在項目中使用log4j很簡單。
以maven項目爲例。
在pom.xml文件中加入log4j的依賴，如：
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
接着定義.properties文件，放在/resource目錄下。
編寫測試類：
@Controller
@RequestMapping("/test")
public class HelloController {
private static final Logger logger = Logger.getLogger(HelloController.class); //log4j
@RequestMapping("/hello")
public String index(){
logger.debug("this is a debug message");
logger.info("this is a info message");
logger.warn("this is a warn message");
logger.error("this is a error message");
return "hello";
}
}
運行該測試用例就行了。這裏，測試用例用的是spring，其實只要一個簡單的Junit就可以了。
就因爲我用的是spring項目，所以我需要配置tomcat。問題來了：
我按網上的步驟，一步步配置，pom 文件 等都沒有配置錯，查看本地的.m2/repo 目錄，也能找到log4j的包，而且，爲了避免jar包衝突，我把除了1.2.17版本的jar包都刪除了。
但。。。運行程序時，一直報沒有找到log4j相關類的錯誤。
控制檯的錯誤如下：
02-Aug-2018 21:30:29.740 信息 [RMI TCP Connection(2)-127.0.0.1] org.apache.jasper.servlet.TldScanner.scanJars At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
02-Aug-2018 21:30:29.785 信息 [RMI TCP Connection(2)-127.0.0.1] org.springframework.web.context.ContextLoader.initWebApplicationContext Root WebApplicationContext: initialization started
02-Aug-2018 21:30:29.844 信息 [RMI TCP Connection(2)-127.0.0.1] org.springframework.web.context.support.XmlWebApplicationContext.prepareRefresh Refreshing Root WebApplicationContext: startup date [Thu Aug 02 21:30:29 CST 2018]; root of context hierarchy
02-Aug-2018 21:30:29.892 信息 [RMI TCP Connection(2)-127.0.0.1] org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions Loading XML bean definitions from class path resource [spring/applicationContext.xml]
02-Aug-2018 21:30:30.053 信息 [RMI TCP Connection(2)-127.0.0.1] org.springframework.web.context.ContextLoader.initWebApplicationContext Root WebApplicationContext: initialization completed in 267 ms
02-Aug-2018 21:30:30.120 信息 [RMI TCP Connection(2)-127.0.0.1] org.springframework.web.servlet.DispatcherServlet.initServletBean FrameworkServlet 'springmvc': initialization started
02-Aug-2018 21:30:30.124 信息 [RMI TCP Connection(2)-127.0.0.1] org.springframework.web.context.support.XmlWebApplicationContext.prepareRefresh Refreshing WebApplicationContext for namespace 'springmvc-servlet': startup date [Thu Aug 02 21:30:30 CST 2018]; parent: Root WebApplicationContext
02-Aug-2018 21:30:30.125 信息 [RMI TCP Connection(2)-127.0.0.1] org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions Loading XML bean definitions from class path resource [spring/springmvc-servlet.xml]
02-Aug-2018 21:30:30.405 警告 [RMI TCP Connection(2)-127.0.0.1] org.springframework.web.context.support.XmlWebApplicationContext.refresh Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'helloController' defined in file [/Users/horven/personalWorkspace/springmvc4/out/artifacts/springmvc4_war_exploded/WEB-INF/classes/com/controller/HelloController.class]: Instantiation of bean failed; nested exception is java.lang.NoClassDefFoundError: org/apache/log4j/Logger
02-Aug-2018 21:30:30.405 嚴重 [RMI TCP Connection(2)-127.0.0.1] org.springframework.web.servlet.DispatcherServlet.initServletBean Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'helloController' defined in file [/Users/horven/personalWorkspace/springmvc4/out/artifacts/springmvc4_war_exploded/WEB-INF/classes/com/controller/HelloController.class]: Instantiation of bean failed; nested exception is java.lang.NoClassDefFoundError: org/apache/log4j/Logger
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1163)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1107)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:312)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:308)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
at org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:668)
at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:634)
at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:682)
at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:553)
at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:494)
at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:171)
at javax.servlet.GenericServlet.init(GenericServlet.java:158)
at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1144)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1091)
at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:983)
at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4978)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5290)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:754)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1736)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:300)
at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:483)
at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:432)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:300)
at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
at javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1468)
at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:76)
at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1309)
at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1401)
at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:829)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:357)
at sun.rmi.transport.Transport$1.run(Transport.java:200)
at sun.rmi.transport.Transport$1.run(Transport.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Transport.java:196)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:573)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:835)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:688)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:687)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NoClassDefFoundError: org/apache/log4j/Logger
at com.controller.HelloController.<clinit>(HelloController.java:16)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:142)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1155)
... 65 more
Caused by: java.lang.ClassNotFoundException: org.apache.log4j.Logger
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1309)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1137)
... 73 more
[2018-08-02 09:30:30,423] Artifact springmvc4:war exploded: Artifact is deployed successfully
[2018-08-02 09:30:30,423] Artifact springmvc4:war exploded: Deploy took 1,716 milliseconds
02-Aug-2018 21:30:38.256 信息 [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory [/Users/horven/Library/apache-tomcat-8.5.32/webapps/manager]
02-Aug-2018 21:30:38.283 信息 [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory [/Users/horven/Library/apache-tomcat-8.5.32/webapps/manager] has finished in [27] ms
網上看了很多教程，很多都是說缺log4j的jar包。
後來突然明白，我的程序要跑在tomcat上，這個錯誤是在啓動tomcat時報的，說明tomcat不認識log4j的相關類。
於是，我把log4j的jar包copy到tomcat的lib文件夾內，再次運行，就成功了，問題解決！