| author | uvangapally |
| Tue, 01 Aug 2017 10:33:47 +0530 | |
| changeset 46050 | f51c14dc540f |
| parent 32034 | 05676cfd40b5 |
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<title>javax.management.monitor package</title> |
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Copyright (c) 1999, 2017, Oracle and/or its affiliates. All rights reserved. |
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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 |
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under the terms of the GNU General Public License version 2 only, as |
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published by the Free Software Foundation. Oracle designates this |
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particular file as subject to the "Classpath" exception as provided |
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by Oracle in the LICENSE file that accompanied this code. |
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This code is distributed in the hope that it will be useful, but WITHOUT |
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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version 2 for more details (a copy is included in the LICENSE file that |
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accompanied this code). |
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You should have received a copy of the GNU General Public License version |
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2 along with this work; if not, write to the Free Software Foundation, |
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Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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or visit www.oracle.com if you need additional information or have any |
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questions. |
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<p>Provides the definition of the monitor classes. A Monitor is |
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an MBean that periodically observes the value of an attribute in |
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one or more other MBeans. If the attribute meets a certain |
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condition, the Monitor emits a {@link
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javax.management.monitor.MonitorNotification |
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MonitorNotification}. When the monitor MBean periodically calls |
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{@link javax.management.MBeanServer#getAttribute getAttribute}
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to retrieve the value of the attribute being monitored it does |
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so within the access control context of the |
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{@link javax.management.monitor.Monitor#start} caller.</p>
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<p id="complex">The value being monitored can be a simple value |
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contained within a complex type. For example, the {@link
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java.lang.management.MemoryMXBean MemoryMXBean} defined in |
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{@code java.lang.management} has an attribute
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{@code HeapMemoryUsage} of type {@link
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java.lang.management.MemoryUsage MemoryUsage}. To monitor the |
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amount of <i>used</i> memory, described by the {@code used}
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property of {@code MemoryUsage}, you could monitor
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"{@code HeapMemoryUsage.used}". That string would be the
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argument to {@link
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javax.management.monitor.MonitorMBean#setObservedAttribute(String) |
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setObservedAttribute}.</p> |
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<p>The rules used to interpret an {@code ObservedAttribute} like
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{@code "HeapMemoryUsage.used"} are as follows. Suppose the string is
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<i>A.e</i> (so <i>A</i> would be {@code "HeapMemoryUsage"} and <i>e</i>
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would be {@code "used"} in the example).</p>
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<p>First the value of the attribute <i>A</i> is obtained. Call it |
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<i>v</i>. A value <i>x</i> is extracted from <i>v</i> as follows:</p> |
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<li>If <i>v</i> is a {@link javax.management.openmbean.CompositeData
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CompositeData} and if <i>v</i>.{@link
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javax.management.openmbean.CompositeData#get(String) get}(<i>e</i>) |
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returns a value then <i>x</i> is that value.</li> |
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<li>If <i>v</i> is an array and <i>e</i> is the string {@code "length"}
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then <i>x</i> is the length of the array.</li> |
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<li>If the above rules do not produce a value, and if introspection, as |
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if by calling {@link java.beans.Introspector#getBeanInfo(Class)
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Introspector.getBeanInfo}, for the class of <i>v</i> |
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(<i>v</i>.{@code getClass()}) identifies a property with the name
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<i>e</i>, then <i>x</i> is the result of reading the property value. </li> |
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</ul> |
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<p>The third rule means for example that if the attribute |
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{@code HeapMemoryUsage} is a {@code MemoryUsage}, monitoring
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{@code "HeapMemoryUsage.used"} will obtain the observed value by
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calling {@code MemoryUsage.getUsed()}.</p>
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<p>If the {@code ObservedAttribute} contains more than one period,
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for example {@code "ConnectionPool.connectionStats.length"}, then the
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above rules are applied iteratively. Here, <i>v</i> would initially be |
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the value of the attribute {@code ConnectionPool}, and <i>x</i> would
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be derived by applying the above rules with <i>e</i> equal to |
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{@code "connectionStats"}. Then <i>v</i> would be set to this <i>x</i>
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and a new <i>x</i> derived by applying the rules again with <i>e</i> |
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equal to {@code "length"}.</p>
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<p>Although it is recommended that attribute names be valid Java |
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identifiers, it is possible for an attribute to be called |
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{@code HeapMemoryUsage.used}. This means that an
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{@code ObservedAttribute} that is {@code HeapMemoryUsage.used}
