<h2>应用场景</h2>    <p>随着项目的逐渐扩大，日志的增加也变得更快。Log4j是常用的日志记录工具，在有些时候，我们可能需要将Log4j的日志发送到专门用于记录日志的远程服务器，特别是对于稍微大一点的应用。这么做的优点有：</p>    <ul>     <li><strong>可以集中管理日志</strong> ：可以把多台服务器上的日志都发送到一台日志服务器上，方便管理、查看和分析</li>     <li><strong>可以减轻服务器的开销</strong> ：日志不在服务器上了，因此服务器有更多可用的磁盘空间</li>     <li><strong>可以提高服务器的性能</strong> ：通过异步方式，记录日志时服务器只负责发送消息，不关心日志记录的时间和位置，服务器甚至不关心日志到底有没有记录成功</li>    </ul>    <p>远程打印日志的原理：项目A需要打印日志，而A调用Log4j来打印日志，Log4j的JMSAppender又给配置的地址（ActiveMQ地址）发送一条JMS消息，此时绑定在Queue上的项目B的监听器发现有消息到来，于是立即唤醒监听器的方法开始输出日志。</p>    <p>本文将使用两个Java项目Product和Logging，其中Product项目就是模拟线上的项目，而Logging项目模拟运行在专用的日志服务器上的项目。说明：本文的例子是在Windows平台下。</p>    <h2>安装ActiveMQ</h2>    <p>1. 下载： <a href="/misc/goto?guid=4958989520308497935" rel="nofollow,noindex">http://activemq.apache.org/download.html</a></p>    <p>2. 解压后不需要任何配置，进入到bin下对应的系统架构文件夹</p>    <p><img src="https://simg.open-open.com/show/6b46a7108450a03cfa1aab47ca0e2f25.png"></p>    <p>3. 双击activemq.bat启动，如果看到类似下面的页面，就代表activemq启动好了：</p>    <p><img src="https://simg.open-open.com/show/a5a75984bdb8108c15e2db1283c9d543.png"></p>    <p>然后打开浏览器，输入地址：http://localhost:8161进入管理页面，用户名admin，密码admin：</p>    <p><img src="https://simg.open-open.com/show/cf12901414e5ff51b0ef18f245ca3f87.png"></p>    <p>可以点击Manage ActiveMQ broker进入Queue的查看界面。</p>    <h2>实战</h2>    <p>我用Maven来管理项目，方便维护各种依赖的jar包。先看下项目结构：</p>    <p><img src="https://simg.open-open.com/show/e2e764c72dcfb23c0010f65102aede74.png"></p>    <p>项目不复杂，主要是4个文件：pom.xml，Main.java，log4j.properties和jndi.properties</p>    <p>pom.xml中主要是声明项目的依赖包，其余没有什么东西了：</p>    <pre>  <code class="language-java"><!-- Use to call write log methods -->  <dependency>      <groupId>log4j</groupId>      <artifactId>log4j</artifactId>      <version>1.2.17</version>  </dependency>    <!-- Log4j uses this lib -->  <dependency>      <groupId>org.slf4j</groupId>      <artifactId>slf4j-log4j12</artifactId>      <version>1.7.13</version>  </dependency>    <!-- Spring jms lib -->  <dependency>      <groupId>org.springframework</groupId>      <artifactId>spring-jms</artifactId>      <version>4.0.0.RELEASE</version>  </dependency>    <!-- ActiveMQ lib -->  <dependency>      <groupId>org.apache.activemq</groupId>      <artifactId>activemq-core</artifactId>      <version>5.7.0</version>  </dependency></code></pre>    <p>Main.java：</p>    <pre>  <code class="language-java">package com.demo.product;    import javax.jms.Connection;  import javax.jms.Destination;  import javax.jms.Message;  import javax.jms.MessageConsumer;  import javax.jms.MessageListener;  import javax.jms.Session;    import org.apache.activemq.ActiveMQConnectionFactory;  import org.apache.activemq.command.ActiveMQObjectMessage;  import org.apache.log4j.Logger;  import org.apache.log4j.spi.LoggingEvent;    public class Main implements MessageListener {        public Main() throws Exception {          // create consumer and listen queue          ActiveMQConnectionFactory factory =                   new ActiveMQConnectionFactory("tcp://localhost:61616");          Connection connection = factory.createConnection();          Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);          connection.start();          //////////////注意这里JMSAppender只支持TopicDestination，下面会说到////////////////          Destination topicDestination = session.createTopic("logTopic");          MessageConsumer consumer = session.createConsumer(topicDestination);          consumer.setMessageListener(this);            // log a message          Logger logger = Logger.getLogger(Main.class);          logger.info("Info Log.");          logger.warn("Warn Log");          logger.error("Error Log.");            // clean up          Thread.sleep(1000);          