Manifest file
Encyclopedia
On the Java platform, a Manifest file
is a specific file contained within a JAR archive. It is used to define extension and package-related data. It is a metadata
file that contains name-value pairs organized in different sections. If a JAR file is intended to be used as an executable file, the manifest file specifies the main class of the application. The manifest file is named
It is not uncommon to find a computer file described as a manifest in situations unrelated to Java.
The content of the Manifest file
in a JAR file created with version 1.0 of the Java Development Kit
is the following.
Manifest-Version: 1.0
All the entries are as name-value pairs. The name of a header is separated from its value by a colon. The default manifest shows that it conforms to version 1.0 of the manifest specification.
The manifest can also contain information about the other files that are packaged in the archive. Exactly what file information is recorded in the manifest will depend on the intended use for the JAR file. The default manifest file makes no assumptions about what information it should record about other files, so its single line contains data only about itself.
Most uses of JAR files go beyond simple archiving and compression and require special information to be in the manifest file. Summarized below are brief descriptions of the headers that are required for some special-purpose JAR-file functions
Applications Bundled as JAR Files:
If an application is bundled in a JAR file, the Java Virtual Machine needs to be told what the entry point to the application is. An entry point is any class with a
Main-Class: classname
The value classname is to be replaced with the application's entry point.
Download Extensions:
Download extensions are JAR files that are referenced by the manifest files of other JAR files. In a typical situation, an applet will be bundled in a JAR file whose manifest references a JAR file (or several JAR files) that will serve as an extension for the purposes of that applet. Extensions may reference each other in the same way.
Download extensions are specified in the Class-Path header field in the manifest file of an applet, application, or another extension. A Class-Path header might look like this, for example:
Class-Path: servlet.jar infobus.jar acme/beans.jar
With this header, the classes in the files servlet.jar, infobus.jar, and acme/beans.jar will serve as extensions for purposes of the applet or application. The URLs in the Class-Path header are given relative to the URL of the JAR file of the applet or application.
Package Sealing:
A package within a JAR file can be optionally sealed, which means that all classes defined in that package must be archived in the same JAR file. A package might be sealed to ensure version consistency among the classes in your software or as a security measure.
To seal a package, a Name header needs to be added for the package, followed by a Sealed header, similar to this:
Name: myCompany/myPackage/
Sealed: true
The Name header's value is the package's relative pathname. Note that it ends with a '/' to distinguish it from a filename. Any headers following a Name header, without any intervening blank lines, apply to the file or package specified in the Name header. In the above example, because the Sealed header occurs after the Name: myCompany/myPackage header, with no blank lines between, the Sealed header will be interpreted as applying (only) to the package myCompany/myPackage. This code doesn't work.
Package Versioning:
The Package Versioning specification defines several manifest headers to hold versioning information. One set of such headers can be assigned to each package. The versioning headers should appear directly beneath the Name header for the package. This example shows all the versioning headers:
Name: java/util/
Specification-Title: "Java Utility Classes"
Specification-Version: "1.2"
Specification-Vendor: "Sun Microsystems, Inc.".
Implementation-Title: "java.util"
Implementation-Version: "build57"
Implementation-Vendor: "Sun Microsystems, Inc."
Specify Dependencies:
You can use the
Manifest file
On the Java platform, a Manifest file is a specific file contained within a JAR archive. It is used to define extension and package-related data. It is a metadata file that contains name-value pairs organized in different sections. If a JAR file is intended to be used as an executable file, the...
is a specific file contained within a JAR archive. It is used to define extension and package-related data. It is a metadata
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
file that contains name-value pairs organized in different sections. If a JAR file is intended to be used as an executable file, the manifest file specifies the main class of the application. The manifest file is named
MANIFEST.MF.It is not uncommon to find a computer file described as a manifest in situations unrelated to Java.
