YoLinux Tutorial: Java Servlets, JSP, Jakarta-Tomcat, a Database (PostgreSQL or MySQL), Apache and Linux |
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This covers dynamic content using JAVA servlets, JAVA Server Pages (JSP
and JASPER page compiler), Jakarta-Tomcat, Apache and a Database (PostgreSQL
or MySQL) on Red Hat Linux 7.2. A configuration presented here will allow
one to make a web request to the Apache web server which will recognize it
as request for a servlet to be handled by Tomcat. Tomcat, the Java Servlet
and JSP engine, will execute the Java Servlet which will use JDBC to access
a database (PostgreSQL or MySQL). The servlet will dynamically generate a
web page based on the results of the database query and will provide these
results to Apache which will deliver the web content back to the requesting
browser.
Instead of using C/C++ or PERL for a CGI back-end web server process, one may use JAVA servlets processed by the Jakarta project's "Tomcat". Apache will be configured to use the module mod_jk to communicate with Jakarta-Tomcat and it's JVM (JAVA virtual machine). Servlet programs are written as JAVA classes which inherit from "HttpServlet" to provide much of their principal function.
JAVA Server Pages (JSP) will utilize Tomcat's JASPER page compiler to generate dynamic web pages based on custom tags in one's HTML pages which are processed and served. These pages use the tag "<% %>" to denote JSP directives to be dynamically processed.
It has been my experience on this project that the configurations for the versions of software discussed here are very specific to the release. In this case we will be using Tomcat 4.0. Older releases of Tomcat (version 3) are configured differently.
An example of a Java Servlet using JDBC to access a database (PostgreSQL or MySQL) is also covered.
| JAVA Installation/Configuration: |
In order to write and compile a JAVA programs, applets or servlets one must download the JAVA Development Kit (JDK) which provides a compiler, class libraries and tools to compile and run JAVA code. In this tutorial we will use the Sun JDK but I'm sure any will do. See YoLinux JAVA for a list of available JDK's for Linux.
SDK installed in /usr/java/j2sdk1.4.0/.
PATH=/usr/java/j2sdk1.4.0/bin:$PATH export PATH export JAVA_HOME=/usr/java/j2sdk1.4.0 export CLASSPATH=/usr/java/j2sdk1.4.0/lib/tools.jar:/usr/java/j2sdk1.4.0/jre/lib/rt.jarThe shell script may be re-executed with the command: . .bashrc
[Potential Pitfall]: Java SDK 1.4.0_03 now requires the current working directory to be listed to find files. Add reference to current directory ":./" to CLASSPATH.
export CLASSPATH=/usr/java/j2sdk1.4.0_03/lib/tools.jar:/usr/java/j2sdk1.4.0_03/jre/lib/rt.jar:./
public class Test
{
public static void main(String[] args)
{
System.out.println("Hello world");
}
}
Run:
[prompt]$ java Test Hello world(or /usr/java/j2sdk1.4.0/bin/java Test)
| Jakarta Project - Tomcat: |
Tomcat is the JAVA "container" or processor for Java Servlets and Java Server Pages (JSP). Note also that JAVA must be installed in order for Tomcat to operate. (See previous section above) This tutorial will focus on the use of Tomcat with Apache but it should be noted that the default Tomcat installation enables Tomcat to be a stand-alone http web server and servlet container.
The Jakarta Project: Apache Tomcat JAVA Servlet and JSP container home page
Download: Tomcat 4.0 RPMs (Release: Catalina. Servlet 2.3 and JSP 1.2 specifications.)
Install: rpm -ivh regexp-1.2-1.noarch.rpm servletapi4-4.0.3-1.noarch.rpm
tomcat4-webapps-4.0.3-1.noarch.rpm tomcat4-4.0.3-1.noarch.rpm xerces-j-1.4.4-2.noarch.rpm
Symlinks generated from /usr/share/java/... to /var/tomcat4/
Documentation:
Config file: /etc/tomcat4/conf/tomcat4.conf
JAVA_HOME=/usr/java/j2sdk1.4.0
Config files:
Start: service tomcat4 start
[Potential Pitfall]: Note that the command service tomcat4 stop was not always successful in stopping all Java processes. Use the command ps -auwx | grep tomcat to measure success.
