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