- JRE and JDK images now have identical structures.
- Previously a JDK image embedded the JRE in a jre subdirectory; now a JDK image is simply a run-time image that happens to contain the full set of development tools and other items historically found in the JDK.
- The internal files rt.jar, tools.jar, and dt.jar have been removed.
- The extension mechanism has been removed.
- The endorsed-standards override mechanism has been removed.
In this article, we will take one step back to see how "JDK and JRE File Structure" has evolved from Java 6 to 8. Note that the file structure of the JRE is identical to that of the JDK's jre directory.
Java 6
Assuming the JDK software is installed at /jdk1.6.0, here are some of the most important directories:[2]
jdk1.6.0 ___________|____________________ ________________________ | | | | bin lib jre include | | __________|_____________________ java.exe tools.jar | | javac.exe dt.jar bin lib javap.exe _____|____ __________ ________|_______ ________ ________ javah.exe | | | | | | | | javadoc.exe java.exe client server rt.jar ext security applet fonts java.dll | | charsets.jar | awt.dll jvm.dll jvm.dll localedata.jar
Java 7
As part of the Java 7 release, the Java Development Kit (JDK) now includes the SDK for developing JavaFX applications and, more importantly, the JavaFX Runtime is now installed with the JRE.[3] In addition, there is new db sub-folder under the root directory of JDK software installation.
Assuming the JDK software is installed at /jdk1.7.0, here are some of the most important directories:[4]
jdk1.7.0 ___________|____________________ __________________________ _______ | | | | | bin lib jre include db | | __________|________________________ java.exe ant-javafx.jar | | javac.exe dt.jar bin lib javap.exe tools.jar _____|____ __________ __________|_______ ________ ________ javah.exe | | | | | | | | javadoc.exe java.exe client server rt.jar ext security applet fonts java.dll | | charsets.jar | awt.dll jvm.dll jvm.dll jfxrt.jar localedata.jar
Java 8
In Java 8, jfxrt.jar has become one of the optional packages (what used to be known as standard extensions).[6] So, it has been moved into
Assuming the JDK software is installed at /jdk1.8.0, here are some of the most important directories:
jdk1.8.0 ___________|____________________ __________________________ _______ | | | | | bin lib jre include db | | __________|________________________ java.exe ant-javafx.jar | | javac.exe dt.jar bin lib javap.exe tools.jar _____|____ __________ __________|_______ ________ ________ javah.exe | | | | | | | | javadoc.exe java.exe client server rt.jar ext security applet fonts java.dll | | charsets.jar | awt.dll jvm.dll jvm.dll localedata.jar jfxrt.jar
Directory Summary
| Directory |
Contains |
Setup |
| <jdk1.x.0>/bin |
Executables for all the development tools contained in the JDK. |
The PATH environment variable should contain an entry for this directory. |
| <jdk1.x.0>/lib | Files used by the development tools. | |
| <jdk1.x.0>/jre | Root directory of the Java Runtime Environment (JRE) used by the JDK development tools. | This is the directory referred to by the java.home system property. |
| <jdk1.x.0>/jre/bin | Executable files for tools and libraries used by the Java platform. The executable files are identical to files in /jdk1.x.0/bin. |
This directory does not need to be in the PATH environment variable. |
| <jdk1.x.0>/jre/lib | Code libraries, property settings, and resource files used by the JRE. | |
| <jdk1.x.0>/jre/lib/ext | Default installation directory for extensions to the Java platform. |
See The Extension Mechanism |
| <jdk1.x.0>/jre/lib/security | Contains files used for security management. These include the security policy java.policy and security properties java.security files. |
|
| <jdk1.x.0>/jre/lib/amd64 | Contains the .so (shared object) files used by the architecture amd64 release of the Java platform |
|
| <jdk1.x.0>/jre/lib/amd64/server | Contains the .so file used by the Java HotSpot VM server. |
|
| <jdk1.x.0>/jre/lib/applet | JAR files that contain support classes for applets can be placed in the lib/applet/ directory. This reduces startup time for large applets by allowing applet classes to be preloaded from the local file system by the applet class loader and provides the same protections as though they had been downloaded over the Internet. |
|
| <jdk1.x.0>/jre/lib/fonts | Font files used by the platform. |
References
- Project Jigsaw: Modular run-time images
- JDK and JRE File Structure (Java 6, Linux version)
- Java 7 Now Includes JavaFX
- JDK and JRE File Structure (Java 7, Linux version)
- JDK and JRE File Structure (Java 8, Linux version)
- Extension Mechanism Architecture
- WebLogic's Classloading Framework (Xml and More)
- java.lang.UnsatisfiedLinkError: Setting Environment Variable (Xml and More)
- Compatibility Guide for JDK 8
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