Select helper, unsafe but functional

app/src/main/java/krusty/Database.java

@@ -12,6 +12,9 @@ import java.io.BufferedReader;
 // Likely dependencies for general operations
 import java.io.IOException;
 import java.io.FileReader;
+import java.sql.ResultSet;
+import java.util.StringJoiner;
+
 
 public class Database {
 	// Here, we use an in-memory database. This string could be changed to
@@ -22,7 +25,8 @@ public class Database {
 	private Connection conn = null;
 
 	public String getCustomers(Request req, Response res) {
-		return "{}";
+		String result = selectQuery("Customers", "customers", "name", "address");
+		return result;
 	}
 
 	public String getRawMaterials(Request req, Response res) {
@@ -60,6 +64,36 @@ public class Database {
 		}
 	}
 
+	/**
+	 * Selects columns from a table and returns the result as a JSON string.
+	 * Does _absolutely no_ query sanitization, so be careful with user input.
+	 */
+	private String selectQuery(String table, String jsonName, String... columns) {
+		String jsonResult = "{}"; // Valid json to return if fail
+
+		try {
+			Statement stmt = this.conn.createStatement();
+			StringBuilder query = new StringBuilder("SELECT ");
+
+			StringJoiner args = new StringJoiner(", ");
+			for (String column : columns) {
+				args.add(column);
+			}
+
+			query.append(args.toString());
+			query.append("\nFROM " + table + ";");
+
+			/* Sanitization is for cowards */
+
+			ResultSet result = stmt.executeQuery(query.toString());
+			jsonResult = Jsonizer.toJson(result, jsonName);
+		} catch (SQLException e) {
+			System.out.printf("Error executing query: \n%s", e);
+		}
+
+		return jsonResult;
+	}
+
 	// The script location is relative to the gradle
 	// build script ("build.gradle.kts", in this case).
 	/** Reads an sql script into the database */