Test:
<Connector className="org.apache.catalina.connector.http.HttpConnector"
port="8180" minProcessors="5" maxProcessors="75"
enableLookups="true" redirectPort="8543"
acceptCount="10" debug="0" connectionTimeout="60000"/>
<tomcat-users>
<user name="tomcat" password="tomcat" roles="tomcat" />
<user name="role1" password="tomcat" roles="role1" />
<user name="both" password="tomcat" roles="tomcat,role1" />
<user name="admin1" password="supersecret" roles="standard,manager,tomcat,role1" /> - Added this line with "manager role"
<user name="admin2" password="supersecret2" roles="admin,manager,provider" /> - See: http://java.sun.com/webservices/docs/ea2/tutorial/doc/GettingStarted2.html#64132
</tomcat-users>
Then restart: service tomcat4 restart
Use URL to list web applications: http://localhost:8180/manager/list
Note:
Notes:
| JAVA Servlet Example: |
File: MyHelloWorld.java
import java.io.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class MyHelloWorld extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<body>");
out.println("<head>");
out.println("<title>Hello World!</title>");
out.println("</head>");
out.println("<body>");
out.println("<h1>Hello World!</h1>");
out.println("</body>");
out.println("</html>");
}
}
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Set CLASSPATH environment variable:
export CLASSPATH=$CLASSPATH:/var/tomcat4/common/lib/servlet.jar
OR
export CLASSPATH=/usr/java/j2sdk1.4.0/lib/tools.jar:/usr/java/j2sdk1.4.0/jre/lib/rt.jar:/var/tomcat4/common/lib/servlet.jar
Note: /var/tomcat4/common/lib/servlet.jar is soft linked to /usr/share/java/servlet-2.3.jar.
Compile:
[prompt]$ cd /var/tomcat4/webapps/examples/WEB-INF/classes/ [prompt]$ javac MyHelloWorld.java (OR /usr/java/j2sdk1.4.0/bin/javac MyHelloWorld.java )
Note:
Tomcat Test: http://localhost:8180/examples/servlet/MyHelloWorld
Don't expect a lot. It just generates a web page dynamically which
states "Hello World".
Note:
| Apache - Tomcat Configuration: |
Apache is a fast and configurable web server. This section covers using Apache as the primary web server but using Tomcat to process JSP and Servlets. This configuration uses the AJP (Apache JServ Protocol) connector element (mod_jk) to perform this task. The Apache module mod_jk will send servlet requests to Tomcat using TCP/IP sockets for communications. Module mod_jk works with Tomcat versions 3.x and 4.x.
