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| 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> | ||
| 2 | <html> | ||
| 3 | <head> | ||
| 4 | <!-- | ||
| 5 | Copyright (c) 2001, 2006, Oracle and/or its affiliates. All rights reserved. | ||
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| 15 | ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
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| 18 | accompanied this code). | ||
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| 28 | |||
| 29 | </head> | ||
| 30 | <body bgcolor="white"> | ||
| 31 | <P> | ||
| 32 | Provides the classes and interfaces of | ||
| 33 | the Java<SUP><FONT SIZE="-2">TM</FONT></SUP> 2 | ||
| 34 | platform's core logging facilities. | ||
| 35 | The central goal of the logging APIs is to support maintaining and servicing | ||
| 36 | software at customer sites. | ||
| 37 | |||
| 38 | <P> | ||
| 39 | There are four main target uses of the logs: | ||
| 40 | </P> | ||
| 41 | |||
| 42 | <OL> | ||
| 43 | <LI> <I>Problem diagnosis by end users and system administrators</I>. | ||
| 44 | This consists of simple logging of common problems that can be fixed | ||
| 45 | or tracked locally, such as running out of resources, security failures, | ||
| 46 | and simple configuration errors. | ||
| 47 | |||
| 48 | <LI> <I>Problem diagnosis by field service engineers</I>. The logging information | ||
| 49 | used by field service engineers may be considerably more complex and | ||
| 50 | verbose than that required by system administrators. Typically such information | ||
| 51 | will require extra logging within particular subsystems. | ||
| 52 | |||
| 53 | <LI> <I>Problem diagnosis by the development organization</I>. | ||
| 54 | When a problem occurs in the field, it may be necessary to return the captured logging | ||
| 55 | information to the original development team for diagnosis. This logging | ||
| 56 | information may be extremely detailed and fairly inscrutable. Such information might include | ||
| 57 | detailed tracing on the internal execution of particular subsystems. | ||
| 58 | |||
| 59 | <LI> <I>Problem diagnosis by developers</I>. The Logging APIs may also be | ||
| 60 | used to help debug an application under development. This may | ||
| 61 | include logging information generated by the target application | ||
| 62 | as well as logging information generated by lower-level libraries. | ||
| 63 | Note however that while this use is perfectly reasonable, | ||
| 64 | the logging APIs are not intended to replace the normal debugging | ||
| 65 | and profiling tools that may already exist in the development environment. | ||
| 66 | </OL> | ||
| 67 | |||
| 68 | </P> | ||
| 69 | The key elements of this package include: | ||
| 70 | <UL> | ||
| 71 | <LI> <I>Logger</I>: The main entity on which applications make | ||
| 72 | logging calls. A Logger object is used to log messages | ||
| 73 | for a specific system or application | ||
| 74 | component. | ||
| 75 | <LI> <I>LogRecord</I>: Used to pass logging requests between the logging | ||
| 76 | framework and individual log handlers. | ||
| 77 | <LI> <I>Handler</I>: Exports LogRecord objects to a variety of destinations | ||
| 78 | including memory, output streams, consoles, files, and sockets. | ||
| 79 | A variety of Handler subclasses exist for this purpose. Additional Handlers | ||
| 80 | may be developed by third parties and delivered on top of the core platform. | ||
| 81 | <LI> <I>Level</I>: Defines a set of standard logging levels that can be used | ||
| 82 | to control logging output. Programs can be configured to output logging | ||
| 83 | for some levels while ignoring output for others. | ||
| 84 | <LI> <I>Filter</I>: Provides fine-grained control over what gets logged, | ||
| 85 | beyond the control provided by log levels. The logging APIs support a general-purpose | ||
| 86 | filter mechanism that allows application code to attach arbitrary filters to | ||
| 87 | control logging output. | ||
| 88 | |||
| 89 | <LI> <I>Formatter</I>: Provides support for formatting LogRecord objects. This | ||
| 90 | package includes two formatters, SimpleFormatter and | ||
| 91 | XMLFormatter, for formatting log records in plain text | ||
| 92 | or XML respectively. As with Handlers, additional Formatters | ||
| 93 | may be developed by third parties. | ||
| 94 | </UL> | ||
| 95 | <P> | ||
| 96 | The Logging APIs offer both static and dynamic configuration control. | ||
| 97 | Static control enables field service staff to set up a particular configuration and then re-launch the | ||
| 98 | application with the new logging settings. Dynamic control allows for updates to the | ||
| 99 | logging configuration within a currently running program. The APIs also allow for logging to be | ||
| 100 | enabled or disabled for different functional areas of the system. For example, | ||
| 101 | a field service engineer might be interested in tracing all AWT events, but might have no interest in | ||
| 102 | socket events or memory management. | ||
| 103 | </P> | ||
| 104 | |||
| 105 | <h2>Null Pointers</h2> | ||
| 106 | <p> | ||
| 107 | In general, unless otherwise noted in the javadoc, methods and | ||
| 108 | constructors will throw NullPointerException if passed a null argument. | ||
| 109 | The one broad exception to this rule is that the logging convenience | ||
| 110 | methods in the Logger class (the config, entering, exiting, fine, finer, finest, | ||
| 111 | log, logp, logrb, severe, throwing, and warning methods) | ||
| 112 | will accept null values | ||
| 113 | for all arguments except for the initial Level argument (if any). | ||
| 114 | <p> | ||
| 115 | <H2>Related Documentation</H2> | ||
| 116 | <P> | ||
| 117 | For an overview of control flow, | ||
| 118 | please refer to the | ||
| 119 | <a href="../../../../technotes/guides/logging/overview.html"> | ||
| 120 | Java Logging Overview</a>. | ||
| 121 | </P> | ||
| 122 | |||
| 123 | <!-- Put @see and @since tags down here. --> | ||
| 124 | |||
| 125 | @since 1.4 | ||
| 126 | |||
| 127 | |||
| 128 | </body> | ||
| 129 | </html> | ||
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