public class MLet extends URLClassLoader implements MLetMBean, MBeanRegistration, Externalizable
Allows you to instantiate and register one or several MBeans in the MBean server coming from a remote URL. M-let is a shortcut for management applet. The m-let service does this by loading an m-let text file, which specifies information on the MBeans to be obtained. The information on each MBean is specified in a single instance of a tag, called the MLET tag. The location of the m-let text file is specified by a URL.
The MLET tag has the following syntax:
<MLET
CODE = class | OBJECT = serfile
ARCHIVE = "archiveList"
[CODEBASE = codebaseURL]
[NAME = mbeanname]
[VERSION = version]
>
[arglist]
</MLET>
where:
CODE = class
.class file of the MBean must be contained in one of the .jar files specified by the ARCHIVE attribute. Either CODE or OBJECT must be present. OBJECT = serfile
.ser file that contains a serialized representation of the MBean to be obtained. This file must be contained in one of the .jar files specified by the ARCHIVE attribute. If the .jar file contains a directory hierarchy, specify the path of the file within this hierarchy. Otherwise a match will not be found. Either CODE or OBJECT must be present. ARCHIVE = "archiveList"
.jar files containing MBeans or other resources used by the MBean to be obtained. One of the .jar files must contain the file specified by the CODE or OBJECT attribute. If archivelist contains more than one file: .jar files in archivelist must be stored in the directory specified by the code base URL. CODEBASE = codebaseURL
.jar files specified by the ARCHIVE attribute. Specify this attribute only if the .jar files are not in the same directory as the m-let text file. If this attribute is not specified, the base URL of the m-let text file is used. NAME = mbeanname
MBeanServer.getDefaultDomain(). VERSION = version
.jar files to be obtained. This version number can be used to specify that the .jar files are loaded from the server to update those stored locally in the cache the next time the m-let text file is loaded. version must be a series of non-negative decimal integers each separated by a period from the one that precedes it. ARG TYPE=argumentType VALUE=value>The arguments' type in the argument list should be a Java primitive type or a Java basic type (java.lang.Boolean, java.lang.Byte, java.lang.Short, java.lang.Long, java.lang.Integer, java.lang.Float, java.lang.Double, java.lang.String).
The m-let service extends the java.net.URLClassLoader and can be used to load remote classes and jar files in the VM of the agent.
Note - The MLet class loader uses the MBeanServerFactory.getClassLoaderRepository(javax.management.MBeanServer) to load classes that could not be found in the loaded jar files.
public MLet()
Constructs a new MLet using the default delegation parent ClassLoader.
public MLet(URL[] urls)
Constructs a new MLet for the specified URLs using the default delegation parent ClassLoader. The URLs will be searched in the order specified for classes and resources after first searching in the parent class loader.
urls - The URLs from which to load classes and resources.public MLet(URL[] urls,
ClassLoader parent) Constructs a new MLet for the given URLs. The URLs will be searched in the order specified for classes and resources after first searching in the specified parent class loader. The parent argument will be used as the parent class loader for delegation.
urls - The URLs from which to load classes and resources.parent - The parent class loader for delegation.public MLet(URL[] urls,
ClassLoader parent,
URLStreamHandlerFactory factory) Constructs a new MLet for the specified URLs, parent class loader, and URLStreamHandlerFactory. The parent argument will be used as the parent class loader for delegation. The factory argument will be used as the stream handler factory to obtain protocol handlers when creating new URLs.
urls - The URLs from which to load classes and resources.parent - The parent class loader for delegation.factory - The URLStreamHandlerFactory to use when creating URLs.public MLet(URL[] urls,
boolean delegateToCLR) Constructs a new MLet for the specified URLs using the default delegation parent ClassLoader. The URLs will be searched in the order specified for classes and resources after first searching in the parent class loader.
urls - The URLs from which to load classes and resources.delegateToCLR - True if, when a class is not found in either the parent ClassLoader or the URLs, the MLet should delegate to its containing MBeanServer's ClassLoaderRepository.public MLet(URL[] urls,
ClassLoader parent,
boolean delegateToCLR) Constructs a new MLet for the given URLs. The URLs will be searched in the order specified for classes and resources after first searching in the specified parent class loader. The parent argument will be used as the parent class loader for delegation.
