Null safe expression in Thymeleaf

Using '?' after the variable in Thymeleaf expression, that variable will be null safe.

<td th:text="${user.department?.name}"></td>

For the avoid example, even variable department is null, the expression will still be fine.

OpenLayers blurry map with ArcGIS tiles

Check this out:

https://github.com/openlayers/openlayers/issues/6430

Skip testing in Maven

To skip the unit testing in Maven, we need to set the environment variable "maven.test.skip" to true. Or we can use "-DskipTests"

Sample command:

Prompt> mvn package -Dmaven.test.skip=true

OR

Prompt> mvn package -DskipTests

Reference:

https://www.mkyong.com/maven/how-to-skip-maven-unit-test/

Query windows patch via command line

To check if a windows patch (e.g. KB1234567) has been installed, run the following command line:

     C:> wmic qfe | find "1234567"

KVM with NKRO keyboard

Most KVM (e.g. ATEN CS62U) won't compatible with NKRO (N-Key Roll Over) keyboard (e.g. Most mechanical keyboard are with NKRO).

So please pay more attention when purchasing a KVM for NKRO keyboard.

git commands

There are some useful git commands:

Setup a repository:

     git init --bare

Copy an existing repository:

     git clone drive:

Add file to repository:

     git add file
     git commit
     git push

Get updated files from repository:

     git fetch

Merge updated files to my workspace:

     git merge

Web Application Firewall (WAF)

By definition, WAF is going to filter out web request containing SQL injection, cross-site scripting, etc.

Ref: https://www.owasp.org/index.php/Web_Application_Firewall

Smallest font size in Chrome

Since Chrome has a smallest font size setting, you can't use CSS to set font size less than (12px, by default):

   font-size: 6px !important; /* This has no effect ! Sigh .. */


Instead, you may consider to use transform instead:

   transform: scale(0.833); /* 10/12 = 0.833 */


And you may also consider to shift the <div> container to fix the position changed by transform:

   position: relative;
   left: -15px;

Backup and Restore with PostgreSQL

Enter psql
DOS> psql -U user database_name
DOS> psql database_name (if no password defined)

Drop DB
DOS> dropdb database_name
PSQL# drop database database_name

Create DB
DOS> createdb database_name
PSQL# create database database_name

Dump DB
DOS> pg_dump database_name > file_name

Restore from Dump
DOS> psql -U user -d database_name -f file_name

Make web application start up faster

To make web application start up faster in Tomcat, you may consider the following tuning:

1. Add metadata-complete="true" as an attribute in <web-app> tag
2. Add <absolute-ordering/> inside <web-app> </web-app>