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Diffstat (limited to 'javax')
-rw-r--r-- | javax/management/package.html | 197 | ||||
-rw-r--r-- | javax/management/remote/package.html | 53 |
2 files changed, 250 insertions, 0 deletions
diff --git a/javax/management/package.html b/javax/management/package.html new file mode 100644 index 000000000..3543eec90 --- /dev/null +++ b/javax/management/package.html @@ -0,0 +1,197 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> +<!-- package.html - describes classes in javax.management package. + Copyright (C) 2007 Free Software Foundation, Inc. + +This file is part of GNU Classpath. + +GNU Classpath is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 2, or (at your option) +any later version. + +GNU Classpath is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +General Public License for more details. + +You should have received a copy of the GNU General Public License +along with GNU Classpath; see the file COPYING. If not, write to the +Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA +02110-1301 USA. + +Linking this library statically or dynamically with other modules is +making a combined work based on this library. Thus, the terms and +conditions of the GNU General Public License cover the whole +combination. + +As a special exception, the copyright holders of this library give you +permission to link this library with independent modules to produce an +executable, regardless of the license terms of these independent +modules, and to copy and distribute the resulting executable under +terms of your choice, provided that you also meet, for each linked +independent module, the terms and conditions of the license of that +module. An independent module is a module which is not derived from +or based on this library. If you modify this library, you may extend +this exception to your version of the library, but you are not +obligated to do so. If you do not wish to do so, delete this +exception statement from your version. --> + +<html> +<head><title>GNU Classpath - javax.management</title></head> + +<body> + +<p> +Provides the core classes for the Java Management Extensions (JMX). This API +builds on the notion of Java beans by providing a layer of abstraction between +the beans themselves and the method of accessing them. Instead of being accessed +directly, management beans or <strong>MBeans</strong> are usually accessed via +a management server (an implementation of the @see MBeanServer interface). Thus, +the bean itself may be a simple Java object or it may be something +more complicated (for example, the server may map from Java to SNMP). The server may +also retrieve the bean from some remote location rather than using a local object. +</p> +<p> +Management beans are usually used for monitoring and/or configuration +of a particular entity. For example, the platform management beans +found in the @see java.lang.management package allow the user +to obtain information about the operating system, current memory usage, etc. +as well as turning on and off certain additional facilities. To this end, +an MBean consists of: +</p> +<ul> +<li><emph>attributes</emph> that may be read and/or written to.</li> +<li><emph>operations</emph> which may be performed.</li> +<li><emph>notifications</emph> that may emitted by the bean and listened for by users.</li> +</ul> +<p> +The most common type of management bean is the @see StandardMBean, A standard MBean +relies on the naming patterns established by the JavaBeans framework; the value of an +attribute <code>name</code> is retrieved by an accessor method named <code>getName</code> +and changed by a mutator method called <code>setName</code>. If the mutator is absent, +the attribute is read only. Naming is also used to associate the implementation of a +bean with its interface; an bean <code>Person</code> is assumed to be an implementation +of the interface <code>PersonMBean</code> (and vice versa). To avoid these naming constraints, +the @see StandardMBean class may be used. +</p> +<p> +<h2>Types of Beans</h2> +<p> +The @see StandardMBean class is one example of a @see DynamicMBean where the attributes and +operations of the bean are provided dynamically via the methods provided. With the +@see StandardMBean class, this simply means that the class uses reflection to access the +appropriate methods of the bean implementation. In a more complex scenario, the bean's +data could be supplied from a file or over the network. +</p> +<p> +Once we start talking about accessing beans over network and platform boundaries, we run +in to the issue of how to deal with the types utilised by these beans. Simple types, such +as numbers and strings, are usually fine but more complex types need special treatment. +An <emph>Open MBean</emph> is one that only uses a specific set of types defined in the +@see javax.management.openmbean package, allowing both sides of a remote connection to provide +this subset of types and thus interact. An @see MXBean goes a stage further, and defines +a method whereby a normal Java MBean may become an Open MBean by performing a defined mapping +on the types of the bean. For example, a @see java.util.List or @see java.util.Set of a +particular type becomes an array of the same type. +</p> +<h2>Accessing Beans</h2> +<p> +Although beans can be accessed like normal objects, the normal way of accessing them is +via an @see MBeanServer. This provides the abstraction from the bean's implementation to +a set of attributes, operations and notifications. The server identifies each bean via +an @see ObjectName. This name is unique to a particular bean and is used to identify the +bean when retrieving the value of an attribute or invoking an operation. Essentially, most +methods provided by the server are the same as those provided by the @see DynamicMBean +interface, except that each takes this additional @link ObjectName parameter to identify the +bean being accessed. +</p> +<p> +The @see MBeanServerFactory keeps track of the current MBean servers in use and allows new +ones to be created. A special @see MBeanServer instance, called the <emph>platform MBean +server</emph>, is created when the Java virtual machine is started and a reference to this +may be obtained from the @see ManagementFactory using +@see ManagementFactory#getPlatformMBeanServer(). This primarily exists for the purpose of +creating and registering the platform MBeans, described in @see java.lang.management, which +provide access to information about the underlying operating system, memory usage, the behaviour +of the garbage collector, etc. but is equally suitable