为什么 Java -cp 选项在使用 spring-boot-maven-plugin 时 -jar 不起作用？

Question

I have a simple maven project that creates an executable jar file named test.jar in the target directory.

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
        <main.class>com.me.Main</main.class>
    </properties>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <configuration>
                <fork>true</fork>
                <mainClass>${main.class}</mainClass>
            </configuration>
            <executions>
                <execution>
                    <goals>
                        <goal>repackage</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>

When I run with java -jar target\test.jar everything runs fine but when I try to use the -cp to run the jar without the -jar so I can add things to the classpath like (Windows) java -cp target\test.jar com.me.Main I get...

Error: Could not find or load main class com.me.Main
Caused by: java.lang.ClassNotFoundException: com.me.Main

I also tried other versions like java -cp "target\test.jar" com.me.Main but no matter what it doesn't seem to work. What am I missing?

Update

The MANIFEST.mf looks like this

Main-Class: org.springframework.boot.loader.JarLauncher
Start-Class: com.me.Main
Spring-Boot-Version: 2.2.12.RELEASE
Spring-Boot-Classes: BOOT-INF/classes/
Spring-Boot-Lib: BOOT-INF/lib/

This seems to show that spring-boot is overriding the Main-Class KV.

Answer 1

If I change to the maven-assembly-plugin

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-assembly-plugin</artifactId>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>single</goal>
                    </goals>
                    <configuration>
                        <finalName>${project.name}-${project.version}</finalName>
                        <archive>
                            <manifest>
                                <mainClass>
                                    ${main.class}
                                </mainClass>
                            </manifest>
                        </archive>
                        <descriptorRefs>
                            <descriptorRef>jar-with-dependencies</descriptorRef>
                        </descriptorRefs>
                    </configuration>
                </execution>
            </executions>
        </plugin>

then I can still run as java -jar and I can also run with java -cp

Answer 2

check the contents of JAR file:

jar tvf test.jar

should contain a com/me/Main.class

and contents of its MANIFEST.MF file:

jar xf test.jar META-INF/MANIFEST.MF

and use a text editor to open META-INF/MANIFEST.MF - should contain line starting with Main-Class: and the fully qualified name of the main class, the one with the main method, used when starting the JAR (with java -jar )

(or just use WinZIP, 7-zip, or similar to open and check the JAR file)