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How To Specify JDK for Tomcat7 in Ubuntu

Ubuntu 6

In this article, we will guide you through the process of specifying the Java Development Kit (JDK) for Tomcat7 in Ubuntu. This is a crucial step for running Java-based applications on a Tomcat7 server.

Quick Answer

To specify the JDK for Tomcat7 in Ubuntu, you need to set the JAVA_HOME environment variable in the Tomcat7 configuration file. This variable should be set to the root directory of your JDK installation. Additionally, you can create a symbolic link to your preferred Java installation to ensure that Tomcat7 picks it up even after upgrades. Restart the Tomcat7 server for the changes to take effect.

Prerequisites

Before we begin, ensure that you have Tomcat7 and JDK installed on your Ubuntu system. If not, you can install them using the following commands:

sudo apt-get update
sudo apt-get install tomcat7
sudo apt-get install default-jdk

The sudo apt-get update command updates your package lists for upgrades for packages that need upgrading, as well as new packages that have just come to the repositories.

Setting the JAVA_HOME Environment Variable

Tomcat7 uses the JAVA_HOME environment variable to locate the JDK. This variable should be set to the root directory of your JDK installation.

Here’s how to set it:

  1. Open the Terminal by pressing Ctrl+Alt+T on your keyboard.
  2. Run the command sudo nano /etc/default/tomcat7 to open the Tomcat7 configuration file in the nano text editor.
sudo nano /etc/default/tomcat7

The sudo command allows you to run programs with the security privileges of another user (by default, as the superuser). nano is a simple command-line text editor.

  1. In the opened file, look for the line that sets the JAVA_HOME variable. If it’s commented out with a # at the beginning, uncomment it by removing the #.
  2. Set the JAVA_HOME variable to the root folder of your JDK installation. For example, if your JDK is installed in /usr/lib/jvm/java-8-oracle, the line should look like this:
JAVA_HOME=/usr/lib/jvm/java-8-oracle
  1. Press Ctrl+O to save the file, then Ctrl+X to exit the nano editor.
  2. Finally, restart the Tomcat7 server for the changes to take effect:
sudo service tomcat7 restart

The service command is used to run a System V init script, in this case, to restart the Tomcat7 server.

Using a Symbolic Link

If you’re planning to upgrade your JDK in the future, you can create a symbolic link to your preferred Java installation. This link will be picked up by Tomcat7. Here’s how:

  1. Open the Terminal.
  2. Run the command:
sudo ln -s /usr/lib/jvm/java-8-oracle /usr/lib/jvm/default-java

The ln -s command creates a symbolic link. In this case, it creates a link from /usr/lib/jvm/java-8-oracle to /usr/lib/jvm/default-java.

  1. Restart the Tomcat7 server:
sudo service tomcat7 restart

Please note that creating this symbolic link may conflict with the package default-jre-headless.

Conclusion

In this article, we have learned how to specify the JDK for Tomcat7 in Ubuntu. This is an essential step for running Java applications on a Tomcat7 server. We have also discussed how to create a symbolic link to ensure that Tomcat7 picks up your preferred Java installation, even after upgrades.

Remember to always restart the Tomcat7 server after making changes to the configuration file. If you encounter any issues, check the Tomcat7 logs for error messages.

How do I check if Tomcat7 and JDK are installed on my Ubuntu system?

You can check if Tomcat7 and JDK are installed on your Ubuntu system by running the commands dpkg -l tomcat7 and java -version respectively. If they are installed, you will see the version information for each package.

Can I specify a different version of JDK for Tomcat7?

Yes, you can specify a different version of JDK for Tomcat7 by setting the JAVA_HOME variable to the root directory of the desired JDK installation. Just make sure that the JDK is compatible with Tomcat7.

How can I find the root directory of my JDK installation?

You can find the root directory of your JDK installation by running the command update-alternatives --config java and selecting the appropriate JDK option. The root directory will typically be located in the /usr/lib/jvm/ directory.

What should I do if I encounter errors after specifying the JDK for Tomcat7?

If you encounter errors after specifying the JDK for Tomcat7, you can check the Tomcat7 logs for error messages. The logs are located in the /var/log/tomcat7/ directory. Review the error messages to troubleshoot and resolve the issue.

How can I upgrade my JDK in the future without affecting Tomcat7?

To upgrade your JDK in the future without affecting Tomcat7, you can create a symbolic link to your preferred Java installation. This link will be picked up by Tomcat7. Refer to the section "Using a Symbolic Link" in the article for detailed instructions.

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