org.scijava.util.ConversionUtils Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of scijava-common Show documentation
Show all versions of scijava-common Show documentation
SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.
/*
* #%L
* SciJava Common shared library for SciJava software.
* %%
* Copyright (C) 2009 - 2014 Board of Regents of the University of
* Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
* Institute of Molecular Cell Biology and Genetics.
* %%
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* #L%
*/
package org.scijava.util;
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
/**
* Useful methods for converting and casting between classes and types.
*
* @author Curtis Rueden
* @author Mark Hiner
*/
public class ConversionUtils {
private ConversionUtils() {
// prevent instantiation of utility class
}
// -- Type conversion and casting --
/**
* As {@link #convert(Object, Class)} but capable of creating and populating
* multi-element objects ({@link Collection}s and array types). If a single
* element type is provided, it will be converted the same as
* {@link #convert(Object, Class)}. If a multi-element type is detected, then
* the value parameter will be interpreted as potential collection of values.
* An appropriate container will be created, and the full set of values will
* be type converted and added.
*
* NB: This method should be capable of creating any array type, but if a
* {@link Collection} interface or abstract class is provided we can only make
* a best guess as to what container type to instantiate. Defaults are
* provided for {@link Set} and {@link List} subclasses.
*
*
* @param src The object to convert.
* @param dest Type to which the object should be converted.
*/
public static Object convert(final Object src, final Type dest) {
// NB: Regardless of whether the destination type is an array or collection,
// we still want to cast directly if doing so is possible. But note that in
// general, this check does not detect cases of incompatible generic
// parameter types. If this limitation becomes a problem in the future we
// can extend the logic here to provide additional signatures of canCast
// which operate on Types in general rather than only Classes. However, the
// logic could become complex very quickly in various subclassing cases,
// generic parameters resolved vs. propagated, etc.
final Class c = getClass(dest);
if (c != null && canCast(src, c)) return cast(src, c);
// Handle array types, including generic array types.
if (isArray(dest)) {
return convertToArray(src, getComponentClass(dest));
}
// Handle parameterized collection types.
if (dest instanceof ParameterizedType && isCollection(dest)) {
return convertToCollection(src, (ParameterizedType) dest);
}
// This wasn't a collection or array, so convert it as a single element.
return convert(src, getClass(dest));
}
/**
* Converts the given object to an object of the specified type. The object is
* casted directly if possible, or else a new object is created using the
* destination type's public constructor that takes the original object as
* input (except when converting to {@link String}, which uses the
* {@link Object#toString()} method instead). In the case of primitive types,
* returns an object of the corresponding wrapped type. If the destination
* type does not have an appropriate constructor, returns null.
*
* @param Type to which the object should be converted.
* @param src The object to convert.
* @param dest Type to which the object should be converted.
*/
public static T convert(final Object src, final Class dest) {
// TODO: Would be better to split up this method into some helpers.
if (dest == null) return null;
if (src == null) return getNullValue(dest);
// ensure type is well-behaved, rather than a primitive type
final Class saneDest = getNonprimitiveType(dest);
// cast the existing object, if possible
if (canCast(src, saneDest)) return cast(src, saneDest);
// special case for conversion from number to number
if (src instanceof Number) {
final Number number = (Number) src;
if (saneDest == Byte.class) {
final Byte result = number.byteValue();
@SuppressWarnings("unchecked")
final T typedResult = (T) result;
return typedResult;
}
if (saneDest == Double.class) {
final Double result = number.doubleValue();
@SuppressWarnings("unchecked")
final T typedResult = (T) result;
return typedResult;
}
if (saneDest == Float.class) {
final Float result = number.floatValue();
@SuppressWarnings("unchecked")
final T typedResult = (T) result;
return typedResult;
}
if (saneDest == Integer.class) {
final Integer result = number.intValue();
@SuppressWarnings("unchecked")
final T typedResult = (T) result;
return typedResult;
}
if (saneDest == Long.class) {
final Long result = number.longValue();
@SuppressWarnings("unchecked")
final T typedResult = (T) result;
return typedResult;
}
if (saneDest == Short.class) {
final Short result = number.shortValue();
@SuppressWarnings("unchecked")
final T typedResult = (T) result;
return typedResult;
}
}
// special cases for strings
if (src instanceof String) {
// source type is String
final String s = (String) src;
if (s.isEmpty()) {
// return null for empty strings
return getNullValue(dest);
}
// use first character when converting to Character
if (saneDest == Character.class) {
final Character c = new Character(s.charAt(0));
@SuppressWarnings("unchecked")
final T result = (T) c;
return result;
}
// special case for conversion to enum
if (dest.isEnum()) {
final T result = convertToEnum(s, dest);
if (result != null) return result;
}
}
if (saneDest == String.class) {
// destination type is String; use Object.toString() method
final String sValue = src.toString();
@SuppressWarnings("unchecked")
final T result = (T) sValue;
return result;
}
// wrap the original object with one of the new type, using a constructor
try {
final Constructor ctor = getConstructor(saneDest, src.getClass());
if (ctor == null) return null;
@SuppressWarnings("unchecked")
final T instance = (T) ctor.newInstance(src);
return instance;
}
catch (final Exception exc) {
// TODO: Best not to catch blanket Exceptions here.
