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Your first jSpace applications (with Maven)

If you have successfully built and installed you have You can use Maven to generate an empty jSpace project:

mvn -B archetype:generate \
  -DarchetypeGroupId=org.apache.maven.archetypes \
  -DgroupId=com.mycompany.myjspaceapp \
  -DartifactId=myjspaceapp

The command above generates the skeleton of a Maven project in a folder named myjspaceapp. In particular, inside folder src you can find the two directories main/java and test/java where basic Java files for the app and its tests, respectively.

Maven also generates the pom.xml (in directory myjspaceapp) describing how building your code and all the needed dependencies. Open this file with your preferred editor and declare the dependency to jSpace. In the generated pom.xml file you should find something of the form:

<dependencies>
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>3.8.1</version>
    <scope>test</scope>
  </dependency>
</dependencies>

you have to add above the reference to jSpace:

<dependencies>
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>3.8.1</version>
    <scope>test</scope>
  </dependency>
  <dependency>
    <groupId>io.github.pspaces.jspace</groupId>
    <artifactId>common</artifactId>
    <version>[0.0,)</version>
  </dependency>
</dependencies>

At this point you can change the generated Java code to implement the desired application. In this short guide we simply open:

myjspaceapp/src/main/java/com/mycompany/myjspaceapp/App.java

Add the following code:

package com.mycompany.myjspaceapp;

import org.jspace.FormalField;
import org.jspace.SequentialSpace;
import org.jspace.Space;

public class App {

	public static void main(String[] argv) throws InterruptedException {
		Space inbox = new SequentialSpace();

		inbox.put("Hello World!");
		Object[] tuple = inbox.get(new FormalField(String.class));				
		System.out.println(tuple[0]);

	}

}

To build and test your application with Maven the following command can be executed in the directory myjspaceapp:

mvn clean verify

Generated files are stored in the directory myjspaceapp/target. In particular, you can find the file myjspaceapp-1.0-SNAPSHOT.jar providing an access to the binaries of your application.

To run your app you need also to provide a reference to all the required packages. These are located in your local Maven repository and it may be not convenient to explicitly refer to them.

You can modify file pom.xml to let Maven generate a jar files where all the required classes are included.

Open file myjspaceapp/pom.xml and add the following code just before the closing tag </project>:

<build>
    <plugins>
        <plugin>
            <artifactId>maven-assembly-plugin</artifactId>
            <configuration>
                <archive>
                    <manifest>
                        <addClasspath>true</addClasspath>
                    </manifest>
                </archive>
                <descriptorRefs>
                    <descriptorRef>jar-with-dependencies</descriptorRef>
                </descriptorRefs>
            </configuration>
              <executions>
                  <execution>
                      <id>make-my-jar-with-dependencies</id>
                      <phase>package</phase>
                      <goals>
                          <goal>single</goal>
                      </goals>
                  </execution>
              </executions>
        </plugin>
    </plugins>
</build>

At this point you can re-build and test your application by executing the following command in the directory myjspaceapp:

mvn clean verify

A new file named myjspaceapp-1.0-SNAPSHOT-jar-with-dependencies.jar has been generated in the directory target. Differently from the one previously considered above, this file contains all the dependencies and can be used to execute our application. You have just to enter inside directory target and execute:

java -cp myjspaceapp-1.0-SNAPSHOT-jar-with-dependencies.jar com.mycompany.myjspaceapp.App

Note that if your applications consists of multiple programs, you have only to change the name of main class to use.

It is sometime useful to generate a jar file that can be directly executed. This is possible by including in the jar a MANIFEST file. Maven can do this work for you. You have only to change the build instructions considered above. In particular you have to modify the content of tag configuration as follow:

<configuration>
    <archive>
        <manifest>
            <addClasspath>true</addClasspath>
            <mainClass>com.mycompany.myjspaceapp.App</mainClass>
        </manifest>
    </archive>
    <descriptorRefs>
        <descriptorRef>jar-with-dependencies</descriptorRef>
    </descriptorRefs>
</configuration>

You may notice that a new declaration is now included to say that the mainClass is com.mycompany.myjspaceapp.App. Re-build your application by executing again mvn clean verify in the directory myjspaceapp.

File myjspaceapp-1.0-SNAPSHOT-jar-with-dependencies.jar now contains a MANIFEST where class com.mycompany.myjspaceapp.App is used as entry point of the execution. You can now execute your app by simply executing in the directory myjspaceapp/target the following command:

java -jar myjspaceapp-1.0-SNAPSHOT-jar-with-dependencies.jar