Distinguishing OpenJDK from Oracle JDK

Though OpenJDK is an official reference implementation for the Java platform, certain Oracle-provided software are not open source. The most famous of them is the Java browser plugin, but there are a lot more differences than just that. This recipe will show you how to distinguish OpenJDK from Oracle JDK.

Getting ready

To follow this recipe, you will need an installed OpenJDK instance. It will be good if you have an Oracle JDK instance as well, to feel the difference. Also, we will assume that you have a Linux installation and an update-java-alternatives command installed and ready to use. To know how to install OpenJDK on various systems, see the later recipes in this chapter. To know how to switch the system Java version, if you do not have update-alternatives installed (for Fedora, Gentoo, and so on), visit the Configuring OpenJDK on Linux recipe or refer to your distribution documentation/forums.

How to do it...

Please take a look at the following procedures to know the difference between OpenJDK and Oracle JDK:

1. We will open a terminal and type the following command:

   update-java-alternatives  --list
   

2. We will see a full list of installed Java implementations:

   $ update-java-alternatives  --list
   java-1.6.0-openjdk-amd64 1061 /usr/lib/jvm/java-1.6.0-openjdk-amd64
   java-1.7.0-openjdk-amd64 1071 /usr/lib/jvm/java-1.7.0-openjdk-amd64
   java-6-oracle 1073 /usr/lib/jvm/java-6-oracle
   java-7-oracle 1081 /usr/lib/jvm/java-7-oracle
   java-8-oracle 1082 /usr/lib/jvm/java-8-oracle
   

3. Let's set Oracle Java as default. We will run the following command with root access:

   update-java-alternatives  --set java-7-oracle
   

   Tip

   This command may produce errors such as "no alternatives for apt". It's OK, just ignore them.

4. Then we will go to https://www.java.com/en/download/installed.jsp?detect=jre and check our browser plugin version. We will see the activate link (following the name of the activating entity).

   We can see from the result of our actions that the Java browser plugin has been installed.

5. Let's try to set OpenJDK as the default Java environment (the actual instance name may differ in your case):

   update-java-alternatives  --set java-1.7.0-openjdk-amd64
   

6. Then we will go to our browser page and refresh it. It may be necessary to restart the browser so that the changes can take effect, as shown in the following screenshot:
   

We can see that the plugin is not from the JDK itself but from a project named IcedTea.

IcedTea is an open source project, whose goal is to replace proprietary parts of the Java ecosystem as much as possible. The plugin itself is from IcedTea-Web, an open source implementation of the Java Web Start and Java browser plugins.

In most distributions, the IcedTea plugin is installed by default. But it is necessary to keep in mind that it's an open source plugin, and definitely not a referenced one. This means that its functionality might be slightly different from the Oracle plugin. It is also possible that some features may not work.

How it works…

Oracle JDK still has some proprietary components, and the browser plugin is one example. All we need in this chapter is to see the difference between the work of OpenJDK and Oracle JDK components that are different.

Also, the huge difference between OpenJDK and Oracle JDK lies in the license. OpenJDK is open source, while Oracle JDK contains proprietary pieces, and thus it is licensed under the Oracle binary license. The fact that OpenJDK is open source provides a whole new range of benefits (and exciting discoveries) through the ability to study and modify its source code. It is also worth mentioning that more than 90 percent of Oracle JDK is based on OpenJDK source code. This means the OpenJDK quality is not compromised in any way. The browser plugin is not the only thing that is missed in OpenJDK compared to Oracle JDK.

See also

• In Chapter 5, Building IcedTea, there is a detailed explanation of how to build IcedTea from source.