how to extract zip file in linux

Use unzip command:

Code:

unzip file.zip

many time unzip is not installed by default so install it before using it, use rpm or apt-get/yum command to install unzip

How to open link in new tab on html?

Set the 'target' attribute of the link to _blank:

<a href="#" target="_blank">Link</a>

Edit: for other examples, see here: http://www.w3schools.com/tags/att_a_target.asp

(Note: I previously suggested blank instead of _blank because, if used, it'll open a new tab and then use the same tab if the link is clicked again. However, this is only because, as GolezTrol pointed out, it refers to the name a of a frame/window, which would be set and used when the link is pressed again to open it in the same tab).

First Login: HTTP Status 500 - Request processing failed; nested exception is org.springframework.transaction.CannotCreateTransactionException

It appears that MySQL or a firewall is killing off your inactive connections that are hanging around in your jdbc connection pool for long periods of time:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure 
The last packet successfully received from the server was 4,665,488 milliseconds ago.

Check the value of wait_timeout on MySQL.

You can play around with DBCP settings e.g. validationQuery, testOnBorrow and testWhileIdle.

A a confuguration that is 'belt and braces', and will probably solve your problem at the expense of performance is:

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
  <property name="driverClassName" value="${jdbc.driverClassName}"/>
  <property name="url" value="${jdbc.url}"/>
  <property name="username" value="${jdbc.username}"/>
  <property name="password" value="${jdbc.password}"/>
  <property name="validationQuery" value="SELECT 1"/>
  <property name="testOnBorrow" value="true"/>
</bean>

The above will test connections every time you borrow from the pool.

Solving the mySQL “The security settings could not be applied” error

Yesterday I got this error message during the last step of the MySQL Windows installer: “The security settings could not be applied to the database because the connection has failed with the following error”.

The issue can be solved issue this procedure from the MySQL website.

First, cancel the wizard and make sure that the MySQL service is stopped.

Then, create a text file using a SQL query that will reset the root password.

1 2	UPDATE mysql.user SET Password=PASSWORD('admin') WHERE User='root'; FLUSH PRIVILEGES;

Then, launch mySQL using the following command line:

1	mysqld --defaults-file="C:\Program Files\MySQL\MySQL Server 5.5\my.ini" --init-file="C:\mysql-init.txt" --console

Note: it’s better to use the ”–console” option so that error messages are correctly displayed.

Finally, open a new DOS shell and execute the following command line to shutdown mySQL:

1	mysqladmin -u root -p shutdown

You can now restart the mySQL installer and choose the “Repair” option:

2 solution of java.lang.OutOfMemoryError in Java

ava.lang.OutOfMemoryError now and then, OutOfMemoryError in Java is one problem which is more due to system's limitation (memory) rather than due to programming mistakes in most cases though in certain cases you could have memory leak which causing OutOfMemoryError. I have found that even though java.lang.OutOfMemoryError is quite common basic knowledge of its cause and solution is largely unknown among junior developers. In this article we will explore what is java.lang.OutOfMemoryError; Why OutOfMemoryError comes in Java application, different type of OutOfMemoryError and How to fix OutOfMemoryError in Java. This article is purely meant to provide basic knowledge of java.lang.OutMemoryError and won't discuss profiling in detail.

What is java.lang.OutOfMemoryError in Java

OutOfMemoryError in Java is a subclass of java.lang.VirtualMachineError and JVM throws java.lang.OutOfMemoryError when it ran out of memory in heap. OutOfMemoryError in Java can come any time in heap mostly while you try to create an object and there is not enough space in heap to allocate that object. javavdoc of OutOfMemoryError is not very informative about this though.

Types of OutOfMemoryError in Java

I have seen mainly two types of OutOfMemoryError in Java:

1) Java.lang.OutOfMemoryError: Java heap space
2) Java.lang.OutOfMemoryError: PermGen space

Though both of them occur because JVM ran out of memory they are quite different to each other and there solutions are independent to each other.

