struts2源码解析一 Struts2 日记原理及配置方法

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转自：http://www.myexception.cn/software/1518737.html

Struts2 日志原理及配置方法

Struts2没有直接使用Log4j、JCL(Apache Java Commons Logger)或slf4j。

它编写了自己的LoggerFactory（com.opensymphony.xwork2.util.logging.LoggerFactory），然后让其选择使用何种LoggerFactory，然后再进行日志处理。

在action中使用，可以按照以下的方式编码：

private Logger logger = LoggerFactory.getLogger(FooAction.class);

String msg="debug level logger Info";
logger.debug(msg);

struts2中日志源码涉及的有：

在org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter类中init方法中，初始化日志对象，如下：

public void init(FilterConfig filterConfig) throws ServletException {        InitOperations init = new InitOperations();        Dispatcher dispatcher = null;        try {            FilterHostConfig config = new FilterHostConfig(filterConfig);            <span style="color:#ff0000;">init.initLogging(config);</span>            dispatcher = init.initDispatcher(config);            init.initStaticContentLoader(config, dispatcher);            prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher);            execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher);            this.excludedPatterns = init.buildExcludedPatternsList(dispatcher);            postInit(dispatcher, filterConfig);        } finally {            if (dispatcher != null) {                dispatcher.cleanUpAfterInit();            }            init.cleanup();        }    }

在org.apache.struts2.dispatcher.ng.InitOperations类中的initLogging方法，

public void initLogging( HostConfig filterConfig ) {        <span style="color:#ff0000;">String factoryName = filterConfig.getInitParameter("loggerFactory");</span>        if (factoryName != null) {            try {                <span style="color:#ff0000;">Class cls = ClassLoaderUtil.loadClass(factoryName, this.getClass());                LoggerFactory fac = (LoggerFactory) cls.newInstance();                LoggerFactory.setLoggerFactory(fac);</span>            } catch ( InstantiationException e ) {                System.err.println("Unable to instantiate logger factory: " + factoryName + ", using default");                e.printStackTrace();            } catch ( IllegalAccessException e ) {                System.err.println("Unable to access logger factory: " + factoryName + ", using default");                e.printStackTrace();            } catch ( ClassNotFoundException e ) {                System.err.println("Unable to locate logger factory class: " + factoryName + ", using default");                e.printStackTrace();            }        }    }

以下代码显示,Struts会通过名为loggerFactory的参数加载LoggerFactory,
则可以通过在web.xml中设置
<filter>
<filter-name>strut2</filter-name>
<filter-class>
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter
</filter-class>
<init-param>
<param-name>loggerFactory</param-name>
<param-value>
com.opensymphony.xwork2.util.logging.commons.CommonsLoggerFactory
</param-value>
</init-param>
</filter>

以下看看LoggerFactory.getLogger();方法的实现

见com.opensymphony.xwork2.util.logging.LoggerFactory类。

public static void setLoggerFactory(LoggerFactory factory) {        lock.writeLock().lock();        try {            LoggerFactory.factory = factory;        } finally {            lock.writeLock().unlock();        }    }

设置日志处理类，此处用到了写锁处理。

public static Logger getLogger(String name) {        return getLoggerFactory().getLoggerImpl(name);    }

protected static LoggerFactory getLoggerFactory() {        lock.readLock().lock();        try {            if (factory != null) {                return factory;            }        } finally {            lock.readLock().unlock();        }        lock.writeLock().lock();        try {            if (factory == null) {                <span style="color:#ff0000;">String userLoggerFactory = System.getProperty(XWorkConstants.XWORK_LOGGER_FACTORY);</span>                if (userLoggerFactory != null) {                    try {                       <span style="color:#ff0000;"> Class clazz = Class.forName(userLoggerFactory);</span>                        factory = (LoggerFactory) clazz.newInstance();                    } catch (Exception e) {                        throw new XWorkException("System property [" + XWorkConstants.XWORK_LOGGER_FACTORY +                                "] was defined as [" + userLoggerFactory + "] but there is a problem to use that LoggerFactory!", e);                    }                } else {                    try {                        <span style="color:#ff0000;">Class.forName("org.apache.commons.logging.LogFactory");</span>                        factory = new com.opensymphony.xwork2.util.logging.commons.CommonsLoggerFactory();                    } catch (ClassNotFoundException ex) {                        //commons-logging not found try slf4j LogFactory                        try {                            <span style="color:#ff0000;">Class.forName("org.slf4j.LoggerFactory");</span>                            factory = new Slf4jLoggerFactory();                        } catch (ClassNotFoundException cnfex) {                            // slf4j not found, falling back to jdk logging                            <span style="color:#ff0000;">factory = new JdkLoggerFactory();</span>                        }                    }                }            }            return factory;        } finally {            lock.writeLock().unlock();        }    }

日志获取类共取了四次，

1，webwork的配置文件读取

2，org.apache.commons.logging.LogFactory
3，org.slf4j.LoggerFactory
4，JdkLoggerFactory

备注：我这里的struts的版本为2.3.16.3

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