Why would you need the JDK then? Because the application server will convert JSP into Java servlets and needs to use the JDK to compile the servlets.

For example, if you are deploying a web application with JSP, you are technically just running Java programs inside the application server. Sometimes, even if you are not planning to do any Java development on a computer, you still need the JDK installed. On the other hand, if you are planning to do some Java programming, you need to install the JDK instead. Usually, if you only care about running Java programs on computer you will only install the JRE. It is capable of creating and compiling programs. It has everything the JRE has, but also the compiler (javac) and tools (like javadoc and jdb).

The JDK is the Java Development Kit, the full-featured SDK for Java. However, it cannot be used to create new programs. It is a package of everything necessary to run a compiled Java program, including the Java Virtual Machine (JVM), the Java Class Library, the java command, and other infrastructure. Contains everything required to run Java applications on your system. The JRE is the Java Runtime Environment, it covers most end-users needs. Installing this update will ensure that your Java applications continue to run as safely and efficiently as always. It's also integral to the intranet applications and other e-business solutions that are the foundation of corporate computing.

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