这里只是比较简单的介绍一下Dropwizard中的log，更详细的信息可以参考Logback和后续配置章节中对log配置的专门的介绍。
一、简介
Dropwizard使用Logback做日志处理，它提供了slf4j的实现，甚至还把java.util.logging,Log4j, Apache Commons Logging都指向了Logback。（原话：and even routes all java.util.logging, Log4j, and Apache Commons Logging usage through Logback.）
slf4j提供五种日志级别
ERROR: 错误，打印错误日志并不代表app挂了，通常在写代码的时候，我习惯在catch块中或者其他业务出错的地方，使用这个级别打印日志。
WARN:可能对应用有害的高精
INFO:主要显示app功能进展的信息。通常业务正常进度的日志，我也会使用这个级别。
DEBUG: 比INFO更细一点的日志，更多是用再DEBUG程序的时候使用，release版本都会过滤掉这个级别。
TRACE: 比DEBUG更细一点的日志，没用过。
三步实现去掉logback，使用别的日志：
-
pom中去掉引用
io.dropwizard
dropwizard-core
{$dropwizard.version}
ch.qos.logback
logback-classic
ch.qos.logback
logback-access
org.slf4j
log4j-over-slf4j
- 配置文件中去掉
logback的配置
server:
type: simple
applicationContextPath: /application
adminContextPath: /admin
requestLog:
type: external
logging:
type: external
- 在
Application中重写log方法
public class ExampleApplication extends Application {
@Override
protected void bootstrapLogging() {
}
}
二、Log Format 格式化日志
Dropwizard的日志格式化的目标有三：
Be human readable.
Be machine parsable.
Be easy for sleepy ops folks to figure out why things are pear-shaped at 3:30AM using standard UNIXy tools liketailandgrep
也就是程序员可读性，机器可解析性。第三点说的是提供类似tail和grep的命令差错，这一点我不是很明白，我觉得大部分的日志文件都可以支持这种方式吧。
注意点：
- 所有的时间都是UTC的并且是以ISO 8601规范格式化。
- 可以使用
grep筛选日志级别、类、以及完整的一次堆栈和附带的日志消息
tail -f dw.log | grep '^WARN'
tail -f dw.log | grep 'com.example.dw.Thing'
tail -f dw.log | grep -B 1 '^\!'
- The ! prefix does not apply to syslog appenders, as stack traces are sent separately from the main message. Instead, t is used (this is the default value of the SyslogAppender that comes with Logback). This can be configured with the stackTracePrefix option when defining your appender.(由于堆栈信息和主消息是分开发送的，所以系统日志的
appenders，!不能作为开头，要用t，在你定义appenders的时候，可以使用stackTracePrefix配置这个问题)
三、日志配置
在application.properties中我们可以配置日志的总级别，然后为不同类型、不同包名的日志，根据需要重写他们的日志级别、日志格式、日志文件等。
# Logging settings.
logging:
# The default level of all loggers. Can be OFF, ERROR, WARN, INFO, DEBUG, TRACE, or ALL.
level: INFO
# Logger-specific levels.
loggers:
# Overrides the level of com.example.dw.Thing and sets it to DEBUG.
"com.example.dw.Thing": DEBUG
# Enables the SQL query log and redirect it to a separate file
"org.hibernate.SQL":
level: DEBUG
# This line stops org.hibernate.SQL (or anything under it) from using the root logger
additive: false
appenders:
- type: file
currentLogFilename: ./logs/example-sql.log
archivedLogFilenamePattern: ./logs/example-sql-%d.log.gz
archivedFileCount: 5
Console
logging:
appenders:
- type: console
threshold: WARN
target: stderr
File
这里可以根据需要配置日志的分割方式。可以按时间等。比如下面的例子，如果文件格式为./logs/example-%d.log.gz事默认以天分割并压缩，如果在d后边加上时间格式，它就会根据你规定的格式去分割打包。
logging:
appenders:
- type: file
# The file to which current statements will be logged.
currentLogFilename: ./logs/example.log
# When the log file rotates, the archived log will be renamed to this and gzipped. The
# %d is replaced with the previous day (yyyy-MM-dd). Custom rolling windows can be created
# by passing a SimpleDateFormat-compatible format as an argument: "%d{yyyy-MM-dd-hh}".
archivedLogFilenamePattern: ./logs/example-%d.log.gz
# The number of archived files to keep.
archivedFileCount: 5
# The timezone used to format dates. HINT: USE THE DEFAULT, UTC.
timeZone: UTC
Syslog
Finally, Dropwizard can also log statements to syslog.
Note
Because Java doesn’t use the native syslog bindings, your syslog server must have an open network socket.
logging:
appenders:
- type: syslog
# The hostname of the syslog server to which statements will be sent.
# N.B.: If this is the local host, the local syslog instance will need to be configured to
# listen on an inet socket, not just a Unix socket.
host: localhost
# The syslog facility to which statements will be sent.
facility: local0
平时我们在配置日志的时候，实际上是会根据需要混合不同类型日志的配置：
logging:
# Permit DEBUG, INFO, WARN and ERROR messages to be logged by appenders.
level: DEBUG
appenders:
# Log warnings and errors to stderr
- type: console
threshold: WARN
target: stderr
# Log info, warnings and errors to our apps' main log.
# Rolled over daily and retained for 5 days.
- type: file
threshold: INFO
currentLogFilename: ./logs/example.log
archivedLogFilenamePattern: ./logs/example-%d.log.gz
archivedFileCount: 5
# Log debug messages, info, warnings and errors to our apps' debug log.
# Rolled over hourly and retained for 6 hours
- type: file
threshold: DEBUG
currentLogFilename: ./logs/debug.log
archivedLogFilenamePattern: ./logs/debug-%d{yyyy-MM-dd-hh}.log.gz
archivedFileCount: 6
注：在配置章节会有专门的大篇幅的讲解日志配置。
四、通过http请求修改日志配置
在Task章节我们有提过，Dropwizard默认提供了log-level的task，这样我们就可以通过HTTP请求多日志做一些操作，比如修改日志的等级：
curl -X POST -d "logger=com.example.helloworld&level=INFO" http://localhost:8081/tasks/log-level
五、日志过滤器
除了按照日志级别配置日志外，有时候我们还需要对同一级别不同类型的日志进行过滤。日志过滤对普通日志和HTTP请求日志都有效。有时候我们需要过滤掉一些请求的日志，比如说：只打印请求body较大的，只打印请求响应较慢的，只打印请求失败的，不打印URL里面包含敏感信息的。下面我们举例过滤掉/secret请求的日志。
@JsonTypeName("secret-filter-factory")
public class SecretFilterFactory implements FilterFactory {
@Override
public Filter build() {
return new Filter() {
@Override
public FilterReply decide(IAccessEvent event) {
if (event.getRequestURI().equals("/secret")) {
return FilterReply.DENY;
} else {
return FilterReply.NEUTRAL;
}
}
};
}
}
然后在日志中加上：
server:
requestLog:
appenders:
- type: console
filterFactories:
- type: secret-filter-factory
最后：
The last step is to add our class (in this case
com.example.SecretFilterFactory) toMETA-INF/services/io.dropwizard.logging.filter.FilterFactoryin our resources folder.