Chapter15

Chapter 15: Packages and Packaging

15.6 Running a Program from a JAR

Problem

You want to distribute a single large file containing all the classes of your application and run the main program from within the JAR.

Solution

Create a JAR file with a Main-Class: line in the manifest; run the program with the java -jar option.

Using Maven, the POM file would look like:

<project ...>
    ...
    <packaging>jar</packaging>
    ...
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>${maven-jar-plugin-version}</version>
                <configuration>
                    <archive>
                        <manifest>
                            <addclasspath>true</addclasspath>
                            <mainClass>${main.class}</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
          
            <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-assembly-plugin</artifactId>
              <version>${maven-assembly-plugin-version}</version>
              <configuration>
                  <descriptorRefs>
                      <descriptorRef>jar-with-dependencies</descriptorRef>
                  </descriptorRefs>
                  <archive>
                      <manifest>
                          <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
                          <mainClass>${main.class}</mainClass>
                          <!-- <manifestFile>manifest.txt</manifestFile> -->
                      </manifest>
                      <manifestEntries>
                          <Vendor-URL>http://YOURDOMAIN.com/SOME_PATH/</Vendor-URL>
                      </manifestEntries>
                  </archive>
              </configuration>
            </plugin>
        </plugins>
    </build>
</project>

From this POM file, using mvn package assembly:single will produce a runnable JAR with all dependencies.

15.8 Creating a Smaller Distribution with jlink

Problem

You are distributing your application to end users, and you want to minimize the size of your download.

Solution

Modularize your application, use jdeps to get a complete list of the modules it uses, then use jlink to create the mini-Java, and distribute that to your users.