快速將log4j.xml轉換為logback.xml

應用的日誌輸出頻率太高，log4j同步日誌輸出的時候鎖競爭太過激烈，導致業務執行緒阻塞。系統load 200+，執行緒數2000+ 。所以想通過切換到logback 來提升日誌輸出的內容。

想要切換到logback要做兩件事情：

* 切換pom中依賴的jar包
* 將log4j.xml 轉換成 logback.xml 

第一件事情比較簡單，但是第二件事情稍微有些麻煩，特別是碰到原本日誌Appender就非常多的情況下（我們配置了超過50個Appender）一個一個手動改就很繁瑣了。在網上找了很多都是從 log4j.properties 轉換為 logback.xml 的，我們這邊還是很少有用到log4j.properties的。 在Google 上找了好久找到了一個文章 http://rpuchkovskiy.blogspot.com/2014/11/xslt-to-convert-log4jxml-config-to.html。通過他可以把 log4j.xml 轉換為 logback.xml ，不過他的實現比較老，我結合我們的使用場景稍微修改了下。

<!--
     This XLST script converts log4j.xml.bak file to logback.xml file
     trying to mimic its behavior as close as possible

     @author Roman Puchkovskiy
 -->
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                exclude-result-prefixes="log4j xalan"
                xmlns:log4j="http://jakarta.apache.org/log4j/"
                xmlns:xalan="http://xml.apache.org/xslt"
                xmlns:xslt="http://www.w3.org/1999/XSL/Transform">

    <xsl:output indent="yes" xalan:indent-amount="4"/>

    <xsl:variable name="vLower" select="`abcdefghijklmnopqrstuvwxyz`"/>

    <xsl:variable name="vUpper" select="`ABCDEFGHIJKLMNOPQRSTUVWXYZ`"/>

    <xsl:template match="/log4j:configuration">
        <configuration>
            <xsl:apply-templates select="appender"/>
            <xsl:apply-templates select="logger"/>
            <xsl:apply-templates select="root"/>
            <xsl:apply-templates select="comment()"/>
        </configuration>
    </xsl:template>

    <xsl:template match="appender">
        <appender>
            <xsl:attribute name="name">
                <xsl:value-of select="@name"/>
            </xsl:attribute>
            <xsl:attribute name="class">
                <xsl:choose>
                    <!-- 定義了Appender 之間的對映關係 -->
                    <xsl:when test="@class = `org.apache.log4j.DailyRollingFileAppender`">ch.qos.logback.core.rolling.RollingFileAppender</xsl:when>
                    <xsl:when test="@class = `com.alibaba.common.logging.spi.log4j.DailyRollingFileAppender`">ch.qos.logback.core.rolling.RollingFileAppender</xsl:when>
                    <xsl:when test="@class = `org.apache.log4j.AsyncAppender`">ch.qos.logback.classic.AsyncAppender</xsl:when>
                    <xsl:when test="@class = `org.apache.log4j.ConsoleAppender`">ch.qos.logback.core.ConsoleAppender</xsl:when>
                    <xsl:when test="@class = `org.apache.log4j.net.SMTPAppender`">ch.qos.logback.classic.net.SMTPAppender</xsl:when>
                    <xsl:when test="@class = `org.apache.log4j.net.SocketAppender`">ch.qos.logback.classic.net.SocketAppender</xsl:when>
                    <xsl:when test="@class = `org.apache.log4j.net.SyslogAppender`">ch.qos.logback.classic.net.SyslogAppender</xsl:when>
                    <xsl:otherwise>
                        <xsl:message terminate="yes">Unknown appender class:
                            <xsl:value-of select="@class"/>
                        </xsl:message>
                    </xsl:otherwise>
                </xsl:choose>
            </xsl:attribute>
            <xsl:apply-templates select="param"/>
            <xsl:apply-templates select="layout"/>
            <xsl:apply-templates select="filter"/>
        </appender>
        <xsl:call-template name="newline"/>
    </xsl:template>

    <xsl:template match="param">
        <xsl:choose>
            <!-- 將log4j file 轉換為 logback 的file -->
            <xsl:when test="@name = `file`">
                <xsl:element name="{concat(translate(substring(@name,1,1), $vUpper, $vLower),substring(@name, 2))}">
                    <xsl:value-of select="@value"/>
                </xsl:element>
            </xsl:when>
        </xsl:choose>
    </xsl:template>

