code improvments

code imprs

code improvements

code improvs

README.md

@@ -44,10 +44,13 @@ The application's main class is `Main` class, it runs the entire application. It
 ### Improvements
 Here are some points that I could have improved upon, but did not go through with it because of either time constraints, or because it might be too much for the scope of this assignment.
 
++ Ideally all the services, and inner services and APIs being used, should be injected in by dependency injection. In Dart, [get_it](https://pub.dev/packages/get_it), is makes this very easy with a Locator file. But for Java, I was not able to find something that was as easy.
 + The DatabaseService class is tightly coupling the DatabaseApi class. It's better to make the DatabaseApi class a singleton and inject it into the DatabaseService class.
 + The DatabaseApi class is doing more than just communicating with the database, it's also handling error handling. It would be better to extract the error handling logic into a separate class.
+  + Could be rectified by using lots of custom Exceptions in general, but overkill for this scope.
 + The QueryResultsRepository class is tightly coupled to the PersistentResultSetModel class. It would be better to extract the PersistentResultSetModel class into a separate package, and use a factory pattern to create instances of it.
 + The App class is doing too much. It would be better to extract the logic for each endpoint into separate classes, and use a factory pattern to create instances of them.
+  + But then again, too much inheritance.
 + The Main class should be refactored to use dependency injection, so that the dependencies can be easily swapped out for testing.
 + The AppConfigService class should be refactored to use a more robust input validation library, to handle more edge cases.
 + The ReportGenerationService class should be refactored to support more output formats, such as HTML, CSV and PDF.

src/Main.java

@@ -53,16 +53,44 @@ class App {
      * generates reports using the `ReportGenerationService` class, and prompts the user for input using the `AppConfigService` class.
      */
     public void run() {
-        try {
-            QueryResultsRepository resultsRepository;
-            for (final CustomPreparedStatementsRead query : reportEndpoints) {
-                resultsRepository = databaseService.executeReadReportsEndpoint(new QueryDTO(query));
-                reportGenerationService.reportBaseResults(resultsRepository);
-            }
+        executeNoInteractionEndpointPipeline(reportEndpoints);
+        executeInteractiveEndpointPipeline(queryEndpoints);
+    }
 
+    /**
+     * This method is responsible for executing a pipeline of read-only queries, using a provided set of
+     * {@link CustomPreparedStatementsRead} queryEndpoints, without any user interaction.
+     * The method will iterate over the provided queryEndpoints, and for each query it will:
+     * Execute the read query using {@link DatabaseService#getReadReportsEndpoint(QueryDTO)}
+     * Store the results in a new {@link QueryResultsRepository}
+     * Generate a report for the stored results using {@link ReportGenerationService#reportBaseResults(QueryResultsRepository)}
+     * @param queryEndpoints an array of {@link CustomPreparedStatementsRead} containing the queries to be executed.
+     * @throws RuntimeException when there is a SQLException thrown by {@link DatabaseService#getReadReportsEndpoint(QueryDTO)}
+     */
+    private void executeNoInteractionEndpointPipeline(CustomPreparedStatementsRead[] queryEndpoints) {
+        QueryResultsRepository resultsRepository;
+        for (final CustomPreparedStatementsRead query : queryEndpoints) {
+            try {
+                resultsRepository = databaseService.getReadReportsEndpoint(new QueryDTO(query));
+            } catch (SQLException e) {
+                throw new RuntimeException(e);
+            }
+            reportGenerationService.reportBaseResults(resultsRepository);
+        }
+    }
+
+    /**
+     * Executes a series of read queries specified in the {@code queryEndpoints} parameter, and prompts the user for input of country name and date.
+     * The results of the queries are passed to reportGenerationService to be reported.
+     * @param queryEndpoints the endpoints to execute in the pipeline
+     * @throws RuntimeException if a SQLException occurs when getting the read reports endpoint
+     */
+    private void executeInteractiveEndpointPipeline(CustomPreparedStatementsRead[] queryEndpoints) {
+        QueryResultsRepository resultsRepository;
+        try {
             for(final CustomPreparedStatementsRead query: queryEndpoints) {
                 appConfigService.promptAndSetUserArguments();
-                resultsRepository = databaseService.executeReadReportsEndpoint(new QueryDTO(query, new Object[]{appConfigService.countryName, appConfigService.date,}));
+                resultsRepository = databaseService.getReadReportsEndpoint(new QueryDTO(query, new Object[]{appConfigService.getCountryName(), appConfigService.getDate(),}));
                 reportGenerationService.reportBaseResults(resultsRepository);
             }
 

src/apis/DatabaseApi.java

@@ -5,24 +5,22 @@ import org.postgresql.util.PSQLException;
 
 import java.sql.*;
 import java.util.Date;
-import java.util.MissingFormatArgumentException;
 
