A servlet can fetch the value of a form field using the getParameter() method of the servlet request. The HTML form can submit a value of the form fields by using a URL pattern of the servlet into the action attribute of the form tag. If the method attribute contains Get as its value and destination servlet is a sub-class of the Http servlet then doGet() method gets invoked. If the method attribute contains post as its value and destination servlet is a sub-class of http servlet then doPost() method of the servlet gets invoked. If the destination servlet is a sub-class of Generic servlet then the service() method gets invoked without depending upon the value of method attribute. The getParameter() method of request accepts the name of the form field as its arguments and returns value of the form fields as a string. If the specified form field does not exist in the request then the getParameter() method returns Null. If the form exists in a servlet and it requires submission of the form into the current servlet then the action attribute does not need to be used in the form tag.
Example
A servlet to receive two numbers and display the addition.
- import javax.servlet.*;
- import javax.servlet.http.*;
- import java.io.*;
- public class number extends HttpServlet
- {
- public void doGet(HttpServletRequest req,HttpServletResponse res)throws IOException,ServletException
- {
- String s1=req.getParameter("t1");
- String s2=req.getParameter("t2");
- PrintWriter out=res.getWriter();
- out.println("<html><body>");
- if(s1 ==null)
- {
- out.println("<form>");
- out.println("<h1>Enter No1<input type='text' name='t1'></h1>");
- out.println("<input type='submit' value='submit'>");
- out.println("</form>");
- }
- else if(s2 ==null)
- {
- out.println("<form>");
- out.println("<h1>Enter No2<input type='text' name='t2'></h1>");
- out.println("<input type='hidden' name='t1' value='"+s1+"'>");
- out.println("<input type='submit' value='submit'>");
- out.println("<form>");
- }
- else
- {
- int x=Integer.parseInt(s1);
- int y=Integer.parseInt(s2);
- out.println("<h1>Result is "+(x+y)+"</h1>");
- }
- out.println("</body></html>");
- }
- }
Storing and Compiling
Store the file inside the class folder of the context (
E:\Servlet\WEB-INF\classes).
Compile the file as below:
javac -cp servlet-api.jar number.java (for tomcat 6.0)
Setting in web.xml file
Note: - Note the Highlighted or bold portion in the below web.xml file, to be added.
- <?xml version="1.0" encoding="ISO-8859-1" ?>
- - <!--
- 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.
- -->
- --<web-appxmlnsweb-appxmlns=http://java.sun.com/xml/ns/javaee
- xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance
- xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
- http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
- <servlet>
- <servlet-name>number</servlet-name>
- <servlet-class>number</servlet-class>
- </servlet>
- <servlet-mapping>
- <servlet-name>number</servlet-name>
- <url-pattern>/number</url-pattern>
- </servlet-mapping>
- </web-app>
Running it in web browser
First start the Apache Tomcat 6.0, which is a web server. Then type the below URL.
http://localhost:8082/x/number
Here x is the context path location, which we have to give in the server.xml file, which is present inside the Tomcat installation directory (E:\Program Files\Apache Software Foundation\Tomcat 6.0\conf)
Server.xml settings
Note: - In the below server.xml file we have to specify the context path as below.
<Context path="/x" docBase="E:\Servlet" reloadable="true" debug="0" />
server.xml file
- <?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.
- -->
- <!-- Note: A "Server" is not itself a "Container", so you may not
- define subcomponents such as "Valves" at this level.
- Documentation at /docs/config/server.html
- -->
- <Server port="8005" shutdown="SHUTDOWN">
-
-
- <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />
-
- <Listener className="org.apache.catalina.core.JasperListener" />
-
- <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" />
- <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
-
- <!-- Global JNDI resources
- Documentation at /docs/jndi-resources-howto.html
- -->
- <GlobalNamingResources>
- <!-- Editable user database that can also be used by
- UserDatabaseRealm to authenticate users
- -->
- <Resource name="UserDatabase" auth="Container"
- type="org.apache.catalina.UserDatabase"
- description="User database that can be updated and saved"
- factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
- pathname="conf/tomcat-users.xml" />
- </GlobalNamingResources>
-
- <!-- A "Service" is a collection of one or more "Connectors" that share
- a single "Container" Note: A "Service" is not itself a "Container",
- so you may not define subcomponents such as "Valves" at this level.
- Documentation at /docs/config/service.html
- -->
- <Service name="Catalina">
-
-
- <!--
- <Executor name="tomcatThreadPool" namePrefix="catalina-exec-"
- maxThreads="150" minSpareThreads="4"/>
- -->
-
- <!-- A "Connector" represents an endpoint by which requests are received
- and responses are returned. Documentation at :
- Java HTTP Connector: /docs/config/http.html (blocking & non-blocking)
- Java AJP Connector: /docs/config/ajp.html
- APR (HTTP/AJP) Connector: /docs/apr.html
- Define a non-SSL HTTP/1.1 Connector on port 8080
- -->
- <Connector port="8082" protocol="HTTP/1.1"
- connectionTimeout="20000"
- redirectPort="8443" />
-
- <!--
- <Connector executor="tomcatThreadPool"
- port="8080" protocol="HTTP/1.1"
- connectionTimeout="20000"
- redirectPort="8443" />
- -->
- <!-- Define a SSL HTTP/1.1 Connector on port 8443
- This connector uses the JSSE configuration, when using APR, the
- connector should be using the OpenSSL style configuration
- described in the APR documentation -->
- <!--
- <Connector port="8443" protocol="HTTP/1.1" SSLEnabled="true"
- maxThreads="150" scheme="https" secure="true"
- clientAuth="false" sslProtocol="TLS" />
- -->
-
-
- <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />
-
- <!-- An Engine represents the entry point (within Catalina) that processes
- every request. The Engine implementation for Tomcat stand alone
- analyzes the HTTP headers included with the request, and passes them
- on to the appropriate Host (virtual host).
- Documentation at /docs/config/engine.html -->
-
- <!-- You should set jvmRoute to support load-balancing via AJP ie :
- <Engine name="Standalone" defaultHost="localhost" jvmRoute="jvm1">
- -->
- <Engine name="Catalina" defaultHost="localhost">
-
- <!--For clustering, please take a look at documentation at:
- /docs/cluster-howto.html (simple how to)
- /docs/config/cluster.html (reference documentation) -->
-
-
-
-
- <!-- The request dumper valve dumps useful debugging information about
- the request and response data received and sent by Tomcat.
- Documentation at: /docs/config/valve.html -->
-
-
-
-
- <!-- This Realm uses the UserDatabase configured in the global JNDI
- resources under the key "UserDatabase". Any edits
- that are performed against this UserDatabase are immediately
- available for use by the Realm. -->
- <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
- resourceName="UserDatabase"/>
-
- <!-- Define the default virtual host
- Note: XML Schema validation will not work with Xerces 2.2.
- -->
- <Host name="localhost" appBase="webapps"
- unpackWARs="true" autoDeploy="true"
- xmlValidation="false" xmlNamespaceAware="false">
-
- <!-- SingleSignOn valve, share authentication between web applications
- Documentation at: /docs/config/valve.html -->
-
-
-
-
- <!-- Access log processes all example.
- Documentation at: /docs/config/valve.html -->
- <!--
- <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
- prefix="localhost_access_log." suffix=".txt" pattern="common" resolveHosts="false"/>
- -->
- <Context path="/x" docBase="E:\Servlet" reloadable="true" debug="0" />
- </Host>
- </Engine>
- </Service>
- </Server>
Output
Thanks for reading and please be kind enough to give the feedback.