運行一個基於maven的web-app骨架創建的工程時，報瞭如下[警告]：
The POM for com.alibaba:druid:jar:1.1.21 is invalid, transitive dependencies (if any) will not be available, enable debug logging for more details
-> 開啓debug模式，查看詳細信息
[Windows]+R快捷鍵打開【cmd】命令行，cd進入當前項目所在目錄：E:\IdeaProjects\maven_advanced_01
--cmd輸出DEBUG信息
mvn clean install -X
--或者直接把DEBUG信息輸出到本地的debug.txt文件
mvn clean install -X > debug.txt
打印輸出項目運行的DEBUG信息，發出一個警告
[WARNING] The POM for com.alibaba:druid:jar:1.1.21 is invalid, transitive dependencies (if any) will not be available: 4 problems were encountered while building the effective model for com.alibaba:druid:1.1.21
[ERROR] 'dependencies.dependency.systemPath' for com.sun:tools:jar must specify an absolute path but is ${project.basedir}/lib/openjdk-1.8-tools.jar @
[ERROR] 'dependencies.dependency.systemPath' for com.sun:jconsole:jar must specify an absolute path but is ${project.basedir}/lib/openjdk-1.8-jconsole.jar @
[WARNING] 'dependencies.dependency.systemPath' for com.alibaba:jconsole:jar refers to a non-existing file D:\Program Files\Java\jdk-13.0.2\lib\jconsole.jar @
[WARNING] 'dependencies.dependency.systemPath' for com.alibaba:tools:jar refers to a non-existing file D:\Program Files\Java\jdk-13.0.2\lib\tools.jar @
-> 查看依賴包關係樹結構
--cmd輸出
mvn dependency:tree
--cmd輸出到本地tree.txt
mvn dependency:tree > tree.txt
[INFO] Scanning for projects...
[INFO]
[INFO] ----------------------< com.yy:maven_advanced_01 >----------------------
[INFO] Building maven_advanced_01 1.0-SNAPSHOT
[INFO] --------------------------------[ war ]---------------------------------
[WARNING] The POM for com.alibaba:druid:jar:1.1.21 is invalid, transitive dependencies (if any) will not be available, enable debug logging for more details
[INFO]
[INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ maven_advanced_01 ---
[INFO] com.yy:maven_advanced_01:war:1.0-SNAPSHOT
[INFO] +- org.mybatis:mybatis:jar:3.5.4:compile
[INFO] +- org.mybatis:mybatis-spring:jar:2.0.4:compile
[INFO] +- com.github.pagehelper:pagehelper:jar:5.1.11:compile
[INFO] | \- com.github.jsqlparser:jsqlparser:jar:2.0:compile
[INFO] +- mysql:mysql-connector-java:jar:8.0.19:runtime
[INFO] | \- com.google.protobuf:protobuf-java:jar:3.6.1:runtime
[INFO] +- com.alibaba:druid:jar:1.1.21:compile
[INFO] +- c3p0:c3p0:jar:0.9.1.2:compile
[INFO] +- org.springframework:spring-context:jar:5.2.4.RELEASE:compile
[INFO] | +- org.springframework:spring-aop:jar:5.2.4.RELEASE:compile
[INFO] | +- org.springframework:spring-core:jar:5.2.4.RELEASE:compile
[INFO] | | \- org.springframework:spring-jcl:jar:5.2.4.RELEASE:compile
[INFO] | \- org.springframework:spring-expression:jar:5.2.4.RELEASE:compile
[INFO] +- org.springframework:spring-beans:jar:5.2.4.RELEASE:compile
[INFO] +- org.springframework:spring-web:jar:5.2.4.RELEASE:compile
[INFO] +- org.springframework:spring-webmvc:jar:5.2.4.RELEASE:compile
[INFO] +- org.springframework:spring-jdbc:jar:5.2.4.RELEASE:compile
[INFO] +- org.springframework:spring-aspects:jar:5.2.4.RELEASE:compile
[INFO] | \- org.aspectj:aspectjweaver:jar:1.9.5:compile
