A custom mapping between Java types and Open types for use in MXBeans. * To define such a mapping, subclass this class and define at least the * {@link #fromOpenValue fromOpenValue} and {@link #toOpenValue toOpenValue} * methods, and optionally the {@link #checkReconstructible} method. * Then either use an {@link MXBeanMappingClass} annotation on your custom * Java types, or include this MXBeanMapping in an * {@link MXBeanMappingFactory}.
* *For example, suppose we have a class {@code MyLinkedList}, which looks * like this:
* *
* public class MyLinkedList {
* public MyLinkedList(String name, MyLinkedList next) {...}
* public String getName() {...}
* public MyLinkedList getNext() {...}
* }
*
*
* This is not a valid type for MXBeans, because it contains a * self-referential property "next" defined by the {@code getNext()} * method. MXBeans do not support recursive types. So we would like * to specify a mapping for {@code MyLinkedList} explicitly. When an * MXBean interface contains {@code MyLinkedList}, that will be mapped * into a {@code String[]}, which is a valid Open Type.
* *To define this mapping, we first subclass {@code MXBeanMapping}:
* *
* public class MyLinkedListMapping extends MXBeanMapping {
* public MyLinkedListMapping(Type type) throws OpenDataException {
* super(MyLinkedList.class, ArrayType.getArrayType(SimpleType.STRING));
* if (type != MyLinkedList.class)
* throw new OpenDataException("Mapping only valid for MyLinkedList");
* }
*
* {@literal @Override}
* public Object fromOpenValue(Object openValue) throws InvalidObjectException {
* String[] array = (String[]) openValue;
* MyLinkedList list = null;
* for (int i = array.length - 1; i >= 0; i--)
* list = new MyLinkedList(array[i], list);
* return list;
* }
*
* {@literal @Override}
* public Object toOpenValue(Object javaValue) throws OpenDataException {
* ArrayList<String> array = new ArrayList<String>();
* for (MyLinkedList list = (MyLinkedList) javaValue; list != null;
* list = list.getNext())
* array.add(list.getName());
* return array.toArray(new String[0]);
* }
* }
*
*
* The call to the superclass constructor specifies what the * original Java type is ({@code MyLinkedList.class}) and what Open * Type it is mapped to ({@code * ArrayType.getArrayType(SimpleType.STRING)}). The {@code * fromOpenValue} method says how we go from the Open Type ({@code * String[]}) to the Java type ({@code MyLinkedList}), and the {@code * toOpenValue} method says how we go from the Java type to the Open * Type.
* *With this mapping defined, we can annotate the {@code MyLinkedList} * class appropriately:
* *
* {@literal @MXBeanMappingClass}(MyLinkedListMapping.class)
* public class MyLinkedList {...}
*
*
* Now we can use {@code MyLinkedList} in an MXBean interface and it * will work.
* *If we are unable to modify the {@code MyLinkedList} class, * we can define an {@link MXBeanMappingFactory}. See the documentation * of that class for further details.
* * @see MXBean specification, section * "Custom MXBean type mappings" */ public abstract class MXBeanMapping { private final Type javaType; private final OpenType openType; private final Class openClass; /** *Construct a mapping between the given Java type and the given * Open Type.
* * @param javaType the Java type (for example, {@code MyLinkedList}). * @param openType the Open Type (for example, {@code * ArrayType.getArrayType(SimpleType.STRING)}) * * @throws NullPointerException if either argument is null. */ protected MXBeanMapping(Type javaType, OpenType openType) { if (javaType == null || openType == null) throw new NullPointerException("Null argument"); this.javaType = javaType; this.openType = openType; this.openClass = makeOpenClass(javaType, openType); } /** *The Java type that was supplied to the constructor.
* @return the Java type that was supplied to the constructor. */ public final Type getJavaType() { return javaType; } /** *The Open Type that was supplied to the constructor.
* @return the Open Type that was supplied to the constructor. */ public final OpenType getOpenType() { return openType; } /** *The Java class that corresponds to instances of the * {@linkplain #getOpenType() Open Type} for this mapping.
* @return the Java class that corresponds to instances of the * Open Type for this mapping. * @see OpenType#getClassName */ public final Class getOpenClass() { return openClass; } private static Class makeOpenClass(Type javaType, OpenType openType) { if (javaType instanceof Class && ((Class) javaType).isPrimitive()) return (Class) javaType; try { String className = openType.getClassName(); return Class.forName(className, false, MXBeanMapping.class.getClassLoader()); } catch (ClassNotFoundException e) { throw new RuntimeException(e); // should not happen } } /** *Convert an instance of the Open Type into the Java type. * @param openValue the value to be converted. * @return the converted value. * @throws InvalidObjectException if the value cannot be converted. */ public abstract Object fromOpenValue(Object openValue) throws InvalidObjectException; /** *
Convert an instance of the Java type into the Open Type. * @param javaValue the value to be converted. * @return the converted value. * @throws OpenDataException if the value cannot be converted. */ public abstract Object toOpenValue(Object javaValue) throws OpenDataException; /** *
Throw an appropriate InvalidObjectException if we will not * be able to convert back from the open data to the original Java * object. The {@link #fromOpenValue fromOpenValue} throws an * exception if a given open data value cannot be converted. This * method throws an exception if no open data values can * be converted. The default implementation of this method never * throws an exception. Subclasses can override it as * appropriate.
* @throws InvalidObjectException if {@code fromOpenValue} will throw * an exception no matter what its argument is. */ public void checkReconstructible() throws InvalidObjectException {} }