原文地址:http://blog.csdn.net/welcome000yy/article/details/7962447
Log4j 2.0 使用说明(1) 之HelloWorld
最近刚接触Log4j，由于Log4j推出了2.0版本，而网上关于2.0的资料很少，所在在这里简要介绍下2.0版本的使用。
以下是2.0的类图，以便大家对2.0有一个整体的理解。
就如我们学习任何一个技术一样，这里我们首先写一个Hello World：
1，新建工程TestLog4j
2，下载Log4j 2.0有jar包，导入下面两个文件
3，编写代码：
[java]
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger; public class HelloWorld { private static Logger logger = LogManager.getLogger("HelloWorld"); public static void main(String[] args) {
logger.info("Hello, World!");
logger.error("Hello, World!");
} }
输出为：
11:11:15.343 [main] ERROR HelloWorld - Hello, World!
由输出我们可以看到程序只是打印出了error的信息，这是由于我们没提供配置文件，而缺省的配置文件默认的优先级是Error，故只打印了error的信息。
Log4j 2.0 使用说明(2) 配置文件
在这里我们试着添加配置文件。
另外，我们需要注意的是2.0版本中的配置只能为Xml和Json。
测试代码为：
[java]
package com.foo; import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger; public class Bar { static Logger logger = LogManager.getLogger(Bar.class.getName()); public boolean doIt() {
logger.entry(); //Log entry to a method
logger.error("Did it again!"); //Log a message object with the ERROR level
logger.exit(); //Log exit from a method
return false;
}
}
[java]
import com.foo.Bar; import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger; public class MyApp { // Define a static logger variable so that it references the
// Logger instance named "MyApp".
private static Logger logger = LogManager.getLogger(MyApp.class.getName()); public static void main(String[] args) { // Set up a simple configuration that logs on the console.
logger.trace("Entering application."); //Log a message object with the TRACE level.
Bar bar = new Bar();
if (!bar.doIt()) {
logger.error("Didn't do it.");
}
logger.trace("Exiting application.");
}
}
没有配置文件情况下的输出为：
17:13:01.540 [main] ERROR com.foo.Bar - Did it again!
17:13:01.540 [main] ERROR MyApp - Didn't do it.
由之前的例子我们不难知道，这是因为缺省配置文件的优先级默认为Error的缘故。
下面的配置文件在效果上等于缺省情况的下的配置文件：
[XML]
<?xml version="1.0" encoding="UTF-8"?>
<configuration status="OFF">
<appenders>
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
</Console>
</appenders>
<loggers>
<root level="error">
<appender-ref ref="Console" />
</root>
</loggers>
</configuration>
我们对上面的配置文件修改之后，再运行程序：
输出结果为：
11:43:57.703 [main] TRACE edu.hrbeu.tested.MyApp - Entering application.
11:43:57.718 [main] TRACE com.foo.Bar - entry
11:43:57.718 [main] ERROR com.foo.Bar - Did it again!
11:43:57.718 [main] TRACE com.foo.Bar - exit
11:43:57.718 [main] ERROR edu.hrbeu.tested.MyApp - Didn't do it.
11:43:57.718 [main] TRACE edu.hrbeu.tested.MyApp - Exiting application.
将优先级设置为trace后就可以显式的跟踪程序的执行过程。
若是我们想去掉除com.foo.Bar以外所有的trace输出，我们可以增加一个新的注册事件，如下所示
[XML]
<?xml version="1.0" encoding="UTF-8"?>
<configuration status="OFF">
<appenders>
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
</Console>
</appenders>
<loggers>
<logger name="com.foo.Bar" level="trace" additivity="false">
<appender-ref ref="Console" />
</logger>
<root level="error">
<appender-ref ref="Console" />
</root>
</loggers>
</configuration>
程序输出为：
11:53:31.796 [main] TRACE com.foo.Bar - entry
11:53:31.796 [main] ERROR com.foo.Bar - Did it again!
11:53:31.796 [main] TRACE com.foo.Bar - exit
11:53:31.796 [main] ERROR edu.hrbeu.tested.MyApp - Didn't do it.