 /**
- * The `DatabaseApi` class provides a way to communicate with the database to perform read operations and return the results.
+ * The `DatabaseApi` class is a DAO that provides a way to communicate with the database to perform read operations and return the results.
  * It contains a single method `performReadQuery()` that takes a `QueryDTO` and a `Connection` object as parameters and
- * returns a `PreparedStatement` object. It throws `SQLException` in case of any SQL error or `MissingFormatArgumentException`
+ * returns a `PreparedStatement` object. It throws `SQLException` in case of any SQL error or `IllegalArgumentException`
  * in case of any missing argument or extra argument.
- *
+ * <p>
  * The class can be abstracted and implemented into constituent action-specific APIs when there is a need for more than a single READ action.
  */
 public class DatabaseApi {
     /**
      * Creates and executes a PreparedStatement, given the QueryDTO.
-     * @param queryDTO
-     * @param connection
-     * @return
-     * @throws MissingFormatArgumentException in case of any missing argument or extra argument.
-     * @throws SQLException
+     * @param queryDTO The query in the form of the queryDTO
+     * @param connection SQL server connection
+     * @return The executed prepared statement, containing the results of the query
+     * @throws IllegalArgumentException in case of any missing argument or extra argument.
      */
     public PreparedStatement performReadQuery(QueryDTO queryDTO, Connection connection) throws SQLException {
         // Set template
@@ -43,12 +41,15 @@ public class DatabaseApi {
 
             statement.execute();
         } catch (PSQLException e) {
-            if (e.getMessage().startsWith("No value specified for parameter")) throw new MissingFormatArgumentException("The templates present in the query, were not correctly mapped to their replacement variables.");
-            else if (e.getMessage().startsWith("The column index is out of range:")) throw new MissingFormatArgumentException("No replacement variables needed, but were they were still supplied.");
+            if (e.getMessage().startsWith("No value specified for parameter"))
+                throw new IllegalArgumentException("The templates present in the query, were not correctly mapped to their replacement variables.");
+            else if (e.getMessage().startsWith("The column index is out of range:")) {
+                throw new IllegalArgumentException("Are you trying to supply replacement variables, when they are not needed?");
+            }
             throw e;
         }
 
         return statement;
     }
 
-}
+}

src/constants/ConstFormatters.java

@@ -2,6 +2,6 @@ package constants;
 
 import java.text.SimpleDateFormat;
 
-public class ConstFormatters{
+public class Formatters {
     final public static SimpleDateFormat APPLICATION_DATE_FORMATTER = new SimpleDateFormat("dd-MM-yyyy");
 }

src/data/dtos/QueryDTO.java

@@ -5,7 +5,7 @@ import data.enums.CustomPreparedStatementsRead;
 /**
  * Container for storing SQL statements to be executed, along with their aruments.
  * @param statement an instance of `CustomPreparedStatementsRead` enum which contains the statement template to be executed.
- * @param templateArgsn an array of `Object` representing the arguments to be used in the statement template.
+ * @param templateArgs an array of `Object` representing the arguments to be used in the statement template.
  */
 public record QueryDTO(CustomPreparedStatementsRead statement, Object[] templateArgs) {
     /**

src/data/enums/CustomPreparedStatementsRead.java

@@ -70,7 +70,7 @@ public enum CustomPreparedStatementsRead {
     public final String statementTemplate;
     public final String description;
 
-    private CustomPreparedStatementsRead(String statementTemplate, String description) {
+    CustomPreparedStatementsRead(String statementTemplate, String description) {
         this.statementTemplate = statementTemplate;
         this.description = description;
     }

src/data/models/PersistentResultSetModel.java

@@ -30,17 +30,16 @@ public class PersistentResultSetModel {
 
         // Retrieving rest of the results
         final List<ResultRowModel> rows = new ArrayList<>();
-        final Object[] rowElements = new Object[columnCount];
         while (resultSet.next()) {
-            for (int columnIndex = 0; columnIndex < rowElements.length; columnIndex++)
+            final Object[] rowElements = new Object[columnCount];
+            for (int columnIndex = 0; columnIndex < columnCount; columnIndex++)
                 rowElements[columnIndex] = resultSet.getObject(columnIndex+1);
 
