Kryo

Issue: Java 14 records : how to deal with them?
• Pull Request: Add support for Records in JDK 14
• 对应版本：kryo-5.1.0

XStream

Issue: Support for record types in JDK 14
• Pull Request: Add support for Record types in JDK 14
• 对应版本：1.5.x，还未发布

这三个框架中实现对于 Record 的兼容思路都很类似，也比较简单，即：

1. 实现一个针对 Record 的专用的 Serializer 以及Deserializer。
2. 通过反射（Java Reflection）或者句柄（Java MethodHandle）验证当前版本的 Java 是否支持 Record，以及获取 Record 的规范构造函数（canonical constructor）以及各种 field 的 getter 进行反序列化和序列化。给大家两个工具类进行参考，分别是使用反射（Java Reflection）和句柄（Java MethodHandle）实现：

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.Comparator;
import common.RecComponent;

/**
* Utility methods for record serialization, using Java Core Reflection.
*/
public class ReflectUtils {
private static final Method IS_RECORD;
private static final Method GET_RECORD_COMPONENTS;
private static final Method GET_NAME;
private static final Method GET_TYPE;

static {
Method isRecord;
Method getRecordComponents;
Method getName;
Method getType;

try {
// reflective machinery required to access the record components
// without a static dependency on Java SE 14 APIs
Class<?> c = Class.forName("java.lang.reflect.RecordComponent");
isRecord = Class.class.getDeclaredMethod("isRecord");
getRecordComponents = Class.class.getMethod("getRecordComponents");
getName = c.getMethod("getName");
getType = c.getMethod("getType");
} catch (ClassNotFoundException | NoSuchMethodException e) {
// pre-Java-14
isRecord = null;
getRecordComponents = null;
getName = null;
getType = null;
}

IS_RECORD = isRecord;
GET_RECORD_COMPONENTS = getRecordComponents;
GET_NAME = getName;
GET_TYPE = getType;
}

/** Returns true if, and only if, the given class is a record class. */
static boolean isRecord(Class<?> type) {
try {
return (boolean) IS_RECORD.invoke(type);
} catch (Throwable t) {
throw new RuntimeException("Could not determine type (" + type + ")");
}
}

/**
* Returns an ordered array of the record components for the given record
* class. The order is imposed by the given comparator. If the given
* comparator is null, the order is that of the record components in the
* record attribute of the class file.
*/
static <T> RecComponent[] recordComponents(Class<T> type,
Comparator<RecComponent> comparator) {
try {
Object[] rawComponents = (Object[]) GET_RECORD_COMPONENTS.invoke(type);
RecComponent[] recordComponents = new RecComponent[rawComponents.length];
for (int i = 0; i < rawComponents.length; i++) {
final Object comp = rawComponents[i];
recordComponents[i] = new RecComponent(
(String) GET_NAME.invoke(comp),
(Class<?>) GET_TYPE.invoke(comp), i);
}
if (comparator != null) Arrays.sort(recordComponents, comparator);
return recordComponents;
} catch (Throwable t) {
throw new RuntimeException("Could not retrieve record components (" + type.getName() + ")");
}
}

/** Retrieves the value of the record component for the given record object. */
static Object componentValue(Object recordObject,
RecComponent recordComponent) {
try {
Method get = recordObject.getClass().getDeclaredMethod(recordComponent.name());
return get.invoke(recordObject);
} catch (Throwable t) {
throw new RuntimeException("Could not retrieve record components ("
+ recordObject.getClass().getName() + ")");
}
}

/**
* Invokes the canonical constructor of a record class with the
* given argument values.
*/
static <T> T invokeCanonicalConstructor(Class<T> recordType,
RecComponent[] recordComponents,
Object[] args) {
try {
Class<?>[] paramTypes = Arrays.stream(recordComponents)
.map(RecComponent::type)
.toArray(Class<?>[]::new);
Constructor<T> canonicalConstructor = recordType.getConstructor(paramTypes);
return canonicalConstructor.newInstance(args);
} catch (Throwable t) {
throw new RuntimeException("Could not construct type (" + recordType.getName() + ")");
}
}
}

package invoke;

import common.RecComponent;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.Comparator;
import static java.lang.invoke.MethodType.methodType;