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could mean that the value to observe is either an attribute of that |
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name, or the property {@code used} within an attribute called
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{@code HeapMemoryUsage}. So for compatibility reasons, when the
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{@code ObservedAttribute} contains a period ({@code .}), the monitor
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will check whether an attribute exists whose name is the full |
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{@code ObservedAttribute} string ({@code HeapMemoryUsage.used} in the
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example). It does this by calling {@link
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javax.management.MBeanServer#getMBeanInfo(javax.management.ObjectName) |
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getMBeanInfo} for the observed MBean and looking for a contained {@link
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javax.management.MBeanAttributeInfo MBeanAttributeInfo} with the given |
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name. If one is found, then that is what is monitored. If more than one |
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MBean is being observed, the behavior is unspecified if some of them have |
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a {@code HeapMemoryUsage.used} attribute and others do not. An
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implementation may therefore call {@code getMBeanInfo} on just one of
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the MBeans in this case. The behavior is also unspecified if the result |
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of the check changes while the monitor is active.</p> |
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<p>The exact behavior of monitors is detailed in the |
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<a href="#spec">JMX Specification</a>. What follows is a |
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summary.</p> |
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<p>There are three kinds of Monitors:</p> |
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<ul> |
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<li> |
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<p>A {@link javax.management.monitor.CounterMonitor
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CounterMonitor} observes attributes of integer |
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type. The attributes are assumed to be non-negative, and |
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monotonically increasing except for a possible |
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<em>roll-over</em> at a specified <em>modulus</em>. Each |
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observed attribute has an associated <em>threshold</em> |
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value. A notification is sent when the attribute exceeds |
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its threshold.</p> |
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<p>An <em>offset</em> value can be specified. When an |
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observed value exceeds its threshold, the threshold is |
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incremented by the offset, or by a multiple of the offset |
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sufficient to make the threshold greater than the new |
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observed value.</p> |
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<p>A <code>CounterMonitor</code> can operate in |
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<em>difference mode</em>. In this mode, the value |
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compared against the threshold is the difference between |
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two successive observations of an attribute.</p> |
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</li> |
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<li> |
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<p>A {@link javax.management.monitor.GaugeMonitor
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GaugeMonitor} observes attributes of numerical type. Each |
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observed attribute has an associated <em>high |
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threshold</em> and <em>low threshold</em>.</p> |
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<p>When an observed attribute crosses the high threshold, if |
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the <em>notify high</em> flag is true, then a notification |
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is sent. Subsequent crossings of the high threshold value |
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will not trigger further notifications until the gauge value |
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becomes less than or equal to the low threshold.</p> |
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<p>When an observed attribute crosses the low threshold, if |
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the <em>notify low</em> flag is true, then a notification |
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is sent. Subsequent crossings of the low threshold value |
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will not trigger further notifications until the gauge |
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value becomes greater than or equal to the high |
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threshold.</p> |
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<p>Typically, only one of the notify high and notify low |
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flags is set. The other threshold is used to provide a |
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<em>hysteresis</em> mechanism to avoid the repeated |
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triggering of notifications when an attribute makes small |
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oscillations around the threshold value.</p> |
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<p>A <code>GaugeMonitor</code> can operate in <em>difference |
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mode</em>. In this mode, the value compared against the |
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high and low thresholds is the difference between two |
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successive observations of an attribute.</p> |
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</li> |
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<li> |
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<p>A {@link javax.management.monitor.StringMonitor
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StringMonitor} observes attributes of type |
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<code>String</code>. A notification is sent when an |
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observed attribute becomes equal and/or not equal to a |
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given string.</p> |
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</li> |
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</ul> |
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<p id="spec"> |
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@see <a href="https://jcp.org/aboutJava/communityprocess/mrel/jsr160/index2.html"> |
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JMX Specification, version 1.4</a> |
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@since 1.5 |
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