What are JSTL mandatory Jars

问题

I am new, and just start learning Java. From the jstl tag, I know a lot about jstl.

I use IDE(eclispe mars) to create a dynamic web project by adding a simple jsp page, then export the war to the tomcat7's webapps folder. I do some testings of the dependence of jstl mandatory jars.

My core project files are:

web.xml: 

  <web-app xmlns:xsi="http:....... version="3.0">   //use servlet 3.0

index.jsp:

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>   
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>jstl Tag Lib</title>
</head>
<body>
<h2>2+2=${2+2}</h2> //this line works, el is a part of jsp.

//below lines work fine if there are proper jstl jars.
<c:set var="salary" scope="session" value="${2000*2}" />
salary:<c:out value="${salary}" />
</body>
</html>

In the WEB-INF/lib/ folder, I have 3 kinds of jars, all of the 3 groups work fine.

1) only contains:

jstl-1.2.jar

what organization deliver it? apache tomcat?

2) only contains:

javax.servlet.jsp.jstl-api-1.2.1.jar
javax.servlet.jsp.jstl-1.2.4.jar

Here, I have a question: What are the two jars difference?

3) only contains:

taglibs-standard-impl-1.2.5.jar
taglibs-standard-compat-1.2.5.jar
taglibs-standard-jstlel-1.2.5.jar
taglibs-standard-spec-1.2.5.jar

Thoes jars download from http://tomcat.apache.org/download-taglibs.cgi Here, I have a quesiton: What are the three jars difference? Because I don't know the difference, I drop the three jars to the lib folder, but I find taglibs-standard-impl.*.jar is mandatory when runnnig time.

回答1:

I think about the qestion over the night, and I realize that maybe the answer is just beside the jar. The last part of the question, about the 4 apache tomcat jars, From the link, there are 2 readme text files(Source README, Binary README)

It says:

There are three primary sub-modules:

    spec            <-- contains Apache's implementation of the API classes
    impl            <-- contains the implementation of tags from the 1.1
                        namespace http://java.sun.com/jsp/jstl/*
    jstlel          <-- contains the implementation of tags from the 1.0
                        namespace http://java.sun.com/jstl/* and uses the
                        original JSTL 1.0 version of EL

In addition, the following modules provide supporting functionality
    build-tools     <-- build support such as checkstyle rules
    compat          <-- contains the implementation of tags from the 1.0
                        namespace but uses the JSP container's implementation
                        of EL (which will be 2.1 or later).

Binary README:

This version of the Standard Tag Library has the following runtime
dependencies:

   1. Dependencies provided by a JSP 2.1 container:
      - Java 1.5 or later
      - Servlet 2.5 or later
      - JSP 2.1 or later

   2. Additional dependencies
      - The XML tag library requires Apache Xalan 2.7.1 or later

---
Apache Xalan 2.7.1

To address performance issues with XSLT processing, this version relies on
implementation specific functionality from Apache Xalan. The following
libraries should be included in the classpath for your application:
   - xalan-2.7.1.jar
   - serializer-2.7.1.jar

---------------------------------------------------------------------------
ADD DEPENDENCIES TO A WEB APPLICATION

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>

I also use jd-gui to decompile the jars, then I find some classes in taglibs-standard-impl-1.2.5.jar, their base classes are in taglibs-standard-spec-1.2.5.jar.

Also use the decompiling methodology, I can find that,

jstl-1.2.jar is a single jar, but it has two main packages in the jar. - 1) org.apache.taglibs.standard - 2) javax.servlet.jsp.jstl

javax.servlet.jsp.jstl-1.2.4.jar and javax.servlet.jsp.jstl-api-1.2.1.jar is another group jar.

each of them has only one main package in each jar, they are org.apache.taglibs.standard namespace in javax.servlet.jsp.jstl-1.2.4.jar, and javax.servlet.jsp.jstl namesapce in javax.servlet.jsp.jstl-api-1.2.1.jar. So we can say the combination of the two jars is equal to the jstl.jar

The situation is similar to the apache tomcat jars group. The difference is that the apache tomcat implementation divide more classes into 3 or 4 different jar files.

So as of now, I can say I understand most of the basic usages of those apache tomcat jars.

来源：https://stackoverflow.com/questions/39953734/what-are-jstl-mandatory-jars

标签

jsp

Tomcat

jstl