Apache Tomcat


Setting up Apache Tomcat 7 on Red Hat Linux ES 7.2
Creating first Java Server Page(JSP)
Creating first Servlet
Implementing Tomcat JDBC Realm security
Setting up Apache Tomcat 7 on Red Hat Linux ES 7.2
  1. login as root or sudo to root
  2. get the distribution and install it using : yum install tomcat
  3. Determine the port you will be running the webserver and open it in the firewall.Default is 8080.For sake of instruction let's use 8081:
    Check open ports: firewall-cmd --list-ports
    open a port 8081: firewall-cmd --add-port=8081/tcp --permanent
    reload firewall rules: firewall-cmd --reload
    Check open ports: firewall-cmd --list-ports
  4. Edit server configuration file:
    go to installation directory : cd /usr/share/tomcat
    go to configuration files directory: cd conf
    edit server.xml file : vi server.xml
    Find the connector port and change it from 8080 to 8081: Connector port="8081" protocol="HTTP/1.1"
    general replace of 8080 to 8081 could look like: 1,$s/8080/8081/g
  5. Change the Host name from localhost to the ip address or name of the host, the server is running at:
    Host name="192.168.1.220" appBase="webapps"
    general replace of localhost could look like: 1,$s/localhost/192.168.1.220/g
  6. Close the server configuration file.
  7. Create web application structure:
    cd /usr/share/tomcat/webapps
    create application root directory: mkdir firstapp
    change directory to the newly created directory: cd firstapp
    create directory for web application code and configuration files: mkdir WEB-INF
    create directory for stylesheets: mkdir css
    create directory for images: mkdir img
    create directory for source files to be compiled into code: mkdir src
    change directory to WEB-INF: cd WEB-INF
    create directory for java classes:mkdir classes
    create directory for CGI scripts and programs: mkdir cgi
  8. create index.html file in the web application root directory:
    cd /usr/share/tomcat/webapps/firstapp
    vi index.html
    <HTML>
    <HEAD><TITLE>Tomcat first application </TITLE></HEAD>
    <BODY>
    <H3> Welcome to the firstapp web application running on Tomcat </H3>
    </BODY>
    </HTML>
  9. Start tomcat webserver:
    /usr/sbin/tomcat start
  10. verify you can see the index page in web browser:
    in the address field of your browser type: http://192.168.1.220:8081/firstapp
  11. Create stylesheet for your website
    In css directory of your application create a cba.css file and add the body tag to maintain your site uniformity,e.g:
    body {
    background-color:#CCCCFF;
    }
Creating first Java Server Page(JSP)
  1. Change directory to /usr/share/tomcat/webapps/firstapp
  2. Create the index.jsp page as following:

    <html>
    <head><title>First JSP</title>
    <link rel="stylesheet" type="text/css" href="css/cba.css">
    </head>
    <%@ page import="java.util.Date" %>
    <body>
    <h2>Time is: </h2><%=new Date() %>
    <%
    double num = Math.random();
    if (num > 0.95) {
    %>
    <h2>Petrol prices will go down</h2>
    <%
    } else {
    >
    <h2>Petrol prices will go up</h2>
    <%
    }
    %>
    <a href="<%= request.getRequestURI() %>"><h3>Try Again</h3></a>
    </body>
    </html>
  3. verify you can see the index.jsp page in web browser:
    in the address field of your browser type: http://192.168.1.220:8081/firstapp/index.jsp
  4. Browse through the code of the underlying servlet generated for your jsp page
    sudo to root
    change directory to /var/cache/tomcat/work/Catalina
    under the hostname or ip address find index_jsp.java and index_jsp.class
    in firstapp/org/apache/jsp
    This is the code generated and compiled by the Jasper component of Tomcat for your first jsp
Creating your first Tomcat servlet
  1. change directory to your src: cd /usr/share/tomcat/webapps/firstapp/src
  2. create a file HelloServlet.java and put the following lines of code there:

    import javax.servlet.*;
    import javax.servlet.http.*;
    import java.io.*;
    import java.util.*;

    public class HelloServlet extends HttpServlet {



    private String greetingMessage;
    private int limit;
    private String configMessage;

    public void init(ServletConfig config) throws ServletException {
    super.init(config);
    limit=Integer.parseInt(config.getInitParameter("limit"));
    greetingMessage="Hello world of Servlets";
    configMessage=config.getServletName();
    }

    public void doGet(HttpServletRequest request,
    HttpServletResponse response)
    throws ServletException, IOException {