Specifications
A JAR file includes a manifest at the canonical locationMETA-INF/MANIFEST.MF . There can be only one manifest file in an archive, and it necessarily has to be in the META-INFJAR (file format)In software, JAR is an archive file format typically used to aggregate many Java class files and associated metadata and resources into one file to distribute application software or libraries on the Java platform.JAR files are built on the ZIP file format and have the .jar file extension...
directory.The content of the Manifest file
Manifest file
On the Java platform, a Manifest file is a specific file contained within a JAR archive. It is used to define extension and package-related data. It is a metadata file that contains name-value pairs organized in different sections. If a JAR file is intended to be used as an executable file, the...
in a JAR file created with version 1.0 of the Java Development Kit
Java Development Kit
The Java Development Kit is an Oracle Corporation product aimed at Java developers. Since the introduction of Java, it has been by far the most widely used Java SDK. On 17 November 2006, Sun announced that it would be released under the GNU General Public License , thus making it free software...
is the following.
Manifest-Version: 1.0
All the entries are as name-value pairs. The name of a header is separated from its value by a colon. The default manifest shows that it conforms to version 1.0 of the manifest specification.
The manifest can also contain information about the other files that are packaged in the archive. Exactly what file information is recorded in the manifest will depend on the intended use for the JAR file. The default manifest file makes no assumptions about what information it should record about other files, so its single line contains data only about itself.
Special-Purpose Manifest Headers
Depending on the intended role of the JAR file, the default manifest may have to be modified. If the JAR file is created only for the purpose of archival, then theMANIFEST.MF file is of no purpose.Most uses of JAR files go beyond simple archiving and compression and require special information to be in the manifest file. Summarized below are brief descriptions of the headers that are required for some special-purpose JAR-file functions
Applications Bundled as JAR Files:
If an application is bundled in a JAR file, the Java Virtual Machine needs to be told what the entry point to the application is. An entry point is any class with a
public static void main(String[] args) method. This information is provided in the Main-Class header, which has the general form:Main-Class: classname
The value classname is to be replaced with the application's entry point.
Download Extensions:
Download extensions are JAR files that are referenced by the manifest files of other JAR files. In a typical situation, an applet will be bundled in a JAR file whose manifest references a JAR file (or several JAR files) that will serve as an extension for the purposes of that applet. Extensions may reference each other in the same way.
Download extensions are specified in the Class-Path header field in the manifest file of an applet, application, or another extension. A Class-Path header might look like this, for example:
Class-Path: servlet.jar infobus.jar acme/beans.jar
With this header, the classes in the files servlet.jar, infobus.jar, and acme/beans.jar will serve as extensions for purposes of the applet or application. The URLs in the Class-Path header are given relative to the URL of the JAR file of the applet or application.
Package Sealing:
A package within a JAR file can be optionally sealed, which means that all classes defined in that package must be archived in the same JAR file. A package might be sealed to ensure version consistency among the classes in your software or as a security measure.
To seal a package, a Name header needs to be added for the package, followed by a Sealed header, similar to this:
Name: myCompany/myPackage/
Sealed: true
The Name header's value is the package's relative pathname. Note that it ends with a '/' to distinguish it from a filename. Any headers following a Name header, without any intervening blank lines, apply to the file or package specified in the Name header. In the above example, because the Sealed header occurs after the Name: myCompany/myPackage header, with no blank lines between, the Sealed header will be interpreted as applying (only) to the package myCompany/myPackage. This code doesn't work.
Package Versioning:
The Package Versioning specification defines several manifest headers to hold versioning information. One set of such headers can be assigned to each package. The versioning headers should appear directly beneath the Name header for the package. This example shows all the versioning headers:
Name: java/util/
Specification-Title: "Java Utility Classes"
Specification-Version: "1.2"
Specification-Vendor: "Sun Microsystems, Inc.".
Implementation-Title: "java.util"
Implementation-Version: "build57"
Implementation-Vendor: "Sun Microsystems, Inc."
Specify Dependencies:
You can use the
MANIFEST.MF file to specify all the classes that must be loaded for an application to be able to run. Source: the sun servlet specification, page 72 (servlet-2_4-fr-spec.pdf)