consumer.close();          session.close();          connection.close();          System.exit(1);      }        public static void main(String[] args) throws Exception {          new Main();      }        public void onMessage(Message message) {          try {              // receive log event in your consumer              LoggingEvent event = (LoggingEvent)((ActiveMQObjectMessage)message).getObject();              System.out.println("Received log [" + event.getLevel() + "]: "+ event.getMessage());          } catch (Exception e) {              e.printStackTrace();          }      }    }</code></pre>    <p>说明：然后是log4j.properties：</p>    <pre>  <code class="language-java">log4j.rootLogger=INFO, stdout, jms    ## Be sure that ActiveMQ messages are not logged to 'jms' appender  log4j.logger.org.apache.activemq=INFO, stdout    log4j.appender.stdout=org.apache.log4j.ConsoleAppender  log4j.appender.stdout.layout=org.apache.log4j.PatternLayout  log4j.appender.stdout.layout.ConversionPattern=%d %-5p %c - %m%n    ## Configure 'jms' appender. You'll also need jndi.properties file in order to make it work  log4j.appender.jms=org.apache.log4j.net.JMSAppender  log4j.appender.jms.InitialContextFactoryName=org.apache.activemq.jndi.ActiveMQInitialContextFactory  log4j.appender.jms.ProviderURL=tcp://localhost:61616  log4j.appender.jms.TopicBindingName=logTopic  log4j.appender.jms.TopicConnectionFactoryBindingName=ConnectionFactory</code></pre>    <p>其实按理说只需要这么三个文件就可以了，但是这时候执行会报错：</p>    <pre>  <code class="language-java">javax.naming.NameNotFoundException: logTopic      at org.apache.activemq.jndi.ReadOnlyContext.lookup(ReadOnlyContext.java:235)      at javax.naming.InitialContext.lookup(Unknown Source)      at org.apache.log4j.net.JMSAppender.lookup(JMSAppender.java:245)      at org.apache.log4j.net.JMSAppender.activateOptions(JMSAppender.java:222)      at org.apache.log4j.config.PropertySetter.activate(PropertySetter.java:307)          ...      at org.apache.activemq.ActiveMQPrefetchPolicy.<clinit>(ActiveMQPrefetchPolicy.java:39)      at org.apache.activemq.ActiveMQConnectionFactory.<init>(ActiveMQConnectionFactory.java:84)      at org.apache.activemq.ActiveMQConnectionFactory.<init>(ActiveMQConnectionFactory.java:137)      at com.demo.product.Main.<init>(Main.java:20)      at com.demo.product.Main.main(Main.java:43)</code></pre>    <p>为什么会报错呢？来看看JMSAppender的javadoc文档，它是这么描述的：</p>    <p><img src="https://simg.open-open.com/show/5c9801eba00f1f413e47eb97dddd350a.png"></p>    <p>大意是说，JMSAppender需要一个jndi配置来初始化一个JNDI上下文（Context）。因为有了这个上下文才能管理JMS Topic和topic的连接。于是为项目配置一个叫jndi.properties的文件，其内容为：</p>    <pre>  <code class="language-java">topic.logTopic=logTopic</code></pre>    <p>然后再运行就不会报错了。我们先来看看ActiveMQ（注意切换到Topic标签页下）：</p>    <p><img src="https://simg.open-open.com/show/ce3c3fe9900862e0b6ddf44cf7d5c974.png"></p>    <p>可以看到，主题为logTopic的消息，有3条进Queue，这3条也出Queue了。而出Queue的消息，已经被我们的监听器收到并打印出来了：</p>    <p><img src="https://simg.open-open.com/show/fa498d6356b34d34ccb57964d7a67b53.png"></p>    <h2>Spring整合</h2>    <p>需要注意的是，本例只是一个很简单的例子，目的是阐明远程打印日志的原理。实际项目中，一般日志服务器上运行着的，不是项目，而是专用的日志记录器。下面，我们就把这个项目拆分成两个项目，并用Spring来管理这些用到的Bean</p>    <h3>修改Product项目</h3>    <p>修改后的Product的项目结构并没有改变，改变的只是Main类：</p>    <pre>  <code class="language-java">package com.demo.product;    import org.apache.log4j.Logger;    public class Main{      private static final Logger logger = Logger.getLogger(Main.class);      public static void main(String[] args) throws Exception {          // just log a message          logger.info("Info Log.");          logger.warn("Warn Log");          logger.error("Error Log.");          System.exit(0);      }  }</code></pre>    <p>这个Main类和普通的logger调用一样，仅仅负责打印日志。