Introduce user migration feature

pom.xml

@@ -81,7 +81,12 @@
             <artifactId>hutool-all</artifactId>
             <version>5.8.18</version>
         </dependency>
-    </dependencies>
+        <dependency>
+            <groupId>com.mysql</groupId>
+            <artifactId>mysql-connector-j</artifactId>
+            <version>8.0.33</version>
+        </dependency>
+      </dependencies>
 
     <build>
         <plugins>

src/main/java/com/dashboardmanager/controller/UserController.java

@@ -7,6 +7,8 @@
 import com.dashboardmanager.repository.UsersRepository;
 import com.dashboardmanager.utils.FileUtils;
 import com.dashboardmanager.utils.SessionHeader;
+import com.mysql.cj.jdbc.ConnectionImpl;
+import jakarta.persistence.EntityManager;
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpServletResponse;
 import org.apache.commons.lang.RandomStringUtils;
@@ -25,6 +27,10 @@
 
 import java.io.*;
 import java.security.SecureRandom;
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.sql.Savepoint;
+import java.util.concurrent.atomic.AtomicReference;
 
 import static org.apache.commons.codec.binary.Base64.decodeBase64;
 
@@ -37,6 +43,9 @@ public class UserController {
     @Autowired
     private SessionsRepository sessionsRepository;
 
+    @Autowired
+    private EntityManager entityManager;
+
     private LRUFileCache fileCache = new LRUFileCache(100);
 
     @GetMapping("/")
@@ -103,6 +112,42 @@ public ResponseEntity<Resource> getUserImage(ServletWebRequest request, @Request
         }
     }
 
+    @PostMapping("/user/migrate")
+    public ResponseEntity<Resource> migrateUser(@RequestParam(value = "username") String username) {
+        try (var connection = getConnection()) {
+            doMigrateUser(username, connection);
+            return ResponseEntity.status(HttpStatus.OK).build();
+        } catch (SQLException e) {
+            return ResponseEntity.status(HttpStatus.BAD_REQUEST).build();
+        }
+    }
+
+    private void doMigrateUser(String username, ConnectionImpl connection) throws SQLException {
+        // migration might fail midway, set a savepoint to keep the database consistent
+        Savepoint savepoint = connection.setSavepoint("before-" + username + "-migration");
+
+        User newUser = new User();
+        newUser.setName("_placeholder_" + username);
+        newUser.setPassword("_placeholder_");
+        usersRepository.save(newUser);
+
+        User user = usersRepository.findByName(username);
+        if (user == null) {
+            connection.rollback(savepoint);
+            return;
+        }
+
+        newUser.setName(user.getName());
+        newUser.setPassword("oldpw:" + user.getPassword());
+        usersRepository.save(newUser);
+    }
+
+    private ConnectionImpl getConnection() {
+        AtomicReference<ConnectionImpl> impl = new AtomicReference<>();
+        var session = entityManager.unwrap(org.hibernate.Session.class);
+        session.doWork(connection -> impl.set((ConnectionImpl) connection.unwrap(Connection.class)));
+        return impl.get();
+    }
 
     private String createSessionHeader(Session session) {
         SessionHeader sessionHeader = new SessionHeader(session.getUser().getName(), session.getSessionId());

src/main/resources/application.properties

@@ -1,15 +1,9 @@
-spring.datasource.url=jdbc:h2:mem:testdb
-spring.datasource.driverClassName=org.h2.Driver
-spring.datasource.username=sa
-spring.datasource.password=
-
-#spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
-#spring.jpa.defer-datasource-initialization=true
-
-#spring.sql.init.mode=always
+spring.datasource.url=jdbc:mysql://localhost:3306/test?allowMultiQueries=true
+spring.datasource.driverClassName=com.mysql.cj.jdbc.Driver
+spring.datasource.username=root
+spring.datasource.password=root
 
 spring.jpa.show-sql=true
-spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.H2Dialect
+spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQLDialect
 spring.jpa.hibernate.ddl-auto= update
 
-spring.h2.console.enabled=true