Category Archives: Programming

Spring Certification

We can now do Spring certification without going for Pivotal training. It was long due and here it is finally!

Can you take Spring certification without Pivotal Training Course?

Read more: http://javarevisited.blogspot.com/2017/05/can-you-take-spring-certification-without-training-course.html#ixzz4hVUNb9fW

5 Spring Framework Books for Java developers (Includes Spring Security and Spring Boot) – Best of lot

Read more: http://www.java67.com/2016/12/5-spring-framework-books-for-java-programmers.html#ixzz4hVU7visy

List of good Curl commands

I use CURL for debugging my REST endpoints every now and then if I don’t want to use Postman or DHC clients. I usually like to copy paste results / statistics from command line into emails to my colleagues. This gives them a plain jane command which they can use to test themselves as well as compare their results with mine. The following article has some good pointers on how to use CURL and some very practical examples have been provided.

15 Practical Linux cURL Command Examples (cURL Download Examples)

Maven: Installing / adding local jar into your local maven repository

I needed to install a local jar file into my laptop’s local maven repository and found this article. I used this approach to install this jar file in my repo:

mvn install:install-file -Dfile=my-model-1.2.1.jar -DgroupId=com.cyberaka.my.package -DartifactId=my-model -Dversion=1.2.1 -Dpackaging=jar -DgeneratePom=true

This duly added the local jar file under appropriate group id and artifact id inside my maven repository and I was able to refer to this dependency through my project’s pom.

 

Measuring UTF-8 character size

Lets say I type something in Hindi and the outcome is listed below:

तीन व्याकितियों की औसत आयु ३३ वर्ष है.

In Hex View it will look like:

e0 a4 a4 e0 a5 80 e0 a4 a8 20 e0 a4 b5 e0 a5 8d e0 a4 af e0 a4 be e0 a4 95 e0 a4 bf e0 a4 a4 e0 a4 bf e0 a4 af e0 a5 8b e0 a4 82 20 e0 a4 95 e0 a5 80 20 e0 a4 94 e0 a4 b8 e0 a4 a4 20 e0 a4 86 e0 a4 af e0 a5 81 20 e0 a5 a9 e0 a5 a9 20 e0 a4 b5 e0 a4 b0 e0 a5 8d e0 a4 b7 20 e0 a4 b9 e0 a5 88 2e e0 a4 85 e0 a4 97 e0 a4 b0 20 e0 a4 89 e0 a4 a8 e0 a4 95 e0 a5 80 20 e0 a4 86 e0 a4 af e0 a5 81 20 e0 a5 a8 3a e0 a5 a9 3a e0 a5 aa 20 e0 a4 95 e0 a5 87 20 e0 a4 85 e0 a4 a8 e0 a5 81 e0 a4 aa e0 a4 be e0 a4 a4 20 e0 a4 ae e0 a5 87 e0 a4 82 20 e0 a4 b9 e0 a5 8b 2c e0 a4 a4 e0 a5 8b e0 a4 b9 20 e0 a4 89 e0 a4 a8 e0 a4 ae e0 a5 87 20 e0 a4 b8 e0 a5 87 20 e0 a4 b8 e0 a4 ac e0 a4 b8 e0 a5 87 20 e0 a4 ac e0 a5 9c e0 a5 87 20 e0 a4 95 e0 a5 80 20 e0 a4 86 e0 a4 af e0 a5 81 20 e0 a4 95 e0 a4 bf e0 a4 af e0 a5 8d e0 a4 a4 e0 a4 a8 e0 a5 87 20 e0 a4 b5 e0 a4 b0 e0 a5 8d e0 a4 b7 20 e0 a4 b9 e0 a5 8b e0 a4 97 e0 a5 80 3f

The main thing to notice here is that every hindi character is starting with the byte “E0”. This is basically a code point which identifies the code size of the UTF-8 character. The following table appropriate highlights it:

