fix(platform): normalize legacy Vietnam timezone

src/main/java/com/lab/labtimesheet/LabtimesheetApplication.java

@@ -1,23 +1,43 @@
 package com.lab.labtimesheet;
 
+import java.util.TimeZone;
+
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 
 import com.lab.labtimesheet.config.SecurityProperties;
 
-/** Application entry point and root component-scan boundary for Lab Timesheet. */
+/**
+ * Application entry point and root component-scan boundary for Lab Timesheet.
+ *
+ * <p>The entry point also canonicalizes the legacy Windows Vietnam timezone alias before database
+ * drivers inspect the JVM default timezone.
+ */
 @SpringBootApplication
 @EnableConfigurationProperties(SecurityProperties.class)
 public class LabtimesheetApplication {
+    private static final String LEGACY_VIETNAM_TIME_ZONE = "Asia/Saigon";
+    private static final String BUSINESS_TIME_ZONE = "Asia/Ho_Chi_Minh";
 
     /**
-     * Starts the standalone Spring Boot process.
+     * Canonicalizes the process timezone and starts the standalone Spring Boot process.
      *
      * @param args command-line arguments forwarded to Spring Boot
      */
     public static void main(String[] args) {
+        normalizeDefaultTimeZone();
         SpringApplication.run(LabtimesheetApplication.class, args);
     }
 
+    /**
+     * Replaces the legacy Windows Vietnam alias before pgJDBC sends it to PostgreSQL as a startup
+     * parameter. Other supported system timezones remain unchanged.
+     */
+    static void normalizeDefaultTimeZone() {
+        if (LEGACY_VIETNAM_TIME_ZONE.equals(TimeZone.getDefault().getID())) {
+            TimeZone.setDefault(TimeZone.getTimeZone(BUSINESS_TIME_ZONE));
+        }
+    }
+
 }

src/test/java/com/lab/labtimesheet/ApplicationTimeZoneIntegrationTest.java

@@ -0,0 +1,80 @@
+package com.lab.labtimesheet;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.mockito.Mockito.mockStatic;
+
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+import java.util.TimeZone;
+
+import org.junit.jupiter.api.Test;
+import org.mockito.MockedStatic;
+import org.springframework.boot.SpringApplication;
+import org.testcontainers.postgresql.PostgreSQLContainer;
+import org.testcontainers.utility.DockerImageName;
+
+class ApplicationTimeZoneIntegrationTest {
+
+    @Test
+    void mainCanonicalizesLegacyAliasBeforeStartingSpring() {
+        TimeZone originalTimeZone = TimeZone.getDefault();
+        String[] args = {"--spring.profiles.active=test"};
+
+        try (MockedStatic<SpringApplication> springApplication = mockStatic(SpringApplication.class)) {
+            TimeZone.setDefault(TimeZone.getTimeZone("Asia/Saigon"));
+
+            LabtimesheetApplication.main(args);
+
+            assertThat(TimeZone.getDefault().getID()).isEqualTo("Asia/Ho_Chi_Minh");
+            springApplication.verify(() -> SpringApplication.run(LabtimesheetApplication.class, args));
+        } finally {
+            TimeZone.setDefault(originalTimeZone);
+        }
+    }
+
+    @Test
+    void canonicalizesLegacyVietnamAliasBeforePostgresConnects() throws SQLException {
+        TimeZone originalTimeZone = TimeZone.getDefault();
+
+        try (PostgreSQLContainer postgres =
+                new PostgreSQLContainer(DockerImageName.parse("postgres:18.4"))) {
+            postgres.start();
+            TimeZone.setDefault(TimeZone.getTimeZone("Asia/Saigon"));
+
+            assertThat(TimeZone.getDefault().getID()).isEqualTo("Asia/Saigon");
+            assertThatThrownBy(() -> openConnection(postgres))
+                    .isInstanceOf(SQLException.class)
+                    .hasMessageContaining("Asia/Saigon");
+
+            LabtimesheetApplication.normalizeDefaultTimeZone();
+
+            assertThat(TimeZone.getDefault().getID()).isEqualTo("Asia/Ho_Chi_Minh");
+            try (Connection connection = openConnection(postgres)) {
+                assertThat(connection.isValid(1)).isTrue();
+            }
+        } finally {
+            TimeZone.setDefault(originalTimeZone);
+        }
+    }
+
+    @Test
+    void leavesSupportedSystemTimeZoneUnchanged() {
+        TimeZone originalTimeZone = TimeZone.getDefault();
+
+        try {
+            TimeZone.setDefault(TimeZone.getTimeZone("Europe/Paris"));
+
+            LabtimesheetApplication.normalizeDefaultTimeZone();
+
+            assertThat(TimeZone.getDefault().getID()).isEqualTo("Europe/Paris");
+        } finally {
+            TimeZone.setDefault(originalTimeZone);
+        }
+    }
+
+    private static Connection openConnection(PostgreSQLContainer postgres) throws SQLException {
+        return DriverManager.getConnection(postgres.getJdbcUrl(), postgres.getUsername(), postgres.getPassword());
+    }
+}