collectd-java - Documentation of collectd's "java plugin"

Florian Forster <octo at collectd.org> 5.12.0.git 2025-08-07 COLLECTD-JAVA(5)

A short outline of this plugin's configuration can be seen in "SYNOPSIS" above. For a complete list of all configuration options and their semantics please read "Plugin "java"" in collectd.conf(5).

The Java plugin embeds a JavaVirtualMachine (JVM) into collectd and provides a Java interface to part of collectd's API. This makes it possible to write additions to the daemon in Java. This plugin is similar in nature to, but shares no code with, the Perl plugin by Sebastian Harl, see collectd-perl(5) for details.

This short example demonstrates how to register a read callback with the daemon: import org.collectd.api.Collectd; import org.collectd.api.ValueList; import org.collectd.api.CollectdReadInterface; public class Foobar implements CollectdReadInterface { public Foobar () { Collectd.registerRead ("Foobar", this); } public int read () { ValueList vl; /* Do something... */ Collectd.dispatchValues (vl); } }

All collectd API functions that are available to Java plugins are implemented as publicstatic functions of the Collectd class. This makes calling these functions pretty straight forward. For example, to send an error message to the daemon, you'd do something like this: Collectd.logError ("That wasn't chicken!"); The following are the currently exported functions. registerConfig Signature: intregisterConfig (String name, CollectdConfigInterface object); Registers the config function of object with the daemon. Returns zero upon success and non-zero when an error occurred. See "config callback" below. registerInit Signature: intregisterInit (String name, CollectdInitInterface object); Registers the init function of object with the daemon. Returns zero upon success and non-zero when an error occurred. See "init callback" below. registerRead Signature: intregisterRead (String name, CollectdReadInterface object) Registers the read function of object with the daemon. Returns zero upon success and non-zero when an error occurred. See "read callback" below. registerWrite Signature: intregisterWrite (String name, CollectdWriteInterface object) Registers the write function of object with the daemon. Returns zero upon success and non-zero when an error occurred. See "write callback" below. registerFlush Signature: intregisterFlush (String name, CollectdFlushInterface object) Registers the flush function of object with the daemon. Returns zero upon success and non-zero when an error occurred. See "flush callback" below. registerShutdown Signature: intregisterShutdown (String name, CollectdShutdownInterface object); Registers the shutdown function of object with the daemon. Returns zero upon success and non-zero when an error occurred. See "shutdown callback" below. registerLog Signature: intregisterLog (String name, CollectdLogInterface object); Registers the log function of object with the daemon. Returns zero upon success and non-zero when an error occurred. See "log callback" below. registerNotification Signature: intregisterNotification (String name, CollectdNotificationInterface object); Registers the notification function of object with the daemon. Returns zero upon success and non-zero when an error occurred. See "notification callback" below. registerMatch Signature: intregisterMatch (String name, CollectdMatchFactoryInterface object); Registers the createMatch function of object with the daemon. Returns zero upon success and non-zero when an error occurred. See "match callback" below. registerTarget Signature: intregisterTarget (String name, CollectdTargetFactoryInterface object); Registers the createTarget function of object with the daemon. Returns zero upon success and non-zero when an error occurred. See "target callback" below. dispatchValues Signature: intdispatchValues (ValueList) Passes the values represented by the ValueList object to the "plugin_dispatch_values" function of the daemon. The "data set" (or list of "data sources") associated with the object are ignored, because "plugin_dispatch_values" will automatically lookup the required data set. It is therefore absolutely okay to leave this blank. Returns zero upon success or non-zero upon failure. getDS Signature: DataSetgetDS (String) Returns the appropriate type or null if the type is not defined. logError Signature: voidlogError (String) Sends a log message with severity ERROR to the daemon. logWarning Signature: voidlogWarning (String) Sends a log message with severity WARNING to the daemon. logNotice Signature: voidlogNotice (String) Sends a log message with severity NOTICE to the daemon. logInfo Signature: voidlogInfo (String) Sends a log message with severity INFO to the daemon. logDebug Signature: voidlogDebug (String) Sends a log message with severity DEBUG to the daemon.

collectd-java - Documentation of collectd's "java plugin"

When writing additions for collectd in Java, the underlying C base is mostly hidden from you. All complex data types are converted to their Java counterparts before they're passed to your functions. These Java classes reside in the org.collectd.api namespace. The Java plugin will create one object of each class configured with the LoadPlugin option. The constructor of this class can then register "callback methods", i. e. methods that will be called by the daemon when appropriate. The available classes are: org.collectd.api.Collectd All API functions exported to Java are implemented as static functions of this class. See "EXPORTED API FUNCTIONS" below. org.collectd.api.OConfigValue Corresponds to "oconfig_value_t", defined in src/liboconfig/oconfig.h. org.collectd.api.OConfigItem Corresponds to "oconfig_item_t", defined in src/liboconfig/oconfig.h. org.collectd.api.DataSource Corresponds to "data_source_t", defined in src/plugin.h. org.collectd.api.DataSet Corresponds to "data_set_t", defined in src/plugin.h. org.collectd.api.ValueList Corresponds to "value_list_t", defined in src/plugin.h. org.collectd.api.Notification Corresponds to "notification_t", defined in src/plugin.h. In the remainder of this document, we'll use the short form of these names, for example ValueList. In order to be able to use these abbreviated names, you need to import the classes.

