【斗医】【3】Web应用开发20天

在上面提及异常的中英文从资源文件中读取，若读取失败需要日志记录，所以使用网上正在闹腾的Logback来记录。关于Logback与Log4j这里不做评判和说明，所有疑问可以请教谷歌。

一、Logback的使用前期准备

1、在官网Http://logback.qos.ch/download.html下载Logback；在官网http://www.slf4j.org/download.html下载slf4j

2、在D:\medical\war\WEB-INF下创建lib文件夹，用于放置本应用的所需jar包

3、解压上面的下载，把logback-access-1.0.13.jar、logback-classic-1.0.13.jar、logback-core-1.0.13.jar和slf4j-api-1.7.5.jar复制到D:\medical\war\WEB-INF\lib中

二、测试类

下面着手写一个与本应用无关的测试类FrameLogger.java

1、打开Eclipse，在medical工程上右键，选择“New > Class”，Package填写“com.medical.frame”，Name填写“FrameLoggerDemo”，点击“Finish”

2、要使用日志类，应用先定义一个Logger，然后再使用这个对象，所以代码如下：

package com.medical.frame;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class FrameLoggerDemo
{
    private static final Logger logger = LoggerFactory.getLogger(FrameLoggerDemo.class);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
    public static void main(String[] args)
    {
        logger.info("It's test for logback.");
    }
}

3、你会发现上面代码编译不通过。这很正常，因为Eclipse没有导入所需的jar包。右键medical工程选择“Properties > Java Build Path > Libraries > Add JARs...”，在JAR选择窗口中把D:\medical\war\WEB-INF\lib下的jar包添加进来，如图：

4、我想不仅把日志打印到控制台还要打印到日志文件中，更甚者想插入到数据库中，XML配置文件可以协助完成。在D:\medical\war\下创建etc文件夹，然后在etc下创建loGConfig.xml文件。

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <!--日志文件的存储地址,一定要使用绝对路径-->
    <property name="LOG_HOME" value="D:/log" />
    <!--日志文件后缀格式-->
    <timestamp key="fileSuffix" datePattern="yyyyMMdd'_'HHmm" />
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
    <!--控制台输出-->
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <!--输出在控制台上的日志字符串编码-->
        <Encoding>UTF-8</Encoding>
        <!--输出在控制台上的日志格式-->
        <layout class="ch.qos.logback.classic.PatternLayout">
            <!--%d表示日期; %thread表示线程名; %-5level表示从左显示5个字符宽度的级别名; %logger表示日志类; %msg表示日志消息; %n表示换行-->
            <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{60} - %msg%n</pattern>
        </layout>
    </appender>
    <!--文件输出-->
    <appender name="FILE"  class="ch.qos.logback.core.rolling.RollingFileAppender">
        <!--输出在控制台上的日志字符串编码-->
        <Encoding>UTF-8</Encoding>
        <!--日志对应的文件名-->
        <file>${LOG_HOME}/trace${fileSuffix}.txt</file>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
        <!--日志文件记录滚动策略-->
        <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
            <!--当日志文件超过大小时就压缩为zip包-->
            <fileNamePattern>${LOG_HOME}/trace${fileSuffix}.%i.zip</fileNamePattern>
            <!--最多有10个zip压缩包,超过10就覆盖之前的-->
            <minIndex>1</minIndex>
            <maxIndex>10</maxIndex>
        </rollingPolicy>  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
        <!--文件超过5M就重新生成新的日志文件,老的日志文件压缩成zip包-->
        <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
            <maxFileSize>5MB</maxFileSize>
        </triggeringPolicy>
        <!--输出在文件上的日志格式-->
        <encoder>
            <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{60} - %msg%n </pattern>
        </encoder>
    </appender>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
    <!--日志输出级别-->
    <root level="INFO">
        <appender-ref ref="STDOUT" />
        <appender-ref ref="FILE" />
    </root>
</configuration>

【备注】：关于这个配置文件建议感兴趣的读者，自己亲自配置一下，这样才能体验每个标签的含义。

5、运行FrameLoggerDemo发现并没有在指定的D:/log下输出日志文件。试想一下，我们都没有告诉Logback输出策略是什么，它怎么又会知道呢？所以这里需要在main()运行之前把logconfig.xml加载进来，怎么加载？怎么只加载一次？方法很多，可以使用spring的单例工厂，而这里我们使用单例类。

private static FrameLoggerDemo instance = new FrameLoggerDemo();
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
private FrameLoggerDemo()
{
    String logbackCfg = "D:\\medical\\war\\etc\\logconfig.xml";
    ILoggerFactory loggerFactory = LoggerFactory.getILoggerFactory();
    JoranConfigurator configurator = new JoranConfigurator();
    configurator.setContext((LoggerContext) loggerFactory);
    try
    {
        configurator.doConfigure(logbackCfg);
    }
    catch (JoranException e)
    {
        e.printStackTrace();
    }
}

