
*
* @param array the array to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final Object[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final Object element : array) {
append(element);
}
}
return this;
}
/**
* Append a hashCode for a short.
*
* @param value the short to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final short value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a hashCode for a short array.
*
* @param array the array to add to the hashCode
* @return this
*/
public HashCodeBuilder append(final short[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final short element : array) {
append(element);
}
}
return this;
}
/**
* Adds the result of super.hashCode() to this builder.
*
* @param superHashCode the result of calling super.hashCode()
* @return this HashCodeBuilder, used to chain calls.
* @since 2.0
*/
public HashCodeBuilder appendSuper(final int superHashCode) {
iTotal = iTotal * iConstant + superHashCode;
return this;
}
/**
* Return the computed hashCode.
*
* @return hashCode based on the fields appended
*/
public int toHashCode() {
return iTotal;
}
/**
* Returns the computed hashCode.
*
* @return hashCode based on the fields appended
* @since 3.0
*/
@Override
public Integer build() {
return Integer.valueOf(toHashCode());
}
/**
* The computed hashCode from toHashCode() is returned due to the likelihood of bugs
* in mis-calling toHashCode() and the unlikeliness of it mattering what the hashCode for
* HashCodeBuilder itself is.
*
* @return hashCode based on the fields appended
* @since 2.5
*/
@Override
public int hashCode() {
return toHashCode();
}
}