Modulo of power of 2 [without division]

A very efficient way is with binary operators:

n % 2^i = n & (2^i - 1)

See modulo without division

Multithreaded compression – pigz

Install pigz:

sudo apt install pigz

To compress a single directory recursively:

tar --use-compress-program="pigz -k " -cf output.tar.gz sourcedir

To compress each directory separately:

find . -maxdepth 1 -mindepth 1 -type d -exec tar --use-compress-program="pigz -k " -cf {}.tar.gz {} \;

Lock and load – flawless victory

Flawless victory

Malware – flawless victory

Flawless victory

Maven error 501 (HTTPS)

If you installed an old version of Netbeans, it is possible that you are getting error 501 (see this post). This is because the included maven version in Netbeans is too old.

Step 1 – Install maven

sudo apt install maven

Step 2 – Configure netbeans

Options -> java -> Maven: set up : /usr/share/maven

CORS – test with curl

Send an OPTIONS message and check Access-Control-Allow-Origin is in the response:

curl -X OPTIONS 'https://domain/path/file.png' -H "Origin: http://yoursitedomain" -H "Access-Control-Request-Method: POST" -H "Access-Control-Request-Headers: X-Requested-With"  --verbose 

Or if you want to ignore the output:

curl -X OPTIONS 'https://domain/path/file.png' -H "Origin: https://yoursitedomain" -H "Access-Control-Request-Method: POST" -v -o /dev/null

For input string: “0x100”

Do all of the following:

echo "export TERM=xterm-color" >> ~/.bashrc

source ~./bashrc

JAVA_HOME not set

To find the home of the installed Java JDKs use the command:

update-java-alternatives -l

The add it to /etc/environment

echo "JAVA_HOME=<path found>" | sudo tee -a /etc/environment

Ubuntu etherneT not working

If is it not a driver problem, try the following:

• sudo lshw -C network or ip a to find the interface
• sudo ifconfig ethXXXX up
• sudo dhclient -r
• sudo dhclient

If it works, then you can persist the changes by editing the file: /etc/network/interfaces:

1. auto ethXXXX
2. iface ethXXXX inet dhcp

Spring vs Jax-RS annotations

SPRING ANNOTATION	JAX-RS ANNOTATION
@RequestMapping(path = “/troopers”	@Path(“/troopers”)
@PostMapping	@POST
@PutMapping	@PUT
@GetMapping	@GET
@DeleteMapping	@DELETE
@ResponseBody	N/A
@RequestBody	N/A
@PathVariable(“id”)	@PathParam(“id”)
@RequestParam(“xyz”)	@QueryParam(‘xyz”)
@RequestParam(value=”xyz”)	@FormParam(“xyz”)
@RequestMapping(produces = {“application/json”})	@Produces(“application/json”)
@RequestMapping(consumes = {“application/json”})	@Consumes(“application/json”)