// no known way to convert
return null;
}
}
/**
* Converts the given string value to an enumeration constant of the specified
* type.
*
* @param src The value to convert.
* @param dest The type of the enumeration constant.
* @return The converted enumeration constant, or null if the type is not an
* enumeration type or has no such constant.
*/
public static T convertToEnum(final String src, final Class dest) {
if (src == null || !dest.isEnum()) return null;
try {
@SuppressWarnings({ "rawtypes", "unchecked" })
final Enum result = Enum.valueOf((Class) dest, src);
@SuppressWarnings("unchecked")
final T typedResult = (T) result;
return typedResult;
}
catch (final IllegalArgumentException exc) {
// no such enum constant
return null;
}
}
/**
* Checks whether objects of the given class can be converted to the specified
* type.
*
* @see #convert(Object, Type)
*/
public static boolean canConvert(final Class src, final Type dest) {
// NB: Regardless of whether the destination type is an array or collection,
// we still want to cast directly if doing so is possible. But note that in
// general, this check does not detect cases of incompatible generic
// parameter types. If this limitation becomes a problem in the future we
// can extend the logic here to provide additional signatures of canCast
// which operate on Types in general rather than only Classes. However, the
// logic could become complex very quickly in various subclassing cases,
// generic parameters resolved vs. propagated, etc.
final Class c = getClass(dest);
if (c != null && canCast(src, c)) return true;
// Handle array types, including generic array types.
if (isArray(dest)) return true;
// Handle parameterized collection types.
if (dest instanceof ParameterizedType && isCollection(dest)) {
return createCollection(getClass(dest)) != null;
}
// This wasn't a collection or array, so convert it as a single element.
return canConvert(src, getClass(dest));
}
/**
* Checks whether objects of the given class can be converted to the specified
* type.
*
* @see #convert(Object, Class)
*/
public static boolean canConvert(final Class src, final Class dest) {
// ensure type is well-behaved, rather than a primitive type
final Class saneDest = getNonprimitiveType(dest);
// OK if the existing object can be casted
if (canCast(src, saneDest)) return true;
// OK for numerical conversions
if (canCast(getNonprimitiveType(src), Number.class) &&
(ClassUtils.isByte(dest) || ClassUtils.isDouble(dest) ||
ClassUtils.isFloat(dest) || ClassUtils.isInteger(dest) ||
ClassUtils.isLong(dest) || ClassUtils.isShort(dest)))
{
return true;
}
// OK if string
if (saneDest == String.class) return true;
if (canCast(src, String.class)) {
// OK if source type is string and destination type is character
// (in this case, the first character of the string would be used)
if (saneDest == Character.class) return true;
// OK if source type is string and destination type is an enum
if (dest.isEnum()) return true;
}
// OK if appropriate wrapper constructor exists
try {
return getConstructor(saneDest, src) != null;
}
catch (final Exception exc) {
// TODO: Best not to catch blanket Exceptions here.
// no known way to convert
return false;
}
}
/**
* Checks whether the given object's type can be converted to the specified
* type.
*
* Note that this does not necessarily entail that
* {@link #convert(Object, Type)} on that specific object will succeed. For
* example: {@code canConvert("5.1", int.class)} will return {@code true}
* because a {@link String} can in general be converted to an {@code int}, but
* calling {@code convert("5.1", int.class)} will throw a
* {@link NumberFormatException} when the conversion is actually attempted
* via the {@link Integer#Integer(String)} constructor.
*
*
* @see #convert(Object, Type)
*/
public static boolean canConvert(final Object src, final Type dest) {
if (src == null) return true;
return canConvert(src.getClass(), dest);
}
/**
* Checks whether the given object's type can be converted to the specified
* type.
*
* Note that this does not necessarily entail that
* {@link #convert(Object, Class)} on that specific object will succeed. For
* example: {@code canConvert("5.1", int.class)} will return {@code true}
* because a {@link String} can in general be converted to an {@code int}, but
* calling {@code convert("5.1", int.class)} will throw a
* {@link NumberFormatException} when the conversion is actually attempted
* via the {@link Integer#Integer(String)} constructor.
*
*
* @see #convert(Object, Class)
*/
public static boolean canConvert(final Object src, final Class dest) {
if (src == null) return true;
return canConvert(src.getClass(), dest);
}
/**
* Casts the given object to the specified type, or null if the types are
* incompatible.
