package-info.java https://www.intertech.com/Blog/whats-package-info-java-for/
mybatis-3/src/main/java/org/apache/ibatis/cache/package-info.java
What’s package-info.java for?
https://www.intertech.com/Blog/whats-package-info-java-for/
mybatis-3/src/main/java/org/apache/ibatis/cache/package-info.java
In some recent classes, my students have encountered a package-info.java file tucked inside of some of the sample code we get from courseware providers. “What’s that thing?”, they usually ask.
package-info.java’s purpose
The package-info.java is a Java file that can be added to any Java source package. Its purpose is to provide a home for package level documentation and package level annotations. Simply create the package-info.java file and add the package declaration that it relates to in the file. In fact, the only thing the package-info.java file must contain is the package declaration.
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package com.intertech.services;
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The package-info.java file above must sit in the com.intertech.services package.
Package Documentation
Prior to Java 5, package level documentation (the documentation shown in Javadocs for a package) was placed in package.html. Today, the description and other related documentation for a package can be written up in the package-info.java file and it gets used in the production of the Javadocs. As a demonstration, the example package-info.java…
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/**
* Domain classes used to produce the JSON and XML output for the RESTful services.
* <p>
* These classes contain the JAXB annotations.
*
* @since 1.0
* @author jwhite
* @version 1.1
*/
package com.intertech.cms.domain;
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… results in the following Javadocs.
Package Annotations
Perhaps more importantly to today’s annotation driven programmer, the package-info.java file contains package level annotations. An annotation with ElementType.PACKAGE as one of its targets is a package-level annotation and there are many of them. Using your favorite IDE’s code assistant (shown in Eclipse below) in a package-info.java file and you will find a number package annotation options.
For example, perhaps you want to deprecate all the types in a package. You could annotate each individual type (the classes, interfaces, enums, etc. defined in their .java files) with @Deprecated (as shown below).
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@Deprecated
public class Contact {
}
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Or, you could use the @Deprecated on the package declaration in package-info.java. This has the effect of deprecating everything in the package in one fell swoop.
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@Deprecated
package com.intertech.cms.domain;
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Help adding package-info.java to your packages
While you can add the package-info.java file to your packages by hand (just as you can create Java classes by hand), IDE’s often offer you the option to include a package-info.java file each time you create a new package. Eclipse, shown below, offers a simple (and often overlooked) checkbox in the New Java Package creation wizard.
Wrap Up
So now you know what that package-info.java file is all about and you know how to use it.
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