src/java.management/share/classes/javax/management/QueryEval.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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
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 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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package javax.management;

import java.io.Serializable;

/**
 * Allows a query to be performed in the context of a specific MBean server.
 *
 * @since 1.5
 */
public abstract class QueryEval implements Serializable {

    /* Serial version */
    private static final long serialVersionUID = 2675899265640874796L;

    private static ThreadLocal<MBeanServer> server =
        new InheritableThreadLocal<>();

    /**
     * Constructor for subclasses to call.
     */
    public QueryEval() {}

    /**
     * <p>Sets the MBean server on which the query is to be performed.
     * The setting is valid for the thread performing the set.
     * It is copied to any threads created by that thread at the moment
     * of their creation.</p>
     *
     * <p>For historical reasons, this method is not static, but its
     * behavior does not depend on the instance on which it is
     * called.</p>
     *
     * @param s The MBean server on which the query is to be performed.
     *
     * @see #getMBeanServer
     */
    public void setMBeanServer(MBeanServer s) {
        server.set(s);
    }

    /**
     * <p>Return the MBean server that was most recently given to the
     * {@link #setMBeanServer setMBeanServer} method by this thread.
     * If this thread never called that method, the result is the
     * value its parent thread would have obtained from
     * <code>getMBeanServer</code> at the moment of the creation of
     * this thread, or null if there is no parent thread.</p>
     *
     * @return the MBean server.
     *
     * @see #setMBeanServer
     *
     */
    public static MBeanServer getMBeanServer() {
        return server.get();
    }
}