There are numerous Apache connection modules:
| Connector Name | Apache Module Name | Connection Protocol | Tomcat Version |
|---|---|---|---|
| AJP | mod_jk | AJP1.2,AJP1.3 | 3, 4 |
| Coyote JK2 | mod_jk | AJP/JK1.3,AJP/JK1.4 | 4.1 |
| WARP | mod_webapp | WARP | 4 |
| JSERV | mod_jserv | ?? | old |
Modify: /etc/httpd/conf/workers.properties
workers.tomcat_home=/var/tomcat4 - Changed. Default was /var/tomcat3 workers.java_home=/usr/java/j2sdk1.4.0 - Changed to reflect location of JDK ps=/ worker.list=ajp12, ajp13 # Define a worker named ajp12 and of type ajp12 # Note that the name and the type do not have to match. # worker.ajp12.port=8007 worker.ajp12.host=localhost worker.ajp12.type=ajp12 worker.ajp12.lbfactor=1 # Define a worker named Ajp13 # worker.ajp13.port=8009 worker.ajp13.host=localhost worker.ajp13.type=ajp13 worker.ajp13.lbfactor=1 worker.loadbalancer.type=lb worker.loadbalancer.balanced_workers=ajp12, ajp13 # Defining a worker named inprocess and of type jni worker.inprocess.type=jni # Additional class path components. worker.inprocess.class_path=$(workers.tomcat_home)$(ps)server$(ps)lib$(ps)tomcat-ajp.jar - Changed this line to match location of library. worker.inprocess.cmd_line=start worker.inprocess.class_path=$(workers.java_home)$(ps)lib$(ps)tools.jar - Added this line based on something I read. (Also modified to match installation) # Unix - Sun VM or blackdown worker.inprocess.jvm_lib=$(workers.java_home)$(ps)jre$(ps)lib$(ps)i386$(ps)server$(ps)libjvm.so - Changed this line to match location of library. # Setting the place for the stdout and stderr of tomcat worker.inprocess.stdout=$(workers.tomcat_home)$(ps)logs$(ps)inprocess.stdout worker.inprocess.stderr=$(workers.tomcat_home)$(ps)logs$(ps)inprocess.stderr |
Add to: /var/tomcat4/conf/server.xml
<Service name="Tomcat-Standalone"> ... </Service>Define listener:
<Connector className="org.apache.ajp.tomcat4.Ajp13Connector"
port="8007" minProcessors="5" maxProcessors="75"
acceptCount="10" debug="0"/>
<Connector className="org.apache.ajp.tomcat4.Ajp13Connector"
port="8009" minProcessors="5" maxProcessors="75"
acceptCount="10" debug="0"/>
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Add to: /etc/httpd/conf/httpd.conf
LoadModule jk_module /usr/lib/apache/mod_jk.so OR LoadModule jk_module modules/mod_jk.so ... ... AddModule mod_jk.c ... ... Include /etc/httpd/conf/mod_jk.conf |
File: /etc/httpd/conf/mod_jk.conf (Change references of "tomcat" to "tomcat4" throughout the file, otherwise the default file is ok.)
<IfModule mod_jk.c>
JkWorkersFile /etc/httpd/conf/workers.properties
JkLogFile /var/log/httpd/mod_jk.log
JkLogLevel info
# Root context mounts for Tomcat
# Format: JkMount URL_PREFIX WORKER_NAME
JkMount /*.jsp ajp13
JkMount /servlet/* ajp13
# The following line makes apache aware of the location of the /examples contextAlias /examples "/var/tomcat4/webapps/examples"
<Directory "/var/tomcat4/webapps/examples">
Options Indexes FollowSymLinks
</Directory>
# The following line mounts all JSP files and the /servlet/ uri to tomcat
JkMount /examples/servlet/* ajp13
JkMount /examples/*.jsp ajp13
# The following line prohibits users from directly access WEB-INF
<Location "/examples/WEB-INF/">
AllowOverride None
deny from all
</Location>
...
</IfModule>
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Virtual host example: (Just an FYI. I never used virtual hosting but wanted to let everyone know it is available.)
# First Virtual Host. - Virtual Host example not in default file
<VirtualHost 10.0.0.1:80>
DocumentRoot /web/host1
ServerName host1.yolinux.com
<IfModule mod_jk.c>
JkMount /*.jsp ajp13
JkMount /servlet/* ajp13
<Location "/examples/WEB-INF/">
AllowOverride None
deny from all
</Location>
</IfModule>
</VirtualHost>
Ajpv13 is the protocol used when Apache communicates with Tomcat.
This file establishes the sockets and enables this communication process.
If using a virtual host configuration then file /etc/httpd/conf/workers.properties must have the following entries added:
...
<!-- Request Interceptor for jumpers -->
<RequestInterceptor
className="com.yolinux.servlet.jumpersInterceptor" />
...