urls - The URLs from which to load classes and resources.parent - The parent class loader for delegation.delegateToCLR - True if, when a class is not found in either the parent ClassLoader or the URLs, the MLet should delegate to its containing MBeanServer's ClassLoaderRepository.public MLet(URL[] urls,
ClassLoader parent,
URLStreamHandlerFactory factory,
boolean delegateToCLR) Constructs a new MLet for the specified URLs, parent class loader, and URLStreamHandlerFactory. The parent argument will be used as the parent class loader for delegation. The factory argument will be used as the stream handler factory to obtain protocol handlers when creating new URLs.
urls - The URLs from which to load classes and resources.parent - The parent class loader for delegation.factory - The URLStreamHandlerFactory to use when creating URLs.delegateToCLR - True if, when a class is not found in either the parent ClassLoader or the URLs, the MLet should delegate to its containing MBeanServer's ClassLoaderRepository.public void addURL(URL url)
Appends the specified URL to the list of URLs to search for classes and resources.
addURL in interface MLetMBean
addURL in class URLClassLoader
url - the URL to be added to the search path of URLspublic void addURL(String url)
throws ServiceNotFoundException Appends the specified URL to the list of URLs to search for classes and resources.
addURL in interface MLetMBean
url - the URL to add.ServiceNotFoundException - The specified URL is malformed.public URL[] getURLs()
Returns the search path of URLs for loading classes and resources. This includes the original list of URLs specified to the constructor, along with any URLs subsequently appended by the addURL() method.
getURLs in interface MLetMBean
getURLs in class URLClassLoader
public Set<Object> getMBeansFromURL(URL url)
throws ServiceNotFoundException Loads a text file containing MLET tags that define the MBeans to be added to the MBean server. The location of the text file is specified by a URL. The MBeans specified in the MLET file will be instantiated and registered in the MBean server.
getMBeansFromURL in interface MLetMBean
url - The URL of the text file to be loaded as URL object.ServiceNotFoundException - One of the following errors has occurred: The m-let text file does not contain an MLET tag, the m-let text file is not found, a mandatory attribute of the MLET tag is not specified, the value of url is null.IllegalStateException - MLet MBean is not registered with an MBeanServer.public Set<Object> getMBeansFromURL(String url)
throws ServiceNotFoundException Loads a text file containing MLET tags that define the MBeans to be added to the MBean server. The location of the text file is specified by a URL. The MBeans specified in the MLET file will be instantiated and registered in the MBean server.
getMBeansFromURL in interface MLetMBean
url - The URL of the text file to be loaded as String object.ServiceNotFoundException - One of the following errors has occurred: The m-let text file does not contain an MLET tag, the m-let text file is not found, a mandatory attribute of the MLET tag is not specified, the url is malformed.IllegalStateException - MLet MBean is not registered with an MBeanServer.public String getLibraryDirectory()
Gets the current directory used by the library loader for storing native libraries before they are loaded into memory.
getLibraryDirectory in interface MLetMBean
UnsupportedOperationException - if this implementation does not support storing native libraries in this way.setLibraryDirectory(java.lang.String)public void setLibraryDirectory(String libdir)
Sets the directory used by the library loader for storing native libraries before they are loaded into memory.
setLibraryDirectory in interface MLetMBean
libdir - The directory used by the library loader.UnsupportedOperationException - if this implementation does not support storing native libraries in this way.getLibraryDirectory()public ObjectName preRegister(MBeanServer server,
ObjectName name)
throws Exception Allows the m-let to perform any operations it needs before being registered in the MBean server. If the ObjectName is null, the m-let provides a default name for its registration <defaultDomain>:type=MLet
preRegister in interface MBeanRegistration
server - The MBean server in which the m-let will be registered.name - The object name of the m-let.Exception - This exception should be caught by the MBean server and re-thrown as an MBeanRegistrationException.public void postRegister(Boolean registrationDone)
Allows the m-let to perform any operations needed after having been registered in the MBean server or after the registration has failed.