*/
public static T cast(final Object src, final Class dest) {
if (!canCast(src, dest)) return null;
@SuppressWarnings("unchecked")
final T result = (T) src;
return result;
}
/**
* Checks whether objects of the given class can be cast to the specified
* type.
*
* @see #cast(Object, Class)
*/
public static boolean canCast(final Class src, final Class dest) {
return dest.isAssignableFrom(src);
}
/**
* Checks whether the given object can be cast to the specified type.
*
* @see #cast(Object, Class)
*/
public static boolean canCast(final Object src, final Class dest) {
return src == null || canCast(src.getClass(), dest);
}
/**
* Returns the non-primitive {@link Class} closest to the given type.
*
* Specifically, the following type conversions are done:
*
* - boolean.class becomes Boolean.class
* - byte.class becomes Byte.class
* - char.class becomes Character.class
* - double.class becomes Double.class
* - float.class becomes Float.class
* - int.class becomes Integer.class
* - long.class becomes Long.class
* - short.class becomes Short.class
* - void.class becomes Void.class
*
* All other types are unchanged.
*
*/
public static Class getNonprimitiveType(final Class type) {
final Class destType;
if (type == boolean.class) destType = Boolean.class;
else if (type == byte.class) destType = Byte.class;
else if (type == char.class) destType = Character.class;
else if (type == double.class) destType = Double.class;
else if (type == float.class) destType = Float.class;
else if (type == int.class) destType = Integer.class;
else if (type == long.class) destType = Long.class;
else if (type == short.class) destType = Short.class;
else if (type == void.class) destType = Void.class;
else destType = type;
@SuppressWarnings("unchecked")
final Class result = (Class) destType;
return result;
}
/**
* Gets the "null" value for the given type. For non-primitives, this will
* actually be null. For primitives, it will be zero for numeric types, false
* for boolean, and the null character for char.
*/
public static T getNullValue(final Class type) {
final Object defaultValue;
if (type == boolean.class) defaultValue = false;
else if (type == byte.class) defaultValue = (byte) 0;
else if (type == char.class) defaultValue = '\0';
else if (type == double.class) defaultValue = 0d;
else if (type == float.class) defaultValue = 0f;
else if (type == int.class) defaultValue = 0;
else if (type == long.class) defaultValue = 0L;
else if (type == short.class) defaultValue = (short) 0;
else defaultValue = null;
@SuppressWarnings("unchecked")
final T result = (T) defaultValue;
return result;
}
/**
* Gets the raw class corresponding to the given type.
*
* If the type is a {@link Class} it is simply casted. In the case of a
* {@link ParameterizedType}, then {@link ParameterizedType#getRawType()} is
* returned. Otherwise, returns null.
*
*/
public static Class getClass(final Type type) {
if (type instanceof Class) return (Class) type;
if (type instanceof ParameterizedType) {
return getClass(((ParameterizedType) type).getRawType());
}
if (type instanceof TypeVariable) {
final Type[] types = ((TypeVariable) type).getBounds();
if (types.length == 1) return getClass(types[0]);
}
return null;
}
/**
* Gets the component type of the given array type, or null if not an array.
* Supports both regular array types (i.e., {@link Class#getComponentType()}
* if {@code type} is a {@link Class}) and generic array types (i.e.,
* {@link GenericArrayType#getGenericComponentType()} if {@code type} is a
* {@link GenericArrayType}).
*/
public static Class getComponentClass(final Type type) {
if (type instanceof Class) return ((Class) type).getComponentType();
if (type instanceof GenericArrayType) {
return getClass(((GenericArrayType) type).getGenericComponentType());
}
return null;
}
// -- Helper methods --
private static Constructor getConstructor(final Class type,
final Class argType)
{
for (final Constructor ctor : type.getConstructors()) {
final Class[] params = ctor.getParameterTypes();
if (params.length == 1 && canCast(argType, params[0])) {
return ctor;
}
}
return null;
}
private static boolean isArray(final Type type) {
return getComponentClass(type) != null;
}
private static boolean isCollection(final Type type) {
return canCast(getClass(type), Collection.class);
}
private static Object convertToArray(final Object value,
final Class componentType)
{
// First we make sure the value is a collection. This provides the simplest
// interface for iterating over all the elements. We use SciJava's
// PrimitiveArray collection implementations internally, so that this
// conversion is always wrapping by reference, for performance.
final Collection items = ArrayUtils.toCollection(value);
final Object array = Array.newInstance(componentType, items.size());
// Populate the array by converting each item in the value collection
// to the component type.
int index = 0;
for (final Object item : items) {
Array.set(array, index++, convert(item, componentType));
}
return array;
}
private static Object convertToCollection(final Object value,
final ParameterizedType pType)
{
final Collection