    <xsl:template match="layout">
        <xsl:choose>
            <!-- 將PatternLayout 做轉換 -->
            <xsl:when test="@class = `org.apache.log4j.PatternLayout`">
                <xsl:choose>
                    <xsl:when
                            test="../@class = `org.apache.log4j.ConsoleAppender` or ../@class = `org.apache.log4j.DailyRollingFileAppender` or ../@class = `com.alibaba.common.logging.spi.log4j.DailyRollingFileAppender`">
                        <encoder>
                            <pattern>
                                <xsl:value-of select="param[@name = `ConversionPattern`]/@value"/>
                            </pattern>
                            <charset>UTF-8</charset>
                        </encoder>
                        <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
                            <xsl:element name="fileNamePattern">
                                <xsl:value-of select="../param[@name = `file`]/@value" />.%d{yyyy-MM-dd}</xsl:element>
                            <maxHistory>7</maxHistory>
                        </rollingPolicy>
                    </xsl:when>
                    <xsl:when
                            test="../@class = `org.apache.log4j.net.SocketAppender` or ../@class = `org.apache.log4j.net.SyslogAppender`">
                        <xsl:comment>this is NOT needed tor this logger, so it is commented out</xsl:comment>
                        <xsl:comment><![CDATA[
                            <layout>
                                <pattern>]]><xsl:value-of select="param[@name = `ConversionPattern`]/@value"/><![CDATA[</pattern>
                            </layout>]]>
                        </xsl:comment>
                    </xsl:when>
                    <xsl:otherwise>
                        <layout>
                            <pattern>
                                <xsl:value-of select="param[@name = `ConversionPattern`]/@value"/>
                            </pattern>
                        </layout>
                    </xsl:otherwise>
                </xsl:choose>
            </xsl:when>
            <xsl:otherwise>
                <xsl:message terminate="yes">Unknown layout class:
                    <xsl:value-of select="@class"/>
                </xsl:message>
            </xsl:otherwise>
        </xsl:choose>
    </xsl:template>

    <xsl:template match="filter">
        <xsl:choose>
            <xsl:when
                    test="@class = `org.apache.log4j.varia.LevelRangeFilter` and param[@name = `LevelMin`]/@value != `` and param[@name = `LevelMax`]/@value = `FATAL`">
                <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
                    <level>
                        <xsl:value-of select="param[@name = `LevelMin`]/@value"/>
                    </level>
                </filter>
            </xsl:when>
            <xsl:otherwise>
                <xsl:message terminate="yes">Don`t know what to do with filter</xsl:message>
            </xsl:otherwise>
        </xsl:choose>
    </xsl:template>

    <xsl:template match="logger">
        <logger>
            <xsl:attribute name="name">
                <xsl:value-of select="@name"/>
            </xsl:attribute>
            <xsl:attribute name="level">
                <xsl:choose>
                    <xsl:when test="level/@value = `FATAL`">OFF</xsl:when>
                    <xsl:otherwise>
                        <xsl:value-of select="level/@value"/>
                    </xsl:otherwise>
                </xsl:choose>
            </xsl:attribute>
            <xsl:if test="@additivity != ``">
                <xsl:attribute name="additivity">
                    <xsl:value-of select="@additivity"/>
                </xsl:attribute>
            </xsl:if>
            <xsl:apply-templates select="appender-ref"/>
        </logger>
    </xsl:template>

    <xsl:template match="appender-ref">
        <appender-ref>
            <xsl:attribute name="ref">
                <xsl:value-of select="@ref"/>
            </xsl:attribute>
        </appender-ref>
    </xsl:template>

    <xsl:template match="root">
        <xsl:call-template name="newline"/>
        <root>
            <xsl:attribute name="level">
                <xsl:value-of select="level/@value"/>
            </xsl:attribute>
            <xsl:apply-templates select="appender-ref"/>
            <xsl:apply-templates select="comment()"/>
        </root>
    </xsl:template>

    <xsl:template match="comment()">
        <xsl:copy-of select="."/>
    </xsl:template>

    <xsl:template name="newline">
        <!-- don`t reformat this! -->
        <xsl:text>

        </xsl:text>
    </xsl:template>

</xsl:stylesheet>

使用方式很簡單:

String[] parmas = {"-IN", "log4j.xml",
                            "-XSL", "log4j-to-logback.xsl",
                            "-OUT", "logback.xml"};

org.apache.xalan.xslt.Process.Process.main(parmas);