JDK8/Java8源码在线阅读

/*
 * Copyright (c) 1999, 2006, 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 java.security.AccessController;

import com.sun.jmx.mbeanserver.GetPropertyAction;

/**
 * This class represents the name of the Java implementation class of
 * the MBean. It is used for performing queries based on the class of
 * the MBean.
 * @serial include
 *
 * <p>The <b>serialVersionUID</b> of this class is <code>-1081892073854801359L</code>.
 *
 * @since 1.5
 */
@SuppressWarnings("serial")  // serialVersionUID is not constant
class ClassAttributeValueExp extends AttributeValueExp {

    // Serialization compatibility stuff:
    // Two serial forms are supported in this class. The selected form depends
    // on system property "jmx.serial.form":
    //  - "1.0" for JMX 1.0
    //  - any other value for JMX 1.1 and higher
    //
    // Serial version for old serial form
    private static final long oldSerialVersionUID = -2212731951078526753L;
    //
    // Serial version for new serial form
    private static final long newSerialVersionUID = -1081892073854801359L;

    private static final long serialVersionUID;
    static {
        boolean compat = false;
        try {
            GetPropertyAction act = new GetPropertyAction("jmx.serial.form");
            String form = AccessController.doPrivileged(act);
            compat = (form != null && form.equals("1.0"));
        } catch (Exception e) {
            // OK: exception means no compat with 1.0, too bad
        }
        if (compat)
            serialVersionUID = oldSerialVersionUID;
        else
            serialVersionUID = newSerialVersionUID;
    }

    /**
     * @serial The name of the attribute
     *
     * <p>The <b>serialVersionUID</b> of this class is <code>-1081892073854801359L</code>.
     */
    private String attr;

    /**
     * Basic Constructor.
     */
    public ClassAttributeValueExp() {
        /* Compatibility: we have an attr field that we must hold on to
           for serial compatibility, even though our parent has one too.  */
        super("Class");
        attr = "Class";
    }


    /**
     * Applies the ClassAttributeValueExp on an MBean. Returns the name of
     * the Java implementation class of the MBean.
     *
     * @param name The name of the MBean on which the ClassAttributeValueExp will be applied.
     *
     * @return  The ValueExp.
     *
     * @exception BadAttributeValueExpException
     * @exception InvalidApplicationException
     */
    public ValueExp apply(ObjectName name)
            throws BadStringOperationException, BadBinaryOpValueExpException,
                   BadAttributeValueExpException, InvalidApplicationException {
        // getAttribute(name);
        Object result = getValue(name);
        if  (result instanceof String) {
            return new StringValueExp((String)result);
        } else {
            throw new BadAttributeValueExpException(result);
        }
    }

    /**
     * Returns the string "Class" representing its value
     */
    public String toString()  {
        return attr;
    }


    protected Object getValue(ObjectName name) {
        try {
            // Get the class of the object
            MBeanServer server = QueryEval.getMBeanServer();
            return server.getObjectInstance(name).getClassName();
        } catch (Exception re) {
            return null;

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