| author | darcy |
| Wed, 23 Oct 2019 13:01:40 -0700 | |
| changeset 58766 | 54ffb15c4839 |
| parent 47216 | 71c04702a3d5 |
| permissions | -rw-r--r-- |
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<head> |
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<title>javax.management package</title> |
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<!-- |
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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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--> |
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</head> |
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<body bgcolor="white"> |
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<p>Provides the core classes for the Java Management Extensions.</p> |
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<p>The Java Management Extensions |
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(JMX™) API is a standard |
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API for management and monitoring. Typical uses include:</p> |
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<ul> |
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<li>consulting and changing application configuration</li> |
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<li>accumulating statistics about application behavior and |
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making them available</li> |
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<li>notifying of state changes and erroneous conditions.</li> |
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</ul> |
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<p>The JMX API can also be used as part of a solution for |
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managing systems, networks, and so on.</p> |
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<p>The API includes remote access, so a remote management |
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program can interact with a running application for these |
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purposes.</p> |
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<h2>MBeans</h2> |
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<p>The fundamental notion of the JMX API is the <em>MBean</em>. |
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An MBean is a named <em>managed object</em> representing a |
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resource. It has a <em id="mgIface">management interface</em> |
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which must be <em>public</em> and consist of:</p> |
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<ul> |
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<li>named and typed attributes that can be read and/or |
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written</li> |
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<li>named and typed operations that can be invoked</li> |
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<li>typed notifications that can be emitted by the MBean.</li> |
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</ul> |
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<p>For example, an MBean representing an application's |
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configuration could have attributes representing the different |
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configuration items. Reading the <code>CacheSize</code> |
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attribute would return the current value of that item. |
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Writing it would update the item, potentially changing the |
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behavior of the running application. An operation such as |
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<code>save</code> could store the current configuration |
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persistently. A notification such as |
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<code>ConfigurationChangedNotification</code> could be sent |
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every time the configuration is changed.</p> |
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<p>In the standard usage of the JMX API, MBeans are implemented |
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as Java objects. However, as explained below, these objects are |
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not usually referenced directly.</p> |
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<h3>Standard MBeans</h3> |
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<p>To make MBean implementation simple, the JMX API includes the |
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notion of <em>Standard MBeans</em>. A Standard MBean is one |
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whose attributes and operations are deduced from a Java |
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interface using certain naming patterns, similar to those used |
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by JavaBeans™. For example, consider an interface like this:</p> |
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<pre> |
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public interface ConfigurationMBean {
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public int getCacheSize(); |
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public void setCacheSize(int size); |
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public long getLastChangedTime(); |
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public void save(); |
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} |
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</pre> |
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<p>The methods <code>getCacheSize</code> and |
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<code>setCacheSize</code> define a read-write attribute of |
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type <code>int</code> called <code>CacheSize</code> (with an |
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initial capital, unlike the JavaBeans convention).</p> |
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<p>The method <code>getLastChangedTime</code> defines an |
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attribute of type <code>long</code> called |
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<code>LastChangedTime</code>. This is a read-only attribute, |
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since there is no method <code>setLastChangedTime</code>.</p> |
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<p>The method <code>save</code> defines an operation called |
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<code>save</code>. It is not an attribute, since its name |
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does not begin with <code>get</code>, <code>set</code>, or |
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<code>is</code>.</p> |
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<p>The exact naming patterns for Standard MBeans are detailed in |
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the <a href="#spec">JMX Specification</a>.</p> |
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<p>There are two ways to make a Java object that is an MBean |
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with this management interface. One is for the object to be |
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of a class that has exactly the same name as the Java |
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interface but without the <code>MBean</code> suffix. So in |
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the example the object would be of the class |
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<code>Configuration</code>, in the same Java package as |
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<code>ConfigurationMBean</code>. The second way is to use the |
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{@link javax.management.StandardMBean StandardMBean}
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class.</p> |
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<h3>MXBeans</h3> |
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<p>An <em>MXBean</em> is a variant of Standard MBean where complex |
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types are mapped to a standard set of types defined in the |
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{@link javax.management.openmbean} package. MXBeans are appropriate
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if you would otherwise need to reference application-specific |
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classes in your MBean interface. They are described in detail |
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in the specification for {@link javax.management.MXBean MXBean}.</p>
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<h3>Dynamic MBeans</h3> |
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<p>A <em>Dynamic MBean</em> is an MBean that defines its |
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management interface at run-time. For example, a configuration |
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MBean could determine the names and types of the attributes it |
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exposes by parsing an XML file.</p> |
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<p>Any Java object of a class that implements the {@link
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javax.management.DynamicMBean DynamicMBean} interface is a |
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Dynamic MBean.</p> |
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<h3>Open MBeans</h3> |
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<p>An <em>Open MBean</em> is a kind of Dynamic MBean where the |
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types of attributes and of operation parameters and return |
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values are built using a small set of predefined Java classes. |
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Open MBeans facilitate operation with remote management programs |
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that do not necessarily have access to application-specific |
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types, including non-Java programs. Open MBeans are defined by |
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the package <a href="openmbean/package-summary.html"><code> |
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javax.management.openmbean</code></a>.</p> |
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<h3>Model MBeans</h3> |
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<p>A <em>Model MBean</em> is a kind of Dynamic MBean that acts |
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as a bridge between the management interface and the |
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underlying managed resource. Both the management interface and |
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the managed resource are specified as Java objects. The same |
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Model MBean implementation can be reused many times with |
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different management interfaces and managed resources, and it can |
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provide common functionality such as persistence and caching. |
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Model MBeans are defined by the package |
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<a href="modelmbean/package-summary.html"><code> |
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javax.management.modelmbean</code></a>.</p> |
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<h2>MBean Server</h2> |
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<p>To be useful, an MBean must be registered in an <em>MBean |
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Server</em>. An MBean Server is a repository of MBeans. |
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Usually the only access to the MBeans is through the MBean |
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Server. In other words, code no longer accesses the Java |
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object implementing the MBean directly, but instead accesses |
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the MBean by name through the MBean Server. Each MBean has a |
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unique name within the MBean Server, defined by the {@link
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javax.management.ObjectName ObjectName} class.</p> |
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<p>An MBean Server is an object implementing the interface |
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{@link javax.management.MBeanServer MBeanServer}.
