Servlet

It is technology to create dynamic WebPages. This is a Java program, which resides in a web server to process requests from the user and to provide a dynamic response to users.

Storing compilation and deployment of a servlet

  1. Store the servlet file inside the "classes" folder of the context for predefined context (root) the classes folder required to be created inside the WEB-INF folder.
  2. For the compilation of the servlet, files use servlet-api.jar in classpath option of javac command. This jar file contains the package used by the servlet files. This jar file can be found inside the installation folder of the tomcat/lib folder.
  3. Deployment: This is a process to create an URL for the servlet. The user will use the URL to access the servlet. This can be done by providing a few tags in the web.xml file. The tags are as follows:

    In web.xml file present side to classes folder:

    <servlet>
    <servlet-name>name</servlet-name>
    <servlet-class>class</servlet-class>
    </servlet>

    <servlet-mapping>
    <servlet-name>name</servlet-name>
    <url-pattern>/ url-pattern </url-pattern>
    </servlet-mapping>
Program
  1. import java.io.*;
  2. import javax.servlet.*;
  3. import javax.servlet.http.*;
  4. public class httpserv extends HttpServlet
  5. {
  6. public void doGet(HttpServletRequest req ,HttpServletResponse res)throws IOException ,ServletException
  7. {
  8. PrintWriter out = res.getWriter();
  9. res.setContentType("text/html");
  10. out.println("<html><body>");
  11. out.println("<h1> First servlet</h1>");
  12. out.println("</body></html>");
  13. }
  14. }

How to run this program


First create a folder named Servlet in any drive (here e: drive). Inside that folder create a WEB-INF folder (all letters will be capped mandatory). Copy the web.xml file from the (E:\Program Files\Apache Software Foundation\Tomcat 6.0\conf) folder. Again inside the WEB-INF folder, create a folder named classes. In the classes folder, we will store the Servlet files by their class name; here httpserv.java. Copy the servlet-api.jar (E:\Program Files\Apache Software Foundation\Tomcat 6.0\lib) file in the classes folder.

