Tomcat：At least one JAR was scanned for TLDs yet contained no TLDs

启动Tomcat的时候，经常见到这样的BUG:

 

14-Apr-2019 13:53:25.198 信息 [localhost-startStop-1] 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.

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以前不知道怎么处理，怎么处理才是正确的，最近研究了点点Tomcat源码，也算知其一，知其二，不知其三四五六七了，下面先贴上解决方案：

 

解决方案：

catalina-home/conf/Catalina.properties中有这样一个属性：jarsToSkip

 

tomcat.util.scan.StandardJarScanFilter.jarsToSkip= bootstrap.jar,commons-daemon.jar,tomcat-juli.jar, annotations-api.jar,el-api.jar,jsp-api.jar,servlet-api.jar,websocket-api.jar, catalina.jar,catalina-ant.jar,catalina-ha.jar,catalina-storeconfig.jar, catalina-tribes.jar, jasper.jar,jasper-el.jar,ecj-*.jar, tomcat-api.jar,tomcat-util.jar,tomcat-util-scan.jar,tomcat-coyote.jar, tomcat-dbcp.jar,tomcat-jni.jar,tomcat-websocket.jar, tomcat-i18n-en.jar,tomcat-i18n-es.jar,tomcat-i18n-fr.jar,tomcat-i18n-ja.jar, tomcat-juli-adapters.jar,catalina-jmx-remote.jar,catalina-ws.jar, tomcat-jdbc.jar, tools.jar, commons-beanutils*.jar,commons-codec*.jar,commons-collections*.jar, commons-dbcp*.jar,commons-digester*.jar,commons-fileupload*.jar, commons-httpclient*.jar,commons-io*.jar,commons-lang*.jar,commons-logging*.jar, commons-math*.jar,commons-pool*.jar, jstl.jar,taglibs-standard-spec-*.jar, geronimo-spec-jaxrpc*.jar,wsdl4j*.jar, ant.jar,ant-junit*.jar,aspectj*.jar,jmx.jar,h2*.jar,hibernate*.jar,httpclient*.jar, jmx-tools.jar,jta*.jar,log4j*.jar,mail*.jar,slf4j*.jar, xercesImpl.jar,xmlParserAPIs.jar,xml-apis.jar, junit.jar,junit-*.jar,ant-launcher.jar, cobertura-*.jar,asm-*.jar,dom4j-*.jar,icu4j-*.jar,jaxen-*.jar,jdom-*.jar, jetty-*.jar,oro-*.jar,servlet-api-*.jar,tagsoup-*.jar,xmlParserAPIs-*.jar, xom-*.jar

 

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我们只需要将上面的属性改成：

tomcat.util.scan.StandardJarScanFilter.jarsToSkip=*.jar

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再次启动Tomcat，查看容器启动时候效果：发现果然没有了之前的那个提示信息.

Why?

这个提示信息取消掉它出现，这是其一解决方案，其二呢？这样做会带来什么效果

  可能JSP后端的动态渲染技术一定程度上会影响响应速度，如果jar包中没有tld，没有自定义tld等标签的话，我们可以放心使用上述方式。上述方式原理呢下面简单记录下:

 

解析上述tld代码方法位于：TldScanner#scanJars.

解析方式会按照

  解释说明： 会扫描该项目所有加载到的jar包，包括jre/lib下的包，遍历每个jar检测是否有tld，而Catalina.properties配置中的两个jarsToSkip和jarsToScan作用呢？

check方法中tldSkipSet就是取的jarsToSkip的值，tldScanSet取的就是jarsToSkip的值；tldSkipSet通过正则表达式匹配当前check的jar包，所有的jar都会匹配上*.jar，但是tldScanSet就不一定可以匹配上，Catalina.properties中jarsToScan都是日志相关的jar包，无法和当前正在校验的jar包正则匹配上，所有这个jar包Tomcat不会做任何扫描处理。上述方法在一定程度上提高了Tomcat启动速度，如果在当前项目加载jar包特别多的情况下提升应该明显。

  

public boolean check(JarScanType jarScanType, String jarName) {
        Lock readLock = configurationLock.readLock();
        readLock.lock();
        try {
            final boolean defaultScan;
            final Set<String> toSkip;
            final Set<String> toScan;
            switch (jarScanType) {
                case TLD: {
                    defaultScan = defaultTldScan;
                    toSkip = tldSkipSet;
                    toScan = tldScanSet;
                    break;
                }
                case PLUGGABILITY: {
                    defaultScan = defaultPluggabilityScan;
                    toSkip = pluggabilitySkipSet;
                    toScan = pluggabilityScanSet;
                    break;
                }
                case OTHER:
                default: {
                    defaultScan = true;
                    toSkip = defaultSkipSet;
                    toScan = defaultScanSet;
                }
            }
            if (defaultScan) {
                if (Matcher.matchName(toSkip, jarName)) {
                    if (Matcher.matchName(toScan, jarName)) {
                        return true;
                    } else {
                        return false;
                    }
                }
                return true;
            } else {
                if (Matcher.matchName(toScan, jarName)) {
                    if (Matcher.matchName(toSkip, jarName)) {
                        return false;
                    } else {
                        return true;
                    }
                }
                return false;
            }
        } finally {
            readLock.unlock();
        }
    }

 

 

How?

    假如当前情况下使用到的jar包中有使用tld文件，我们又不想全部扫描所有jar，并且不想看到上述信息At least one JAR 出现，解决方案是：

 

tomcat.util.scan.StandardJarScanFilter.jarsToSkip=*.jar

tomcat.util.scan.StandardJarScanFilter.jarsToScan=yourjarFile.jar

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总结

   通过修改Catalina.properties可以提高程序启动速度，如果有使用到tld文件，再配置比较合适。