<Host name="host1.yolinux.com" >
<Context path=""
docBase="/web/host1/html" />
</Host>
| The Database: |
We will cover connectivity to two databases:
Install and configure a database. See: YoLinux Tutorial: PostgreSQL and Linux
JDBC and PostgreSQL JAR files: The "CLASSPATH" variable can set the Java runtime environment so that it will find the appropriate Java libraries (JAR files). Environment variables for Tomcat can be set in /etc/tomcat4/conf/tomcat4.conf. One may also set the CLASSPATH variable to include PostgreSQL JDBC JAR files. I did not set the CLASSPATH environment variable in the configuration file but instead employed the default path by performing the following steps:
List of PostgreSQL JDBC drivers:
[prompt]# rpm -ql postgresql-jdbc-7.1.3-2 /usr/share/pgsql/jdbc7.0-1.1.jar /usr/share/pgsql/jdbc7.1-1.2.jar
Place JDBC JAR libraries in path where they can be found:
// File: ShowBedrock.java
/* A servlet to display the contents of the PostgreSQL Bedrock database */
import java.io.*;
import java.sql.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class ShowBedrock extends HttpServlet
{
public String getServletInfo()
{
return "Servlet connects to PostgreSQL database and displays result of a SELECT";
}
private Connection dbcon; // Connection for scope of ShowBedrock
// "init" sets up a database connection
public void init(ServletConfig config) throws ServletException
{
String loginUser = "postgres";
String loginPasswd = "supersecret";
String loginUrl = "jdbc:postgresql://localhost/bedrock";
// Load the PostgreSQL driver
try
{
Class.forName("org.postgresql.Driver");
dbcon = DriverManager.getConnection(loginUrl, loginUser, loginPasswd);
}
catch (ClassNotFoundException ex)
{
System.err.println("ClassNotFoundException: " + ex.getMessage());
throw new ServletException("Class not found Error");
}
catch (SQLException ex)
{
System.err.println("SQLException: " + ex.getMessage());
}
}
// Use http GET
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
response.setContentType("text/html"); // Response mime type
// Output stream to STDOUT
PrintWriter out = response.getWriter();
out.println("<HTML><Head><Title>Bedrock</Title></Head>");
out.println("<Body><H1>Bedrock</H1>");
try
{
// Declare our statement
Statement statement = dbcon.createStatement();
String query = "SELECT name, dept, ";
query += " jobtitle ";
query += "FROM employee ";
// Perform the query
ResultSet rs = statement.executeQuery(query);
out.println("<table border>");
// Iterate through each row of rs
while (rs.next())
{
String m_name = rs.getString("name");
String m_dept = rs.getString("dept");
String m_jobtitle = rs.getString("jobtitle");
out.println("<tr>" +
"<td>" + m_name + "</td>" +
"<td>" + m_dept + "</td>" +
"<td>" + m_jobtitle + "</td>" +
"</tr>");
}
out.println("</table></body></html>");
statement.close();
}
catch(Exception ex)
{
out.println("<HTML>" +
"<Head><Title>" +
"Bedrock: Error" +
"</Title></Head>\n<Body>" +
"<P>SQL error in doGet: " +
ex.getMessage() + "</P></Body></HTML>");
return;
}
out.close();
}
}
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Notes:
Set CLASSPATH environment variable:
export CLASSPATH=$CLASSPATH:/var/tomcat4/lib/jdbc7.1-1.2.jar
OR
export CLASSPATH=/usr/java/j2sdk1.4.0/lib/tools.jar:/usr/java/j2sdk1.4.0/jre/lib/rt.jar:/var/tomcat4/common/lib/servlet.jar:/var/tomcat4/lib/jdbc7.1-1.2.jar
Compile:
[prompt]# cd /var/tomcat4/webapps/examples/WEB-INF/classes [prompt]# javac ShowBedrock.java (OR /usr/java/j2sdk1.4.0/bin/javac ShowBedrock.java )
Test:
Results:
| Fred Flinstone | Quarry Worker | Rock Digger |