Difference between "java.lang.OutOfMemoryError: Java heap space" and "java.lang.OutOfMemoryError: PermGen space"

If you are familiar with different generations on heap and How garbage collection works in java and aware of new, old and permanent generation of heap space then you would have easily figured out this OutOfMemoryError in Java. Permanent generation of heap is used to store String pool and various Meta data required by JVM related to Class, method and other java primitives. Since in most of JVM default size of Perm Space is around "64MB" you can easily ran out of memory if you have too many classes or huge number of Strings in your project. Important point to remember is that it doesn't depends on –Xmx value so no matter how big your total heap size you can ran OutOfMemory in perm space. Good think is you can specify size of permanent generation using JVM options "-XX:PermSize" and  "-XX:MaxPermSize" based on your project need.

One small thing to remember is that "=" is used to separate parameter and value while specifying size of perm space in heap while "=" is not required while setting maximum heap size in java, as shown in below example.

export JVM_ARGS="-Xmx1024m -XX:MaxPermSize=256m"

Another reason of "java.lang.OutOfMemoryError: PermGen" is memory leak through Classloaders and it’s very often surfaced in WebServer and application server like tomcat, webshere, glassfish or weblogic. In Application server different classloaders are used to load different web application so that you can deploy and undeploy one application without affecting other application on same server, but while undeploying if container some how keeps reference of any class loaded by application class loader than that class and all other related class will not be garbage collected and can quickly fill the PermGen space if you deploy and undeploy your application many times. "java.lang.OutOfMemoryError: PermGen” has been observed many times in tomcat in our last project but solution of this problem are really tricky because first you need to know which class is causing memory leak and then you need to fix that. Another reason of OutOfMemoryError in PermGen space is if any thread started by application doesn't exit when you undeploy your application.

These are just some example of infamous classloader leaks, anybody who is writing code for loading and unloading classes have to be very careful to avoid this. You can also use visualgc for monitoring PermGen space, this tool will show graph of PermGen space and you can see how and when Permanent space getting increased. I suggest using this tool before reaching to any conclusion.

Another rather unknown but interesting cause of "java.lang.OutOfMemoryError: PermGen" we found is introduction of JVM options "-Xnoclassgc". This option sometime used to avoid loading and unloading of classes when there is no further live references of it just to avoid performance hit due to frequent loading and unloading, but using this option is J2EE environment can be very dangerous because many framework e.g. Struts, spring etc uses reflection to create classes and with frequent deployment and undeployment you can easily ran out of space in PermGen if earlier references was not cleaned up. This instance also points out that some time bad JVM arguments or configuration can cause OutOfMemoryError in Java.

So conclusion is avoid using "-Xnoclassgc" in J2EE environment especially with AppServer.

Tomcat to Solve OutOfMemoryError in PermGen Space

From tomcat > 6.0 onward tomcat provides memory leak detection feature which can detect many common memory leaks on web-app perspective e.g ThreadLocal memory leaks, JDBC driver registration, RMI targes, LogFactory and Thread spawned by web-apps. You can check complete details on htp://wiki.apache.org/tomcat/MemoryLeakProtection you can also detect memory leak by accessing manager application which comes with tomcat, in case you are experiencing memory leak on any java web-app its good idea to run it on tomcat.

How to solve java.lang.OutOfMemoryError: Java heap space

1) Easy way to solve OutOfMemoryError in java is to increase the maximum heap size by using JVM options "-Xmx512M", this will immediately solve your OutOfMemoryError. This is my preferred solution when I get OutOfMemoryError in Eclipse, Maven or ANT while building project because based upon size of project you can easily ran out of Memory.here is an example of increasing maximum heap size of JVM, Also its better to keep -Xmx to -Xms ration either 1:1 or 1:1.5 if you are setting heap size in your java application

export JVM_ARGS="-Xms1024m -Xmx1024m"

2) Second way to resolve OutOfMemoryError in Java is rather hard and  comes when you don't have much memory and even after increase maximum heap size you are still getting java.lang.OutOfMemoryError, in this case you probably want to profile your application and look for any memory leak. You can use Eclipse Memory Analyzer to examine your heap dump or you can use any profiler like Netbeans or JProbe. This is tough solution and requires some time to analyze and find memory leaks.

