JAVA9 new Features-Multiple version compatible jar package

1. Official feature

238:multi-release JAR Files

2. Instructions for use

When a new version of Java appears, it takes a few years for your library user to switch to this new version. This means that the library has to be backwards compatible with the oldest Java version you want to support (in many cases Java 6 or JAVA7). This actually means that for a long time to come, you can't use the new features provided by Java 9 in the library. Fortunately, the multi-version compatible Jar feature allows you to create a class version that you can choose to use only in a specific version of the Java environment where the library program is run.

Example 1:

Jar Root

-A.class

-B.class

-C.class

-D.class

-Meta-inf

-Versions

-9

-A.class

-B.class

Description

In the above scenario, Root.jar can be used in Java 9, but the A or class B uses two classes that are not the top-level root.a or root.b, but are in the two below "META-INF/VERSIONS/9". This is a class version specially prepared for JAVA9 and can be used with the features and libraries provided by Java 9. It is also possible to use this jar in earlier versions of Java, because older versions of Java only see the top Class A or class B.

Example 2:

Jar Root

-A.class

-B.class

-C.class

-D.class

-Meta-inf

-Versions

-9

-A.class

-B.class

-10

           -

A.class

Official Note:

By this scheme, it's possiblefor versions of a class designed for a later Java platform release to overridethe version of That's same class designed for a earlier Java platform release.

3. Examples of Use

Step one: Provide the necessary classes

The following classes are available under the specified directory (E:\TEACH\01_JAVA9\MULTIJAR\SRC\MAIN\JAVA\COM\ATGUIGU):

"Generator.java"

"Application.java"

A class with the same name is provided under the following directory (E:\teach\01_Java9\multijar\src\main\java-9\com\atguigu):

"Generator.java"

Step Two: Pack

The instructions are as follows:

javac-d Build--release 8 Src/main/java/com/atguigu/*.java

javac-d build9--release 9 Src/main/java-9/com/atguigu/*.java

Jar--create--main-class=application--file multijar.jar-c build. --release 9-c build9.

Step three: Test in Java 9 and prior versions of the environment

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JAVA9 new Features-Multiple version compatible jar package