feat: add RMI exercies

RMI/.gitignore

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+/target/
+.project
+.settings
+.classpath

RMI/Makefile

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+
+build:
+	mvn package
+
+clean:
+	mvn clean
+
+server:
+	java -jar target/rmi-1.0-SNAPSHOT-jar-with-dependencies.jar --server
+
+client:
+	java -jar target/rmi-1.0-SNAPSHOT-jar-with-dependencies.jar --client
+
+registry:
+	# Source: https://stackoverflow.com/a/23643744
+	rmiregistry -J-Djava.rmi.server.codebase=file:target/rmi-1.0-SNAPSHOT-jar-with-dependencies.jar &

RMI/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>me.srvstr.rmi</groupId>
+  <artifactId>rmi</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <name>rmi</name>
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.release>17</maven.compiler.release>
+  </properties>
+  <dependencyManagement>
+    <dependencies>
+    </dependencies>
+  </dependencyManagement>
+  <dependencies>
+  </dependencies>
+  <build>
+  <plugins>
+     <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <version>3.13.0</version>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <configuration>
+           <source>16</source>
+           <target>16</target>
+        </configuration>
+     </plugin>
+     <!-- Source: https://stackoverflow.com/a/41383973 -->
+     <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <executions>
+           <execution>
+              <phase>package</phase>
+              <goals>
+                 <goal>single</goal>
+              </goals>
+           </execution>
+        </executions>
+        <configuration>
+           <archive>
+              <manifest>
+                 <mainClass>me.srvstr.rmi.Main</mainClass>
+              </manifest>
+           </archive>
+           <descriptorRefs>
+              <descriptorRef>jar-with-dependencies</descriptorRef>
+           </descriptorRefs>
+        </configuration>
+     </plugin>
+  </plugins>
+  </build>
+</project>

RMI/src/main/java/me/srvstr/rmi/Hello.java

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+package me.srvstr.rmi;
+
+import java.rmi.Remote;
+import java.rmi.RemoteException;
+import java.util.Date;
+
+public interface Hello extends Remote {
+
+  void sayHello() throws RemoteException;
+
+  String printMessage(String input) throws RemoteException;
+
+  Date timestampToDate(long timestamp) throws RemoteException;
+}

RMI/src/main/java/me/srvstr/rmi/HelloServer.java

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+package me.srvstr.rmi;
+
+import java.rmi.RemoteException;
+import java.rmi.server.UnicastRemoteObject;
+import java.time.Instant;
+import java.util.Date;
+
+public class HelloServer extends UnicastRemoteObject implements Hello {
+
+  public HelloServer() throws RemoteException {
+    super();
+  }
+
+  @Override
+  public Date timestampToDate(long timestamp) throws RemoteException {
+    return Date.from(Instant.ofEpochMilli(timestamp));
+  }
+
+  @Override
+  public String printMessage(String input) throws RemoteException {
+    System.out.println(input);
+
+    return "Hallo zurück!";
+  }
+
+  @Override
+  public void sayHello() throws RemoteException {
+    System.out.println("Hello, World!!!");
+  }
+}

RMI/src/main/java/me/srvstr/rmi/Main.java

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+package me.srvstr.rmi;
+
+import java.net.MalformedURLException;
+import java.rmi.Naming;
+import java.rmi.NotBoundException;
+import java.rmi.RemoteException;
+
+public class Main {
+
+  private static void client() {
+    try {
+      // locate remote object
+      Hello stub = (Hello) Naming.lookup("rmi://localhost/HelloServer");
+
+      stub.sayHello();
+
+      System.out.println(stub.printMessage("Hallo vom Client!"));
+
+      System.out.println(stub.timestampToDate(System.currentTimeMillis()));
+
+    } catch (NotBoundException | RemoteException | MalformedURLException ex) {
+      System.out.println(ex.getMessage());
+    }
+  }
+
+  private static void server() {
+    try {
+      Naming.rebind("rmi://localhost/HelloServer", new HelloServer());
+      System.out.println("Server ready");
+    } catch (RemoteException | MalformedURLException ex) {
+      System.out.println(ex.getMessage());
+    }
+  }
+
+  public static void main(String[] args) {
+
+    if ("--client".equals(args[0])) {
+      System.out.println("Running in client mode");
+
+      client();
+
+    } else if ("--server".equals(args[0])) {
+      System.out.println("Running in server mode");
+
+      server();
+    }
+  }
+}