How to solve java.lang.OutOfMemoryError: PermGen space

As explained in above paragraph this OutOfMemory error in java comes when Permanent generation of heap filled up. To fix this OutOfMemoryError in Java you need to increase heap size of Perm space by using JVM option   "-XX:MaxPermSize". You can also specify initial size of Perm space by using    "-XX:PermSize" and keeping both initial and maximum Perm Space you can prevent some full garbage collection which may occur when Perm Space gets re-sized. Here is how you can specify initial and maximu Perm size in Java:

export JVM_ARGS="-XX:PermSize=64M -XX:MaxPermSize=256m"

Some time java.lang.OutOfMemoryError  in Java gets tricky and on those cases profiling remain ultimate solution.Though you have freedom to increase heap size in java, it’s recommended that to follow memory management practices while coding and setting null to any unused references.
That’s all from me on OutOfMemoryError in Java I will try to write more about finding memory leak in java and using profiler in some other post. Please share what is your approach to solve java.lang.OutOfMemoryError in Java.

Important Note: From Tomcat > 6.0 onward tomcat provides memory leak detection feature which can detect many common memory leaks on Java application e.g ThreadLocal memory leaks, JDBC driver registration, RMI targes, LogFactory and Thread spawned by webapps. You can check complete details on htp://wiki.apache.org/tomcat/MemoryLeakProtection. You can also detect memoy leak by accessing manager application which comes with tomcat, in case you are experiencing memory leak on any java webapp its good idea to run it on tomcat to find out reason of OutOfMemoryError in PermGen space.

Tools to investigate and fix OutOfMemoryError in Java

Java.lang.OutOfMemoryError is a kind of error which needs lot of investigation to find out root cause of problem, which object is taking memory, how much memory it is taking or finding dreaded memory leak and you can't do this without having knowledge of available tools in java space. Here I am listing out some free tools which can be used to analyze heap and will help you to find culprit of OutOfMemoryError

1) Visualgc

Visualgc stands for Visual Garbage Collection Monitoring Tool and you can attach it to your instrumented hostspot JVM. Main strength of visualgc is that it displays all key data graphically including class loader, garbage collection and JVM compiler performance data.

The target JVM is identified by its virtual machine identifier also called as vmid. You can read more about visualgc and vmid options here.

2) Jmap

Jmap is a command line utility comes with JDK6 and allows you to take a memory dump of heap in a file. It’s easy to use as shwon below:

jmap -dump:format=b,file=heapdump 6054

Here file specifies name of memory dump file which is "heapdump" and 6054 is PID of your Java progress. You can find the PDI by using "ps -ef” or windows task manager or by using tool called "jps"(Java Virtual Machine Process Status Tool).

3) Jhat

Jhat was earlier known as hat (heap analyzer tool) but it is now part of JDK6. You can use jhat to analyze heap dump file created by using "jmap". Jhat is also a command line utility and you can rum it from cmd window as shown below:

jhat -J-Xmx256m heapdump

Here it will analyze memory-dump contained in file "heapdump". When you start jhat it will read this heap dump file and then start listening on http port, just point your browser into port where jhat is listening by default 7000 and then you can start analyzing objects present in heap dump.

4) Eclipse memory analyzer

Eclipse memory analyzer (MAT) is a tool from eclipse foundation to analyze java heap dump. It helps to find classloader leaks and memory leaks and helps to minimize memory consumption.you can use MAT to analyze heap dump carrying millions of object and it also helps you to extract suspect of memory leak. See here for more information.