Binary    Hex          Comments
0xxxxxxx  0x00..0x7F   Only byte of a 1-byte character encoding
10xxxxxx  0x80..0xBF   Continuation bytes (1-3 continuation bytes)
110xxxxx  0xC0..0xDF   First byte of a 2-byte character encoding
1110xxxx  0xE0..0xEF   First byte of a 3-byte character encoding
11110xxx  0xF0..0xF4   First byte of a 4-byte character encoding

Reference: https://stackoverflow.com/questions/5290182/how-many-bytes-does-one-unicode-character-take/33349765#33349765

 

Embedding images directly into HTML

I needed to email an HTML report and I was not happy with the fact that we have to create zip file containing the HTML, Images etc. I knew it was possible to embed base64 data directly into HTML I started looking for some PoC. My search took me to an online base64 encoder and decoder. This gave me the idea to convert the external image files into base64 string and embed it directly into HTML. On some search I landed up Apache Commons Codec Library which contains a Base64 class which can be used to covert an input stream into a base64 string.

JSON to Java Code Generator

I recently received a couple of REST Web Service endpoints where the implementation technology was not Java. So I had to either rollout my own object and then rely on the object mapper to map the JSON to Java or come up with an approach to generate the relevant POJO file. On a little bit of looking around I found out the following two links for generating Java Code from JSON.

http://json2java.azurewebsites.net/

https://javafromjson.dashingrocket.com/

The POJO generated were decent and got the job done. I didn’t have to write the POJO myself and the code generated by these websites did the job well.

Another link recommended in the posts comments.
http://www.freecodeformat.com/json2pojo.php (Thanks Daniel)

Delete Untracked File Using Git

Sometimes we want to clean out our Git workspace and remove any file which is untracked. A hard reset usually does the job for modified files as shown below:
git reset --hard

But hard reset doesn’t fit in case of untracked files. The following command will do the job:
git clean -d -fx ""

-x means ignored files are also removed as well as files unknown to git.

-d means remove untracked directories in addition to untracked files.

-f is required to force it to run.

Reference:
https://www.kernel.org/pub/software/scm/git/docs/git-clean.html

Configuring Git user name and email

Since I like working using terminal I prefer to do all my operations of git from the command prompt. The first prerequisite to this is to have my name and email configured. This few commands are required to do this simple operation:

To set the name and email:

git config --global user.name "Your Name"
git config --global user.email "Your Email"

To view the name and email which is known to git execute the same commands without any parameter as shown below:

git config --global user.name
git config --global user.email

Finding class inside a bunch of jar

Many times there are some Java linkage errors and I have to find out in which jar files the class files are located. So this has lead me to find out tools which can do this job for me. I usually get the job done by using this excellent open source tools named Jar Explorer inside Github. It is basically a platform independent Swing based utility which allows you to recursively search inside Jar files located inside a folder for any class name String. So it is possible for me to search for a class named “LoggingEvent” inside a folder containing lots of jars and it outputs the list of all the jar files where it found classes containing the text “LoggingEvent”.

However when you are connected to Linux consoles using ssh and don’t have access to X Windowing system then you have to rely on either text based java program or pure vanilla shell scripting. For this situation I use the following snippets of code which I found from a Stackoverflow article.

On Linux/Mac
for i in *.jar; do jar -tvf "$i" | grep -Hsi ClassName && echo "$i"; done

On Windows
for /R %G in (*.jar) do @jar -tvf "%G" | find "ClassName" > NUL && echo %G

Debugging HTTP Traffic in Mac

I use Fiddler extensively in Windows for debugging any HTTP traffic in my web applications. However on Mac Fiddler is not available. On some search I have found out the following tools which can do the job:

Chrome
In Chrome just type “chrome://net-internals/#http2” in the address bar and you will be able to see all the HTTP traffic that is going on in your system. Not sure when it got added to Chrome but it is a very simple yet powerful utility.

Charles Proxy
This is Java based commercial utility which can be used for almost Fiddler like functionality. This works in Windows, Linux and Mac so it is good deal I think for any developer.

Update: On using Charles Proxy I found it to be dead simple to use and it fulfilled all the requirements I had on my Mac. There is 30 minute lockout feature for unlicensed version which seems fair. It is completely worth the 50$ price tag.