有没有觉得太简单了呢？</p>    <h3>Logging项目</h3>    <p>来看看项目结构图：</p>    <p><img src="https://simg.open-open.com/show/e3fdd74a8958fab68876ea97657c2b6f.png"></p>    <p>为了让监听器一直活着，我把Logging写成了一个Web项目，跑在Tomcat上。index.jsp就是个Hello World字符串而已，用来验证Logging活着。注意， 在Logging项目中，已没有Product项目中的log4j.properties和jndi.properties两个文件 。</p>    <p>来看看另外几个文件：</p>    <p>pom.xml（每个包的目的都写在注释里了）：</p>    <pre>  <code class="language-java"><!-- Use to cast object to LogEvent when received a log -->  <dependency>      <groupId>log4j</groupId>      <artifactId>log4j</artifactId>      <version>1.2.17</version>  </dependency>    <!-- Use to receive jms message -->  <dependency>      <groupId>org.springframework</groupId>      <artifactId>spring-jms</artifactId>      <version>4.0.0.RELEASE</version>  </dependency>    <!-- Use to load spring.xml -->  <dependency>      <groupId>org.springframework</groupId>      <artifactId>spring-web</artifactId>      <version>4.0.0.RELEASE</version>  </dependency>    <!-- ActiveMQ lib -->  <dependency>      <groupId>org.apache.activemq</groupId>      <artifactId>activemq-core</artifactId>      <version>5.7.0</version>  </dependency></code></pre>    <p>web.xml</p>    <pre>  <code class="language-java"><!DOCTYPE web-app PUBLIC   "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"   "http://java.sun.com/dtd/web-app_2_3.dtd" >    <web-app>      <context-param>          <param-name>contextConfigLocation</param-name>          <param-value>classpath:spring.xml</param-value>      </context-param>        <!-- Use to load spring.xml -->      <listener>          <listener-class>              org.springframework.web.context.ContextLoaderListener          </listener-class>      </listener>        <welcome-file-list>          <welcome-file>index.jsp</welcome-file>      </welcome-file-list>  </web-app></code></pre>    <p>spring.xml</p>    <pre>  <code class="language-java"><?xml version="1.0" encoding="UTF-8"?>  <beans xmlns="http://www.springframework.org/schema/beans"      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"       xsi:schemaLocation="    http://www.springframework.org/schema/beans      http://www.springframework.org/schema/beans/spring-beans-4.0.xsd">        <bean id="jmsTemplate" class="org.springframework.jms.core.JmsTemplate">          <property name="connectionFactory" ref="connectionFactory"/>      </bean>      <bean id="connectionFactory" class="org.springframework.jms.connection.SingleConnectionFactory">          <property name="targetConnectionFactory" ref="targetConnectionFactory"/>      </bean>      <bean id="targetConnectionFactory" class="org.apache.activemq.ActiveMQConnectionFactory">          <property name="brokerURL" value="tcp://localhost:61616"/>      </bean>  <!-- As JMSAppender only support the topic way to send messages,        thus queueDestination here is useless.      <bean id="queueDestination" class="org.apache.activemq.command.ActiveMQQueue">          <constructor-arg name="name" value="queue" />      </bean>   -->      <bean id="topicDestination" class="org.apache.activemq.command.ActiveMQTopic">          <constructor-arg name="name" value="logTopic" />      </bean>      <bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">          <property name="connectionFactory" ref="connectionFactory" />           <!-- <property name="destination" ref="queueDestination" />  -->           <property name="destination" ref="topicDestination" />           <property name="messageListener" ref="logMessageListener" />      </bean>      <bean id="logMessageListener" class="com.demo.logging.LogMessageListener"/>  </beans></code></pre>    <p>logMessageListener指向我们自己实现的日志消息处理逻辑类，topicDestination则关注topic为“logTopic”的消息，而jmsContainer把这两个对象绑在一起，这样就能接收并处理消息了。