    PrintWriter out = response.getWriter();
    out.println("<HTML>");
    out.println("<HEAD>");
    out.println("<TITLE>Servlet Testing</TITLE>");
    out.println("<link rel=stylesheet type=text/css href=css/cba.css>");
    out.println("</HEAD>");
    out.println("<BODY>");
    out.println("<H1>" + greetingMessage +"</H1>");
    out.println("<h3>------>" + configMessage + "<-----</h3>");

    out.println("<H3> Hi visitor from " + request.getRemoteAddr() + "</H3>");
    for(int i=0;i<limit;i++)
    {
    out.println("Line " + (i+1) +"<BR>");
    }

    out.println("<h4>If you see this, you, most probably, were lucky to compile your first servlet</h4>");
    out.println("</BODY>");
    out.println("</HTML>");
    }

    public void doPost(HttpServletRequest request,
    HttpServletResponse response)
    throws ServletException, IOException {

    doGet(request,response);
    }



    }
  3. make sure your CLASSPATH includes the tomcat servlet jar:

    echo $CLASSPATH
    /usr/share/tomcat/lib/tomcat-servlet-3.0-api.jar
  4. compile the code:
    javac -d ../WEB-INF/classes HelloServlet.java
  5. you can create a makefile in src directory as follows:
    default: Hello
    Hello:
        javac -d ../WEB-INF/classes/ $@Servlet.java
  6. Make sure your target code in makefile is starting with one tab, not spaces
    Now you can compile your servlet from src directory using command: make
  7. verify the compiled code is in your WEB-INF/classes directory:
    ls /usr/share/tomcat/webapps/firstapp/WEB-INF/classes
  8. In your WEB-INF directory create a Web Application Deployment Descriptor file web.xml with information about your first servlet as follows:

    <?xml version="1.0" encoding="ISO-8859-1"?>

    <web-app xmlns="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_3_0.xsd"
    version="3.0">

    <servlet>
    <servlet-name>HelloServlet</servlet-name>
    <servlet-class>HelloServlet</servlet-class>
    <init-param>
    <param-name>limit</param-name>
    <param-value>17</param-value>
    </init-param>
    </servlet>

    <servlet-mapping>
    <servlet-name>HelloServlet</servlet-name>
    <url-pattern>/Hello</url-pattern>
    </servlet-mapping>

    </web-app>
  9. Note the limit parameter is set to 17 and the Url pattern is Hello.
  10. In your browser type in: Host:port/firstapp/Hello
    e.g http://192.168.1.220:8081/firstapp/Hello
Implementing Tomcat JDBC Realm security
  1. put jdbc driver in /usr/share/tomcat/lib, in case of oracle it will be ojdbc7.jar
  2. Create database tables
    Oracle database will be used for this, the usual choice being MySQL, but for Realm purpose they differ only in JDBC driver used
    SQLPLUS> create table users(user_name varchar2(20) primary key,user_pass varchar2(20));
    SQLPLUS> create table user_roles(user_name varchar2(20),role_name varchar2(20), constraint pk_ro primary key (user_name,role_name) );
  3. Populate the tables with users and roles data
    SQLPLUS>INSERT INTO USERS VALUES('bob','builder');
    SQLPLUS>INSERT INTO USER_ROLES VALUES('bob','admin');
  4. Create a directory for protected files: mkdir /usr/share/tomcat/webapps/firstapp/protected
  5. create an html file in the created directory, content is left to your imagination:vi /usr/share/tomcat/webapps/firstapp/protected/index.html
  6. edit server.xml by adding a context tag to the host tag and putting the code inside. This will create realm for only one application, while the others could be using different Realms using MySQL or tomcat_users.xml
    <Host name="192.168.1.220" appBase="webapps" unpackWARs="true" autoDeploy="true" >
    <Context path="/firstapp">
     <Realm className="org.apache.catalina.realm.JDBCRealm"
      driverName="oracle.jdbc.driver.OracleDriver"
      connectionURL="jdbc:oracle:thin:@192.168.1.220:1521/pdbcba1"
      connectionName="SCOTT" connectionPassword="TIGER"
      userTable="users" userNameCol="user_name" userCredCol="user_pass"
      userRoleTable="user_roles" roleNameCol="role_name" />
    </Context>
  7. edit web.xml for your firstapp application:cd /usr/share/tomcat/webapps/firstapp/WEB-INF
    vi web.xml

    enter the following lines withing the web-app tags:
    <security-constraint>
    <web-resource-collection>
    <web-resource-name>protected</web-resource-name>
    <url-pattern>/protected/*</url-pattern>
    <http-method>GET</http-method>
    <http-method>POST</http-method>
    </web-resource-collection>
    <auth-constraint>
    <role-name>admin</role-name>
    </auth-constraint>

    <user-data-constraint>
    <!-- transport-guarantee can be CONFIDENTIAL, INTEGRAL, or NONE -->
    <transport-guarantee>NONE</transport-guarantee>
    </user-data-constraint>
    </security-constraint>

    <login-config>
    <auth-method>BASIC</auth-method>
    </login-config>
  8. Summary: This will create a realm where usernames and roles will be matched to those in oracle database, and resources located in protected directory of your web application will require a user bob, or any other belonging to admin role to enter the credentials on the first access to resources.
    Note: the users can now be added to the database tables without a tomcat restart
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