1. Create simplest project with HttpServlet and JSP.
me@MacBook:~/dev/my-servlet$ find . -type f | grep -v .idea | grep -v target | grep -v *.iml ./pom.xml ./src/main/webapp/index.html ./src/main/webapp/redirected.jsp ./src/main/webapp/forwarded.jsp ./src/main/java/com/bawi/servlet/MyServlet.java
./pom.xml:
<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.bawi</groupId>
<artifactId>my-servlet</artifactId>
<packaging>war</packaging>
<version>0.1-SNAPSHOT</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>3.3.1</version>
</plugin>
<plugin>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-maven-plugin</artifactId>
<version>9.4.35.v20201120</version>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>4.0.1</version>
<scope>provided</scope>
</dependency>
</dependencies>
</project>
./src/main/java/com/bawi/servlet/MyServlet.java:
package com.bawi.servlet;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Date;
@WebServlet(urlPatterns = {"/do"})
public class MyServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String action = req.getParameter("action");
if (action == null) {
resp.setContentType("text/plain;charset=UTF-8");
ServletOutputStream out = resp.getOutputStream();
out.print("Hello from MyServlet!" + new Date());
return;
}
switch (action) {
case "forward": {
ServletContext servletContext = getServletContext();
RequestDispatcher dispatcher = servletContext.getRequestDispatcher("/forwarded.jsp");
dispatcher.forward(req, resp);
break;
}
case "redirect": {
resp.sendRedirect(req.getContextPath() + "/redirected.jsp");
break;
}
}
}
}
./src/main/webapp/index.html:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Home page</title>
</head>
<body>
<p>This is home page.</p>
<p>Call <a href="/do?action=forward">forward</a></p>
<p>Call <a href="/do?action=redirect">redirect</a></p>
</body>
</html>
./src/main/webapp/forwarded.jsp:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Forwarded page</title>
</head>
<body>
<p>Action parameter: <%= request.getParameter("action") %>. This is forwarded page. Go to <a href="/">home</a></p>
</body>
</html>
./src/main/webapp/redirected.jsp:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Redirected page</title>
</head>
<body>
<p>Action parameter: <%= request.getParameter("action") %>. This is redirected page. Go to <a href="/">home</a></p>
</body>
</html>
me@MacBook:~/dev/my-servlet$ mvn jetty:run
[INFO] webAppSourceDirectory not set. Trying src/main/webapp
[INFO] Reload Mechanic: automatic
[INFO] nonBlocking:false
[INFO] Classes = /Users/me/dev/my-servlet/target/classes
[INFO] Configuring Jetty for project: my-servlet
[INFO] Logging initialized @3943ms to org.eclipse.jetty.util.log.Slf4jLog
[INFO] Context path = /
[INFO] Tmp directory = /Users/me/dev/my-servlet/target/tmp
[INFO] Web defaults = org/eclipse/jetty/webapp/webdefault.xml
[INFO] Web overrides = none
[INFO] web.xml file = null
[INFO] Webapp directory = /Users/me/dev/my-servlet/src/main/webapp
[INFO] jetty-9.4.35.v20201120; built: 2020-11-20T21:17:03.964Z; git: bdc54f03a5e0a7e280fab27f55c3c75ee8da89fb; jvm 1.8.0_241-b07
[INFO] Scanning elapsed time=26ms
[INFO] DefaultSessionIdManager workerName=node0
[INFO] No SessionScavenger set, using defaults
[INFO] node0 Scavenging every 660000ms
[INFO] Started o.e.j.m.p.JettyWebAppContext@760cf594{/,file:///Users/me/dev/my-servlet/src/main/webapp/,AVAILABLE}{file:///Users/me/dev/my-servlet/src/main/webapp/}
[INFO] Started ServerConnector@254f906e{HTTP/1.1, (http/1.1)}{0.0.0.0:8080}
[INFO] Started @4422ms
[INFO] Started Jetty Server
2. Testing
curl http://localhost:8080/do
Hello from MyServlet!Wed Dec 02 15:09:17 CET 2020
forward
Note action parameter is passed automatically
me@MacBook:~$ curl -vv http://localhost:8080/do?action=forward
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> GET /do?action=forward HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.64.1
> Accept: */*
>
< HTTP/1.1 200 OK
< Date: Wed, 02 Dec 2020 14:11:26 GMT
< Content-Type: text/html;charset=utf-8
< Set-Cookie: JSESSIONID=node0vruwimbjjsy5uwywzhy51gy81.node0; Path=/
< Expires: Thu, 01 Jan 1970 00:00:00 GMT
< Content-Length: 248
< Server: Jetty(9.4.35.v20201120)
<
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Forwarded page</title>
</head>
<body>
<p>Action parameter: forward. This is forwarded page. Go to <a href="/">home</a></p>
</body>
* Connection #0 to host localhost left intact
</html>* Closing connection 0
redirect
Note response code is 302 and redirect location is returned.
me@MacBook:~$ curl -vv http://localhost:8080/do?action=redirect
* Trying ::1... * TCP_NODELAY set * Connected to localhost (::1) port 8080 (#0) > GET /do?action=redirect HTTP/1.1 > Host: localhost:8080 > User-Agent: curl/7.64.1 > Accept: */* > < HTTP/1.1 302 Found < Date: Wed, 02 Dec 2020 14:11:39 GMT < Location: http://localhost:8080/redirected.jsp < Content-Length: 0 < Server: Jetty(9.4.35.v20201120) < * Connection #0 to host localhost left intact * Closing connection 0
With option to follow redirect location:
Note action parameter is NOT passed to second request.
me@MacBook:~$ curl -v -L http://localhost:8080/do?action=redirect
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> GET /do?action=redirect HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.64.1
> Accept: */*
>
< HTTP/1.1 302 Found
< Date: Wed, 02 Dec 2020 17:14:59 GMT
< Location: http://localhost:8080/redirected.jsp
< Content-Length: 0
< Server: Jetty(9.4.35.v20201120)
<
* Connection #0 to host localhost left intact
* Issue another request to this URL: 'http://localhost:8080/redirected.jsp'
* Found bundle for host localhost: 0x7fe33a818310 [can pipeline]
* Could pipeline, but not asked to!
* Re-using existing connection! (#0) with host localhost
* Connected to localhost (::1) port 8080 (#0)
> GET /redirected.jsp HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.64.1
> Accept: */*
>
< HTTP/1.1 200 OK
< Date: Wed, 02 Dec 2020 17:14:59 GMT
< Content-Type: text/html;charset=utf-8
< Set-Cookie: JSESSIONID=node0gd5vxmsu6xgkh3ltwabj2jh810.node0; Path=/
< Expires: Thu, 01 Jan 1970 00:00:00 GMT
< Content-Length: 247
< Server: Jetty(9.4.35.v20201120)
<
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Redirected page</title>
</head>
<body>
<p>Action parameter: null. This is redirected page. Go to <a href="/">home</a></p>
</body>
* Connection #0 to host localhost left intact
</html>* Closing connection 0
3. Automatically reload classes and resources when debugging (change is seen after first request)
me@MacBook:~$ curl http://localhost:8080/do
Hello from MyServlet!Wed Dec 02 18:47:14 CET 2020
Now modify servlet java code
first request to trigger reloading
me@MacBook:~$ curl http://localhost:8080/do
Hello from MyServlet!Wed Dec 02 18:48:03 CET 2020
second request returns modified response
me@MacBook:~$ curl http://localhost:8080/do
Hello from MyServlet! - modifiedWed Dec 02 18:48:07 CET 2020
Bartosz Wieczorek's blog 