[INFO] +- org.springframework:spring-jms:jar:5.2.4.RELEASE:compile
[INFO] | \- org.springframework:spring-messaging:jar:5.2.4.RELEASE:compile
[INFO] +- org.springframework:spring-context-support:jar:5.2.4.RELEASE:compile
[INFO] +- org.springframework:spring-tx:jar:5.2.4.RELEASE:compile
[INFO] +- org.springframework:spring-test:jar:5.2.4.RELEASE:compile
[INFO] +- org.springframework:spring-orm:jar:5.2.4.RELEASE:compile
[INFO] +- org.springframework.security:spring-security-web:jar:5.3.0.RELEASE:compile
[INFO] +- org.springframework.security:spring-security-config:jar:5.3.0.RELEASE:compile
[INFO] +- org.springframework.security:spring-security-core:jar:5.3.0.RELEASE:compile
[INFO] +- org.springframework.security:spring-security-taglibs:jar:5.3.0.RELEASE:compile
[INFO] | \- org.springframework.security:spring-security-acl:jar:5.3.0.RELEASE:compile
[INFO] +- jstl:jstl:jar:1.2:compile
[INFO] +- javax.servlet:javax.servlet-api:jar:4.0.1:provided
[INFO] +- javax.servlet:jsp-api:jar:2.0:provided
[INFO] | \- javax.servlet:servlet-api:jar:2.4:provided
[INFO] +- log4j:log4j:jar:1.2.17:compile
[INFO] +- org.slf4j:slf4j-api:jar:1.7.30:compile
[INFO] +- org.slf4j:slf4j-log4j12:jar:1.7.30:test
[INFO] +- org.slf4j:slf4j-simple:jar:1.6.6:compile
[INFO] \- junit:junit:jar:4.12:test
[INFO] \- org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.447 s
[INFO] Finished at: 2020-03-22T19:31:38+08:00
[INFO] ------------------------------------------------------------------------
#1-> 警告的詳細內容如下
[WARNING] The POM for com.alibaba:druid:jar:1.1.21 is invalid, transitive dependencies (if any) will not be available: 4 problems were encountered while building the effective model for com.alibaba:druid:1.1.21
[ERROR] 'dependencies.dependency.systemPath' for com.sun:tools:jar must specify an absolute path but is ${project.basedir}/lib/openjdk-1.8-tools.jar @
[ERROR] 'dependencies.dependency.systemPath' for com.sun:jconsole:jar must specify an absolute path but is ${project.basedir}/lib/openjdk-1.8-jconsole.jar @
[WARNING] 'dependencies.dependency.systemPath' for com.alibaba:jconsole:jar refers to a non-existing file D:\Program Files\Java\jdk-13.0.2\lib\jconsole.jar @
[WARNING] 'dependencies.dependency.systemPath' for com.alibaba:tools:jar refers to a non-existing file D:\Program Files\Java\jdk-13.0.2\lib\tools.jar @
#2-> 運行環境 ：InteIliJ IDEA 2019.3.3 (Ultimate Edition) + jdk 13.0.2 + apache maven 3.6.3
#3-> 嘗試解決問題
一開始在網上看了很多博客，都沒有解決這個問題。
- 有人說是JDK的環境變量沒有配好，確認過jdk環境配置沒有問題。
- 有人說要修改這裏的${project.basedir}，但他們基本是在使用gradle的時候遇到這個問題的，感覺跟我遇到的問題也不太一樣。最關鍵的是根本找不到這個默認的${project.basedir}地址在哪裏，也不知道去哪個文件裏修改這個路徑。
所以這裏的兩個 [ERROR] 說要指定一個絕對路徑，但找不到${project.basedir}，修改絕對路徑這條路算是沒法玩了。
這裏還有兩個 [WARNING] 顯示找不到JAVA_HOME\lib下的tools.jar和jconsole.jar，但是我使用的JDK最新版13.0.2默認安裝完成以後本身就沒有JRE目錄，自己生成JRE目錄之後，也找不到這倆文件。
百度了一下，原來新版本的jdk自9.+之後就沒有JRE目錄了，同時這兩個文件也找不到了，配置環境變量的時候也省去了這兩個路徑的配置，直接把JAVA_HOME/bin掛到path就可以了。
那怎麼辦，難道要換JDK版本嗎？但是爲什麼這個警告的提示僅僅只報了com.alibaba.druid這一個單獨的jar包呢？如果jdk有問題整個項目應該都無法運行纔對。
這纔開始考慮是不是跟引入的com.alibaba.druid這個jar包有關，我用的這個連接池是最新版1.1.21，我嘗試降低了jar包的版本，改成1.1.20，就解決了。=b
針對最新版1.1.21，看到很多小夥伴跟我遇到了同樣的問題，所以合理的懷疑這可能是個官方bug。