Download failed : Oracle JDK 7 is NOT installed

Don't worry about installation jdk 7. SDKMAN is here to resolve your issue. SDKMAN installation is given in this link

It gives a list of java version. You can install all of them. If you have multiple java version, you can specify one of them. You can also set default java version as required.

===============================
$ sdk list java
$ sdk install java 7u141-zulu
$ sdk use java 7u141-zulu
$ sdk default java 7u141-zulu
===============================

For Details,

$ sdk list java

It gives a list of java version

$ sdk install java 7u141-zulu

It installs java 7

$ sdk use java 7u141-zulu

• If you want to use java 7, you can run this command.
• For specific project, you can use specific java version using SDKMAN

$ sdk default 7u141-zulu

It is used to set java 7 as default.

rizvi@rizvi-pc:~$ sdk list java

============================================
Available Java Versions
============================================
   * 9.0.1-zulu                                                                    
     9.0.1-oracle                                                                  
     9.0.0-zulu                                                                    
     8u152-zulu                                                                    
     8u151-oracle                                                                  
     8u144-zulu                                                                    
     8u131-zulu                                                                    
   * 7u141-zulu                                                                    
   * 6u93-zulu                                                                     

=========================================================
+ - local version
* - installed
> - currently in use
=========================================================

You can also use this for multiple gradle

$ sdk install gradle 4.3
$ sdk install gradle 3.0
$ sdk use gradle 4.3 
$ sdk default gradle 4.3

For other installation like scala, groovy, you can follow this tutorial

Install JDK9 in Ubuntu

Installation and Configuration of JDK9 is step by step given below:

Install JDK9 in Ubuntu:

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java9-installer

Make it as default:

sudo apt-get install oracle-java9-set-default

Changed in .bashrc, /etc/environment and also set default using

3 sections to change java configuration.

.bashrc:

export JAVA_HOME=/usr/lib/jvm/java-9-oracle
export PATH=$JAVA_HOME/bin:$PATH

/ect/environment:

JAVA_HOME="/usr/lib/jvm/java-9-oracle"
PATH=$PATH:$JAVA_HOME/bin

Then run the following command and set

sudo update-alternatives --config java

sudo update-alternatives --config javac

Then run the command

source /etc/environment

Check in terminal:

java -version
echo $JAVA_HOME
which java
which javac

Issue#1:

Execute "source /etc/environment" in every shell where you want the variables to be updated:

$ source /etc/environment

Resource Link: https://stackoverflow.com/a/5994031

Issue#2:

Just write JAVA_HOME="/usr/lib/jvm/java-9-oracle" on your /etc/environment, without the "export"

/etc/environment is supposed to contain a set of environment variables given as key=value pairs. It is not a shell script, so you can't use shell commands such as export in it.

Resource Link:

How to properly set JAVA_HOME in /etc/environment

Issue#3:

To check if java is properly installed:

$ which java

$ which javac

You should get similar output:

/usr/bin/java

Resource Link: https://stackoverflow.com/a/23124805

Issue#4:

To remove Oracle JDK completely, run the commands below:

Completely remove criteria:

sudo apt-get remove oracle-java9-installer
sudo apt-get remove --auto-remove oracle-java9-installer
sudo apt-get purge oracle-java9-installer
sudo apt-get purge --auto-remove oracle-java9-installer

Resource Link:

https://www.howtoinstall.co/en/ubuntu/trusty/tomcat7?action=remove