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Jul 09

Configuring multiple Tomcat application servers with Apache HTTP server/ Load Balancing with Apache Web Server




In this article, I am going to explain how we can configure multiple Tomcat instances with single Apache Web Server.

There are many solutions posted on the web, but it is the simplest and easiest way to do this.

Prerequisite:

  • Apache HTTP Server 2.x
  • Tomcat 6.x
  • mod_jk.so module for Apache Web server
  • Any text editor, i.e. Notepad, gedit, etc.

if you do not have Apache HTTP server goto http://httpd.apache.org/ and download the appropriate version and install on your machine.

if you do not have Apache Tomcat Server goto http://tomcat.apache.org/ and download the appropriate version and install on your machine.

if you do not have mod_jk.so module, goto http://tomcat.apache.org/download-connectors.cgi and download the appropriate connector for Apache Web Server.

Step 1: Configure Tomcat

If you having one machine per Tomcat, you don’t need to do this. but if you don’t have, you have to configure each tomcat instance for different port to run successfully.

To configure Tomcat’s port, goto conf directory of any tomcat instance you have and open the server.xml file in the text editor.

search these lines in the server.xml and make the value of port property unique for each instance of tomcat.

<Server port=”8005″ shutdown=”SHUTDOWN”>

<Connector port=”8080″ protocol=”HTTP/1.1″ connectionTimeout=”20000″ redirectPort=”8443″ />

<Connector port=”8009″ protocol=”AJP/1.3″ redirectPort=”8443″ />

Step 2: Creating configuration file of Tomcat instances for Apache Web Server

now open text editor and create a file called workers.properties and enter the information of all tomcat instances you have. and save it  under the conf directory of Apache.

A sample workers.properties is given:

# lists the workers by name

worker.list=tomcat1, tomcat2, loadbalancer

Tomcat1 configuration

worker.tomcat1.port=8009 //AJP1.3 Connector’s port

worker.tomcat1.host=localhost //IP of machine where tomcat1 is running

worker.tomcat1.type=ajp13 //AJP Connector type.

worker.tomcat1.lbfactor=100 //Load Balancing factor

Tomcat2 configuration

worker.tomcat2.port=8119 //AJP1.3 Connector’s port

worker.tomcat2.host=localhost //IP of machine where tomcat1 is running

worker.tomcat2.type=ajp13 //AJP Connector type.

worker.tomcat2.lbfactor=100 //Load Balancing factor

#Load Balance worker configuration

worker.loadbalancer.type=lb

worker.loadbalancer.balanced_workers=tomcat1,tomcat2

Step 3: Configure JK module

Copy the downloaded JK module file (mod_jk.so) to the modules directory of Apache Web Server. now goto conf directory of Apache Server, and open the httpd.conf file in the text editor.

and add these lines to the end of httpd.conf

LoadModule jk_module modules/mod_jk.so

JkWorkersFile conf/workers.properties

JkLogFile logs/mod_jk.log

JkLogLevel info

now you have done all the configuration, now you need to configure the JK Module to redirect the requests to specific tomcats. It can be done by the following:

To redirect specific request to specific Tomcat add this line to httpd.conf:

JkMount /abc/* tomcat1

or

JkMount /*.do tomcat2

Or, if you want to configure requests to be served by any of the tomcat then add this:

JkMount /*.jsp loadbalancer

if any of the tomcat is stopped then all the request will be served by other tomcat and if both the tomcat are running then the requests are redirected to tomcat servers according to the lbfactor specified in the workers.properties.

Now start all the Tomcat Servers and Apache Server, and its done.

 

Jun 21

Accessing Private Members of a Java class using Reflection




Somebody asked me that, “Is there any way of accessing private members of a Java Class?

Then I got the idea to write this article, because Java Reflection API provides a feature for accessing private members of a Java Class.

java.lang.reflect package provides the AccessibleObject class that is parent class of Constructor, Method, and Field class. Using the AccessibleObject class, we can change the access control flags of a Reflection Object (Reflection is a feature in the Java programming language. It allows an executing Java program to examine or “introspect” upon itself, and manipulate internal properties of the program. For example, it’s possible for a Java class to obtain the names of all its members and display them.), and the setAccessible(boolean) method is used to change the access control flag of an Object.

package test;

/**

  • @author girish.gaurav

*

*/

class DemoClass {

private int privateInt = 10;

private String privateString = “temp String”;

private long privateLong = 1234567890L;

private void resetFields(int i, String s, long l) {

privateInt = i;

privateString = s;

privateLong = l;

}

public void display() {

System.out.println(“Int = ” + privateInt);

System.out.println(“String = ” + privateString);

System.out.println(“Long = ” + privateLong);

}

}

class Test {

/**

* @param args

*/

public static void main(String[] args) {

DemoClass obj = new DemoClass();

obj.display();

Class clazz = obj.getClass();

try {

Field intField = clazz.getDeclaredField(“privateInt”);

Field strField = clazz.getDeclaredField(“privateString”);

Field longField = clazz.getDeclaredField(“privateLong”);

intField.setAccessible(true);

strField.setAccessible(true);

longField.setAccessible(true);

System.out.println(“value of privateInt field is : ” + intField.get(obj));

System.out.println(“value of privateString field is : ” + strField.get(obj));

System.out.println(“value of privateLong field is : ” + longField.get(obj));

intField.set(obj, 100);

strField.set(obj, “this is new string”);

longField.set(obj, 55555L);

obj.display();

} catch (SecurityException e) {

e.printStackTrace();

} catch (NoSuchFieldException e) {

e.printStackTrace();

} catch (IllegalArgumentException e) {

e.printStackTrace();

} catch (IllegalAccessException e) {

e.printStackTrace();

}

try {

Method method = clazz.getDeclaredMethod(“resetFields”, int.class, String.class, long.class);

method.setAccessible(true);

method.invoke(obj, 25, “new String from resetField method.”, 987654321L);

obj.display();

} catch (SecurityException e) {

e.printStackTrace();

} catch (NoSuchMethodException e) {

e.printStackTrace();

} catch (IllegalArgumentException e) {

e.printStackTrace();

} catch (IllegalAccessException e) {

e.printStackTrace();

} catch (InvocationTargetException e) {

e.printStackTrace();

}

}

}

References:

Java Reflection API

 

Jun 14

Introduction to Nonblocking Sockets




Here, I am going to explain what non-blocking sockets are, how it works, and where it can be useful, everything in details.

Preface:

Non-blocking sockets are introduced in Java 2 Standard Edition 1.4. It allows network communication between applications without blocking processes using the sockets.

A nonblocking socket allows input/output operation on a channel without blocking the processes using it. I’m talking about asynchronous high-performance read/write operations that, as you will see, turn upside-down the techniques for designing and developing socked-based applications.

Java developers who already working or worked on sockets might ask that, “Why we use a new technology to work on Sockets while we already have an old one that working fine? Or whats wrong with the traditional (Java 1.3.x) socket programming? and What are the advantage with new non-blocking socket API?”

Suppose we are going to implement a server application that accepts huge number of client connections and as well as, we want the server that can be able to process multiple requests simultaneously. If we use older socket programming to achieve this requirement we have two ways:

1. Implement a multithread server that manually handles a thread for each connection.
2. By using an external third-party module.

Both the given solution can work fine, but if we adopt first solution then the whole thread-management solution will be developed by the programmer and all the concurrency related issues will also be considered by the programmer. and the second solution may cost money. And by using Non-blocking sockets, you can implement a nonblocking server without directly managing threads or resorting to external modules.

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