java-modernization

name: java-modernization description: | Java EE and legacy Java to modern Spring Boot migration patterns. Use when: User has a Java EE, J2EE, or legacy Java 8/11 application and needs to upgrade to Spring Boot 3.x with Java 21. Triggers on: pom.xml with javax.* dependencies, web.xml files, EJB annotations, JAAS configuration. Covers: EJB to Spring beans, XML to Java/YAML config, JAAS to Spring Security OAuth2, JPA/Hibernate updates.

Java Modernization Skill

Use this skill when modernizing legacy Java applications to Spring Boot 3.x for Azure compatibility.

When to Use This Skill

• Migrating Java EE (J2EE) to Spring Boot
• Upgrading Java 8/11 to Java 17/21
• Converting XML configuration to Java config or YAML
• Migrating EJB to Spring components
• Modernizing JAAS/container security to Spring Security
• Moving from application servers (WebLogic, WebSphere, JBoss) to embedded servers

Framework Version Mapping

Java EE to Spring Boot Mapping

Configuration Transformation

XML to Java Config

// Legacy XML (applicationContext.xml)
// <bean id="userService" class="com.example.UserServiceImpl">
//     <property name="userRepository" ref="userRepository"/>
// </bean>

// Modern Java Config
@Configuration
public class AppConfig {
    @Bean
    public UserService userService(UserRepository userRepository) {
        return new UserServiceImpl(userRepository);
    }
}

// Or simply use component scanning
@Service
public class UserServiceImpl implements UserService {
    private final UserRepository userRepository;
    
    public UserServiceImpl(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
}

XML to YAML Configuration

# Legacy properties file
# database.url=jdbc:sqlserver://localhost:1433;database=mydb
# database.username=user
# database.password=pass

# Modern application.yml
spring:
  datasource:
    url: jdbc:sqlserver://${DB_HOST:localhost}:1433;database=${DB_NAME:mydb}
    username: ${DB_USER}
    password: ${DB_PASSWORD}
  jpa:
    hibernate:
      ddl-auto: validate
    properties:
      hibernate:
        dialect: org.hibernate.dialect.SQLServerDialect

Authentication Migration

JAAS → Spring Security + OAuth2

// Legacy JAAS configuration in web.xml
// <login-config>
//     <auth-method>FORM</auth-method>
// </login-config>

// Modern Spring Security with Entra ID
@Configuration
@EnableWebSecurity
public class SecurityConfig {
    
    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http
            .authorizeHttpRequests(auth -> auth
                .requestMatchers("/public/**").permitAll()
                .anyRequest().authenticated()
            )
            .oauth2Login(Customizer.withDefaults())
            .oauth2ResourceServer(oauth2 -> oauth2.jwt(Customizer.withDefaults()));
        return http.build();
    }
}

application.yml for Entra ID

spring:
  security:
    oauth2:
      client:
        registration:
          azure:
            client-id: ${AZURE_CLIENT_ID}
            client-secret: ${AZURE_CLIENT_SECRET}
            scope: openid, profile, email
        provider:
          azure:
            issuer-uri: https://login.microsoftonline.com/${AZURE_TENANT_ID}/v2.0

Data Access Migration

JDBC → Spring Data JPA

// Legacy JDBC
public class UserDaoImpl implements UserDao {
    public User findById(Long id) {
        Connection conn = dataSource.getConnection();
        PreparedStatement ps = conn.prepareStatement("SELECT * FROM users WHERE id = ?");
        ps.setLong(1, id);
        ResultSet rs = ps.executeQuery();
        // Manual mapping...
    }
}

// Modern Spring Data JPA
public interface UserRepository extends JpaRepository<User, Long> {
    Optional<User> findByEmail(String email);
    List<User> findByActiveTrue();
}

// Usage
@Service
public class UserService {
    private final UserRepository userRepository;
    
    public User findById(Long id) {
        return userRepository.findById(id)
            .orElseThrow(() -> new UserNotFoundException(id));
    }
}

SOAP to REST Migration

See the wcf-to-rest-migration skill for detailed patterns.

Package/Dependency Mapping

Maven POM Modernization

<!-- Legacy parent -->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>3.2.0</version>
</parent>

<properties>
    <java.version>21</java.version>
</properties>

<dependencies>
    <!-- Web -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    
    <!-- Data -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    
    <!-- Azure SQL -->
    <dependency>
        <groupId>com.microsoft.sqlserver</groupId>
        <artifactId>mssql-jdbc</artifactId>
        <scope>runtime</scope>
    </dependency>
    
    <!-- Security -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-oauth2-client</artifactId>
    </dependency>
    
    <!-- Azure Identity -->
    <dependency>
        <groupId>com.azure.spring</groupId>
        <artifactId>spring-cloud-azure-starter-active-directory</artifactId>
    </dependency>
</dependencies>

Template Files

• Application.java - Spring Boot entry point
• application.yml - Configuration template
• Dockerfile - Container template for Java 21

Best Practices

1. Use constructor injection - Prefer over field injection
2. Externalize configuration - Use environment variables for secrets
3. Use Spring Data repositories - Reduce boilerplate
4. Enable virtual threads - For high-concurrency apps (Java 21)
5. Use records for DTOs - Immutable data carriers
6. Configure health endpoints - For Azure monitoring
7. Use SLF4J - Consistent logging abstraction