再运行一次，有日志文件输出出来了

三、斗医应用如何使用Logback呢？

从上面的FrameLoggerDemo可以看到，系统在使用Logger对象之前必须把配置文件加载进来，对于web应用它由多个Servlet构成，所以最好在第一个Servlet启动时加载进来，后续的使用者就直接使用即可。

1、在D:\medical\war\WEB-INF\web.xml中定义名称为action的servlet

<web-app>
    <servlet>
        <servlet-name>action</servlet-name>
        <servlet-class>com.medical.frame.FrameLauncher</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>action</servlet-name>
        <url-pattern>*.act</url-pattern>
    </servlet-mapping>
    <welcome-file-list>
         <welcome-file>index.html</welcome-file>
    </welcome-file-list>
</web-app>

2、该servlet说明当客户端的请求为*.act时，都使用名称为action的servlet处理，处理器为FrameLauncher这个类，它必须继承httpservlet。Servlet一般由init、doGet、doPost、destory方法构成，所以FrameLauncher也不例外，它需要重写这4个方法。

package com.medical.frame;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class FrameLauncher extends HttpServlet
{
    @Override
    public void init() throws ServletException
    {
                                                                                                                                                                                                                                                                                                                                                                                                                           
    }
                                                                                                                                                                                                                                                                                                                                                                                                                       
    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException
    {
                                                                                                                                                                                                                                                                                                                                                                                                                           
    }
                                                                                                                                                                                                                                                                                                                                                                                                                       
    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException
    {
        doGet(request, response);
    }
                                                                                                                                                                                                                                                                                                                                                                                                                       
    @Override
    public void destroy()
    {
                                                                                                                                                                                                                                                                                                                                                                                                                           
    }
}

3、当request请求到达Web容器时，它会根据请求参数判断使用哪个servlet处理，当servlet首次被调用到时，它会反射<servlet-class>定义的类，再调用init()方法进行初始化。而我们的日志加载就可以在这里处理。

定义com.medical.frame.util.FrameConfigUtil.java，里面定义静态方法initLogConfig()用于加载logback日志配置文件。

public class FrameConfigUtil
{
    
    public static void initLogConfig(ServletContext context)
    {
        // 获取logback配置文件
        StringBuilder logConfigPath = new StringBuilder(context.getRealPath("/"));
        logConfigPath.append("etc").append(File.separator).append("logconfig.xml");
                                                                                                                                                                                                                                                                                                                                     
        // 加载logback配置文件
        ILoggerFactory loggerFactory = LoggerFactory.getILoggerFactory();
        JoranConfigurator configurator = new JoranConfigurator();
        configurator.setContext((LoggerContext) loggerFactory);
        try
        {
            configurator.doConfigure(logConfigPath.toString());
        }
        catch (JoranException e)
        {
            System.out.println("[重要] init logback config error.\n" + e.getMessage());
        }
    }
}

4、FrameLauncher.init()方法调用FrameConfigUtil.initLogConfig()

@Override
public void init() throws ServletException
{
    ServletContext context = getServletContext();
    FrameConfigUtil.initLogConfig(context);
}

至此logback的配置文件在action这个servlet初始化时就加载完了，那该如何测试呢？

5、修改D:\medical\war\index.html文件内容，修改后的内容如下：

<html>
    <head>
        <title>medical</title>   
    </head>
    <body>
        <a href="index.act">Test Logback</a>
    </body>
</html>

6、重写com.medical.frame.FrameLauncher.doGet()方法

private static final Logger logger = LoggerFactory.getLogger(FrameLauncher.class);
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException
{
    logger.error("It's test for logback.");
}

这样当在浏览器中输入http://localhost:8080/medical时，由web.xml的<welcome-file-list>定义知系统首先加载index.html文件，当用鼠标点击Test Logback会index.act的HTTP请求发送给Tomcat容器，Tomcat根据web.xml的<url-pattern>*.act</url-pattern>找到对应的<servlet-name>action</servlet-name>，然后反射加载com.medical.frame.FrameLauncher.java，当FrameLaucher加载时调用init()方法把logconfig.xml读入，接着把HTT请求转换为HttpServletReqeust请求交给doGet()，从而把日志打印出来。

【备注1】：若用户从头到尾地写这个应用，有可能会发现，尽管在D:\log下生成了日志文件，但里面没有内容，这有可能是在加载logconfig.xml时使用的JoranConfigurator不正确。应该使用import ch.qos.logback.classic.joran.JoranConfigurator，而非import ch.qos.logback.access.joran.JoranConfigurator。

【备注2】：若在实际操作这个实例时遇到问题，可参见附件，也可评论以便及时交流