-            rows.add(new ResultRowModel(rowElements.clone()));
+            rows.add(new ResultRowModel(rowElements));
         }
 
         resultRowEntries = new ResultRowModel[rows.size()];
         rows.toArray(resultRowEntries);
-
     }
 
     /**
@@ -51,9 +50,6 @@ public class PersistentResultSetModel {
      * Represents column names that appear in the result set.
      */
 
-    /**
-     * It returns the string representation of the result set in tabular format, showing the column names and rowElements.
-     */
     final public String[] columnNames;
 
     /**

src/data/repos/QueryResultsRepository.java

@@ -1,38 +1,40 @@
 package data.repos;
 
-
 import data.models.PersistentResultSetModel;
 
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.ArrayList;
+import java.util.List;
 
 /**
  * Provides a way to store and persist the results of read queries.
- *  It contains an `ArrayList` of `PersistentResultSetModel` called `persistentResults` and a `String` called `queryDescription`.
- *  The class provides a constructor that takes a `queryDescription` as a parameter and an `addResult()` method
- *  that takes a `ResultSet` as a parameter and adds it to the `persistentResults` list.
- *  The class also provides a `toString()` method that returns the string representation of the stored results and their description.
+ * It contains a list of `PersistentResultSetModel` instances called `persistentResults` and a `String` called `queryDescription`.
+ * The class provides a constructor that takes a `queryDescription` as a parameter and an `addResult()` method
+ * that takes a `ResultSet` as a parameter and adds it to the `persistentResults` list.
+ * The class also provides a `toString()` method that returns the string representation of the stored results and their description.
  */
 public class QueryResultsRepository {
+
+    /**
+     * Store for the results
+     */
+    private final List<PersistentResultSetModel> persistentResults = new ArrayList<>();
+
+    /**
+     * Represents a description of the query that was executed.
+     */
+    private final String queryDescription;
+
     public QueryResultsRepository(String queryDescription) {
         this.queryDescription = queryDescription;
     }
 
-    /**
-     * Store for the results
-     */
-    final private ArrayList<PersistentResultSetModel> persistentResults = new ArrayList<>();
-
-    /**
-     * Represents a description of the query that was executed.
-     */
-    final private String queryDescription;
-
     /**
      * Creates a PersistentResultSetModel instance from given ResultSet, and adds it to the persistentResults list
-     * @param resultSet
-     * @throws SQLException
+     *
+     * @param resultSet the resultSet to be added to the persistentResults list
+     * @throws SQLException if an error occurs while creating the PersistentResultSetModel instance
      */
     public void addResult(ResultSet resultSet) throws SQLException {
         persistentResults.add(new PersistentResultSetModel(resultSet));
@@ -40,11 +42,11 @@ public class QueryResultsRepository {
 
     @Override
     public String toString() {
-        StringBuilder templateBuilder = new StringBuilder("\n\nDESCRIPTION: ").append(queryDescription);
+        StringBuilder templateBuilder = new StringBuilder("\n\nQUERY DESCRIPTION: ").append(queryDescription);
         for (final PersistentResultSetModel result : persistentResults) {
             templateBuilder.append("\n").append(result).append("\n>");
         }
 
-        return templateBuilder.deleteCharAt(templateBuilder.length()-1).append("\n\n").toString();
+        return templateBuilder.deleteCharAt(templateBuilder.length() - 1).append("\n\n").toString();
     }
-}
+}

src/services/AppConfigService.java

@@ -1,7 +1,7 @@
 package services;
 
 import utils.Formatters;
-import utils.ConstValues;
+import utils.ConstText;
 
 import java.text.ParseException;
 
@@ -12,37 +12,39 @@ import java.util.Scanner;
  * Prompts and stores the configuration that the app needs to be run with.
  */
 public class AppConfigService {
-    String countryName;
-    Date date;
+    private String countryName;
+    public String getCountryName() {return countryName;}
+    private Date date;
+    public Date getDate() {return date;}
 
