GC logging addition to Tomcat

Add the following to CATALINA_OPTS

 -verbose:gc  -XX:+PrintGCDetails  -XX:+PrintGCTimeStamps  -Xloggc:/home/PATH_TO_LOG/gc.log

Command to remove files older than N days

The below command removes files older than 2 days in the current directory

sudo find .  -mtime +2 -exec rm {} \;

Monitoring open connections in MySQL

Use the following commands

show status like '%onn%';

show processlist

Renew SSL certificates - courier and imap server in Ubuntu

Remove the expired .pem file

rm  /etc/courier/imapd.pem

Just open and check if the entries are recent (like contact email etc). This is NOT a mandatory step.

nano  /etc/courier/imapd.cnf

 Issue the following command to create new .pem file

mkimapdcert

Restart imap SSL service

/etc/init.d/courier-imap-ssl  restart

Configuration parameter to make git ignore carriage return difference

Configuration parameter to make git ignore carriage return difference

in Unix/Linux and Windows

git config core.autocrlf false

Reattaching to a screen in Ubuntu using processid

screen -d -r  pid

Command to enable periodic tasks in Django after configuring in Admin Module

python manage.py celerybeat

Ignoring white spaces and empty lines and comparing two files

diff -Bb  a.txt b.txt

Ubuntu 12.04 and mysql does not start

Once you upgrade to Ubuntu 12.04 and if you had configured mysql to use UTF character set, the mysql server may not start.

This is due to the following deprecated parameters.

default-character-set=utf8
default-collation=utf8_unicode_ci

Replace the above parameters (they are normally in /etc/mysql/my.cnf)

character-set-server = utf8
collation-server = utf8_unicode_ci


Now restart mysql server using the command

sudo service mysql start

Good motivational video

http://www.youtube.com/watch?feature=player_embedded&v=hV63DbQ_qSc

ProGuard - A case to disable shrink

Assume you are obfuscating a jar in a web application (say you deploy it on machines where you want to protect from decompile+disassembling).

If you come across the error message "The output jar is empty. Did you specify the proper '-keep' options?" , disable shrinking (as you may not have a valid main method entry point in a web application.

How to find if Apache is running prefork or worker MPM

Use the command

apache2 -l

It should list modules like  

 Compiled in modules:
  core.c
  mod_log_config.c
  mod_logio.c
  worker.c
  http_core.c
  mod_so.c

As worker.c is displayed then it uses worker MPM. 

Shortcut to show desktop in Ubuntu 11.10

Upgraded to Ubuntu 11.10 today.

The default short cut to show desktop minimizing all windows is Alt+Ctrl+D

Install tint2 (sudo apt-get install tint2) for the taskbar to switch between applications.  Also add it to startup so that it appears after logging in.

PrimeFaces Themes Dependencies

       <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>aristo</artifactId>
            <version>${theme.version}</version>
        </dependency>
      
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>black-tie</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>blitzer</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>bluesky</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>casablanca</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>cupertino</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>dark-hive</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>dot-luv</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>eggplant</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>excite-bike</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>flick</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>glass-x</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>hot-sneaks</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>humanity</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>le-frog</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>midnight</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>mint-choc</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>overcast</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>pepper-grinder</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>redmond</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>rocket</artifactId>
            <version>${theme.version}</version>
        </dependency>
          <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>sam</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>smoothness</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>south-street</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>start</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>sunny</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>swanky-purse</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>trontastic</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>ui-darkness</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>ui-lightness</artifactId>
            <version>${theme.version}</version>
        </dependency>
        <dependency>
            <groupId>org.primefaces.themes</groupId>
            <artifactId>vader</artifactId>
            <version>${theme.version}</version>
        </dependency>

GlassFish 3.1 - Enabling mod_jk

1. Ensure GlassFish server is up and running. (or use asadmin start-domain domain1 command)
2. Execute asadmin create-http-listener --listenerport 8009 --listeneraddress 0.0.0.0 --defaultvs server jk-connector
3. Execute asadmin set configs.config.server-config.network-config.network-listeners.network-listener.jk-connector.jk-enabled=true
4. Final step is to restart GlassFish server. Thats it enjoy.

