Becoming a Junior Java Developer 101

Hello everyone,in order to become a Java developer you don't need much ;), however if you start learning everything you probably will be overwhelmed and will focus on the wrong bits and basically will probably give up.However I have to say DON'T give up. Java is extremely easy language, maybe the easiest to start with, it is the most easy language to understand and to read (in case someone else has written the code) so this is the primary reason why Java is the most commonly used language.The issue with JavaScript is ones you learn the language and bits of the SDK (Standard Development Kit) you will be overwhelmed by a HUGE number of Libraries and Frameworks, you will not know what to learn and how to combine and how to connect different frameworks in order to have a finished product.So I hope this guides will give you some direction and by reading and understanding EVERYTHING in this guide you should be more than ready to join some company as a Junior Java Developer. All materials are completely FREE and are far better then any academy or university course and etc.Why you will choose an Academy or University or Udemy course ? The only reason is if you are lazy. You see in order to understand and start applying something you need to first learn it and then to use it to write something. Most people just read without the writing bit, or try to write before they have learned anything (which is better case then the first in my opinion) but in both cases this creates a huge,...

Use Multiple JVM versions on Mac OS and Linux

LinuxDownload multiple Java versions and put them into /opt/ If you already have some JDK from ubuntu repo or etc not a big deal, just fix the paths bellowRegister them as alternativessudo update-alternatives --install /usr/bin/java java /opt/java-8-oracle/bin/java 1081sudo update-alternatives --install /usr/bin/java java /opt/sap-machine-jdk-11.0.3/bin/java 1080Edit your ~/.bashrc filealias java11='sudo update-alternatives --set java /opt/sapmachine-jdk-11.0.3/bin/java;export JAVA_HOME=/opt/sapmachine-jdk-11.0.3/'alias java8='sudo update-alternatives --set java /opt/java-8-oracle/bin/java;export JAVA_HOME=/usr/lib/java-8-oracle/'SAVE and start a new bash terminalexecutejava8 to use java8java11 to use java11the latest version you have set stays as system wide, but the JAVA_HOME is not :( you can put java8 or java11 as a last line in the bashrc but since it is sudo it will always require password when start and is not great ;(MacInstall homebrew, since it rox !Install Oracle Java 8 or OpenJDK 8.I recommend adoptopenjdkbrew tap adoptopenjdk/openjdkbrew search adoptopenjdkbrew cask install adoptopenjdk8brew cask install adoptopenjdk11On mac since it RULZ you have a java_home executable (that changes and fixes both your path and your JAVA_HOME) , so the .bashrc changes are easy !Edit your ~/.bashrc fileexport JAVA_8_HOME=$(/usr/libexec/java_home -v1.8)export JAVA_11_HOME=$(/usr/libexec/java_home -v11)alias java8='export JAVA_HOME=$JAVA_8_HOME'alias java11='export JAVA_HOME=$JAVA_11_HOME'java8Note: the latest execution of java8 is to make it system wide by defaultSAVE and start a new bash terminalexecutejava8 to use java8java11 to use java11WindowsUse a normal OS or suffer...

Use Multiple JVM versions on Mac OS and Linux

LinuxDownload multiple Java versions and put them into /opt/ If you already have some JDK from ubuntu repo or etc not a big deal, just fix the paths bellowRegister them as alternativessudo update-alternatives --install /usr/bin/java java /opt/java-8-oracle/bin/java 1081sudo update-alternatives --install /usr/bin/java java /opt/sap-machine-jdk-11.0.3/bin/java 1080Edit your ~/.bashrc filealias java11='sudo update-alternatives --set java /opt/sapmachine-jdk-11.0.3/bin/java;export JAVA_HOME=/opt/sapmachine-jdk-11.0.3/'alias java8='sudo update-alternatives --set java /opt/java-8-oracle/bin/java;export JAVA_HOME=/usr/lib/java-8-oracle/'SAVE and start a new bash terminalexecutejava8 to use java8java11 to use java11the latest version you have set stays as system wide, but the JAVA_HOME is not :( you can put java8 or java11 as a last line in the bashrc but since it is sudo it will always require password when start and is not great ;(MacInstall homebrew, since it rox !Install Oracle Java 8 or OpenJDK 8.I recommend adoptopenjdkbrew tap adoptopenjdk/openjdkbrew search adoptopenjdkbrew cask install adoptopenjdk8brew cask install adoptopenjdk11On mac since it RULZ you have a java_home executable (that changes and fixes both your path and your JAVA_HOME) , so the .bashrc changes are easy !Edit your ~/.bashrc fileexport JAVA_8_HOME=$(/usr/libexec/java_home -v1.8)export JAVA_11_HOME=$(/usr/libexec/java_home -v11)alias java8='export JAVA_HOME=$JAVA_8_HOME'alias java11='export JAVA_HOME=$JAVA_11_HOME'java8Note: the latest execution of java8 is to make it system wide by defaultSAVE and start a new bash terminalexecutejava8 to use java8java11 to use java11WindowsUse a normal OS or suffer...