Web.xml setting:
  1. <?xml version="1.0" encoding="ISO-8859-1"?>
  2. <!--
  3. Licensed to the Apache Software Foundation (ASF) under one or more
  4. contributor license agreements. See the NOTICE file distributed with
  5. this work for additional information regarding copyright ownership.
  6. The ASF licenses this file to You under the Apache License, Version 2.0
  7. (the "License"); you may not use this file except in compliance with
  8. the License. You may obtain a copy of the License at
  10. http://www.apache.org/licenses/LICENSE-2.0
  12. Unless required by applicable law or agreed to in writing, software
  13. distributed under the License is distributed on an "AS IS" BASIS,
  14. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  15. See the License for the specific language governing permissions and
  16. limitations under the License.
  17. -->
  18. <web-app xmlns="http://java.sun.com/xml/ns/javaee"
  19. xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  20. xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
  21. version="2.5">
  23. <servlet>
  24. <servlet-name>httpserv</servlet-name>
  25. <servlet-class>httpserv</servlet-class>
  26. </servlet>
  28. <servlet-mapping>
  29. <servlet-name>httpserv</servlet-name>
  30. <url-pattern>/httpserv</url-pattern>
  31. </servlet-mapping
  33. </web-app>
Context path setting: Move to (E:\Program Files\Apache Software Foundation\Tomcat 6.0\conf) folder and open server.xml file. Create a context path (any name) and docBase="E:\Servlet" (this is the folder path where we are storing the (WEB-INF\classes) servlet files).
  1. <Context path="/javaservlet" docBase="E:\Servlet" reloadable="true" debug="0" />
  3. <?xml version='1.0' encoding='utf-8'?>
  4. <!--
  5. Licensed to the Apache Software Foundation (ASF) under one or more
  6. contributor license agreements. See the NOTICE file distributed with
  7. this work for additional information regarding copyright ownership.
  8. The ASF licenses this file to You under the Apache License, Version 2.0
  9. (the "License"); you may not use this file except in compliance with
  10. the License. You may obtain a copy of the License at
  12. http://www.apache.org/licenses/LICENSE-2.0
  14. Unless required by applicable law or agreed to in writing, software
  15. distributed under the License is distributed on an "AS IS" BASIS,
  16. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  17. See the License for the specific language governing permissions and
  18. limitations under the License.
  19. -->
  20. <!-- Note: A "Server" is not itself a "Container", so you may not
  21. define subcomponents such as "Valves" at this level.
  22. Documentation at /docs/config/server.html
  23. -->
  24. <Server port="8005" shutdown="SHUTDOWN">
  26. <!--APR library loader. Documentation at /docs/apr.html -->
  27. <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />
  28. <!--Initialize Jasper prior to webapps are loaded. Documentation at /docs/jasper-howto.html -->
  29. <Listener className="org.apache.catalina.core.JasperListener" />
  30. <!-- JMX Support for the Tomcat server. Documentation at /docs/non-existent.html -->
  31. <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" />
  32. <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
  34. <!-- Global JNDI resources
  35. Documentation at /docs/jndi-resources-howto.html
  36. -->
  37. <GlobalNamingResources>
  38. <!-- Editable user database that can also be used by
  39. UserDatabaseRealm to authenticate users
  40. -->
  41. <Resource name="UserDatabase" auth="Container"
  42. type="org.apache.catalina.UserDatabase"
  43. description="User database that can be updated and saved"
  44. factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
  45. pathname="conf/tomcat-users.xml" />
  46. </GlobalNamingResources>
  48. <!-- A "Service" is a collection of one or more "Connectors" that share
  49. a single "Container" Note: A "Service" is not itself a "Container",
  50. so you may not define subcomponents such as "Valves" at this level.
  51. Documentation at /docs/config/service.html
  52. -->
  53. <Service name="Catalina">
  55. <!--The connectors can use a shared executor, you can define one or more named thread pools-->
  56. <!--
  57. <Executor name="tomcatThreadPool" namePrefix="catalina-exec-"
  58. maxThreads="150" minSpareThreads="4"/>
  59. -->
  61. <!-- A "Connector" represents an endpoint by which requests are received
  62. and responses are returned. Documentation at :
  63. Java HTTP Connector: /docs/config/http.html (blocking & non-blocking)
  64. Java AJP Connector: /docs/config/ajp.html
  65. APR (HTTP/AJP) Connector: /docs/apr.html
  66. Define a non-SSL HTTP/1.1 Connector on port 8080
  67. -->
  68. <Connector port="8081" protocol="HTTP/1.1"
  69. connectionTimeout="20000"
  70. redirectPort="8443" />
  71. <!-- A "Connector" using the shared thread pool-->
  72. <!--
  73. <Connector executor="tomcatThreadPool"
  74. port="8080" protocol="HTTP/1.1"
  75. connectionTimeout="20000"
  76. redirectPort="8443" />
  77. -->
  78. <!-- Define a SSL HTTP/1.1 Connector on port 8443
  79. This connector uses the JSSE configuration, when using APR, the
  80. connector should be using the OpenSSL style configuration
  81. described in the APR documentation -->
  82. <!--
  83. <Connector port="8443" protocol="HTTP/1.1" SSLEnabled="true"
  84. maxThreads="150" scheme="https" secure="true"
  85. clientAuth="false" sslProtocol="TLS" />
  86. -->
  88. <!-- Define an AJP 1.3 Connector on port 8009 -->
  89. <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />
  92. <!-- An Engine represents the entry point (within Catalina) that processes
  93. every request. The Engine implementation for Tomcat stand alone
  94. analyzes the HTTP headers included with the request, and passes them
  95. on to the appropriate Host (virtual host).
  96. Documentation at /docs/config/engine.html -->
  98. <!-- You should set jvmRoute to support load-balancing via AJP ie :
  99. <Engine name="Standalone" defaultHost="localhost" jvmRoute="jvm1">
  100. -->
  101. <Engine name="Catalina" defaultHost="localhost">
  103. <!--For clustering, please take a look at documentation at:
  104. /docs/cluster-howto.html (simple how to)
  105. /docs/config/cluster.html (reference documentation) -->
  106. <!--
  107. <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"/>
  108. -->
  110. <!-- The request dumper valve dumps useful debugging information about
  111. the request and response data received and sent by Tomcat.
  112. Documentation at: /docs/config/valve.html -->
  113. <!--
  114. <Valve className="org.apache.catalina.valves.RequestDumperValve"/>
  115. -->
  117. <!-- This Realm uses the UserDatabase configured in the global JNDI
  118. resources under the key "UserDatabase". Any edits
  119. that are performed against this UserDatabase are immediately
  120. available for use by the Realm. -->
  121. <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
  122. resourceName="UserDatabase"/>
  124. <!-- Define the default virtual host
  125. Note: XML Schema validation will not work with Xerces 2.2.
  126. -->
  127. <Host name="localhost" appBase="webapps"
  128. unpackWARs="true" autoDeploy="true"
  129. xmlValidation="false" xmlNamespaceAware="false">
  131. <!-- SingleSignOn valve, share authentication between web applications
  132. Documentation at: /docs/config/valve.html -->
  133. <!--
  134. <Valve className="org.apache.catalina.authenticator.SingleSignOn" />
  135. -->
  137. <!-- Access log processes all example.
  138. Documentation at: /docs/config/valve.html -->
  139. <!--
  140. <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
  141. prefix="localhost_access_log." suffix=".txt" pattern="common" resolveHosts="false"/>
  142. -->
  143. <Context path="/javaservlet" docBase="E:\Servlet" reloadable="true" debug="0" />
  145. </Host>
  146. </Engine>
  147. </Service>
  148. </Server>

Compiling


javac -cp servlet.jar httpserv.java (for tomcat 4.0)
javac -cp servlet-api.jar httpserv.java (for tomcat 6.0)

cp means classpath

Servlet

Running the servlet in a web browser


First, run the tomcat 6.0

http://localhost:8081/ javaservlet /httpserv