Add all 23 GoF design pattern implementations (2026-06-13)

02-structural/proxy/LoggingProxy.java

@@ -0,0 +1,41 @@
+package proxy;
+
+import java.time.Instant;
+
+/**
+ * Logging Proxy — adds timing and audit logging around every query
+ * without touching RealDatabaseConnection or any of its callers.
+ *
+ * This is the "cross-cutting concern" use case of Proxy,
+ * the same mechanism behind Spring AOP's @Around advice.
+ */
+public class LoggingProxy implements DatabaseConnection {
+
+    private final DatabaseConnection target;
+
+    public LoggingProxy(DatabaseConnection target) {
+        this.target = target;
+    }
+
+    @Override
+    public void connect() {
+        System.out.println("[Log] connect() at " + Instant.now());
+        target.connect();
+    }
+
+    @Override
+    public String executeQuery(String sql) {
+        long start = System.currentTimeMillis();
+        System.out.println("[Log] QUERY START: " + sql);
+        String result = target.executeQuery(sql);
+        long elapsed = System.currentTimeMillis() - start;
+        System.out.println("[Log] QUERY END: " + elapsed + "ms | result: " + result);
+        return result;
+    }
+
+    @Override
+    public void disconnect() {
+        System.out.println("[Log] disconnect() at " + Instant.now());
+        target.disconnect();
+    }
+}