Use Client Certificate Authentication with Java and RestTemplate

As a follow up of the http://gochev.blogspot.com/2019/04/convert-pfx-certificate-to-jks-p12-crt.html we now have a keystore and a truststore (if anyone needs) and we will use this keystore to send client side authentication using Spring's RestTemplate .First copy your keystore.jks and truststore.jks in your classpath, no one wants absolute paths right ?:)The magic happens in the creation of SSLContext. Keep in mind the Spring Boot have a nice RestTemplateBuilder but I will not gonna use it, because someone of you might have an older version or like me, might just use a plain old amazing Spring.If you just want to use the keystore:final String allPassword = "123456";SSLContext sslContext = SSLContextBuilder                .create()                .loadKeyMaterial(ResourceUtils.getFile("classpath:keystore.jks"),                                    allPassword.toCharArray(), allPassword.toCharArray())                .build();if you just want to use the truststorefinal String allPassword = "123456";SSLContext sslContext = SSLContextBuilder                .create()                .loadTrustMaterial(ResourceUtils.getFile("classpath:truststore.jks"), allPassword.toCharArray())                .build();I guess you know how to use both ;), if you want to IGNORE the truststore certificate checking and trust ALL certificates (might be handy for testing purposes and localhost)final String allPassword = "123456";TrustStrategy acceptingTrustStrategy = (X509Certificate[] chain, String authType) -> true;SSLContext sslContext = SSLContextBuilder                .create()                .loadTrustMaterial(ResourceUtils.getFile("classpath:truststore.jks"), allPassword.toCharArray())                .loadTrustMaterial(null, acceptingTrustStrategy) //accept all                .build();Ones you have the sslContext...

Convert PFX certificate to JKS, P12, CRT

I recently had to use a PFX certificate for client authentication (maybe another post will be coming) and for that reason I had to convert it to a Java keystore (JKS). We will create BOTH a truststore and a keystore, because based on your needs you might need one or the other. The difference between truststore and keystore if you are not aware is(quote from the JSSE ref guide: TrustManager: Determines whether the remote authentication credentials (and thus the connection) should be trusted.KeyManager: Determines which authentication credentials to send to the remote host.Ok that's enough what you will need is openssl and Java 7+ ;) !First let's generate a key from the pfx file, this key is later used for p12 keystore.openssl pkcs12 -in example.pfx -nocerts -out example.key  Enter Import Password:MAC verified OKEnter PEM pass phrase:Verifying - Enter PEM pass phrase:As shown here you will be asked for the password of the pfx file, later you will be asked to enter a PEM passphase lets for example use 123456 for everything here.The second commands is almost the same but it is about nokey and a crt this time openssl pkcs12 -in example.pfx -clcerts -nokeys -out example.crtEnter Import Password:MAC verified OKNow we have a key and and a crt fileNext step is to create a truststore.keytool -import -file example.crt -alias exampleCA -keystore truststore.jksEnter keystore password:Re-enter new password:Owner: CN=............Trust this certificate? [no]:  yesCertificate was added to keystoreAs you can see here you just import this crt file into a jks truststore and set some password. For the question do you trust this certificate you say yes, so it is added in the truststore.We are done if you only need a...