"INFO: TLD skipped. URI is already defined"是什么意思？

在eclipse中运行JSF 2应用程序时我得到了几个信息日志，TLD被跳过，因为它已经定义如下:

Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://www.springframework.org/tags/form is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://www.springframework.org/tags is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jstl/core_rt is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jstl/core is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jsp/jstl/core is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jstl/fmt_rt is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jstl/fmt is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jsp/jstl/fmt is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jsp/jstl/functions is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://jakarta.apache.org/taglibs/standard/permittedTaglibs is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://jakarta.apache.org/taglibs/standard/scriptfree is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jstl/sql_rt is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jstl/sql is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jsp/jstl/sql is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jstl/xml_rt is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jstl/xml is already defined
Jan 3, 2012 7:24:45 PM org.apache.catalina.startup.TaglibUriRule body
INFO: TLD skipped. URI: http://java.sun.com/jsp/jstl/xml is already defined

我很想知道，这个日志是什么意思?

这意味着在你的web应用的运行时类路径中有重复的TLD文件。由于tld通常包含在库JAR文件中，这反过来意味着在web应用程序的运行时类路径中有重复的JAR文件。

假设您没有触及appserver的/lib文件夹或JDK的/lib文件夹，那么这些副本在WAR构建的/WEB-INF/lib文件夹中。清理它。

规范要求的uri优先顺序为:

J2EE platform taglibs - Tomcat doesn't provide these
web.xml entries
JARS in WEB-INF/lib & TLDs under WEB-INF (equal priority)
Additional entries from the container

Tomcat加载tld两次。

1，当Tomcat启动时，它加载tld以在tld文件中查找侦听器。

2，当编译第一个JSP文件时，它构建TLD对的缓存。

1、加载tld在tld文件中查找监听器

当从web.xml加载时，它会将来自web.xml的taglib-uri和来自tld文件的uri放到一个集合中。当从WEB-INF jar加载时，uri来自tld文件。

Tomcat需要避免重复的tld侦听器添加，所以它检查uri是否存在于集合中。如果uri已经存在，它记录您发布的消息，并跳过添加tld侦听器。

2、创建cache

1) web.xml条目，标记uri是从web.xml

获得的

2)扫描WEB-INF下的tld文件，标签uri从tld文件中获得

3)扫描jar，标签uri是从TLD文件中获得的。

如果uri已经存在，条目将被忽略

这意味着，例如，如果您使用Tomcat和Maven(或其他服务器)，那么您发布的JSTL库已经在服务器上找到，并且服务器会报错。

    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
    </dependency>

在部署应用程序(在Tomcat上)时，您会得到错误消息:

INFO: TLD skipped. URI: http://java.sun.com/jstl/core_rt is already defined
Mar 02, 2017 2:19:32 PM org.apache.catalina.startup.TaglibUriRule body

解决方案是使用'scope'标签和'提供'值，因为JSTL已经随Tomcat一起发货了(它只适用于您的IDE):

    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
        <scope>provided</scope>
    </dependency>

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