Initial commit

src/main/java/com/mzh/library/util/JdbcUtil.java

@@ -0,0 +1,57 @@
+package com.mzh.library.util;
+
+import com.mzh.library.exception.DaoException;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+import java.util.Properties;
+
+public final class JdbcUtil {
+    private static final String CONFIG_FILE = "db.properties";
+    private static final String DEFAULT_DRIVER = "com.mysql.cj.jdbc.Driver";
+
+    private JdbcUtil() {
+    }
+
+    public static Connection getConnection() {
+        Properties properties = loadProperties();
+        String driver = properties.getProperty("db.driver", DEFAULT_DRIVER);
+        String url = required(properties, "db.url");
+        String username = required(properties, "db.username");
+        String password = required(properties, "db.password");
+
+        try {
+            Class.forName(driver);
+            return DriverManager.getConnection(url, username, password);
+        } catch (ClassNotFoundException | SQLException ex) {
+            throw new DaoException("Unable to open database connection", ex);
+        }
+    }
+
+    private static Properties loadProperties() {
+        try (InputStream inputStream = Thread.currentThread()
+            .getContextClassLoader()
+            .getResourceAsStream(CONFIG_FILE)) {
+            if (inputStream == null) {
+                throw new DaoException("Missing database configuration file: " + CONFIG_FILE, null);
+            }
+
+            Properties properties = new Properties();
+            properties.load(inputStream);
+            return properties;
+        } catch (IOException ex) {
+            throw new DaoException("Unable to read database configuration", ex);
+        }
+    }
+
+    private static String required(Properties properties, String key) {
+        String value = properties.getProperty(key);
+        if (value == null || value.trim().isEmpty()) {
+            throw new DaoException("Missing database configuration value: " + key, null);
+        }
+        return value.trim();
+    }
+}