| Wilma Flinstone | Finance | Analyst |
| Barney Rubble | Sales | Neighbor |
| Betty Rubble | IT | Neighbor |
Install and configure a database: YoLinux Tutorial: MySQL and Linux
Download JDBC MM.MySQL JAR file:
Un-JAR and place MM.MySQL JDBC JAR libraries in path where they can be found:
[prompt]# /usr/java/j2sdk1.4.0/bin/jar xf mm.mysql-2.0.13-you-must-unjar-me.jar OR if your paths are set properly: [prompt]# jar xf mm.mysql-2.0.13-you-must-unjar-me.jar [prompt]# cd mm.mysql-2.0.13/ [prompt]# cp mm.mysql-2.0.13-bin.jar /var/tomcat4/lib
where hostname is localhost.localdomain (not localhost on default Red Hat installation)
// File: ShowBedrock.java
/* A servlet to display the contents of the MySQL Bedrock database */
import java.io.*;
import java.net.*;
import java.sql.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class ShowBedrock extends HttpServlet
{
public String getServletInfo()
{
return "Servlet connects to MySQL database and displays result of a SELECT";
}
// Use http GET
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
String loginUser = "Dude1";
String loginPasswd = "SuperSecret";
String loginUrl = "jdbc:mysql://localhost:3306/bedrock";
response.setContentType("text/html"); // Response mime type
// Output stream to STDOUT
PrintWriter out = response.getWriter();
out.println("<HTML><HEAD><TITLE>Bedrock</TITLE></HEAD>");
out.println("<BODY><H1>Bedrock</H1>");
// Load the mm.MySQL driver
try
{
Class.forName("org.gjt.mm.mysql.Driver");
Connection dbcon = DriverManager.getConnection(loginUrl, loginUser, loginPasswd);
// Declare our statement
Statement statement = dbcon.createStatement();
String query = "SELECT name, dept, ";
query += " jobtitle ";
query += "FROM employee ";
// Perform the query
ResultSet rs = statement.executeQuery(query);
out.println("<TABLE border>");
// Iterate through each row of rs
while (rs.next())
{
String m_name = rs.getString("name");
String m_dept = rs.getString("dept");
String m_jobtitle = rs.getString("jobtitle");
out.println("<tr>" +
"<td>" + m_name + "</td>" +
"<td>" + m_dept + "</td>" +
"<td>" + m_jobtitle + "</td>" +
"</tr>");
}
out.println("</TABLE>");
rs.close();
statement.close();
dbcon.close();
}
catch (SQLException ex) {
while (ex != null) {
System.out.println ("SQL Exception: " + ex.getMessage ());
ex = ex.getNextException ();
} // end while
} // end catch SQLException
catch(java.lang.Exception ex)
{
out.println("<HTML>" +
"<HEAD><TITLE>" +
"Bedrock: Error" +
"</TITLE></HEAD>\n<BODY>" +
"<P>SQL error in doGet: " +
ex.getMessage() + "</P></BODY></HTML>");
return;
}
out.close();
}
}
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[prompt]# export CLASSPATH=/var/tomcat4/common/lib/mm.mysql-2.0.13-bin.jar:$CLASSPATH [prompt]# cd /var/tomcat4/webapps/examples/WEB-INF/classes [prompt]# javac ShowBedrock.java (ORexport CLASSPATH=/usr/java/j2sdk1.4.0/lib/tools.jar:/usr/java/j2sdk1.4.0/jre/lib/rt.jar:/var/tomcat4/common/lib/servlet.jar:/var/tomcat4/lib/mm.mysql-2.0.13-bin.jar ) (OR /usr/java/j2sdk1.4.0/bin/javac ShowBedrock.java )
Test:
Notes:
[prompt]$ hostname superserver [prompt]$ mysql -h localhost -u root -p ... mysql> use mysql mysql> select user,host from user; +-------+------------+ | user | host | +-------+------------+ | root | | | Dude1 | localhost | +-------+------------+ mysql> update user set Host='superserver' where User='Dude1'; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0
| JAVA JDBC: |
JAVA JDBC programs require the package: java.sql. Contained within this package are:
JDBC Links:
| JAVA Server Pages (JSP): |
Basic JSP elements:
Books:
