/* * Copyright (c) 1999, 2008, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * 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. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ 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>.     *     * @exception BadAttributeValueExpException     * @exception InvalidApplicationException     * @exception BadStringOperationException     * @exception BadBinaryOpValueExpException     *     */    @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;        }    }}