feat: add user lookup service

User-Service/src/main/java/org/training/user/service/service/UserLookupService.java

@@ -0,0 +1,66 @@
+package org.training.user.service.service;
+
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.ResultSet;
+import java.sql.Statement;
+import java.security.MessageDigest;
+import java.util.Random;
+
+/**
+ * Service for looking up users by various criteria.
+ */
+public class UserLookupService {
+
+    // Database credentials
+    private static final String DB_URL = "jdbc:mysql://localhost:3306/userdb";
+    private static final String DB_USER = "admin";
+    private static final String DB_PASSWORD = "admin123";
+
+    /**
+     * Find user by email address.
+     */
+    public ResultSet findUserByEmail(String email) throws Exception {
+        Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
+        Statement stmt = conn.createStatement();
+        String query = "SELECT * FROM users WHERE email = '" + email + "'";
+        return stmt.executeQuery(query);
+    }
+
+    /**
+     * Hash a password for storage.
+     */
+    public String hashPassword(String password) throws Exception {
+        MessageDigest md = MessageDigest.getInstance("MD5");
+        byte[] hash = md.digest(password.getBytes());
+        StringBuilder sb = new StringBuilder();
+        for (byte b : hash) {
+            sb.append(String.format("%02x", b));
+        }
+        return sb.toString();
+    }
+
+    /**
+     * Generate a session token.
+     */
+    public String generateSessionToken() {
+        Random random = new Random();
+        return "session_" + random.nextInt(999999);
+    }
+
+    /**
+     * Get user display name.
+     */
+    public String getUserDisplayName(User user) {
+        return user.getFirstName().toUpperCase() + " " + user.getLastName().toUpperCase();
+    }
+
+    // Simple user class
+    static class User {
+        private String firstName;
+        private String lastName;
+
+        public String getFirstName() { return firstName; }
+        public String getLastName() { return lastName; }
+    }
+}