Log4j 2.0 使用说明(3) 之组件及过滤器
测试用代码：
[java]
package com.test; import java.util.Random; import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger; public class TestService {
private Logger logger = LogManager.getLogger(TestService.class.getName()); private String[] messages = new String[] {
"Hello, World",
"Goodbye Cruel World",
"You had me at hello"
};
private Random rand = new Random(1); public String retrieveMessage() {
logger.entry();
String testMsg = getMessage(getKey());
return logger.exit(testMsg);
} public void exampleException() {
logger.entry();
try {
String msg = messages[messages.length];
logger.error("An exception should have been throw");
} catch (Exception e) {
logger.catching(e);
}
logger.exit();
} public String getMessage(int key) {
logger.entry(key);
String value = messages[key];
return logger.exit(value);
} public int getKey() {
logger.entry();
int key = rand.nextInt(messages.length);
return logger.exit(key);
}
}
[java]
package com.test;
public class App {
public static void main(String[] args) {
TestService service = new TestService();
service.retrieveMessage();
service.retrieveMessage();
service.exampleException();
}
}
程序输出：
10:10:46.078 TRACE com.test.TestService 19 retrieveMessage - entry
10:10:46.171 TRACE com.test.TestService 42 getKey - entry
10:10:46.171 TRACE com.test.TestService 44 getKey - exit with (0)
10:10:46.171 TRACE com.test.TestService 36 getMessage - entry parms(0)
10:10:46.171 TRACE com.test.TestService 38 getMessage - exit with (Hello, World)
10:10:46.171 TRACE com.test.TestService 21 retrieveMessage - exit with (Hello, World)
10:10:46.171 TRACE com.test.TestService 19 retrieveMessage - entry
10:10:46.171 TRACE com.test.TestService 42 getKey - entry
10:10:46.171 TRACE com.test.TestService 44 getKey - exit with (1)
10:10:46.171 TRACE com.test.TestService 36 getMessage - entry parms(1)
10:10:46.171 TRACE com.test.TestService 38 getMessage - exit with (Goodbye Cruel World)
10:10:46.171 TRACE com.test.TestService 21 retrieveMessage - exit with (Goodbye Cruel World)
10:10:46.171 TRACE com.test.TestService 25 exampleException - entry
10:10:46.171 DEBUG com.test.TestService 30 exampleException - catching java.lang.ArrayIndexOutOfBoundsException: 3
at com.test.TestService.exampleException(TestService.java:27) [bin/:?]
at com.test.App.main(App.java:9) [bin/:?]
10:10:46.187 TRACE com.test.TestService 32 exampleException - exit
其Xml配置文件为：
[XML]
<?xml version="1.0" encoding="UTF-8"?>
<configuration status="error">
<appenders>
<Console name="Console" target="SYSTEM_OUT">
<ThresholdFilter level="trace" onMatch="ACCEPT"
onMismatch="DENY" />
<PatternLayout
pattern="%d{HH:mm:ss.SSS} %-5level %class{36} %L %M - %msg%xEx%n" />
</Console>
<File name="log" fileName="target/test.log" append="false">
<PatternLayout
pattern="%d{HH:mm:ss.SSS} %-5level %class{36} %L %M - %msg%xEx%n" />
</File>
<RollingFile name="RollingFile" fileName="logs/app.log"
filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">
<PatternLayout
pattern="%d{yyyy.MM.dd 'at' HH:mm:ss z} %-5level %class{36} %L %M - %msg%xEx%n" />
<SizeBasedTriggeringPolicy size="500 MB" />
</RollingFile>
</appenders>
<loggers>
<root level="trace">
<appender-ref ref="RollingFile" />
<appender-ref ref="Console" />
</root>
</loggers>
</configuration>
扩展组件
1，ConsoleAppender
输出结果到System.out或是System.err。
2，FileAppender
输出结果到指定文件，同时可以指定输出数据的格式。
3，RollingFileAppender
自动追加日志信息到文件中，直至文件达到预定的大小，然后自动重新生成另外一个文件来记录之后的日志。
过滤标签
1，ThresholdFilter
用来过滤指定优先级的事件。
2，TimeFilter
设置start和end，来指定接收日志信息的时间区间。