If you have an application bundled in a JAR file, you need some way to indicate which class within the JAR file is your application’s entry point. You provide this information with the Main-Class<\/CODE> header in the manifest, which has the general form:
\nMain-Class: classname<\/EM>
\n<\/PRE><\/BLOCKQUOTE>The value classname<\/CODE><\/EM> is the name of the class that is your application’s entry point.
\nRecall that the entry point is a class having a method with signature public static void main(String[] args)<\/CODE>. <\/P>
\nAfter you have set the Main-Class<\/CODE> header in the manifest, you then run the JAR file using the following form of the java<\/CODE> command: <\/P>
\njava -jar JAR-name<\/EM>
\n<\/PRE><\/BLOCKQUOTE>The main<\/CODE> method of the class specified in the Main-Class<\/CODE> header is executed.
\n<\/P><\/BLOCKQUOTE>
\n
An Example<\/H3>
\nWe want to execute the main<\/CODE> method in the class MyClass<\/CODE> in the package MyPackage<\/CODE> when we run the JAR file.
\nWe first create a text file named Manifest.txt<\/CODE> with the following contents: <\/P>
\nMain-Class: MyPackage.MyClass
\n<\/PRE><\/BLOCKQUOTE>
\n<\/P>
\n
\n
\nWarning<\/FONT>:<\/STRONG> The text file must end with a new line or carriage return. The last line will not be parsed properly if it does not end with a new line or carriage return.
\n
\n<\/BLOCKQUOTE>We then create a JAR file named MyJar.jar<\/CODE> by entering the following command:
\njar cfm MyJar.jar Manifest.txt MyPackage\/*.class
\n<\/PRE><\/BLOCKQUOTE>This creates the JAR file with a manifest with the following contents:
\nManifest-Version: 1.0
\nCreated-By: 1.6.0 (Sun Microsystems Inc.)
\nMain-Class: MyPackage.MyClass
\n<\/PRE><\/BLOCKQUOTE>When you run the JAR file with the following command, the main<\/CODE> method of MyClass<\/CODE> executes:
\njava -jar MyJar.jar
\n<\/PRE><\/BLOCKQUOTE><\/BLOCKQUOTE>
\nSetting an Entry Point with the JAR Tool<\/H3>
\nThe ‘e’ flag (for ‘entrypoint’), introduced in JDK 6, creates or overrides the manifest’s Main-Class<\/CODE> attribute. It can be used while creating or updating a jar file. Use it to specify the application entry point without editing or creating the manifest file.
For example, this command creates app.jar<\/CODE> where the Main-Class<\/CODE> attribute value in the manifest is set to MyApp<\/CODE>:
\njar cfe app.jar MyApp MyApp.class<\/PRE><\/BLOCKQUOTE>
\nYou can directly invoke this application by running the following command: <\/P>
\n
java -jar app.jar<\/PRE><\/BLOCKQUOTE>
\nIf the entrypoint class name is in a package it may use a ‘.’ (dot) character as the delimiter. For example, if Main.class<\/CODE> is in a package called foo<\/CODE> the entry point can be specified in the following ways: <\/P>
\njar cfe Main.jar foo.Main foo\/Main.class<\/PRE><\/BLOCKQUOTE><\/BLOCKQUOTE>
\n<\/DIV><\/p>\n","protected":false},"excerpt":{"rendered":"Setting an Application’s Entry Point If you have an application bundled in a JAR file, you need some way to indicate which class within the JAR file is your application’s entry point. You provide this information with the Main-Class header in the manifest, which has the general form: Main-Class: classname The value classname is the … Continue reading Setting an Application’s Entry Point<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[],"tags":[],"class_list":["post-362","post","type-post","status-publish","format-standard","hentry"],"_links":{"self":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/posts\/362","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=362"}],"version-history":[{"count":0,"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/posts\/362\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=362"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=362"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=362"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}