I don't know what I've done incorrectly, but I can't include JSTL. I have jstl-1.2.jar, but unfortunately I get exception:
org.apache.jasper.JasperException: The absolute uri: http://java.sun.com/jstl/core cannot be resolved in either web.xml or the jar files deployed with this application
I have this in pom.xml:
<dependency>
<groupId>taglibs</groupId>
<artifactId>standard</artifactId>
<version>1.1.2</version>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jstl</artifactId>
<version>1.2</version>
</dependency>
I'm trying to use it as follows:
<%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>
In your specific case,
org.apache.jasper.JasperException: The absolute uri: http://java.sun.com/jstl/core cannot be resolved in either web.xml or the jar files deployed with this application
that URI is for JSTL 1.0, but you're actually using JSTL 1.2 which uses URIs with an additional /jsp path. This URI change is because JSTL, who invented EL expressions, was since version 1.1 integrated as part of JSP 2.0 (released way back in 2001!) in order to share/reuse the EL logic in plain JSP too. See also Difference between JSP EL, JSF EL and Unified EL.
So, fix the taglib URI accordingly based on JSTL 1.2 documentation:
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
Further you need to make absolutely sure that you do not throw multiple different versioned JSTL JAR files together into the runtime classpath or versions which don't match the expected version by the target runtime (the server) or merely the API without impl. Otherwise you risk seeing other errors like below:
org.apache.jasper.JasperException: Can not find the tag library descriptor for "http://java.sun.com/jsp/jstl/core"
org.apache.jasper.JasperException: Unable to find taglib [c] for URI: [jakarta.tags.core]
java.lang.NoClassDefFoundError: javax/servlet/jsp/tagext/TagLibraryValidator
java.lang.NoClassDefFoundError: jakarta/servlet/jsp/tagext/TagLibraryValidator
java.lang.ClassCastException: class org.apache.taglibs.standard.tlv.JstlCoreTLV cannot be cast to class jakarta.servlet.jsp.tagext.TagLibraryValidator
This is a pretty common mistake among Tomcat users. The problem with Tomcat is that it does not offer JSTL out the box and thus you have to manually install it. This is not necessary in normal Jakarta EE servers. See also What exactly is Java EE? and How to properly configure Jakarta EE libraries in Maven pom.xml for Tomcat?
In your specific case, your pom.xml basically tells you that you have jstl-1.2.jar and standard-1.1.2.jar together. This is wrong. You're basically mixing JSTL 1.2 API+impl from Oracle (GlassFish) with JSTL 1.1 impl from Apache. You should remove duplicate JSTL implementations and stick to only one JSTL implementation and the API version must match the impl version and the API version must be supported by the target runtime.
In case you're already on Tomcat 10.1.x (the second Jakartified version, with jakarta.* package instead of javax.* package, but the first version with the updated jakarta.tags.* namespace URNs instead of http://java.sun.com/jsp/jstl/* namespace URLs), use JSTL 3.0 via these dependency using the default Maven scope of compile (because Tomcat doesn't provide it out the box!):
<dependency>
<groupId>jakarta.servlet.jsp.jstl</groupId>
<artifactId>jakarta.servlet.jsp.jstl-api</artifactId>
<version>3.0.0</version>
</dependency>
<dependency>
<groupId>org.glassfish.web</groupId>
<artifactId>jakarta.servlet.jsp.jstl</artifactId>
<version>3.0.1</version>
</dependency>
Note that the API dependency is since this version not transitively included via the impl dependency, so you do need to explicitly declare it.
Non-Maven users can achieve the same by dropping the following two physical files in /WEB-INF/lib folder of the web application project (do absolutely not drop standard*.jar or any loose .tld files in there! remove them if necessary).
As said, the namespace URIs have been changed to become URNs instead of URLs. JSTL core is since JSTL version 3.0 available via an easier to remember namespace URI in URN format:
<%@ taglib prefix="c" uri="jakarta.tags.core" %>
See also JSTL 3.0 documentation.
In case you actually wanted to use the JSTL impl of Apache instead of EE4J then you need to know that they don't have a 3.0 let alone 2.0. The currently latest released version of Apache's JSTL impl is 1.2.3 and it is not anymore actively maintained since Feb 2015. The JSTL impl from EE4J (formerly Oracle / Sun) is currently (Jul 2023) your only choice.
In case you're on Tomcat 10.0.x (the first Jakartified version, with jakarta.* package instead of javax.* package), use JSTL 2.0 via this sole dependency using the default Maven scope of compile (because Tomcat doesn't provide it out the box!):
<dependency>
<groupId>org.glassfish.web</groupId>
<artifactId>jakarta.servlet.jsp.jstl</artifactId>
<version>2.0.0</version>
</dependency>
Note that the API dependency is already transitively included via this impl dependency, so you do not need to explicitly declare it.
Non-Maven users can achieve the same by dropping the following two physical files in /WEB-INF/lib folder of the web application project (do absolutely not drop standard*.jar or any loose .tld files in there! remove them if necessary).
In case you're not on Tomcat 10 yet, but still on Tomcat 9 or older, use JSTL 1.2 via this sole dependency (this is compatible with Tomcat 9 / 8 / 7 / 6 / 5 but not older) using the default Maven scope of compile (because Tomcat doesn't provide it out the box!):
<dependency>
<groupId>org.glassfish.web</groupId>
<artifactId>jakarta.servlet.jsp.jstl</artifactId>
<version>1.2.6</version>
</dependency>
Note that the API dependency is already transitively included via this impl dependency, so you do not need to explicitly declare it.
Non-Maven users can achieve the same by dropping the following two physical files in /WEB-INF/lib folder of the web application project (do absolutely not drop standard*.jar or any loose .tld files in there! remove them if necessary).
In case you're actually using a normal Jakarta EE server such as WildFly, Payara, TomEE, GlassFish, WebSphere, OpenLiberty, WebLogic, etc instead of a barebones servletcontainer such as Tomcat, Jetty, Undertow, etc, then you do not need to explicitly install JSTL at all. Normal Jakarta EE servers already provide JSTL out the box. In other words, you don't need to add JSTL to pom.xml nor to drop any JAR/TLD files in webapp. Solely the provided scoped Jakarta EE coordinate is sufficient:
<dependency>
<groupId>jakarta.platform</groupId>
<artifactId>jakarta.jakartaee-api</artifactId>
<version><!-- 10.0.0, 9.1.0, 9.0.0, 8.0.0, etc depending on your server --></version>
<scope>provided</scope>
</dependency>
Further you should also make sure that your web.xml is declared conform at least Servlet 2.4 and thus not as Servlet 2.3 or older. Otherwise EL expressions inside JSTL tags would in turn fail to work. Pick the highest version matching your target container and make sure that you don't have a <!DOCTYPE> anywhere in your web.xml as that would otherwise still trigger Servlet 2.3 modus. Here's a Servlet 6.0 (Tomcat 10.1.x) compatible example:
<?xml version="1.0" encoding="UTF-8"?>
<web-app
xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_6_0.xsd"
version="6.0">
<!-- Config here. -->
</web-app>
And here's a Servlet 5.0 (Tomcat 10.0.x) compatible example:
<?xml version="1.0" encoding="UTF-8"?>
<web-app
xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
version="5.0">
<!-- Config here. -->
</web-app>
And here's a Servlet 4.0 (Tomcat 9) compatible example:
<?xml version="1.0" encoding="UTF-8"?>
<web-app
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0">
<!-- Config here. -->
</web-app>