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The most convenient MBean Server to use is the |
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<em>Platform MBean Server</em>. This is a |
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single MBean Server that can be shared by different managed |
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components running within the same Java Virtual Machine. The |
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Platform MBean Server is accessed with the method {@link
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java.lang.management.ManagementFactory#getPlatformMBeanServer()}.</p> |
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<p>Application code can also create a new MBean Server, or |
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access already-created MBean Servers, using the {@link
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javax.management.MBeanServerFactory MBeanServerFactory} class.</p> |
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<h3>Creating MBeans in the MBean Server</h3> |
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<p>There are two ways to create an MBean. One is to construct a |
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Java object that will be the MBean, then use the {@link
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javax.management.MBeanServer#registerMBean registerMBean} |
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method to register it in the MBean Server. The other is to |
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create and register the MBean in a single operation using one |
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of the {@link javax.management.MBeanServer#createMBean(String,
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javax.management.ObjectName) createMBean} methods.</p> |
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<p>The <code>registerMBean</code> method is simpler for local |
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use, but cannot be used remotely. The |
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<code>createMBean</code> method can be used remotely, but |
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sometimes requires attention to class loading issues.</p> |
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<p>An MBean can perform actions when it is registered in or |
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unregistered from an MBean Server if it implements the {@link
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javax.management.MBeanRegistration MBeanRegistration} |
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interface.</p> |
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<h3>Accessing MBeans in the MBean Server</h3> |
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<p>Given an <code>ObjectName</code> <code>name</code> and an |
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<code>MBeanServer</code> <code>mbs</code>, you can access |
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attributes and operations as in this example:</p> |
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<pre> |
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int cacheSize = mbs.getAttribute(name, "CacheSize"); |
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{@link javax.management.Attribute Attribute} newCacheSize =
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new Attribute("CacheSize", new Integer(2000));
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mbs.setAttribute(name, newCacheSize); |
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mbs.invoke(name, "save", new Object[0], new Class[0]); |
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</pre> |
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<p id="proxy">Alternatively, if you have a Java interface that |
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corresponds to the management interface for the MBean, you can use an |
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<em>MBean proxy</em> like this:</p> |
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<pre> |
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ConfigurationMBean conf = |
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{@link javax.management.JMX#newMBeanProxy
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JMX.newMBeanProxy}(mbs, name, ConfigurationMBean.class); |
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int cacheSize = conf.getCacheSize(); |
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conf.setCacheSize(2000); |
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conf.save(); |
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</pre> |
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<p>Using an MBean proxy is just a convenience. The second |
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example ends up calling the same <code>MBeanServer</code> |
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operations as the first one.</p> |
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<p>An MBean Server can be queried for MBeans whose names match |
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certain patterns and/or whose attributes meet certain |
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constraints. Name patterns are constructed using the {@link
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javax.management.ObjectName ObjectName} class and constraints |
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are constructed using the {@link javax.management.Query Query}
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class. The methods {@link
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javax.management.MBeanServer#queryNames queryNames} and {@link
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javax.management.MBeanServer#queryMBeans queryMBeans} then |
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perform the query.</p> |
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<h3>MBean lifecycle</h3> |
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<p>An MBean can implement the {@link javax.management.MBeanRegistration
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MBeanRegistration} interface in order to be told when it is registered |
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and unregistered in the MBean Server. Additionally, the {@link
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javax.management.MBeanRegistration#preRegister preRegister} method |
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allows the MBean to get a reference to the <code>MBeanServer</code> |
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object and to get its <code>ObjectName</code> within the MBean |
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Server.</p> |
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<h2>Notifications</h2> |
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<p>A <em>notification</em> is an instance of the {@link
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javax.management.Notification Notification} class or a |
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subclass. In addition to its Java class, it has a |
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<em>type</em> string that can distinguish it from other |
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notifications of the same class.</p> |
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||
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<p>An MBean that will emit notifications must implement the |
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{@link javax.management.NotificationBroadcaster
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NotificationBroadcaster} or {@link
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javax.management.NotificationEmitter NotificationEmitter} |
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interface. Usually, it does this by subclassing |
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{@link javax.management.NotificationBroadcasterSupport
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NotificationBroadcasterSupport} or delegating to an instance of |
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that class. Here is an example:</p> |
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<pre> |
