useful maven command and their usage

usage: mvn [options] [<goal(s)>] [<phase(s)>]

Options:
 -am,--also-make                        If project list is specified, also build projects required by the list
 -amd,--also-make-dependents            If project list is specified, also build projects that depend on projects on the list
 -B,--batch-mode                        Run in non-interactive (batch) mode
 -b,--builder <arg>                     The id of the build strategy to use.
 -C,--strict-checksums                  Fail the build if checksums don't match
 -c,--lax-checksums                     Warn if checksums don't match
 -cpu,--check-plugin-updates            Ineffective, only kept for backward compatibility
 -D,--define <arg>                      Define a system property
 -e,--errors                            Produce execution error messages
 -emp,--encrypt-master-password <arg>   Encrypt master security password
 -ep,--encrypt-password <arg>           Encrypt server password
 -f,--file <arg>                        Force the use of an alternate POM file (or directory with pom.xml).
 -fae,--fail-at-end                     Only fail the build afterwards; allow all non-impacted builds to continue
 -ff,--fail-fast                        Stop at first failure in reactorized builds
 -fn,--fail-never                       NEVER fail the build, regardless of project result
 -gs,--global-settings <arg>            Alternate path for the global settings file
 -gt,--global-toolchains <arg>          Alternate path for the global toolchains file
 -h,--help                              Display help information
 -l,--log-file <arg>                    Log file where all build output will go.
 -llr,--legacy-local-repository         Use Maven 2 Legacy Local Repository behaviour, ie no use of _remote.repositories. Can also be
                                        activated by using -Dmaven.legacyLocalRepo=true
 -N,--non-recursive                     Do not recurse into sub-projects
 -npr,--no-plugin-registry              Ineffective, only kept for backward compatibility
 -npu,--no-plugin-updates               Ineffective, only kept for backward compatibility
 -nsu,--no-snapshot-updates             Suppress SNAPSHOT updates
 -o,--offline                           Work offline
 -P,--activate-profiles <arg>           Comma-delimited list of profiles to activate
 -pl,--projects <arg>                   Comma-delimited list of specified reactor projects to build instead of all projects. A project can be
                                        specified by [groupId]:artifactId or by its relative path.
 -q,--quiet                             Quiet output - only show errors
 -rf,--resume-from <arg>                Resume reactor from specified project
 -s,--settings <arg>                    Alternate path for the user settings file
 -T,--threads <arg>                     Thread count, for instance 2.0C where C is core multiplied
 -t,--toolchains <arg>                  Alternate path for the user toolchains file
 -U,--update-snapshots                  Forces a check for missing releases and updated snapshots on remote repositories
 -up,--update-plugins                   Ineffective, only kept for backward compatibility
 -V,--show-version                      Display version information WITHOUT stopping build
 -v,--version                           Display version information
 -X,--debug                             Produce execution debug output

How to throw NullPointerException in a Java program

Exception Handling in Java program.

Throwable interface has three class.

1. Error
2. Runtime Exception
3. Exception

There are two types of exception in Java.

Checked: Which can be handle using try and catch block

• Exception class comes under the checked exception which we can handle.
• NullPointerException
• DivideByZeroException
• IndexOutOfBoundException
• ClassCastException

Unchecked : Which cannot be handle.

• Error and Runtime Exception come under the unchecked exception which we can't handle.

Below is a example program:

package rashid;

public class testException {

public static void main(String[] args) {
String var1=null;

System.out.println(var1.length());
}

}

Output:
Exception in thread "main" java.lang.NullPointerException
at rashid.testException.main(testException.java:8)

How to change default start page in AEM?

Today we are going to learn about Day CQ Root Mapping configuration setting in AEM. 
This configuration is for default landing page of your AEM instance when you browse your AEM instance with URI http://localhost:4502 only and don't specify the any page name after that.

Steps to be follow to change the default landing page:
Step 1: Open http://localhost:4503
Step 2: Login with admin credentials.
Step 3: Go to http://localhost:4502/system/console/configMgr
Step 4: Go to find option [shortcut key Press Ctrl+f] then find for CQ Root Mapping
Step 5: Click on Day CQ Root Mapping configuration which will open a pop as showing in the below email.
Step 6: Change the target value with to new target page.

• Default the value of this configuration will be : /projects.html 
• Possible value: You can put any page name here which you want to open. e.g. if you want to open website site admin then put the value /siteadmin

Step 7: Save the settings and logout. Go for Login gain to verify the changes.

Below is the screen shot:

CQ Root Mapping