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 * published by the Free Software Foundation.  Sun designates this

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 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

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 *

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package javax.management.openmbean;

import java.io.InvalidObjectException;

import java.lang.reflect.Type;

/**

 * <p>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}.</p>

 *

 * <p>For example, suppose we have a class {@code MyLinkedList}, which looks

 * like this:</p>

 *

 * <pre>

 * public class MyLinkedList {

 *     public MyLinkedList(String name, MyLinkedList next) {...}

 *     public String getName() {...}

 *     public MyLinkedList getNext() {...}

 * }

 * </pre>

 *

 * <p>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.</p>

 *

 * <p>To define this mapping, we first subclass {@code MXBeanMapping}:</p>

 *

 * <pre>

 * 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]);

 *     }

 * }

 * </pre>

 *

 * <p>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.</p>

 *

 * <p>With this mapping defined, we can annotate the {@code MyLinkedList}

 * class appropriately:</p>

 *

 * <pre>

 * {@literal @MXBeanMappingClass}(MyLinkedListMapping.class)

 * public class MyLinkedList {...}

 * </pre>

 *

 * <p>Now we can use {@code MyLinkedList} in an MXBean interface and it

 * will work.</p>

 *

 * <p>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.</p>

 */

public abstract class MXBeanMapping {

    private final Type javaType;

    private final OpenType<?> openType;

    private final Class<?> openClass;

    /**

     * <p>Construct a mapping between the given Java type and the given

     * Open Type.</p>

     *

     * @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);

    }

    /**

     * <p>The Java type that was supplied to the constructor.</p>

     * @return the Java type that was supplied to the constructor.

     */

    public final Type getJavaType() {

        return javaType;

    }

    /**

     * <p>The Open Type that was supplied to the constructor.</p>

     * @return the Open Type that was supplied to the constructor.

     */

    public final OpenType<?> getOpenType() {

        return openType;

    }

    /**

     * <p>The Java class that corresponds to instances of the

     * {@linkplain #getOpenType() Open Type} for this mapping.</p>

     * @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.validClassName(openType.getClassName());

            return Class.forName(className, false, null);

        } catch (ClassNotFoundException e) {

            throw new RuntimeException(e);  // should not happen

        } catch (OpenDataException e) {

            throw new IllegalArgumentException("Bad OpenType: " + openType, e);

        }

    }

    /**

     * <p>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;

    /**

     * <p>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;

    /**

     * <p>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 <em>no</em> open data values can

     * be converted.  The default implementation of this method never

     * throws an exception.  Subclasses can override it as

     * appropriate.</p>

     * @throws InvalidObjectException if {@code fromOpenValue} will throw

     * an exception no matter what its argument is.

     */

    public void checkReconstructible() throws InvalidObjectException {}

}