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public class Configuration <b>extends NotificationBroadcasterSupport</b> |
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implements ConfigurationMBean {
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... |
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private void updated() {
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Notification n = new Notification(...); |
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<b>{@link javax.management.NotificationBroadcasterSupport#sendNotification
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sendNotification}(n)</b>; |
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} |
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} |
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</pre> |
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||
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||
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<p>Notifications can be received by a <em>listener</em>, which |
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is an object that implements the {@link
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javax.management.NotificationListener NotificationListener} |
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interface. You can add a listener to an MBean with the method |
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{@link
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javax.management.MBeanServer#addNotificationListener(ObjectName, |
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NotificationListener, NotificationFilter, Object)}. |
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You can optionally supply a <em>filter</em> to this method, to |
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select only notifications of interest. A filter is an object |
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that implements the {@link javax.management.NotificationFilter
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NotificationFilter} interface.</p> |
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<p>An MBean can be a listener for notifications emitted by other |
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MBeans in the same MBean Server. In this case, it implements |
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{@link javax.management.NotificationListener
|
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NotificationListener} and the method {@link
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javax.management.MBeanServer#addNotificationListener(ObjectName, |
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ObjectName, NotificationFilter, Object)} is used to listen.</p> |
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||
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<h2>Remote Access to MBeans</h2> |
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<p>An MBean Server can be accessed remotely through a |
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<em>connector</em>. A connector allows a remote Java |
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application to access an MBean Server in essentially the same |
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way as a local one. The package |
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<a href="remote/package-summary.html"><code> |
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javax.management.remote</code></a> defines connectors.</p> |
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<p>The JMX specification also defines the notion of an |
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<em>adaptor</em>. An adaptor translates between requests in a |
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protocol such as SNMP or HTML and accesses to an MBean Server. |
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So for example an SNMP GET operation might result in a |
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<code>getAttribute</code> on the MBean Server.</p> |
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<h3 id="interop">Interoperability between versions of the JMX |
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specification</h3> |
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<p>When a client connects to a server using the JMX Remote |
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API, it is possible that they do not have the same version |
|
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of the JMX specification. The version of the JMX |
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specification described here is version 1.4. Previous |
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versions were 1.0, 1.1, and 1.2. (There was no 1.3.) |
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The standard JMX Remote API is defined to work with version |
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1.2 onwards, so in standards-based deployment the only |
|
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interoperability questions that arise concern version 1.2 |
|
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onwards.</p> |
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<p>Every version of the JMX specification continues to |
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implement the features of previous versions. So when the |
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client is running an earlier version than the server, there |
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should not be any interoperability concerns.</p> |
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<p>When the client is running a later version than the server, |
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certain newer features may not be available, as detailed in |
|
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the next sections. The client can determine the server's |
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version by examining the {@link
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javax.management.MBeanServerDelegateMBean#getSpecificationVersion |
|
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SpecificationVersion} attribute of the {@code
|
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MBeanServerDelegate}.</p> |
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<h4 id="interop-1.2">If the remote MBean Server is 1.2</h4> |
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<ul> |
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<li><p>You cannot use wildcards in a key property of an |
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{@link javax.management.ObjectName ObjectName}, for
|
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example {@code domain:type=Foo,name=*}. Wildcards that
|
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match whole properties are still allowed, for example |
|
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{@code *:*} or {@code *:type=Foo,*}.</p>
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|
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<li><p>You cannot use {@link
|
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javax.management.Query#isInstanceOf Query.isInstanceOf} |
|
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in a query.</p> |
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|
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<li><p>You cannot use dot syntax such as {@code
|
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HeapMemoryUsage.used} in the {@linkplain
|
|
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javax.management.monitor.Monitor#setObservedAttribute |
|
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observed attribute} of a monitor, as described in the |
|
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documentation for the {@link javax.management.monitor}
|
|
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package.</p> |
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|
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</ul> |
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|
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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> |
| 833 | 394 |
|
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@since 1.5 |
|
| 2 | 396 |
|
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</body> |
|
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</html> |