Log4j 2.0 使用说明

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。