The following plugins are implemented in Java. Both, the LoadPlugin option and the Plugin block must be inside the <Pluginjava> block (see above). GenericJMXplugin The GenericJMX plugin reads ManagedBeans (MBeans) from an MBeanServer using JMX. JMX is a generic framework to provide and query various management information. The interface is used by Java processes to provide internal statistics as well as by the JavaVirtualMachine (JVM) to provide information about the memory used, threads and so on. The configuration of the GenericJMXplugin consists of two blocks: MBean blocks that define a mapping of MBean attributes to the “types” used by collectd, and Connection blocks which define the parameters needed to connect to an MBeanServer and what data to collect. The configuration of the SNMPplugin is similar in nature, in case you know it. MBeanblocksMBean blocks specify what data is retrieved from MBeans and how that data is mapped on the collectd data types. The block requires one string argument, a name. This name is used in the Connection blocks (see below) to refer to a specific MBean block. Therefore, the names must be unique. The following options are recognized within MBean blocks: ObjectNamepattern Sets the pattern which is used to retrieve MBeans from the MBeanServer. If more than one MBean is returned you should use the InstanceFrom option (see below) to make the identifiers unique. See also: <http://java.sun.com/javase/6/docs/api/javax/management/ObjectName.html> InstancePrefixprefix Prefixes the generated plugininstance with prefix. (optional)InstanceFromproperty The objectnames used by JMX to identify MBeans include so called “properties” which are basically key-value-pairs. If the given object name is not unique and multiple MBeans are returned, the values of those properties usually differ. You can use this option to build the plugininstance from the appropriate property values. This option is optional and may be repeated to generate the plugininstance from multiple property values. <value/> blocks The value blocks map one or more attributes of an MBean to a value list in collectd. There must be at least one Value block within each MBean block. Type type Sets the data set used within collectd to handle the values of the MBean attribute. InstancePrefixprefix Works like the option of the same name directly beneath the MBean block, but sets the type instance instead. (optional)InstanceFromprefix Works like the option of the same name directly beneath the MBean block, but sets the type instance instead. (optional)PluginNamename When set, overrides the default setting for the plugin field ("GenericJMX"). Tabletrue|false Set this to true if the returned attribute is a compositetype. If set to true, the keys within the compositetype is appended to the typeinstance. Attributepath Sets the name of the attribute from which to read the value. You can access the keys of composite types by using a dot to concatenate the key name to the attribute name. For example: “attrib0.key42”. If Table is set to truepath must point to a compositetype, otherwise it must point to a numeric type. Connectionblocks Connection blocks specify how to connect to an MBeanServer and what data to retrieve. The following configuration options are available: Hostname Host name used when dispatching the values to collectd. The option sets this field only, it is not used to connect to anything and doesn't need to be a real, resolvable name. ServiceURLURL Specifies how the MBeanServer can be reached. Any string accepted by the JMXServiceURL is valid. See also: <http://java.sun.com/javase/6/docs/api/javax/management/remote/JMXServiceURL.html> Username Use name to authenticate to the server. If not configured, “monitorRole” will be used. Passwordpassword Use password to authenticate to the server. If not given, unauthenticated access is used. InstancePrefixprefix Prefixes the generated plugininstance with prefix. If a second InstancePrefix is specified in a referenced MBean block, the prefix specified in the Connection block will appear at the beginning of the plugininstance, the prefix specified in the MBean block will be appended to it. Collectmbean_block_name Configures which of the MBean blocks to use with this connection. May be repeated to collect multiple MBeans from this server.

