How to Get a Java servlet running how to get Tomcat working get a backend java servlet working that you can deploy on AWS
Before you can post a java web app to AWS via Elastic Beanstalk, you gotta be able to get a working java app running on your own machine.
Spend ONE HOUR going through steps below and after that you should have a pretty good map in your head of what's what with Java servlets.
BRIEF RAMBLE
Whenever I need to learn something very complex, at first I create a handful of what I call "vignettes." If you are a painter, before you create a huge complex painting, you will first prepare yourself by creating a whole bunch of smaller paintings. These smaller paintings are done with no real fear of failure. They are usually left incomplete with only part of the canvas covered in paint. They are done just to get a working mastery of the different components that will support the overall finished project. These smaller paintings are called vignettes. I apply the same principle for coding projects, especially when I am learning some new technology or framework for the first time.
My overall goal is to start writing Java web applications and hosting them on AWS. What follows is one of the vignettes I started out with to begin learning this.
ADDITIONAL RESOURCES
But first, here are the blogs and YouTube vids that really helped me begin to understand how to do this:
https://www.c-sharpcorner.com/UploadFile/fd0172/how-to-configure-and-install-apache-tomcat-server-in-windows/
https://www.youtube.com/watch?v=qImCqaxuhgQ
http://www.ides01.com/2020/05/26/javaweb-error-the-superclassjavax-servlet-http-httpservlet-was-not-found-on-the-java-build-path/
SPEND ONE HOUR GOING THROUGH THESE STEPS:
The surest problem you will encounter in this whole process is that Eclipse just never gets hooked up properly to Tomcat. This means you have to spend some time carefully getting everything downloaded and installed correctly....
1. Clear out delete and uninstall all previous versions of jdk, jre, tomcat, eclipse, whatever. CLEAR OUT EVERYTHING FROM ALL PREVIOUS ATTEMPTS – you don’t want any confusing junk left behind while you are doing the stuff below
2. Delete all variables and paths to JDK or JRE in your Environmental Variables - again the object here is to avoid confusion in the near future
3. Go to the Oracle Install page: https://www.oracle.com/java/technologies/javase-jdk11-downloads.html
a. Download BOTH the Windows X64 installer and the Windows X64 Compressed Archive
b. Go to the folder where the installer is (most likely the Downloads folder) and run the exe
c. Go to C:\Program Files\Java\jdk-11.0.8 and make sure there are folders and files in there (bin, conf, etc.)
d. Go to Environmental Variables
e. Create a variable called JAVA_HOME and point it at C:\Program Files\Java\jdk-11.0.8
f. Add an element to path C:\Program Files\Java\jdk-11.0.8\bin
g. OK and save everything in Environmental Variables
h. Go to the command prompt and verify you have done everything correctly:
"Microsoft Windows [Version 10.0.18363.1082]
(c) 2019 Microsoft Corporation. All rights reserved.
C:\Users\-redacted->set JAVA_HOME
JAVA_HOME=C:\Program Files\Java\jdk-11.0.8
C:\Users\-redacted->java -version
java version "11.0.8" 2020-07-14 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.8+10-LTS)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.8+10-LTS, mixed mode)"
4. Download Tomcat 8 from https://tomcat.apache.org/download-80.cgi
a. Click the 64-bit Windows zip (pgp, sha512)
b. Extract the files directly to C drive (for example, the path to \bin should just end up being C:\apache-tomcat-8.5.58\bin
c. Open the configuration file "web.xml" in the Tomcat "conf" folder (edit with plain old Notepad so as not to introduce any formatting).
d. Enable the directory listing by changing "listings" from "false" to "true" for the "default" servlet.
e. Open the Tomcat "server.xml" file and make sure the default port is set to 8080
'<Connector port="8080" protocol="HTTP/1.1"'
5. Test the Tomcat server installation by going into the bin folder and clicking the startup.bat file then point your browser at "http://localhost:8080" - the default Apache Tomcat page should appear
6. Turn the server off by going into the bin folder and clicking the shutdown.bat file (At this point if you hit F5 on the tomcat page on your browser, the browser will return "unable to connect")
7. Download Eclipse Java EE IDE - make sure it is the "Eclipse IDE for Enterprise Java Developers"
a. Download the zip file and extract it directly to the C drive (for example, the path to the configuration folder should be "C:\eclipse\configuration")
Now, you gotta make sure everything is working. The best way to do that is by creating and running a simple servlet...
1. Run Eclipse by going into the, right-clicking on Eclipse.exe, and clicking "Run as Administrator"
2. Go ahead and click Launch for whatever Workspace that Eclipse suggests
3. Close the Welcome tab that appears by default on Eclipse and make sure you can see the "Project Explorer" on the left
4. Now its time to connect Eclipse and Tomcat. In Eclipse, click on Window -> Preferences; in Preferences, expand the Server list
5. Click on Runtime Environments then click the Add button - a list of Apache Tomcat servers
should be available
6. Select the server you want (this should be Tomcat 8.5 if you are following this guide)
7. Click the Next button
8. On the next page, click Browse and select the tomcat folder on your C drive
9. Click Finish then Apply and Close
So at this point Tomcat is hooked up with Eclipse. For example, Eclipse will start and stop Tomcat for you when in the future you want to run one of your applications.