Read more: http://javarevisited.blogspot.com/2011/09/javalangoutofmemoryerror-permgen-space.html#ixzz3QwKpSS91

Rename a file in Linux with simple command line options

Linux is a very popular operating system and is widely used today on servers and also on standalone systems. It is based on UNIX and is a free OS. There are many people who love to work on it and consider it the most reliable and robust of all the operating systems available today. Working in Linux requires some prior knowledge as the commands have to be given through command line text. In this tutorial, we’ll show you how to rename files in Linux, with different commands. Linux has several ways of renaming files and directories in Linux like cp (copy), rm (remove), mv (move or rename),etc. We’ll walk you through them shortly.

Renaming a file

In order to rename a file in Linux you can use either of two approaches

1.    Create a copy of the existing file with the new desired name and then delete the old file.

2.    Rename the file by moving it with the mv command.

Lets take up some examples one by one:

Rename with copy and delete

$ cp oldfile newfile

This creates a copy of the same file with a new name in the same location.

$ rm oldfile

This will delete the old file keeping the newfile intact.

Rename by moving

$mv old-file-name  new-file-name

This just moves the old file, to a new name.

Renaming multiple files

This is extremely easy case when we are dealing with one file but the complexity increases when we are dealing with multiple files, and this is something with which we encounter very often in real life.

Lets take an example where we want to rename multiple files.

In order to rename multiple files at once we can make use of wildcard characters (for ex: ‘*’). In the below example we will rename all the files with .txt to .dat.

We can achieve this by simply typing the following command:

$ mv *.txt *.dat

Now, let us assume you have a file whose name is misspelled or if there is an alphabet missing from the name of the file then in order to fix this we can leverage the mv command with other wildcard characters.

For example: we have a file with a name RR#.txt, whereas the filename should contain only alphanumeric values instead of any special characters. This can be fixed with the following command:

$ mv RR?.txt RR1.txt

Where ? is the wildcard character used in place of the unknown character.

Interactive renaming

Many times during your day to day work you may make a mistake you cannot undo. For example, moving or renaming a file accidentally. To avoid this problem Linux provides an interactive renaming option wherein the user will be prompted  for confirmation before overwriting the file name. This empowers the end user to choose an option “Y” or “N” from the keyboard in order to finalize the action. In order to leverage this capability one must use -i option with mv command in the following manner.

$ mv -i RR1.txt ST1.txt

Once we run this command the Linux will prompt the end with following line:

mv: overwrite ‘RR1.txt’ ?

User can choose “Y” to continue or “N” to abort this action.

Renaming a directory

Renaming a directory in Linux and Unix is similar to renaming a file. All we need to do is replace the file name with the directory name that is to be renamed.

For example, if we wanted to rename the directory “RR1″ to “ST1″, then we can use the following command.

$ mv RR1 ST1

Rename file to different location

If you want to change not only the name of the file, but also it’s location, use the following command:

$ mv RR2 newdir/.

This command moves the file RR2 from its current location and places it under the directory newdir/.

Track what’s happening with Verbose option

If you’re renaming a number of files, or doing other mass operations, you may want to track what is happening. Linux has an easy way of doing that with the -v or -verbose option. Here is the syntax

$ mv -v source.txt new_source.txt

Mass move and rename

Linux has another command, mmv, which stands for mass, move and rename. This is extremely helpful for renaming multiple files at a go. Its utility is not just limited to renaming of files. It can be used for moving, linking and appending multiple files as well. The reason why I like it most because it is the safest way to do these tasks. mmv does it all without any sudden destruction of files due to collisions of target names with existing file names. Moreover, before doing anything, mmv tries to identify any errors that would result from the entire set of actions specified and equips the user with the option of either terminating before beginning, or proceeding by avoiding the offending parts.The syntax for this command is:

$ mmv [options]

This should give you a good insight into how to rename files in Linux. If you want to try out more options, just use the ‘man’ command, and Linux will list out all the options, along with how to use them.

$ man move

From PHP to Tomcat server

http://stackoverflow.com/questions/2865289/php-redirection-with-post-parameters