When starting up, collectd creates an object of each configured class. The constructor of this class should then register "callbacks" with the daemon, using the appropriate static functions in Collectd, see "EXPORTED API FUNCTIONS" above. To register a callback, the object being passed to one of the register functions must implement an appropriate interface, which are all in the org.collectd.api namespace. A constructor may register any number of these callbacks, even none. An object without callback methods is never actively called by collectd, but may still call the exported API functions. One could, for example, start a new thread in the constructor and dispatch (submit to the daemon) values asynchronously, whenever one is available. Each callback method is now explained in more detail: configcallback Interface: org.collectd.api.CollectdConfigInterface Signature: intconfig (OConfigItem ci) This method is passed a OConfigItem object, if both, method and configuration, are available. OConfigItem is the root of a tree representing the configuration for this plugin. The root itself is the representation of the <Plugin/> block, so in next to all cases the children of the root are the first interesting objects. To signal success, this method has to return zero. Anything else will be considered an error condition and the plugin will be disabled entirely. See "registerConfig" above. initcallback Interface: org.collectd.api.CollectdInitInterface Signature: intinit () This method is called after the configuration has been handled. It is supposed to set up the plugin. e. g. start threads, open connections, or check if can do anything useful at all. To signal success, this method has to return zero. Anything else will be considered an error condition and the plugin will be disabled entirely. See "registerInit" above. readcallback Interface: org.collectd.api.CollectdReadInterface Signature: intread () This method is called periodically and is supposed to gather statistics in whatever fashion. These statistics are represented as a ValueList object and sent to the daemon using dispatchValues. To signal success, this method has to return zero. Anything else will be considered an error condition and cause an appropriate message to be logged. Currently, returning non-zero does not have any other effects. In particular, Java "read"-methods are not suspended for increasing intervals like C "read"-functions. See "registerRead" above. writecallback Interface: org.collectd.api.CollectdWriteInterface Signature: intwrite (ValueList vl) This method is called whenever a value is dispatched to the daemon. The corresponding C "write"-functions are passed a "data_set_t", so they can decide which values are absolute values (gauge) and which are counter values. To get the corresponding "List<DataSource>", call the getDataSource method of the ValueList object. To signal success, this method has to return zero. Anything else will be considered an error condition and cause an appropriate message to be logged. See "registerWrite" above. flushcallback Interface: org.collectd.api.CollectdFlushInterface Signature: intflush (int timeout, String identifier) This method is called when the daemon received a flush command. This can either be done using the "USR1" signal (see collectd(1)) or using the unixsock plugin (see collectd-unixsock(5)). If timeout is greater than zero, only values older than this number of seconds should be flushed. To signal that all values should be flushed regardless of age, this argument is set to a negative number. The identifier specifies which value should be flushed. If it is not possible to flush one specific value, flush all values. To signal that all values should be flushed, this argument is set to null. To signal success, this method has to return zero. Anything else will be considered an error condition and cause an appropriate message to be logged. See "registerFlush" above. shutdowncallback Interface: org.collectd.api.CollectdShutdownInterface Signature: intshutdown () This method is called when the daemon is shutting down. You should not rely on the destructor to clean up behind the object but use this function instead. To signal success, this method has to return zero. Anything else will be considered an error condition and cause an appropriate message to be logged. See "registerShutdown" above. logcallback Interface: org.collectd.api.CollectdLogInterface Signature: voidlog (int severity, String message) This callback can be used to receive log messages from the daemon. The argument severity is one of: • org.collectd.api.Collectd.LOG_ERR • org.collectd.api.Collectd.LOG_WARNING • org.collectd.api.Collectd.LOG_NOTICE • org.collectd.api.Collectd.LOG_INFO • org.collectd.api.Collectd.LOG_DEBUG The function does not return any value. See "registerLog" above. notificationcallback Interface: org.collectd.api.CollectdNotificationInterface Signature: intnotification (Notification n) This callback can be used to receive notifications from the daemon. To signal success, this method has to return zero. Anything else will be considered an error condition and cause an appropriate message to be logged. See "registerNotification" above. matchcallback The match (and target, see "target callback" below) callbacks work a bit different from the other callbacks above: You don't register a match callback with the daemon directly, but you register a function which, when called, creates an appropriate object. The object creating the "match" objects is called "match factory". See "registerMatch" above. Factoryobject Interface: org.collectd.api.CollectdMatchFactoryInterface Signature: CollectdMatchInterfacecreateMatch (OConfigItem ci); Called by the daemon to create "match" objects. Returns: A new object which implements the CollectdMatchInterface interface. Matchobject Interface: org.collectd.api.CollectdMatchInterface Signature: intmatch (DataSet ds, ValueList vl); Called when processing a chain to determine whether or not a ValueList matches. How values are matches is up to the implementing class. Has to return one of: • Collectd.FC_MATCH_NO_MATCH • Collectd.FC_MATCH_MATCHEStargetcallback The target (and match, see "match callback" above) callbacks work a bit different from the other callbacks above: You don't register a target callback with the daemon directly, but you register a function which, when called, creates an appropriate object. The object creating the "target" objects is called "target factory". See "registerTarget" above. Factoryobject Interface: org.collectd.api.CollectdTargetFactoryInterface Signature: CollectdTargetInterfacecreateTarget (OConfigItem ci); Called by the daemon to create "target" objects. Returns: A new object which implements the CollectdTargetInterface interface. Targetobject Interface: org.collectd.api.CollectdTargetInterface Signature: intinvoke (DataSet ds, ValueList vl); Called when processing a chain to perform some action. The action performed is up to the implementing class. Has to return one of: • Collectd.FC_TARGET_CONTINUE • Collectd.FC_TARGET_STOP • Collectd.FC_TARGET_RETURN

collectd(1), collectd.conf(5), collectd-perl(5), types.db(5)

LoadPlugin "java" <Plugin "java"> JVMArg "-verbose:jni" JVMArg "-Djava.class.path=/opt/collectd/lib/collectd/bindings/java" LoadPlugin "org.collectd.java.Foobar" <Plugin "org.collectd.java.Foobar"> # To be parsed by the plugin </Plugin> </Plugin>