How to inject Tomcat Data Source using @Resource in Jakarta-EE project?

I was also facing the same issue.

Finally, I got the solution after two days of rigorous research.

I tried with Tomcat 7.0.104, PostgresSQL 12 and JDK 8.

Note: You can use any tomcat version and injection doesn't have anything to do with the tomcat version, you need to do proper configuration for a particular DI framework so that it can the inject external datasource like tomcat datasource.

@Bozho was right at this question : Getting null pointer exception @Resource annotation in tomcat 7

You will need dependency-injection framework to do the injection. For dependency-injection to work properly, you need to configure framework in such a way that it can find that particular resource.

Now, coming to the answer :

The things you need to update in tomcat.

context.xml :

<?xml version="1.0" encoding="UTF-8"?>
<!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor 
    license agreements. See the NOTICE file distributed with this work for additional 
    information regarding copyright ownership. The ASF licenses this file to 
    You under the Apache License, Version 2.0 (the "License"); you may not use 
    this file except in compliance with the License. You may obtain a copy of 
    the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required 
    by applicable law or agreed to in writing, software distributed under the 
    License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS 
    OF ANY KIND, either express or implied. See the License for the specific 
    language governing permissions and limitations under the License. --><!-- The contents of this file will be loaded for each web application -->
<Context>

    <!-- Default set of monitored resources -->
    <WatchedResource>WEB-INF/web.xml</WatchedResource>
    
    <Resource auth="Container"
            driverClassName="org.postgresql.Driver" maxActive="20" maxIdle="10"
            maxWait="-1" name="jdbc/postgres" password="" type="javax.sql.DataSource"
            url="jdbc:postgresql://localhost:5432/demo" username="anish" />

    <!-- Uncomment this to disable session persistence across Tomcat restarts -->
    <!-- <Manager pathname="" /> -->

    <!-- Uncomment this to enable Comet connection tacking (provides events 
        on session expiration as well as webapp lifecycle) -->
    <!-- <Valve className="org.apache.catalina.valves.CometConnectionManagerValve" 
        /> -->

</Context>

You need to update the project's web.xml (by referring to the data source that you have created in the context.xml):

<?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_3_1.xsd"
    version="3.1">
    <display-name>Archetype Created Web Application</display-name>
    <resource-ref>
        <description>Test</description>
        <res-ref-name>jdbc/postgres</res-ref-name>
        <res-type>javax.sql.DataSource</res-type>
        <res-auth>Container</res-auth>
    </resource-ref>
</web-app>
    

TestController class :

package com.example;

import java.io.IOException;
import java.sql.Connection;
import java.sql.SQLException;

import javax.annotation.Resource;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;

    @WebServlet(name = "TestController", urlPatterns = "/test")
    public class TestController extends HttpServlet {
    
        private static final long serialVersionUID = 1L;
    
        @Resource(name = "jdbc/postgres")
        private DataSource dataSource;
    
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
    
            try (Connection connection = dataSource.getConnection();) {
                System.out.println(connection.getAutoCommit());
            } catch (SQLException e) {
                e.printStackTrace();
            }
    
        }
    
    }

Success Log :

Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: Server version name:   Apache Tomcat/7.0.104
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: Server built:          May 7 2020 19:31:18 UTC
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: Server version number: 7.0.104.0
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: OS Name:               Mac OS X
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: OS Version:            10.15.4
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: Architecture:          x86_64
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: Java Home:             /Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: JVM Version:           1.8.0_231-b11
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: JVM Vendor:            Oracle Corporation
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: CATALINA_BASE:         /Volumes/Local Disk/STS-workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: CATALINA_HOME:         /Users/anish/Downloads/apache-tomcat-7.0.104
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dcatalina.base=/Volumes/Local Disk/STS-workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dcatalina.home=/Users/anish/Downloads/apache-tomcat-7.0.104
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dwtp.deploy=/Volumes/Local Disk/STS-workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Djava.endorsed.dirs=/Users/anish/Downloads/apache-tomcat-7.0.104/endorsed
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dfile.encoding=UTF-8
Jun 26, 2020 10:10:19 AM org.apache.catalina.core.AprLifecycleListener lifecycleEvent
INFO: The Apache Tomcat Native library which allows using OpenSSL was not found on the java.library.path: [/Users/anish/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.]
Jun 26, 2020 10:10:19 AM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-bio-8080"]
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 413 ms
Jun 26, 2020 10:10:19 AM org.apache.catalina.core.StandardService startInternal
INFO: Starting service [Catalina]
Jun 26, 2020 10:10:19 AM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/7.0.104
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.TldConfig execute
INFO: 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.
Jun 26, 2020 10:10:19 AM org.apache.catalina.deploy.WebXml setVersion
WARNING: Unknown version string [3.1]. Default version will be used.
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.TldConfig execute
INFO: 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.
Jun 26, 2020 10:10:19 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["http-bio-8080"]
Jun 26, 2020 10:10:19 AM org.apache.catalina.startup.Catalina start
INFO: Server startup in 341 ms

When you access this http://localhost:8080/sample-ds-test/test url, it will give the message true that will denote that datasource is loaded properly.

This will work for you smoothly.

My Github repo for testing :

• My Updated Tomcat Repo : https://github.com/anish-fullstack/Tomcat-7.0.104

(Just change the database name, username, password)

• My Project Test Repo : https://github.com/anish-fullstack/sample-ds-test