老师这个在类里面是如何写的 logger
来源：4-3 应用 log4j 调试动态 SQL
丶子非鱼
2017-06-19 11:04
如何实现的在MessageDao类里面
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- 丶子非鱼
- 2017-06-19 11:10:27
我的可以实现但是提示logger这个对象空指针 这个Logger对象如何实例化
2017-06-19 10:50:13,034[http-bio-8080-exec-3]DEBUG [Message.selectbycommand]-==> Preparing: SELECT ID,COMMAND,DESCRIPTION,CONTENT FROM message where 1=1 2017-06-19 10:50:13,036[http-bio-8080-exec-3]DEBUG [Message.selectbycommand]-==> Parameters: 2017-06-19 10:50:13,043[http-bio-8080-exec-3]DEBUG [Message.selectbycommand]-<== Total: 6 六月 19, 2017 10:50:13 上午 org.apache.catalina.core.StandardWrapperValve invoke 严重: Servlet.service() for servlet [ListServlet] in context with path [/Mybatis] threw exception java.lang.NullPointerException at Com.DAO.Service.selectbycommand(Service.java:40) at Com.Servlet.ListServlet.doGet(ListServlet.java:34) at Com.Servlet.ListServlet.doPost(ListServlet.java:49) at javax.servlet.http.HttpServlet.service(HttpServlet.java:647) at javax.servlet.http.HttpServlet.service(HttpServlet.java:728) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589) at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745)
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