Maven: Missed compiled classes under 'target' folder

Question

I am using Maven and when trying to turn it into a jar file it says build success but it says No sources to compile.

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building UrbanAC Booking Manager 1.2.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ UrbanAC --    -
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources,     i.e. build is platform dependent!
[INFO] Copying 24 resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.7.0:compile (default-compile) @ UrbanAC ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @     UrbanAC ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources,     i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory C:\Users\Akhil Maganti\eclipse-    workspace\New\src\test\resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.7.0:testCompile (default-testCompile) @     UrbanAC ---
[INFO] No sources to compile
[INFO] 
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ UrbanAC ---
[INFO] No tests to run.
[INFO] 
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ UrbanAC ---
[INFO] Building jar: C:\Users\Akhil Maganti\eclipse-workspace\New\target\UrbanAC-1.2.1-SNAPSHOT.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.413 s
[INFO] Finished at: 2017-11-11T00:19:22+00:00
[INFO] Final Memory: 11M/245M
[INFO] ------------------------------------------------------------------------

This is the error which is shown and I do not know why this is being shown.

Answer 1

Maven requires a fixed structure of project.

src/main/java - Application/Library sources
src/main/resources - Application/Library resources
...

https://maven.apache.org/guides/introduction/introduction-to-the-standard-directory-layout.html

You need moved you source files in src/main/java/...

It's need becose maven not know where you can keep *.class files, maven try find in "src/main/java", and not found.

This structure is contract

Answer 2

No sources to compile is related to unit tests.

The production code is already compiled. It says:

Nothing to compile - all classes are up to date

If you really need a jar file of your application you may do this via maven-assembly-plugin :

        <plugin>
            <artifactId>maven-assembly-plugin</artifactId>
            <configuration>
                <archive>
                    <manifest>
                        <mainClass>your.main.class</mainClass>
                    </manifest>
                </archive>
                <descriptorRefs>
                    <descriptorRef>jar-with-dependencies</descriptorRef>
                </descriptorRefs>
            </configuration>
            <executions>
                <execution>
                    <phase>install</phase>
                    <goals>
                        <goal>single</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>

Now run mvn clean install and find a jar file under target folder.

And make sure your project structure follows this standard .

Answer 3

Once you have your source and resources files in correct location, you can add maven-jar-plugin in pom.xml and run command mvn jar:jar

src/main/java      - sources
src/main/resources - resources

Reference : https://maven.apache.org/plugins/maven-jar-plugin/

<project>
  ...
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>3.0.2</version>
        <configuration>
          <archive>
            <manifestFile>${project.build.outputDirectory}/META-INF/MANIFEST.MF</manifestFile>
          </archive>
        </configuration>
        ...
      </plugin>
    </plugins>
  </build>
  ...
</project>

NOTE: I usually do not give non-documentation links because they may be deleted or expire but here is an example from where i learned long time back https://www.mkyong.com/maven/how-to-create-a-jar-file-with-maven/