Android中Log机制详解

Android中Log的输出有如下几种：

Log.v(String tag, String msg); //VERBOSE

Log.d(String tag, String msg); //DEBUG

Log.i(String tag, String msg); //INFO

Log.w(String tag, String msg); //WARN

Log.e(String tag, String msg); //ERROR

以上log的级别依次升高，VERBOSE DEBUG信息应当只存在于开发中，INFO,WARN，ERROR这三种log将出现在发布版本中。

对于JAVA类中，可以声明一个字符串常量TAG，Logcat可以根据他来区分不同的log,例如在WindowsManagerService.java的类中，定义如下所示：

static final Sting TAG = "WindowManager"

需要打log的地方

Log.v(TAG, "Figuring out where to add app window" + client.asBinder() + "(token=" + token + ")");

logcat使用方法如下所示:

logcat [options] [filterspecs]

option "-s" 用来设置过滤器，格式是这样的 <tag>[:priority]

其中 <tag> 表示log的component， tag (或者使用 * 表示所有) ，priority如下所示:

V Verbose

D Debug

I Info

W Warn

E Error

F Fatal

S Silent

例：

logcat -s *:s 不打任何log

logcat -s WindowMnager:V <-- 打印WindowManagerService 中 Verbose 信息

如果在eclipse中查看Android log 输出，也就是logcat信息，可以 选择Windows > Show View > Other... > Android > LogCat。

附

logcat的参数说明:

Usage: logcat [options] [filterspecs]

options include:

-s Set default filter to silent.

Like specifying filterspec '*:s'

-f <filename> Log to file. Default to stdout

-r [<kbytes>] Rotate log every kbytes. (16 if unspecified). Requires -f

-n <count> Sets max number of rotated logs to <count>, default 4

-v <format> Sets the log print format, where <format> is one of:

brief process tag thread raw time long

-c clear (flush) the entire log and exit

-d dump the log and then exit (don't block)

-g get the size of the log's ring buffer and exit

-b <buffer> request alternate ring buffer, defaults to 'main'

filterspecs are a series of

<tag>[:priority]

where <tag> is a log component tag (or * for all) and priority is:

V Verbose

D Debug

I Info

W Warn

E Error

F Fatal

S Silent (supress all output)

'*' means '*:d' and <tag> by itself means <tag>:v

If not specified on the commandline, filterspec is set from ANDROID_LOG_TAG

If no filterspec is found, filter defaults to '*:I'

If not specified with -v, format is set from ANDROID_PRINTF_LOG

or defaults to "brief"