10. Now, click File -> New -> Dynamic Web Project
11. In Project Name just type "Test00" - leave everything else on that page at its default and clcikc Next
12. Don't change anything on the next page where it says "Source folders on build path" - just click Next
13. On the next page, check the box that says "Generate web.xml deployment descriptor" then click Finish
14. After several moments, the dialogue will close and you will see "Test00" over on the left in the Project Explorer
15. Now let's go ahead and create a servlet. Expand the Java Resources folder and you will see the src folder
16. Right-click on the src folder, then click New -> Servlet
17. In the Create Servlet dialogue, enter "testservlet" into the Class name field
18. Delete the text in the Superclass field - we don't need it for now
19. Click next - in the URL mapping field where it says "/testservlet" change it to say "/welcome" then click Next
20. Don't click anything on the next page - just click Finish
21. OK now Eclipse has open the "testservlet.java" file you just created
20. Here's where it gets a little tricky: Highlight everything below "public class testservlet implements Servlet {" and replace it just with a "}"
21. Click on the red 'X' that appears to the left of "public class testservlet implements Servlet" and double-click on the "Add unimplemented methods" option
22. Your code should now look like this (NOTE update the two methods Init and Service by adding some writeline commands!):
import java.io.IOException;
import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebServlet;
/**
* Servlet implementation class testservlet
*/
@WebServlet("/welcome")
public class testservlet implements Servlet {
@Override
public void destroy() {
// TODO Auto-generated method stub
}
@Override
public ServletConfig getServletConfig() {
// TODO Auto-generated method stub
return null;
}
@Override
public String getServletInfo() {
// TODO Auto-generated method stub
return null;
}
@Override
public void init(ServletConfig arg0) throws ServletException {
// TODO Auto-generated method stub
System.out.println("This is printed from Init");
}
@Override
public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException {
// TODO Auto-generated method stub
System.out.println("This is printed from Service");
}
}
23. You now have to update web.xml with the servlet for this to work. In the Project Explorer under Web Content -> WEB Inf -> lib click on the web.xml file
24. When the web.xml file opens, down at the bottom click the Source tab
25. It starts out looking like this:
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
<display-name>Test00</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
</web-app>
26. Change it to look like this:
<?xml version="1.0" encoding="UTF-8"?>
<element>
<servlet>
<servlet-name>whatever</servlet-name>
<servlet-class>testservlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>whatever</servlet-name>
<url-patter>/welcome</url-patter>
</servlet-mapping>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
<display-name>Test00</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
</web-app>
</element>
27. OK that's it. Right-click on Test00 in the Project Explorer and click Run As -> 1 Run on Server
28. On the Run on Server dialogue, just click Next
29. On the Add and Remove dialogue, just click Finish
30. This will fire up Tomcat and a browser session will start up right inside of Eclipse.
31. It will not look like much but if you change the url from "http://localhost:8080/Test00/" to "http://localhost:8080/Test00/welcome" then hit the refresh button, you will see output in the Console tab (by that I mean the Console tab down at the bottom of Eclipse over to the right of Snippets)
32. In Console you now should see "This is printed from Init This is printed from Service"
33. If you keep hitting the refresh button, you will see new lines of "This is printed from Service" appear
That's it! You got a java servlet working! Now, lets get a little more complicated....
- Hit the red button in Eclipse to stop Tomcat running.
- Click File -> New -> Dynamic Web Project
- In Project Name just type "Test01" - leave everything else on that page at its default and click Next
- Don't change anything on the next page where it says "Source folders on build path" - just click Next
- On the next page, check the box that says "Generate web.xml deployment descriptor" then click Finish
- After several moments, the dialogue will close and you will see "Test01" over on the left in the Project Explorer
- Right-click on src folder (in the Java Resources folder) and click New -> servlet
- In Class name type "samplepage"; change NOTHING else and click Next, Next, Finish
- Your samplepage.java file should look like this:
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class samplepage
*/
@WebServlet("/samplepage")
public class samplepage extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public samplepage() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
response.getWriter().append("Served at: ").append(request.getContextPath());
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
10. Do Run As and make sure the server fires up as expected
11. Now, go back to the servlet and add "import java.io.PrintWriter;"
12. Update the doGet method as follows:
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
PrintWriter out = response.getWriter();
out.println("Hello World!");
response.setContentType("text/html");
PrintWriter out1 = response.getWriter();
// send HTML page to client
out1.println("<html>");
out1.println("<head><title>A Test Servlet</title></head>");
out1.println("<body>");
out1.println("<h1>Test</h1>");
out1.println("<p>This page is not from an HTML file. Rather, it is from a servlet!</p>");
out1.println("<form><textarea id=\"w3review\" name=\"w3review\" rows=\"4\" cols=\"50\">\r\n"
+ "This form is not from an HTML file. Servlets can injsct HTML for working forms too!\r\n"
+ "</textarea></form>");
out1.println("</body></html>");
}
13. Save, then go back to the Eclipse browser tab and extend the url to this: http://localhost:8080/Test01/samplepage
14. Give it a second to update then hit the refresh button on the Eclipse browser. You should now see this:
Hello World!
Test
This page is not from an HTML file. Rather, it is from a servlet!
This form is not from an HTML file. Servlets can injsct HTML for working forms too!
15. Go ahead and stop the server at this point. You are ready to create your WAR file. The WAR file is the "bridge", if you will, between you creating a working java servlet app on your own computer and getting your work to appear on a web page generated by AWS.
16. Right-click on Test01 and click Export. Create the WAR file with the WAR Export wizard and just save it to a folder somewhere.
Log on to your AWS console, go to Elastic Beanstalk, click the Create Application button, follow the wizard, and import the WAR file from your machine when prompted. Once the AWS service is running and the web page it generates is running in your browser, extend the browser with "/samplepage" to see the HTML that the servlet is producing.