/**
* Utility methods for record serialization, using MethodHandles.
*/
public class InvokeUtils {
private static final MethodHandle MH_IS_RECORD;
private static final MethodHandle MH_GET_RECORD_COMPONENTS;
private static final MethodHandle MH_GET_NAME;
private static final MethodHandle MH_GET_TYPE;
private static final MethodHandles.Lookup LOOKUP;

static {
MethodHandle MH_isRecord;
MethodHandle MH_getRecordComponents;
MethodHandle MH_getName;
MethodHandle MH_getType;
LOOKUP = MethodHandles.lookup();

try {
// reflective machinery required to access the record components
// without a static dependency on Java SE 14 APIs
Class<?> c = Class.forName("java.lang.reflect.RecordComponent");
MH_isRecord = LOOKUP.findVirtual(Class.class, "isRecord", methodType(boolean.class));
MH_getRecordComponents = LOOKUP.findVirtual(Class.class, "getRecordComponents",
methodType(Array.newInstance(c, 0).getClass()))
.asType(methodType(Object[].class, Class.class));
MH_getName = LOOKUP.findVirtual(c, "getName", methodType(String.class))
.asType(methodType(String.class, Object.class));
MH_getType = LOOKUP.findVirtual(c, "getType", methodType(Class.class))
.asType(methodType(Class.class, Object.class));
} catch (ClassNotFoundException | NoSuchMethodException e) {
// pre-Java-14
MH_isRecord = null;
MH_getRecordComponents = null;
MH_getName = null;
MH_getType = null;
} catch (IllegalAccessException unexpected) {
throw new AssertionError(unexpected);
}

MH_IS_RECORD = MH_isRecord;
MH_GET_RECORD_COMPONENTS = MH_getRecordComponents;
MH_GET_NAME = MH_getName;
MH_GET_TYPE = MH_getType;
}

/** Returns true if, and only if, the given class is a record class. */
static boolean isRecord(Class<?> type) {
try {
return (boolean) MH_IS_RECORD.invokeExact(type);
} catch (Throwable t) {
throw new RuntimeException("Could not determine type (" + type + ")");
}
}

/**
* Returns an ordered array of the record components for the given record
* class. The order is imposed by the given comparator. If the given
* comparator is null, the order is that of the record components in the
* record attribute of the class file.
*/
static <T> RecComponent[] recordComponents(Class<T> type,
Comparator<RecComponent> comparator) {
try {
Object[] rawComponents = (Object[]) MH_GET_RECORD_COMPONENTS.invokeExact(type);
RecComponent[] recordComponents = new RecComponent[rawComponents.length];
for (int i = 0; i < rawComponents.length; i++) {
final Object comp = rawComponents[i];
recordComponents[i] = new RecComponent(
(String) MH_GET_NAME.invokeExact(comp),
(Class<?>) MH_GET_TYPE.invokeExact(comp), i);
}
if (comparator != null) Arrays.sort(recordComponents, comparator);
return recordComponents;
} catch (Throwable t) {
throw new RuntimeException("Could not retrieve record components (" + type.getName() + ")");
}
}

/** Retrieves the value of the record component for the given record object. */
static Object componentValue(Object recordObject,
RecComponent recordComponent) {
try {
MethodHandle MH_get = LOOKUP.findVirtual(recordObject.getClass(),
recordComponent.name(),
methodType(recordComponent.type()));
return (Object) MH_get.invoke(recordObject);
} catch (Throwable t) {
throw new RuntimeException("Could not retrieve record components ("
+ recordObject.getClass().getName() + ")");
}
}

/**
* Invokes the canonical constructor of a record class with the
* given argument values.
*/
static <T> T invokeCanonicalConstructor(Class<T> recordType,
RecComponent[] recordComponents,
Object[] args) {
try {
Class<?>[] paramTypes = Arrays.stream(recordComponents)
.map(RecComponent::type)
.toArray(Class<?>[]::new);
MethodHandle MH_canonicalConstructor =
LOOKUP.findConstructor(recordType, methodType(void.class, paramTypes))
.asType(methodType(Object.class, paramTypes));
return (T)MH_canonicalConstructor.invokeWithArguments(args);
} catch (Throwable t) {
throw new RuntimeException("Could not construct type (" + recordType.getName() + ")");
}
}
}