速记

1. 背景描述

在使用springboot开发web项目的过程中，前期工作一直很顺利，着实感觉到了springboot所提供的便利性。然而，一直没有踩太多坑的我心里反而不踏实，哈哈哈，贱癌入骨，无药可治。可就在今天正式线上部署（线上采用外部tomcat的方式进行部署，自配日志方便问题排查）的过程中，遇到了那么一点点滴问题：自配log4j配置文件不生效，配置路径无日志输出，但catalina.out日志正常输出。下面就简单记录描述一下。

2. 问题定位

第一感觉是觉得tomcat配置有误，可在经过了各种方式尝试无果后，开始怀疑是不是log4j文件被所引用项目中的默认的log4j所吞没了。顺着这个思路，开始进行尝试。

首先打印依赖树关系，找到冲突依赖排除掉。根据依赖关系，很明显，springboot 自带 logging 嫌疑最大，首当其冲将其排除掉，重新打包测试运行。如下：

<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

重新部署运行后，查看catalina.out日志输出，发现明显不一样了。如下：

01-Nov-2018 19:21:34.890 INFO [main] org.apache.jasper.servlet.TldScanner.scanJars At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
log4j: Trying to find [log4j.xml] using context classloader ParallelWebappClassLoader
  context: xcar_hbase
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@238e0d81
.
log4j: Trying to find [log4j.xml] using ParallelWebappClassLoader
  context: xcar_hbase
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@238e0d81
 class loader.
log4j: Trying to find [log4j.xml] using ClassLoader.getSystemResource().
log4j: Trying to find [log4j.properties] using context classloader ParallelWebappClassLoader
  context: xcar_hbase
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@238e0d81
.
log4j: Using URL [file:/export/tomcat/hbase-api/webapps/xcar_hbase/WEB-INF/classes/log4j.properties] for automatic log4j configuration.
log4j: Reading configuration from URL file:/export/tomcat/hbase-api/webapps/xcar_hbase/WEB-INF/classes/log4j.properties
log4j: Parsing for [root] with value=[INFO,console,DRFA,RFA,RFAW].
log4j: Level token is [INFO].
log4j: Category root set to INFO
log4j: Parsing appender named "console".
log4j: Parsing layout options for "console".
log4j: Setting property [conversionPattern] to [%d{yy/MM/dd HH:mm:ss} %p %c{2}: %m%n].
log4j: End of parsing for "console".
log4j: Setting property [target] to [System.out].
log4j: Parsed "console" options.
log4j: Parsing appender named "DRFA".
log4j: Parsing layout options for "DRFA".
log4j: Setting property [conversionPattern] to [%d{yy/MM/dd HH:mm:ss} %-5p [%t] %c{2}: %m%n].
log4j: End of parsing for "DRFA".
log4j: Setting property [encoding] to [UTF-8].
log4j: Setting property [datePattern] to [.yyyy-MM-dd].
log4j: Setting property [threshold] to [INFO].
log4j: Setting property [file] to [/export/tomcat/hbase-api/logs/dls/info.log].
log4j: setFile called: /export/tomcat/hbase-api/logs/dls/info.log, true
log4j: setFile ended
log4j: Appender [DRFA] to be rolled at midnight.
log4j: Parsed "DRFA" options.
log4j: Parsing appender named "RFA".
log4j: Parsing layout options for "RFA".
log4j: Setting property [conversionPattern] to [%d{yy/MM/dd HH:mm:ss} %p [%t] %c{2} >>> %m%n].
log4j: End of parsing for "RFA".
log4j: Setting property [encoding] to [UTF-8].
log4j: Setting property [file] to [/export/tomcat/hbase-api/logs/dls/error.log].
log4j: Setting property [maxBackupIndex] to [5].
log4j: Setting property [threshold] to [ERROR].
log4j: Setting property [maxFileSize] to [200MB].
log4j: setFile called: /export/tomcat/hbase-api/logs/dls/error.log, true
log4j: setFile ended
log4j: Parsed "RFA" options.
log4j: Parsing appender named "RFAW".
log4j: Parsing layout options for "RFAW".
log4j: Setting property [conversionPattern] to [%d{yy/MM/dd HH:mm:ss} %p [%t] %c{2} >>> %m%n].
log4j: End of parsing for "RFAW".
log4j: Setting property [encoding] to [UTF-8].
log4j: Setting property [maxBackupIndex] to [1].
log4j: Setting property [file] to [/export/tomcat/hbase-api/logs/dls/debug.log].
log4j: Setting property [threshold] to [DEBUG].
log4j: Setting property [maxFileSize] to [20MB].
log4j: setFile called: /export/tomcat/hbase-api/logs/dls/debug.log, true
log4j: setFile ended
log4j: Parsed "RFAW" options.
log4j: Finished configuring.

可以看到，日志中打出了自配log4j被加载的过程，tomcat在加载spring的过程中首先查找系统资源路径下是否有spring相关[log4j.xml]或是[log4j.properties]文件，直到检测结果均为 false 时才会到 tomcat classes 路径下查找项目自身的log4j相关配置文件并加载。

3. 完整POM

下面给大家贴出springboot相关完整pom文件：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.xxxx.xxxx</groupId>
    <artifactId>xxxxx</artifactId>xxxxx
    <packaging>war</packaging>
    <version>1.0.1</version>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <!--指定Java编译版本-->
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
        <junit.version>4.11</junit.version>
        <springboot.version>1.5.8.RELEASE</springboot.version>
    </properties>

    <!--Inherit defaults from Spring Boot-->
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.8.RELEASE</version>
    </parent>

    <!-- Package as an executable jar -->
    <dependencies>
        <!-- Web 依赖 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

        <!--打包可执行包并部署到外部Tomcat容器需添加该依赖-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <scope>provided</scope>
        </dependency>

        <!-- 测试依赖 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <finalName>xcar_hbase</finalName>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>${springboot.version}</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.6</version>
                <configuration>
                    <!--项目中没有引入web.xml声明，否则报错-->
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>