</p>    <p>最后就是伟大的监听器了LogMessageListener了：</p>    <pre>  <code class="language-java">package com.demo.logging;    import javax.jms.Message;  import javax.jms.MessageListener;  import org.apache.activemq.command.ActiveMQObjectMessage;  import org.apache.log4j.spi.LoggingEvent;    public class LogMessageListener implements MessageListener {      public void onMessage(Message message) {          try {              // receive log event in your consumer              LoggingEvent event = (LoggingEvent)((ActiveMQObjectMessage)message).getObject();              System.out.println("Logging project: [" + event.getLevel() + "]: "+ event.getMessage());          } catch (Exception e) {              e.printStackTrace();          }      }  }</code></pre>    <p>哈哈，说伟大，其实太简单了。但是可以看到，监听器里面就是之前Product项目中Main类里面移除的实现了MessageListener接口中的代码。</p>    <h3>测试</h3>    <p>在执行测试前，删掉ActiveMQ中所有的Queue，确保测试效果。</p>    <p>先运行Logging项目，开始Queue的监听。再运行Product的Main类的main函数，可以先看到Main类打印到控制台的日志：</p>    <p><img src="https://simg.open-open.com/show/ec376fe86eeaeaf1983aa3c7c80ea07d.png"></p>    <p>接下来去看看Queue中的情况：</p>    <h2><img src="https://simg.open-open.com/show/8819849c9ac7c020f2addff57eec8b9d.png"></h2>    <p>可以看到有个叫logTopic的主题的消息，进了3条，出了3条。不用想，出Queue的3条日志已经被Logging项目的Listener接收并打印出来了，现在去看看Tomcat的控制台：</p>    <p><img src="https://simg.open-open.com/show/82928d33de88f684ba9fdc19bac702b7.png"></p>    <p>还要注意Queue中的logTopic的Consumer数量为1而不是0，这与开始的截图不同。我们都知道这个Consumer是Logging项目中的LogMessageListener对象，它一直活着，是因为Tomcat一直活着；之前的Consumer数量为0，是因为在main函数执行完后，Queue的监听器（也是写日志的对象）就退出了。</p>    <p>通过把Product和Logging项目分别放在不同的机器上执行，在第三台机器上部署ActiveMQ（当然你可以把ActiveMQ搭建在任意可以访问的地方），再配置一下Product项目的log4j.properties文件和Logging项目的spring.xml文件就能用于生产环境啦。</p>    <h2>JMSAppender类的分析</h2>    <p>JMSAppender类将LoggingEvent实例序列化成ObjectMessage，并将其发送到JMS Server的一个指定Topic中， 因此，使用此种将日志发送到远程的方式只支持Topic方式发送，不支持Queue方式发送。 我们再log4j.properties中配置了这一句：</p>    <pre>  <code class="language-java">log4j.appender.jms=org.apache.log4j.net.JMSAppender</code></pre>    <p>这一句指定了使用的Appender，打开这个Appender，在里面可以看到很多setter，比如：</p>    <p><img src="https://simg.open-open.com/show/43a89f651d8a80987096d6d75f8f1a2d.png"></p>    <p>这些setter不是巧合，而正是对应了我们在log4j.properties中设置的其他几个选项：</p>    <pre>  <code class="language-java">log4j.appender.jms.InitialContextFactoryName=org.apache.activemq.jndi.ActiveMQInitialContextFactory  log4j.appender.jms.ProviderURL=tcp://localhost:61616  log4j.appender.jms.TopicBindingName=logTopic  log4j.appender.jms.TopicConnectionFactoryBindingName=ConnectionFactory</code></pre>    <p>来看看JMSAppender的activeOptions方法，这个方法是用于使我们在log4j.properties中的配置生效的：</p>    <pre>  <code class="language-java">/**   * Options are activated and become effective only after calling this method.   */  public void activateOptions() {      TopicConnectionFactory topicConnectionFactory;      try {          Context jndi;          LogLog.debug("Getting initial context.");          if (initialContextFactoryName != null) {              Properties env = new Properties();              env.put(Context.INITIAL_CONTEXT_FACTORY, initialContextFactoryName);              if (providerURL != null) {                  env.put(Context.PROVIDER_URL, providerURL);              } else {                  LogLog.warn("You have set InitialContextFactoryName option but not the "                          + "ProviderURL. This is likely to cause problems.");              }              if (urlPkgPrefixes != null) {                  env.put(Context.URL_PKG_PREFIXES, urlPkgPrefixes);              }                if (securityPrincipalName != null) {                  env.put(Context.SECURITY_PRINCIPAL, securityPrincipalName);                  