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() {
-    dbManager.connect();
+    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.");
+    }
   }
 
   /**
@@ -39,19 +42,23 @@ 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));
+      if (iterable.first() == null) {
+        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;
+      }
     }
-    var iterable = db
-            .getCollection(CachingConstants.USER_ACCOUNT)
-            .find(new Document(USER_ID, userId));
-    if (iterable.first() == null) {
-      return null;
-    }
-    Document doc = iterable.first();
-    String userName = doc.getString(USER_NAME);
-    String appInfo = doc.getString(ADD_INFO);
-    return new UserAccount(userId, userName, appInfo);
   }
 
   /**
@@ -62,15 +69,15 @@ 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())
+                      .append(ADD_INFO, userAccount.getAdditionalInfo())
+      );
+      return userAccount;
     }
-    db.getCollection(USER_ACCOUNT).insertOne(
-            new Document(USER_ID, userAccount.getUserId())
-                    .append(USER_NAME, userAccount.getUserName())
-                    .append(ADD_INFO, userAccount.getAdditionalInfo())
-    );
-    return userAccount;
   }
 
   /**
@@ -81,15 +88,15 @@ 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());
+      db.getCollection(CachingConstants.USER_ACCOUNT)
+              .updateOne(id, new Document("$set", dataSet));
+      return userAccount;
     }
-    Document id = new Document(USER_ID, userAccount.getUserId());
-    Document dataSet = new Document(USER_NAME, userAccount.getUserName())
-            .append(ADD_INFO, userAccount.getAdditionalInfo());
-    db.getCollection(CachingConstants.USER_ACCOUNT)
-            .updateOne(id, new Document("$set", dataSet));
-    return userAccount;
   }
 
   /**
@@ -100,21 +107,21 @@ 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();
+      db.getCollection(CachingConstants.USER_ACCOUNT).updateOne(
+              new Document(USER_ID, userId),
+              new Document("$set",
+                      new Document(USER_ID, userId)
+                              .append(USER_NAME, userName)
+                              .append(ADD_INFO, additionalInfo)
+              ),
+              new UpdateOptions().upsert(true)
+      );
+      return userAccount;
     }
-    String userId = userAccount.getUserId();
-    String userName = userAccount.getUserName();
-    String additionalInfo = userAccount.getAdditionalInfo();
-    db.getCollection(CachingConstants.USER_ACCOUNT).updateOne(
-            new Document(USER_ID, userId),
-            new Document("$set",
-                    new Document(USER_ID, userId)
-                            .append(USER_NAME, userName)
-                            .append(ADD_INFO, additionalInfo)
-            ),
-            new UpdateOptions().upsert(true)
-    );
-    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);
+  }
+}