     /**
      * Prompts the user to input the country name and date, and stores the input.
      * It will keep prompting the user until the date is in the correct format.
      */
     public void promptAndSetUserArguments() {
-        final Scanner scanner = new Scanner(System.in);
-        System.out.println(ConstValues.inputCountryName);
-        countryName = scanner.nextLine();
-        System.out.println();
+        // Closing even on an uncaught exception
+        try (Scanner scanner = new Scanner(System.in)) {
+            System.out.println(ConstText.inputCountryName);
+            countryName = scanner.nextLine();
+            System.out.println();
 
-        System.out.println(ConstValues.inputDate);
-        while (true) {
-            try {
-                date = Formatters.APPLICATION_DATE_FORMATTER.parse(scanner.nextLine());
-                // Always using exact current date. Otherwise, different day possible at the start of the run.
-                if (date.after(new Date())) {
-                    System.out.println("There is no data available for the future yet... Try again:");
-                    continue;
+            System.out.println(ConstText.inputDate);
+            while (true) {
+                try {
+                    date = Formatters.APPLICATION_DATE_FORMATTER.parse(scanner.nextLine());
+                    // Always using exact current date. Otherwise, different day possible at the start of the run.
+                    if (date.after(new Date())) {
+                        System.out.println(ConstText.dateInFuture);
+                        continue;
+                    }
+
+                    // Not doing anymore month/day validations.
+
+                    break;
+                } catch (ParseException e) {
+                    System.out.printf(ConstText.unableParseDate, Formatters.APPLICATION_DATE_FORMATTER.toPattern());
                 }
-
-                // Not doing anymore month/day validations.
-
-                break;
-            } catch (ParseException e) {
-                System.out.printf("Unable to parse date. Should be in format '%s'.\nTry again:%n", Formatters.APPLICATION_DATE_FORMATTER.toPattern());
             }
         }
-
-        scanner.close();
     }
 }

src/services/DatabaseService.java

@@ -3,6 +3,7 @@ package services;
 import apis.DatabaseApi;
 import data.dtos.QueryDTO;
 import data.repos.QueryResultsRepository;
+import utils.ConstText;
 
 import java.sql.*;
 
@@ -30,7 +31,7 @@ public class DatabaseService {
      * @param queryDTO The query with its arguments.
      * @return Persisting (non-lazy) results from executing the query.
      */
-    public QueryResultsRepository executeReadReportsEndpoint(QueryDTO queryDTO) throws SQLException {
+    public QueryResultsRepository getReadReportsEndpoint(QueryDTO queryDTO) throws SQLException {
         final PreparedStatement resultStatement = databaseApi.performReadQuery(queryDTO, connection);
 
         final QueryResultsRepository resultSets = new QueryResultsRepository(queryDTO.statement().description);
@@ -52,9 +53,9 @@ public class DatabaseService {
         Connection connection = null;
         try {
             connection = DriverManager.getConnection(url, user, password);
-            System.out.println("Connected to the PostgreSQL server successfully.");
+            System.out.println(ConstText.successServerConnection);
         } catch (SQLException e) {
-            System.out.println("Unable to connect to PostgreSQL server.");
+            System.out.println(ConstText.failureServerConnection);
             throw new RuntimeException();
         }
 

src/utils/ConstText.java

@@ -0,0 +1,24 @@
+package utils;
+
+/**
+ * Contains string constants used in the application for the purpose of user I/O.
+ * <p>
+ * Effectively a simpler standalone for l10n localization.
+ */
+public class ConstText {
+    //D
+    public static final String dateInFuture = "There is no data available for the future yet... Try again:";
+
+    //F
+    public static final String failureServerConnection = "Unable to connect to PostgreSQL server.";
+
+    //I
+    public static final String inputCountryName = "Enter country: ";
+    public static final String inputDate = "Enter date: ";
+
+    //S
+    public static final String successServerConnection = "Connected to the PostgreSQL server successfully.";
+
+    //U
+    public static final String unableParseDate = "Unable to parse date. Should be in format '%s'.\nTry again:%n";
+}

src/utils/ConstValues.java

@@ -1,7 +0,0 @@
-package utils;
-
-public class ConstValues {
-    //I
-    final public static String inputCountryName = "Enter country: ";
-    final public static String inputDate = "Enter date: ";
-}