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| </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="jetty-jmx-annotations"></a>Jetty JMX Annotations</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="section"><a href="jetty-jmx-annotations.html#jmx-annotation-introspection">Annotation Introspection</a></span></dt><dt><span class="section"><a href="jetty-jmx-annotations.html#jmx-managed-object">@ManagedObject</a></span></dt><dt><span class="section"><a href="jetty-jmx-annotations.html#jmx-managed-attribute">@ManagedAttribute</a></span></dt><dt><span class="section"><a href="jetty-jmx-annotations.html#jmx-managed-operation">@ManagedOperation</a></span></dt><dt><span class="section"><a href="jetty-jmx-annotations.html#jmx-name-annotation">@Name</a></span></dt><dt><span class="section"><a href="jetty-jmx-annotations.html#jmx-annotation-example">Example</a></span></dt></dl></div><p>When the <code class="literal">jetty-jmx</code> libraries are present on startup and the wiring is enabled for exposing Jetty MBeans to JMX, there are three annotations that govern when and how MBeans are created and exposed.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="jmx-annotation-introspection"></a>Annotation Introspection</h3></div></div></div><p>When JMX is configured and enabled in Jetty, any time an object is registered with the Server it is introspected as a potential MBean to be exposed. |
| This introspection proceeds as follows assuming the class is named <code class="literal">com.acme.Foo</code>:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">All influences for <code class="literal">com.acme.Foo</code> determined. |
| These include each class in the chain of super classes, and by convention each of these classes following a form of <code class="literal">com.acme.jmx.FooMBean</code>. |
| All super classes and their corresponding MBean representations are then used in the next step.</li><li class="listitem">Each potential influencing class is checked for the <code class="literal">@ManagedObject</code> annotation. |
| Should this annotation exist at any point in the chain of influencers then an MBran is created with the description of the version <code class="literal">@ManagedObject</code> discovered.</li><li class="listitem">Once a MBean has been created for an object then each potential influencing object is introspected for <code class="literal">@ManagedAttribute</code> and <code class="literal">@ManagedOperation</code> annotations and the corresponding type is exposed to the MBean.</li></ol></div><p>The convention of looking for <code class="literal">@ManagedObject</code> annotations on <code class="literal">.jmx.ClassMBean</code> allows for a normal POJOs to be wrapped in an MBean without itself without requiring it being marked up with annotations. |
| Since the POJO is passed to these wrapped derived Mbean instances and is an internal variable then the MBean can be used to better expose a set of attributes and operations that may not have been anticipated when the original object was created.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="jmx-managed-object"></a>@ManagedObject</h3></div></div></div><p>The <code class="literal">@ManagedObject</code> annotation is used on a class at the top level to indicate that it should be exposed as an MBean. |
| It has only one attribute to it which is used as the description of the MBean. |
| Should multiple <code class="literal">@ManagedObject</code> annotations be found in the chain of influence then the first description is used.</p><p>The list of attributes available are:</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">value</span></dt><dd>The description of the Managed Object.</dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="jmx-managed-attribute"></a>@ManagedAttribute</h3></div></div></div><p>The <code class="literal">@ManagedAttribute</code> annotation is used to indicate that a given method exposes a JMX attribute. |
| This annotation is placed always on the reader method of a given attribute. |
| Unless it is marked as read-only in the configuration of the annotation a corresponding setter is looked for following normal naming conventions. |
| For example if this annotation is on a method called <code class="literal">getFoo()</code> then a method called <code class="literal">setFoo()</code> would be looked for and if found wired automatically into the JMX attribute.</p><p>The list of attributes available are:</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">value</span></dt><dd>The description of the Managed Attribute.</dd><dt><span class="term">name</span></dt><dd>The name of the Managed Attribute.</dd><dt><span class="term">proxied</span></dt><dd>Value is true if the corresponding MBean for this object contains the method of this JMX attribute in question.</dd><dt><span class="term">readonly</span></dt><dd>By default this value is false which means that a corresponding setter will be looked for an wired into the attribute should one be found. |
| Setting this to true make the JMX attribute read only.</dd><dt><span class="term">setter</span></dt><dd>This attribute can be used when the corresponding setter for a JMX attribute follows a non-standard naming convention and it should still be exposed as the setter for the attribute.</dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="jmx-managed-operation"></a>@ManagedOperation</h3></div></div></div><p>The <code class="literal">@ManagedOperation</code> annotation is used to indicate that a given method should be considered a JMX operation.</p><p>The list of attributes available are:</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">value</span></dt><dd>The description of the Managed Operation.</dd><dt><span class="term">impact</span></dt><dd>The impact of an operation. |
| By default this value is "UNKNOWN" and acceptable values are "ACTION", "INFO", "ACTION_INFO" and should be used according to their definitions with JMX.</dd><dt><span class="term">proxied</span></dt><dd>Value is true if the corresponding MBean for this object contains the method of this JMX operation in question.</dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="jmx-name-annotation"></a>@Name</h3></div></div></div><p>A fourth annotation is often used in conjunction with the JMX annotations mentioned above. |
| This annotation is used to describe variables in method signatures so that when rendered into tools like JConsole it is clear what the parameters are. |
| For example:</p><p>The list of attributes available are:</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">value</span></dt><dd>The name of the parameter.</dd><dt><span class="term">description</span></dt><dd>The description of the parameter.</dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="jmx-annotation-example"></a>Example</h3></div></div></div><p>The following is an example of each of the annotations mentioned above in practice.</p><pre xmlns:jfetch="java:org.eclipse.jetty.xslt.tools.JavaSourceFetchExtension" xmlns:fetch="java:org.eclipse.jetty.xslt.tools.SourceFetchExtension" xmlns:d="http://docbook.org/ns/docbook" xmlns:l="http://docbook.sourceforge.net/xmlns/l10n/1.0" xmlns:xslthl="http://xslthl.sf.net" xmlns:gcse="http://www.google.com" xmlns:date="http://exslt.org/dates-and-times"><code>package com.acme; |
| |
| import org.eclipse.jetty.util.annotation.ManagedAttribute; |
| import org.eclipse.jetty.util.annotation.ManagedObject; |
| import org.eclipse.jetty.util.annotation.ManagedOperation; |
| import org.eclipse.jetty.util.annotation.Name; |
| |
| @ManagedObject("Test MBean Annotations") |
| public class Derived extends Base implements Signature |
| { |
| String fname="Full Name"; |
| |
| @ManagedAttribute(value="The full name of something", name="fname") |
| public String getFullName() |
| { |
| return fname; |
| } |
| |
| public void setFullName(String name) |
| { |
| fname=name; |
| } |
| |
| @ManagedOperation("Doodle something") |
| public void doodle(@Name(value="doodle", description="A description of the argument") String doodle) |
| { |
| System.err.println("doodle "+doodle); |
| } |
| }</code></pre></div></div><script type="text/javascript"> |
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