| author | ohair |
| Wed, 26 May 2010 20:28:04 -0700 | |
| changeset 5551 | 327690766109 |
| parent 5506 | 202f599c92aa |
| child 9693 | ee89bfc8fa66 |
| permissions | -rw-r--r-- |
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<html> |
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<title>javax.management.monitor package</title> |
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327690766109
6956202: Fix a few missed rebranding issues, please contact lines etc.
ohair
parents:
5506
diff
changeset
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Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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327690766109
6956202: Fix a few missed rebranding issues, please contact lines etc.
ohair
parents:
5506
diff
changeset
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or visit www.oracle.com if you need additional information or have any |
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327690766109
6956202: Fix a few missed rebranding issues, please contact lines etc.
ohair
parents:
5506
diff
changeset
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questions. |
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--> |
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</head> |
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<body bgcolor="white"> |
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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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<tt>java.lang.management</tt> has an attribute |
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<tt>HeapMemoryUsage</tt> 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 <tt>used</tt> |
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property of <tt>MemoryUsage</tt>, you could monitor |
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"<tt>HeapMemoryUsage.used</tt>". 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 <tt>ObservedAttribute</tt> like |
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<tt>"HeapMemoryUsage.used"</tt> are as follows. Suppose the string is |
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<i>A.e</i> (so <i>A</i> would be <tt>"HeapMemoryUsage"</tt> and <i>e</i> |
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would be <tt>"used"</tt> 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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<ul> |
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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 <tt>"length"</tt> |
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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 {@link
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java.beans.Introspector#getBeanInfo(Class) Introspector.getBeanInfo} |
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for the class of <i>v</i> (<i>v</i>.<tt>getClass()</tt>) contains a |
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{@link java.beans.PropertyDescriptor PropertyDescriptor} with the name
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<i>e</i>, then <i>x</i> is the result of calling the property's {@link
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java.beans.PropertyDescriptor#getReadMethod() read method} on |
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<i>v</i>.</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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<tt>HeapMemoryUsage</tt> is a <tt>MemoryUsage</tt>, monitoring |
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<tt>"HeapMemoryUsage.used"</tt> will obtain the observed value by |
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calling <tt>MemoryUsage.getUsed()</tt>.</p> |
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<p>If the <tt>ObservedAttribute</tt> contains more than one period, |
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for example <tt>"ConnectionPool.connectionStats.length"</tt>, 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 <tt>ConnectionPool</tt>, 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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<tt>"connectionStats"</tt>. 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 <tt>"length"</tt>.</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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<tt>HeapMemoryUsage.used</tt>. This means that an |
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<tt>ObservedAttribute</tt> that is <tt>HeapMemoryUsage.used</tt> |
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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 <tt>used</tt> within an attribute called |
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<tt>HeapMemoryUsage</tt>. So for compatibility reasons, when the |
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<tt>ObservedAttribute</tt> contains a period (<tt>.</tt>), the monitor |
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will check whether an attribute exists whose name is the full |
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<tt>ObservedAttribute</tt> string (<tt>HeapMemoryUsage.used</tt> 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 <tt>HeapMemoryUsage.used</tt> attribute and others do not. An |
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implementation may therefore call <tt>getMBeanInfo</tt> 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="{@docRoot}/../technotes/guides/jmx/">
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Java SE 6 Platform documentation on JMX technology</a>, |
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in particular the |
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<a href="{@docRoot}/../technotes/guides/jmx/JMX_1_4_specification.pdf">
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JMX Specification, version 1.4(pdf).</a> |
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@since 1.5 |
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