for creating and registering your own +beans. Alternatively, a server instance may be obtained from the @see MBeanServerFactory. +</p> +<p> +A bean obtains an @link ObjectName by registering with the server. This operation can be +performed either by passing an existing instance to the @see MBeanServer#registerMBean method +or by using the @see MBeanServer#createMBean method to simultaneously create the bean and +register it with the server. During the registration process, the bean may perform some +arbitrary behaviour if it implements the @link MBeanRegistration interface. The same is +true when unregistering a bean. +</p> +<p> +To actually access the attributes and operations of a bean via the server, we use code +like the following: +</p> +<pre> +// First we obtain the platform MBean server which has the platform MBeans registered +MBeanServer server = ManagementFactory.getPlatformMBeanServer(); +// We also need the object name of the memory bean so we can address it +ObjectName name = new ObjectName(ManagementFactory.MEMORY_MXBEAN_NAME); +// Next we obtain the value of the 'verbose' attribute +// What actually happens here is that the server invokes the 'isVerbose' method of +// the MemoryMXBean +boolean verbose = server.getAttribute(name, "verbose"); +// We can also set the value of verbose. Again the server is actually performing +// a setVerbose(val) on the bean but we don't need to know this. +Attribute attrib = new Attribute("verbose", true); +server.setAttribute(name, attrib); +// We can also invoke the 'gc' operation which calls the garbage collector. +server.invoke(name, "gc", new Object[]{}, new String[]{}); +</pre> +<p> +As noted above, the server is simply making basic method calls on the object using +reflection. However, the server provides a layer of abstraction which means that something +more complicated could actually be going on. The lines above are equally applicable, for +example, if <code>server</code> is instead an @see MBeanServerConnection connecting us +to a distant computer. +</p> +<p> +This rather hideous code can be simplified back into simple method calls on an object, +so that we get the best of both worlds. This is achieved using a <emph>MBean proxy</emph>: +<pre> +MBeanServer server = ManagementFactory.getPlatformMBeanServer(); +ObjectName name = new ObjectName(ManagementFactory.MEMORY_MXBEAN_NAME); +MemoryMXBean bean = JMX.newMBeanProxy(server, name, MemoryMXBean.class); +boolean verbose = bean.isVerbose(); +bean.setVerbose(true); +bean.gc(); +</pre> +<p> +See how much simpler the operations are? The proxy handles the task of translating the method +calls into appropriate invocations of methods on the server, simplifying the code for the user. +</p> +<p> +Finally, we have assumed in the code above that the @see ObjectName of the bean is known. +If this is not the case, then the server's database can be searched. The @see Query class +provides appropriate operators (e.g. boolean (and,or), value comparison (>, <)) for +building up relatively complex queries. Once constructed, a query may be passed to either +the @see MBeanServer#queryNames or @see MBeanServer#queryMBeans to obtain an appropriate +set of @see ObjectName or MBean instances. +</p> +<h2>Notifications</h2> +<p> +MBeans also have the capability to emit events. Beans which do so implement either the +@see NotificationBroadcaster or @see NotificationEmitter interface (the difference between +the two is simply the existence of a better removal method in the newer +@see NotificationEmitter interface, which otherwise extends @see NotificationBroadcaster), +usually by extending the @see NotificationBroadcasterSupport class. As is usual with event +handling, other classes may <emph>signup</emph> to receive events via the +@see NotificationListener interface. The signup process can include registering a filter +(an implementation of @see NotificationFilter) so that only certain events reach the +listener and others are discarded. +</p> +<h2>Remote Access</h2> +<p> +The subpackage @see javax.management.remote provides facilities to access remote MBean +servers. This consists of a <emph>connector</emph> framework which abstracts the method +of accessing remote servers from the actual implementation, so that the same method is +used to connect to a remote server, regardless of how it is accessed. +</p> +</body> +</html> diff --git a/javax/management/remote/package.html b/javax/management/remote/package.html new file mode 100644 index 000000000..f1d469f3a --- /dev/null +++ b/javax/management/remote/package.html @@ -0,0 +1,53 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> +<!-- package.html - describes classes in javax.management.remote package. + Copyright (C) 2006 Free Software Foundation, Inc. + +This file is part of GNU Classpath. + +GNU Classpath is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 2, or (at your option) +any later version. + +GNU Classpath is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +General Public License for more details. + +You should have received a copy of the GNU General Public License +along with GNU Classpath; see the file COPYING. If not, write to the +Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA +02110-1301 USA. + +Linking this library statically or dynamically with other modules is +making a combined work based on this library. Thus, the terms and +conditions of the GNU General Public License cover the whole +combination. + +As a special exception, the copyright holders of this library give you +permission to link this library with independent modules to produce an +executable, regardless of the license terms of these independent +modules, and to copy and distribute the resulting executable under +terms of your choice, provided that you also meet, for each linked +independent module, the terms and conditions of the license of that +module. An independent module is a module which is not derived from +or based on this library. If you modify this library, you may extend +this exception to your version of the library, but you are not +obligated to do so. If you do not wish to do so, delete this +exception statement from your version. --> + +<html> +<head><title>GNU Classpath - javax.management.remote</title></head> + +<body> + +<p> +Provides a framework for accessing remote MBean servers. The JMX +remote API introduces the notion of a <emph>connector</emph>. On +the server side, the connector wraps the MBean server, processing +calls from remote clients. The client sends its requests via +a connector which is responsible for transmitting the request +to the server. +</p> +</body> +</html> |