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

啓動Tomcat的時候，常常見到這樣的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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之前不知道怎麼處理，怎麼處理纔是正確的，最近研究了點點Tomcat源碼，也算知其一，知其二，不知其三四五六七了，下面先貼上解決方案：

 

解決方案：

catalina-home/conf/Catalina.properties中有這樣一個屬性：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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咱們只須要將上面的屬性改爲：

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

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再次啓動Tomcat，查看容器啓動時候效果：發現果真沒有了以前的那個提示信息.

 

 

Why?

這個提示信息取消掉它出現，這是其一解決方案，其二呢？這樣作會帶來什麼效果

  可能JSP後端的動態渲染技術必定程度上會影響響應速度，若是jar包中沒有tld，沒有自定義tld等標籤的話，咱們能夠放心使用上述方式。上述方式原理呢下面簡單記錄下:

 

解析上述tld代碼方法位於：TldScanner#scanJars.

解析方式會按照

  解釋說明： 會掃描該項目全部加載到的jar包，包括jre/lib下的包，遍歷每一個jar檢測是否有tld，而Catalina.properties配置中的兩個jarsToSkip和jarsToScan做用呢？

check方法中tldSkipSet就是取的jarsToSkip的值，tldScanSet取的就是jarsToSkip的值；tldSkipSet經過正則表達式匹配當前check的jar包，全部的jar都會匹配上*.jar，可是tldScanSet就不必定能夠匹配上，Catalina.properties中jarsToScan都是日誌相關的jar包，沒法和當前正在校驗的jar包正則匹配上，全部這個jar包Tomcat不會作任何掃描處理。上述方法在必定程度上提升了Tomcat啓動速度，若是在當前項目加載jar包特別多的狀況下提高應該明顯。

  

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?

    假如當前狀況下使用到的jar包中有使用tld文件，咱們又不想所有掃描全部jar，而且不想看到上述信息At least one JAR 出現，解決方案是：

 

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

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

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總結

   經過修改Catalina.properties能夠提升程序啓動速度，若是有使用到tld文件，再配置比較合適。