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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * 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,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

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 */

package javax.management;

import com.sun.jmx.mbeanserver.Introspector;

import java.io.IOException;

import java.io.ObjectInputStream;

/**

 * <p>Represents attributes used as arguments to relational constraints.

 * Instances of this class are usually obtained using {@link Query#attr(String)

 * Query.attr}.</p>

 *

 * <p>An <CODE>AttributeValueExp</CODE> may be used anywhere a

 * <CODE>ValueExp</CODE> is required.

 *

 * @since 1.5

 */

public class AttributeValueExp implements ValueExp  {

    /* Serial version */

    private static final long serialVersionUID = -7768025046539163385L;

    /**

     * @serial The name of the attribute

     */

    private String attr;

    /**

     * An <code>AttributeValueExp</code> with a null attribute.

     * @deprecated An instance created with this constructor cannot be

     * used in a query.

     */

    @Deprecated

    public AttributeValueExp() {

    }

    /**

     * Creates a new <CODE>AttributeValueExp</CODE> representing the

     * specified object attribute, named attr.

     *

     * @param attr the name of the attribute whose value is the value

     * of this {@link ValueExp}.

     */

    public AttributeValueExp(String attr) {

        this.attr = attr;

    }

    /**

     * Returns a string representation of the name of the attribute.

     *

     * @return the attribute name.

     */

    public String getAttributeName()  {

        return attr;

    }

    /**

     * <p>Applies the <CODE>AttributeValueExp</CODE> on an MBean.

     * This method calls {@link #getAttribute getAttribute(name)} and wraps

     * the result as a {@code ValueExp}.  The value returned by

     * {@code getAttribute} must be a {@code Number}, {@code String},

     * or {@code Boolean}; otherwise this method throws a

     * {@code BadAttributeValueExpException}, which will cause

     * the containing query to be false for this {@code name}.</p>

     *

     * @param name The name of the MBean on which the <CODE>AttributeValueExp</CODE> will be applied.

     *

     * @return  The <CODE>ValueExp</CODE>.

     *

     */

    @Override

    public ValueExp apply(ObjectName name) throws BadStringOperationException, BadBinaryOpValueExpException,

        BadAttributeValueExpException, InvalidApplicationException {

        Object result = getAttribute(name);

        if (result instanceof Number) {

            return new NumericValueExp((Number)result);

        } else if (result instanceof String) {

            return new StringValueExp((String)result);

        } else if (result instanceof Boolean) {

            return new BooleanValueExp((Boolean)result);

        } else {

            throw new BadAttributeValueExpException(result);

        }

    }

    /**

     * Returns the string representing its value.

     */

    @Override

    public String toString()  {

        return attr;

    }

    /**

     * Sets the MBean server on which the query is to be performed.

     *

     * @param s The MBean server on which the query is to be performed.

     *

     * @deprecated This method has no effect.  The MBean Server used to

     * obtain an attribute value is {@link QueryEval#getMBeanServer()}.

     */

    /* There is no need for this method, because if a query is being

       evaluted an AttributeValueExp can only appear inside a QueryExp,

       and that QueryExp will itself have done setMBeanServer.  */

    @Deprecated

    @Override

    public void setMBeanServer(MBeanServer s)  {

    }

    /**

     * <p>Return the value of the given attribute in the named MBean.

     * If the attempt to access the attribute generates an exception,

     * return null.</p>

     *

     * <p>The MBean Server used is the one returned by {@link

     * QueryEval#getMBeanServer()}.</p>

     *

     * @param name the name of the MBean whose attribute is to be returned.

     *

     * @return the value of the attribute, or null if it could not be

     * obtained.

     */

    protected Object getAttribute(ObjectName name) {

        try {

            // Get the value from the MBeanServer

            MBeanServer server = QueryEval.getMBeanServer();

            return server.getAttribute(name, attr);

        } catch (Exception re) {

            return null;

        }

    }

}