Fix Bug with mongo connection. Used "Try with resources"

caching/src/main/java/com/iluwatar/caching/AppManager.java

@@ -24,6 +24,7 @@
 package com.iluwatar.caching;
 
 import com.iluwatar.caching.database.DbManager;
+import com.iluwatar.caching.database.exceptions.DatabaseConnectionException;
 import java.util.Optional;
 
 import lombok.Data;
@@ -68,7 +69,11 @@ public class AppManager {
    * to (temporarily) store the data/objects during runtime.
    */
   public void initDb() {
+    try {
       dbManager.connect();
+    } catch (DatabaseConnectionException e) {
+      LOGGER.error("Could not connect to DB: {}", e.getMessage());
+    }
   }
 
   /**

caching/src/main/java/com/iluwatar/caching/database/DbManager.java

@@ -1,6 +1,7 @@
 package com.iluwatar.caching.database;
 
 import com.iluwatar.caching.UserAccount;
+import com.iluwatar.caching.database.exceptions.DatabaseConnectionException;
 
 /**
  * <p>DBManager handles the communication with the underlying data store i.e.
@@ -11,7 +12,7 @@ public interface DbManager {
   /**
    * Connect to DB.
    */
-  void connect();
+  void connect() throws DatabaseConnectionException;
 
   /**
    * Read from DB.

caching/src/main/java/com/iluwatar/caching/database/MongoDb.java

@@ -7,28 +7,31 @@ import static com.iluwatar.caching.constants.CachingConstants.USER_NAME;
 
 import com.iluwatar.caching.UserAccount;
 import com.iluwatar.caching.constants.CachingConstants;
+import com.iluwatar.caching.database.exceptions.DatabaseConnectionException;
 import com.mongodb.MongoClient;
 import com.mongodb.client.MongoDatabase;
 import com.mongodb.client.model.UpdateOptions;
+import lombok.extern.slf4j.Slf4j;
 import org.bson.Document;
 
 /**
  * Implementation of DatabaseManager.
  * implements base methods to work with MongoDb.
  */
+@Slf4j
 public class MongoDb implements DbManager {
-  /**
+  private static final String DATABASE_NAME = "test";
-   * Mongo db.
-   */
-  private MongoDatabase db;
 
   /**
-   * Connect to Db.
+   * Connect to Db. Check th connection
    */
   @Override
-  public void connect() {
+  public void connect() throws DatabaseConnectionException {
-    MongoClient mongoClient = new MongoClient();
+    try (MongoClient mongoClient = new MongoClient()) {
-    db = mongoClient.getDatabase("test");
+      mongoClient.getDatabase("test");
+    } catch (NoClassDefFoundError e) {
+      throw new DatabaseConnectionException("Could not connect to DB.");
+    }
   }
 
   /**
@@ -39,9 +42,8 @@ public class MongoDb implements DbManager {
    */
   @Override
   public UserAccount readFromDb(final String userId) {
-    if (db == null) {
+    try (MongoClient mongoClient = new MongoClient()) {
-      connect();
+      MongoDatabase db = mongoClient.getDatabase(DATABASE_NAME);
-    }
       var iterable = db
               .getCollection(CachingConstants.USER_ACCOUNT)
               .find(new Document(USER_ID, userId));
@@ -49,9 +51,14 @@ public class MongoDb implements DbManager {
         return null;
       }
       Document doc = iterable.first();
+      if (doc != null) {
         String userName = doc.getString(USER_NAME);
         String appInfo = doc.getString(ADD_INFO);
         return new UserAccount(userId, userName, appInfo);
+      } else {
+        return null;
+      }
+    }
   }
 
   /**
@@ -62,9 +69,8 @@ public class MongoDb implements DbManager {
    */
   @Override
   public UserAccount writeToDb(final UserAccount userAccount) {
-    if (db == null) {
+    try (MongoClient mongoClient = new MongoClient()) {
-      connect();
+      MongoDatabase db = mongoClient.getDatabase(DATABASE_NAME);
-    }
       db.getCollection(USER_ACCOUNT).insertOne(
               new Document(USER_ID, userAccount.getUserId())
                       .append(USER_NAME, userAccount.getUserName())
@@ -72,6 +78,7 @@ public class MongoDb implements DbManager {
       );
       return userAccount;
     }
+  }
 
   /**
    * Update DB.
@@ -81,9 +88,8 @@ public class MongoDb implements DbManager {
    */
   @Override
   public UserAccount updateDb(final UserAccount userAccount) {
-    if (db == null) {
+    try (MongoClient mongoClient = new MongoClient()) {
-      connect();
+      MongoDatabase db = mongoClient.getDatabase(DATABASE_NAME);
-    }
       Document id = new Document(USER_ID, userAccount.getUserId());
       Document dataSet = new Document(USER_NAME, userAccount.getUserName())
               .append(ADD_INFO, userAccount.getAdditionalInfo());
@@ -91,6 +97,7 @@ public class MongoDb implements DbManager {
               .updateOne(id, new Document("$set", dataSet));
       return userAccount;
     }
+  }
 
   /**
    * Update data if exists.
@@ -100,9 +107,8 @@ public class MongoDb implements DbManager {
    */
   @Override
   public UserAccount upsertDb(final UserAccount userAccount) {
-    if (db == null) {
+    try (MongoClient mongoClient = new MongoClient()) {
-      connect();
+      MongoDatabase db = mongoClient.getDatabase(DATABASE_NAME);
-    }
       String userId = userAccount.getUserId();
       String userName = userAccount.getUserName();
       String additionalInfo = userAccount.getAdditionalInfo();
@@ -118,3 +124,4 @@ public class MongoDb implements DbManager {
       return userAccount;
     }
   }
+}

caching/src/main/java/com/iluwatar/caching/database/exceptions/DatabaseConnectionException.java

@@ -0,0 +1,7 @@
+package com.iluwatar.caching.database.exceptions;
+
+public class DatabaseConnectionException extends Exception {
+  public DatabaseConnectionException(String s) {
+    super(s);
+  }
+}