if (securityCredentials != null) {                      env.put(Context.SECURITY_CREDENTIALS, securityCredentials);                  } else {                      LogLog.warn("You have set SecurityPrincipalName option but not the "                              + "SecurityCredentials. This is likely to cause problems.");                  }              }              jndi = new InitialContext(env);          } else {              jndi = new InitialContext();          }            LogLog.debug("Looking up [" + tcfBindingName + "]");          topicConnectionFactory = (TopicConnectionFactory) lookup(jndi, tcfBindingName);          LogLog.debug("About to create TopicConnection.");            ///////////////////////////////注意这里只会创建TopicConnection////////////////////////////          if (userName != null) {              topicConnection = topicConnectionFactory.createTopicConnection(userName, password);          } else {              topicConnection = topicConnectionFactory.createTopicConnection();          }            LogLog.debug("Creating TopicSession, non-transactional, " + "in AUTO_ACKNOWLEDGE mode.");          topicSession = topicConnection.createTopicSession(false, Session.AUTO_ACKNOWLEDGE);            LogLog.debug("Looking up topic name [" + topicBindingName + "].");          Topic topic = (Topic) lookup(jndi, topicBindingName);            LogLog.debug("Creating TopicPublisher.");          topicPublisher = topicSession.createPublisher(topic);            LogLog.debug("Starting TopicConnection.");          topicConnection.start();            jndi.close();      } catch (JMSException e) {          errorHandler.error("Error while activating options for appender named [" + name + "].", e,                  ErrorCode.GENERIC_FAILURE);      } catch (NamingException e) {          errorHandler.error("Error while activating options for appender named [" + name + "].", e,                  ErrorCode.GENERIC_FAILURE);      } catch (RuntimeException e) {          errorHandler.error("Error while activating options for appender named [" + name + "].", e,                  ErrorCode.GENERIC_FAILURE);      }  }</code></pre>    <p>上面初始化了一个TopicConnection，一个TopicSession，一个TopicPublisher。咱们再来看看这个Appender的append方法：</p>    <pre>  <code class="language-java">/**   * This method called by {@link AppenderSkeleton#doAppend} method to do most   * of the real appending work.   */  public void append(LoggingEvent event) {      if (!checkEntryConditions()) {          return;      }      try {          ObjectMessage msg = topicSession.createObjectMessage();          if (locationInfo) {              event.getLocationInformation();          }          msg.setObject(event);          topicPublisher.publish(msg);///////////////注意这一句//////////////      } catch (JMSException e) {          errorHandler.error("Could not publish message in JMSAppender [" + name + "].",               e, ErrorCode.GENERIC_FAILURE);      } catch (RuntimeException e) {          errorHandler.error("Could not publish message in JMSAppender [" + name + "].",               e, ErrorCode.GENERIC_FAILURE);      }  }</code></pre>    <p>这里使用TopicPublisher.publish()方法，把序列化的消息发布出去。可见这也证明了JMSAppender只支持以Topic方式发送消息。</p>    <p>样例下载：百度网盘</p>    <p>链接: <a href="/misc/goto?guid=4959647188939313389" rel="nofollow,noindex">http://pan.baidu.com/s/1pJF1ybx</a> 密码: x5r6</p>    <p>参考：</p>    <p><a href="/misc/goto?guid=4959647189016275912" rel="nofollow,noindex">http://activemq.apache.org/how-do-i-use-log4j-jms-appender-with-activemq.html</a></p>    <p> </p>    <p>来自： <a href="/misc/goto?guid=4959675005962494893" rel="nofollow">http://www.importnew.com/20532.html</a></p>    <p> </p>