postRegister in interface MBeanRegistration
registrationDone - Indicates whether or not the m-let has been successfully registered in the MBean server. The value false means that either the registration phase has failed.public void preDeregister()
throws Exception Allows the m-let to perform any operations it needs before being unregistered by the MBean server.
preDeregister in interface MBeanRegistration
Exception - This exception should be caught by the MBean server and re-thrown as an MBeanRegistrationException.public void postDeregister()
Allows the m-let to perform any operations needed after having been unregistered in the MBean server.
postDeregister in interface MBeanRegistration
public void writeExternal(ObjectOutput out)
throws IOException,
UnsupportedOperationException Save this MLet's contents to the given ObjectOutput. Not all implementations support this method. Those that do not throw UnsupportedOperationException. A subclass may override this method to support it or to change the format of the written data.
The format of the written data is not specified, but if an implementation supports writeExternal(java.io.ObjectOutput) it must also support readExternal(java.io.ObjectInput) in such a way that what is written by the former can be read by the latter.
writeExternal in interface Externalizable
out - The object output stream to write to.IOException - If a problem occurred while writing.UnsupportedOperationException - If this implementation does not support this operation.public void readExternal(ObjectInput in)
throws IOException,
ClassNotFoundException,
UnsupportedOperationException Restore this MLet's contents from the given ObjectInput. Not all implementations support this method. Those that do not throw UnsupportedOperationException. A subclass may override this method to support it or to change the format of the read data.
The format of the read data is not specified, but if an implementation supports readExternal(java.io.ObjectInput) it must also support writeExternal(java.io.ObjectOutput) in such a way that what is written by the latter can be read by the former.
readExternal in interface Externalizable
in - The object input stream to read from.IOException - if a problem occurred while reading.ClassNotFoundException - if the class for the object being restored cannot be found.UnsupportedOperationException - if this implementation does not support this operation.public Class<?> loadClass(String name,
ClassLoaderRepository clr)
throws ClassNotFoundException Load a class, using the given ClassLoaderRepository if the class is not found in this MLet's URLs. The given ClassLoaderRepository can be null, in which case a ClassNotFoundException occurs immediately if the class is not found in this MLet's URLs.
name - The name of the class we want to load.clr - The ClassLoaderRepository that will be used to search for the given class, if it is not found in this ClassLoader. May be null.ClassNotFoundException - The specified class could not be found in this ClassLoader nor in the given ClassLoaderRepository.protected Class<?> findClass(String name)
throws ClassNotFoundException This is the main method for class loaders that is being redefined.
findClass in class URLClassLoader
name - The name of the class.ClassNotFoundException - The specified class could not be found.protected String findLibrary(String libname)
Returns the absolute path name of a native library. The VM invokes this method to locate the native libraries that belong to classes loaded with this class loader. Libraries are searched in the JAR files using first just the native library name and if not found the native library name together with the architecture-specific path name (OSName/OSArch/OSVersion/lib/nativelibname), i.e.
the library stat on Solaris SPARC 5.7 will be searched in the JAR file as:
More specifically, let nativelibname be the result of System.mapLibraryName(libname). Then the following names are searched in the JAR files, in order:
nativelibname
<os.name>/<os.arch>/<os.version>/lib/nativelibname
where <X> means System.getProperty(X) with any spaces in the result removed, and / stands for the file separator character (File.separator).
If this method returns null, i.e. the libraries were not found in any of the JAR files loaded with this class loader, the VM searches the library along the path specified as the java.library.path property.
findLibrary in class ClassLoader
libname - The library name.System.loadLibrary(String), System.mapLibraryName(String)
protected URL check(String version,
URL codebase,
String jarfile,
MLetContent mlet)
throws Exception This method is to be overridden when extending this service to support caching and versioning. It is called from getMBeansFromURL when the version, codebase, and jarfile have been extracted from the MLet file, and can be used to verify that it is all right to load the given MBean, or to replace the given URL with a different one.
The default implementation of this method returns codebase unchanged.
version - The version number of the .jar file stored locally.codebase - The base URL of the remote .jar file.jarfile - The name of the .jar file to be loaded.mlet - The MLetContent instance that represents the MLET tag.Exception - if the MBean is not to be loaded for some reason. The exception will be added to the set returned by getMBeansFromURL.
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