要在我的log4j appender中使用数据源，我编写了一个自定义appender。 appender试图将数据源作为spring bean。但是，appender无法获取bean。我使用的技术堆栈是：mybatis，tomcat和spring。
我的log4j文件如下所示：
#configuring the requestinterceptor
log4j.category.com.db.wscis.core.web.interceptor=INFO, sql
log4j.appender.sql=com.db.wscis.core.util.appender.CustomJDBCAppender
log4j.appender.sql.sql=INSERT INTO LOGS VALUES ('%x', current_timestamp ,'%C','%p','%m')
log4j.appender.sql.layout=org.apache.log4j.PatternLayout
自定义appender的代码如下：
public class CustomJDBCAppender extends org.apache.log4j.jdbc.JDBCAppender {
protected java.sql.Connection getConnection() throws java.sql.SQLException {
if(connection == null) {
org.springframework.jdbc.datasource.DataSourceTransactionManager dstm = (org.springframework.jdbc.datasource.DataSourceTransactionManager) ExternalBeanFactory.getBean("txManager");
if(dstm==null) throw new java.sql.SQLException("dstm is null");
System.out.println("here");
connection = DataSourceUtils.getConnection(dstm.getDataSource());
return connection;
} else{
return connection;
}
}
/* protected void execute(String sql) throws java.sql.SQLException {
Connection con = null;
Statement stmt = null;
try {
con = getConnection();
stmt = con.createStatement();
stmt.executeUpdate(sql);
con.commit();
} catch (SQLException e) {
if (stmt != null)
stmt.close();
closeConnection(con);
throw e;
}
}
*/
protected void closeConnection() throws java.sql.SQLException {
if (connection != null && !connection.isClosed())
connection.close();
}
}
外部Bean工厂类看起来像这样：
/*
*/
package com.db.wscis.core.util;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
public class ExternalBeanFactory implements BeanFactoryAware {
/**
* Bean factory instance.
*/
private static BeanFactory beanFactory;
/**
* Sets beanfactory.
*
* @param beanFactory
* BeanFactory object
*
* @see org.springframework.beans.factory.BeanFactoryAware#
* setBeanFactory(org.springframework.beans.factory.BeanFactory)
* @exception BeansException
* if failed to set factory
*/
public final void setBeanFactory(final BeanFactory beanFactory) throws BeansException {
this.beanFactory = beanFactory;
}
/**
* DO NOT use this method in the application classes. This is meant to be
* used by the framework level classes ONLY!!!!
*
* Finds from bean from the factory.
*
* @param beanName
* Name of the bean
* @return bean object
*/
@Deprecated
public static final Object getBean(final String beanName) {
// if(beanFactory==null) System.out.println("Bean factory is null");
return beanFactory.getBean(beanName);
}
public final Object getBeanInstance(final String beanName) {
return beanFactory.getBean(beanName);
}
}
现在，当tomcat服务器启动时，我的猜测是它尝试初始化log4j。因此，它在自定义appender中调用getConnection方法。此inturn调用ExernalFactory.getBean（），但是，外部BeanFactory中的beanfactory属性尚未初始化。
错误堆栈跟踪如下：
SEVERE: Error configuring application listener of class com.db.wscis.core.web.context.FWContextLoaderLis
java.lang.NullPointerException
at com.db.wscis.core.util.ExternalBeanFactory.getBean(ExternalBeanFactory.java:64)
at com.db.wscis.core.util.appender.CustomJDBCAppender.getConnection(CustomJDBCAppender.java:27)
at org.apache.log4j.jdbc.JDBCAppender.execute(JDBCAppender.java:215)
at org.apache.log4j.jdbc.JDBCAppender.flushBuffer(JDBCAppender.java:289)
at org.apache.log4j.jdbc.JDBCAppender.append(JDBCAppender.java:186)
at org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:251)
at org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.
at org.apache.log4j.Category.callAppenders(Category.java:206)
at org.apache.log4j.Category.forcedLog(Category.java:391)
at org.apache.log4j.Category.log(Category.java:856)
at org.apache.commons.logging.impl.Log4JLogger.info(Log4JLogger.java:176)
at com.db.wscis.core.web.context.FWContextLoaderListener.<init>(FWContextLoaderListener.java:34)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.j
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at java.lang.Class.newInstance(Class.java:374)
at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:140)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4888)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5467)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:632)
at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:1073)
at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1857)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:724)
请告诉我我做错了什么以及如何在appender类中获取数据源bean实例。
答案 0 :(得分：0)
我设法解决了这个问题：
因此，我的数据源bean是在应用程序上下文中声明的。另一方面，我的外部bean工厂在根上下文中声明。现在，根上下文中的bean无法在应用程序Context中看到bean。因此，我的External Bean Factory中的beanfactory属性从未被初始化。我花了一些时间才弄明白，但谢天谢地，它有效！