Configuring JDBC Realm in GlassFish 3.1

Use the following sample in domain.xml (under config folder) in GlassFish. Change the digest-algorithm and encoding accordingly.

  <security-service>
 <auth-realm classname="com.sun.enterprise.security.auth.realm.jdbc.JDBCRealm" name="jdbcRealm">
          <property name="jaas-context" value="jdbcRealm"></property>
          <property name="datasource-jndi" value="jdbc/srack"></property>
          <property name="user-table" value="users"></property>
          <property name="user-name-column" value="username"></property>
          <property name="password-column" value="password"></property>
          <property name="group-table" value="groups"></property>
          <property name="group-name-column" value="groupname"></property>
          <property name="digest-algorithm" value="MD5"></property>
          <property name="encoding" value="Base64"></property>
          <property name="assign-groups" value=""></property>
   </auth-realm>
............
More config here
.............

SEVERE: Exception while loading the app GlassFish error CDI JPA

Verify if one of your @Named annotated backing bean which is ViewScoped or ConversationScoped is Serializable if you receive the error SEVERE: Exception while loading the app without any stacktrace in GlassFish 3.1

DataExporter dependent jars - iText and Apache POI version

If you are using PrimeFaces 3.x and wish to use dataExporter for producing pdf and xls files, iText and Apache POI jars are required. If you are using Maven please include the following dependencies.

         <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi</artifactId>
            <version>3.7</version>
        </dependency>

         <dependency>
            <groupId>com.lowagie</groupId>
            <artifactId>itext</artifactId>
            <version>2.1.7</version>
          </dependency>

Listing long running conversations in CDI based web application

I am not sure if CDI provides APIs to list all long running conversations. So I came up with the below class.

Note: Time-out and eviction of conversations by the container when not in use for a long time to save resoruces is NOT considered in the code below.

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import javax.enterprise.context.SessionScoped;
import javax.inject.Named;

@Named
@SessionScoped
public class SRackWorkSpace implements Serializable{
   
    private List<String> cids=new ArrayList<String>();
   
    public void addConversation(String cid){
        cids.add(cid);
    }
   
    public void removeConversation(String cid){
        cids.remove(cid);
    }
   
    public boolean isConversationActive(String cid){
        return cids.contains(cid);
    }
   
   
}

Inject conversation and the above session scoped bean and invoke

 -  addConversation method when you begin a conversation like

                 conversation.begin("deliverexam");
                 sRackWorkSpace.addConversation("deliverexam");

- removeConversation when we end a conversation like

   sRackWorkSpace.removeConversation(conversation.getId());
            conversation.end();.

You can check of a long running conversation for a desired use case is already active like

 if (sRackWorkSpace.isConversationActive("deliverexam")) {

           return "/YOUR_PATH_TO_XHTML_VIEW?cid=deliverexam&faces-redirect=true";

}

Validating email field programmatically - Hibernate Validator

First the Email.java class

public class Email {

    @org.hibernate.validator.constraints.Email(message = "Email is not valid")
    private String email;

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

 Let us say you have to validate a Collection of email values,

import javax.validation.ConstraintViolation;
import javax.validation.Validation;
import javax.validation.Validator;
import javax.validation.ValidatorFactory;

 //More code here

Email emailClass = new Email();
        ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
        Validator validator = factory.getValidator();
      
        for (String e : emails) {
            emailClass.setEmail(e.trim());
            Set<ConstraintViolation<Email>> constraintViolations =validator.validate(emailClass);
            if (!constraintViolations.isEmpty()) {
               //Email is not valid. Perform the logic
            }
        }

I use Hibernate Validator implementation. Since I use Maven for build, the dependency is as below.

  <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-validator</artifactId>
            <version>4.2.0.Final</version>
  </dependency>