log4j 用法

关于getLogger：

public static Logger getLogger(Class clazz)

Shorthand for getLogger(clazz.getName()).

Parameters:

clazz - The name of clazz will be used as the name of the logger to retrieve. SeegetLogger(String) for more detailed information.

public static Logger getLogger(String name)

Retrieve a logger named according to the value of the name parameter. If the named logger already exists, then the existing instance will be returned. Otherwise, a new instance is created.

By default, loggers do not have a set level but inherit it from their neareast ancestor with a set level. This is one of the central features of log4j.

Parameters:

name - The name of the logger to retrieve.

即getLogger如果没有这个name对应的logger，那么将产生一个新的logger

关于log4j.properties：

除了rootLogger以外，还可以设置更多的logger,只要设置好log级别，appender，以及输出样式就可以了，例如下面的例子，rootLogger是DONG, INFO级别，打到文件dong.log, 另外定义了一个logger SUN, INFO级别，打到文件sun.log， 值得注意的是

log4j.additivity.xxx

的设置，默认为true,即其他logger的也会输出到rootLogger，置为false可以只打到子logger本身,

除非通过Logger.getlogger指定配置文件中定义好的logger,否则将采用rootLogger的配置，

通过

setLevel(Level.toLevel("DEBUG"))

可以在程序中设置logLevel为DEBUG

log4j.properties:

log4j.rootLogger=INFO, DONGlog4j.logger.sun=INFO, SUNlog4j.additivity.sun=falselog4j.appender.CONSOLE=org.apache.log4j.ConsoleAppenderlog4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayoutlog4j.appender.CONSOLE.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%nlog4j.appender.CONSOLE.Threshold=INFOlog4j.appender.CONSOLE.Target=System.outlog4j.appender.CONSOLE.Encoding=GBKlog4j.appender.DONG = org.apache.log4j.RollingFileAppenderlog4j.appender.DONG.File = dong.loglog4j.appender.DONG.Encoding=GBKlog4j.appender.DONG.MaxFileSize = 10MBlog4j.appender.DONG.MaxBackupIndex = 20log4j.appender.DONG.layout = org.apache.log4j.PatternLayoutlog4j.appender.DONG.layout.ConversionPattern = %d{yyyy-MM-dd HH:mm:ss,SSS} [%t] [%c] [%p] - %m%nlog4j.appender.SUN = org.apache.log4j.RollingFileAppenderlog4j.appender.SUN.File = sun.loglog4j.appender.SUN.Encoding=GBKlog4j.appender.SUN.MaxFileSize = 10MBlog4j.appender.SUN.MaxBackupIndex = 20log4j.appender.SUN.layout = org.apache.log4j.PatternLayoutlog4j.appender.SUN.layout.ConversionPattern = %d{yyyy-MM-dd HH:mm:ss,SSS} [%t] [%c] [%p] - %m%n

以下是一个程序例子：

java文件：

package dong.sun;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;import java.util.Properties;import org.apache.log4j.Level;import org.apache.log4j.Logger;import org.apache.log4j.PropertyConfigurator;public class logTest {public static void main(String[] args) {System.out.println("This is a test for log4j");try {            String confFileName = "./log4j.properties";            File confFile = new File(confFileName);            FileInputStream is;            is = new FileInputStream(confFile);            Properties properties = new Properties();            properties.load(is);            PropertyConfigurator.configure(properties);        }        catch (FileNotFoundException e) {            e.printStackTrace();        }        catch (IOException e) {            e.printStackTrace();        }Logger log1 = Logger.getLogger("dong.sun.logTest1");if (log1.isDebugEnabled()) {log1.debug("debug message for dong.sun.logTest1 after setting log4j.properties");}if (log1.isInfoEnabled()) {log1.info("info message for dong.sun.logTest1 after setting log4j.properties");}Logger log2 = Logger.getLogger("sun");if (log2.isDebugEnabled()) {log2.debug("debug message for dong.sun before setting log level");}if (log2.isInfoEnabled()) {log2.info("info message for dong.sun before setting log level");}log2.setLevel(Level.toLevel("DEBUG"));if (log2.isDebugEnabled()) {log2.debug("debug message for dong.sun after setting log level");}if (log2.isInfoEnabled()) {log2.info("info message for dong.sun after setting log level");}}} 

pom文件：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">  <modelVersion>4.0.0</modelVersion>  <groupId>com.sun</groupId>  <artifactId>logTest</artifactId>  <version>1.0</version>  <name>logTest</name>  <description>test for logger4j</description>    <dependencies><dependency><groupId>log4j</groupId><artifactId>log4j</artifactId><version>1.2.9</version></dependency>  </dependencies>  <build><plugins><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><version>2.3.2</version><configuration><source>1.6</source><target>1.6</target><encoding>UTF-8</encoding></configuration></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-jar-plugin</artifactId><configuration><archive><manifest><addClasspath>true</addClasspath><classpathPrefix>lib/</classpathPrefix><mainClass>dong.sun.logTest</mainClass></manifest></archive></configuration></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-dependency-plugin</artifactId><executions><execution><id>copy</id><phase>install</phase><goals><goal>copy-dependencies</goal></goals><configuration><outputDirectory>${project.build.directory}/lib</outputDirectory></configuration></execution></executions></plugin></plugins></build></project>

build以后的target为：

target

    |__logTest-1.0.jar

    |__ lib

            |__log4j-1.2.9.jar

最后将logTest-1.0.jar，lib以及log4j.properties置于同一目录下运行java -jar  logTest-1.0.jar，结果如下：

dong.log:

2013-01-05 00:56:56,668 [main] [dong.sun.logTest1] [INFO] - info message for dong.sun.logTest1 after setting log4j.properties

sun.log:

2013-01-05 00:56:56,668 [main] [sun] [INFO] - info message for dong.sun before setting log level
2013-01-05 00:56:56,668 [main] [sun] [DEBUG] - debug message for dong.sun after setting log level
2013-01-05 00:56:56,668 [main] [sun] [INFO] - info message for dong.sun after setting log level