JAVA-10605: Move multimodulemavenproject from core-java-modules to (#12309)

* JAVA-10605: Move multimodulemavenproject from core-java-modules to
maven-modules

* JAVA-10605: Move multimodulemavenproject to jdk9 build

maven-modules/multimodulemavenproject/userdaomodule/src/main/java/com/baeldung/userdaomodule/UserDao.java

@@ -0,0 +1,32 @@
+package com.baeldung.userdaomodule;
+
+import com.baeldung.daomodule.Dao;
+import com.baeldung.entitymodule.User;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+
+public class UserDao implements Dao<User> {
+
+    private final Map<Integer, User> users;
+
+    public UserDao() {
+        users = new HashMap<>();
+    }
+
+    public UserDao(Map<Integer, User> users) {
+        this.users = users;
+    }
+
+    @Override
+    public List<User> findAll() {
+        return new ArrayList<>(users.values());
+    }
+
+    @Override
+    public Optional<User> findById(int id) {
+        return Optional.ofNullable(users.get(id));
+    }
+}

maven-modules/multimodulemavenproject/userdaomodule/src/main/java/module-info.java

@@ -0,0 +1,6 @@
+module com.baeldung.userdaomodule {
+    requires com.baeldung.entitymodule;
+    requires com.baeldung.daomodule;
+    provides com.baeldung.daomodule.Dao with com.baeldung.userdaomodule.UserDao;
+    exports com.baeldung.userdaomodule;
+}