jstl那几个包到底分别用来干什么的？为什么项目中引入了还出错？

taglibs-standard-compat-1.2.5.jar

taglibs-standard-impl-1.2.5.jar

taglibs-standard-spec-1.2.5.jar

Exception

javax.servlet.ServletException: java.lang.NoClassDefFoundError: javax/servlet/jsp/jstl/core/LoopTag
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
com.yzb.cart.servlet.ProductServlet.service(ProductServlet.java:19)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
com.yzb.cart.filter.CharsetEncodingFilter.doFilter(CharsetEncodingFilter.java:19)

Root Cause

java.lang.NoClassDefFoundError: javax/servlet/jsp/jstl/core/LoopTag
java.base/java.lang.ClassLoader.defineClass1(Native Method)
java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1009)
java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:174)
org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2352)
org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:833)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1278)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1138)
org.apache.jasper.compiler.Parser.parseCustomTag(Parser.java:1238)
org.apache.jasper.compiler.Parser.parseElements(Parser.java:1470)
org.apache.jasper.compiler.Parser.parse(Parser.java:144)
org.apache.jasper.compiler.ParserController.doParse(ParserController.java:244)
org.apache.jasper.compiler.ParserController.parse(ParserController.java:105)
org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:206)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:385)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:362)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:346)
org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:603)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:383)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
com.yzb.cart.servlet.ProductServlet.service(ProductServlet.java:19)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
com.yzb.cart.filter.CharsetEncodingFilter.doFilter(CharsetEncodingFilter.java:19)

Root Cause

java.lang.ClassNotFoundException: javax.servlet.jsp.jstl.core.LoopTag
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1309)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1138)
java.base/java.lang.ClassLoader.defineClass1(Native Method)
java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1009)
java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:174)
org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2352)
org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:833)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1278)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1138)
org.apache.jasper.compiler.Parser.parseCustomTag(Parser.java:1238)
org.apache.jasper.compiler.Parser.parseElements(Parser.java:1470)
org.apache.jasper.compiler.Parser.parse(Parser.java:144)
org.apache.jasper.compiler.ParserController.doParse(ParserController.java:244)
org.apache.jasper.compiler.ParserController.parse(ParserController.java:105)
org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:206)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:385)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:362)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:346)
org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:603)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:383)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
com.yzb.cart.servlet.ProductServlet.service(ProductServlet.java:19)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
com.yzb.cart.filter.CharsetEncodingFilter.doFilter(CharsetEncodingFilter.java:19)

渐丶忘 2018-10-21

源自：项目：商品展示及购物车 2-2 列表页及本地缓存创建（下）

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1回答

chrismorgen 回答被采纳获得+3积分 2018-10-22 11:01:04

这些包是jsp的标签库，用了这些包，就可以使用jstl和El表达式了，你的报错原因如下图，即找不到编译之后的文件了，建议你检查一下是否将相关的jar包添加到build Path中，祝学习愉快~

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渐丶忘提问者 #1

我加到build Path里面了，昨天找了一下资料 ,顺便把源码下下来看了一下README，里面写到 To use this distribution with your own web applications, add the following JAR files to the '/WEB-INF/lib' directory of your application: - taglibs-standard-spec-1.2.5.jar - taglibs-standard-impl-1.2.5.jar - taglibs-standard-jstlel-1.2.5.jar - xalan-2.7.1.jar - serializer-2.7.1.jar If you do not use JSTL 1.0 tags then the "taglibs-standard-jstlel" JAR may be omitted. If you do not use the XML library, then the Apache Xalan dependencies may also be omitted. If you build you application with Maven, add the following dependencies to your pom.xml file: <dependency> <groupId>org.apache.taglibs</groupId> <artifactId>taglibs-standard-spec</artifactId> <version>1.2.5</version> </dependency> <dependency> <groupId>org.apache.taglibs</groupId> <artifactId>taglibs-standard-impl</artifactId> <version>1.2.5</version> </dependency> 故应该需要的是两个包，spec和impl。。

2018-10-22 11:19:45