spring3.0使用annotation完全代替XML
spring3.0使用annotation完全代替XML(续)
用java config来代替XML,当时还遗留下一些问题:
- <tx:annotation-driven />声明性事务等配置无法用简单代码来实现
- web.xml无法去掉
先来说说web.xml,有两种方法来替代
(一)annotation
@WebServlet(urlPatterns="/hello") public class HelloServlet extends HttpServlet {}
servlet3.0增加了@WebServlet, @WebFilter, @WebListener等注解,servlet容器会在classpath扫描并注册所有的标注好的servlet, filter和listener。这种方法只针对你能访问源代码的情况,对于像spring_mvc用到的DispatcherServlet,无法在源码上加annotation,可以用第二种方法来实现bootstrap
(二)ServletContainerInitializer
这是servlet3的一个接口,我们来看看spring-web提供的实现
@HandlesTypes(WebApplicationInitializer.class) public class SpringServletContainerInitializer implements ServletContainerInitializer { public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext) throws ServletException { //implemention omitted } }
@HandlesTypes也是servlet3中的注解,这里它处理的是WebApplicationInitializer,也就是说servlet容器会扫描classpath,将所有实现了WebApplicationInitializer接口的类传给onStartup方法中的webAppInitializerClasses,并调用onStartup方法来注册servlet。具体的注册代码可以这样写:
public class WebInit implements WebApplicationInitializer { @Override public void onStartup(ServletContext sc) throws ServletException { sc.addFilter("hibernateFilter", OpenSessionInViewFilter.class).addMappingForUrlPatterns(null, false, "/*"); // Create the 'root' Spring application context AnnotationConfigWebApplicationContext root = new AnnotationConfigWebApplicationContext(); root.scan("septem.config.app"); // Manages the lifecycle of the root application context sc.addListener(new ContextLoaderListener(root)); AnnotationConfigWebApplicationContext webContext = new AnnotationConfigWebApplicationContext(); webContext.setConfigLocation("septem.config.web"); ServletRegistration.Dynamic appServlet = sc.addServlet("appServlet", new DispatcherServlet(webContext)); appServlet.setLoadOnStartup(1); appServlet.addMapping("/"); } }
以上的代码分别调用了sc.addFilter, sc.addListener, sc.addServlet来注册filter, listener和servlet.
用以上的方法就能将WEB-INF/web.xml删除了.spring3.1.M2开始增加了一系列annotation来实现声明性事务及简化spring_mvc配置。WebInit中注册的DispatcherServlet所对应的配置在septem.config.web包里面:
@Configuration @ComponentScan(basePackages="septem.controller") @EnableWebMvc public class WebConfig { }
一行@EnableWebMvc就导入了spring_mvc需要的诸多bean,再配合@ComponentScan扫描septem.controller包里面所有的@Controller,基本的mvc配置就完成了。
声明性事务也是类似,通过spring root application context扫描包septem.config.app:
@Configuration @EnableTransactionManagement public class DataConfig { @Bean public AnnotationSessionFactoryBean sessionFactory() { AnnotationSessionFactoryBean sessionFactoryBean = new AnnotationSessionFactoryBean(); sessionFactoryBean.setDataSource(dataSource()); sessionFactoryBean.setNamingStrategy(new ImprovedNamingStrategy()); sessionFactoryBean.setPackagesToScan("septem.model"); sessionFactoryBean.setHibernateProperties(hProps()); return sessionFactoryBean; } private DataSource dataSource() { BasicDataSource source = new BasicDataSource(); source.setDriverClassName("org.hsqldb.jdbcDriver"); source.setUrl("jdbc:hsqldb:mem:s3demo_db"); source.setUsername("sa"); source.setPassword(""); return source; } @Bean public HibernateTransactionManager transactionManager() { HibernateTransactionManager hibernateTransactionManager = new HibernateTransactionManager(); hibernateTransactionManager.setSessionFactory(sessionFactory().getObject()); return hibernateTransactionManager; } private Properties hProps() { Properties p = new Properties(); p.put("hibernate.dialect", "org.hibernate.dialect.HSQLDialect"); p.put("hibernate.cache.use_second_level_cache", "true"); p.put("hibernate.cache.use_query_cache", "true"); p.put("hibernate.cache.provider_class", "org.hibernate.cache.EhCacheProvider"); p.put("hibernate.cache.provider_configuration_file_resource_path", "ehcache.xml"); p.put("hibernate.show_sql", "true"); p.put("hibernate.hbm2ddl.auto", "update"); p.put("hibernate.generate_statistics", "true"); p.put("hibernate.cache.use_structured_entries", "true"); return p; } }
DataConfig定义了所有与数据库和hibernate相关的bean,通过@EnableTransactionManagement实现声明性事务。
service是如何注册的呢?
@Configuration @ComponentScan(basePackages="septem.service") public class AppConfig { }
通过@ComponentScan扫描包septem.service里定义的所有service,一个简单service实现如下:
@Service @Transactional public class GreetingService { @Autowired private SessionFactory sessionFactory; @Transactional(readOnly=true) public String greeting() { return "spring without xml works!"; } @Transactional(readOnly=true) public Book getBook(Long id) { return (Book) getSession().get(Book.class, id); } @Transactional(readOnly=true) public Author getAuthor(Long id){ return (Author) getSession().get(Author.class, id); } public Book newBook() { Book book = new Book(); book.setTitle("java"); getSession().save(book); return book; } public Author newAuthor() { Book book = newBook(); Author author = new Author(); author.setName("septem"); author.addBook(book); getSession().save(author); return author; } private Session getSession() { return sessionFactory.getCurrentSession(); } }
这样整个项目中就没有XML文件了。在写这些代码的过程中也碰到不少问题,纪录如下:
(一)项目没有web.xml,maven的war插件要加上failOnMissingWebXml=false
<plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-war-plugin</artifactId> <version>2.1.1</version> <configuration> <failOnMissingWebXml>false</failOnMissingWebXml> </configuration> </plugin>
(二) tomcat-embeded7.0.16还有点小BUG,不能把DispatcherServlet映射为"/",所以代码里把它映射为"/s3/"
appServlet.addMapping("/s3/");
(三) 如果要使用spring提供的OpenSessionInViewFilter,在定义Hibernate SessionFactory的时候,不能直接new SessionFactory出来,即以下代码是不能实现声明性事务的:
@Bean public SessionFactory sessionFactory() { org.hibernate.cfg.Configuration config = new org.hibernate.cfg.Configuration(); config.setProperties(hProps()); config.addAnnotatedClass(Book.class); return config.buildSessionFactory(); }
必须使用spring提供的FactoryBean:
@Bean public AnnotationSessionFactoryBean sessionFactory() { AnnotationSessionFactoryBean sessionFactoryBean = new AnnotationSessionFactoryBean(); sessionFactoryBean.setDataSource(dataSource()); sessionFactoryBean.setNamingStrategy(new ImprovedNamingStrategy()); sessionFactoryBean.setPackagesToScan("septem.model"); sessionFactoryBean.setHibernateProperties(hProps()); return sessionFactoryBean; }
后记:在spring3.1以servlet3中annotation已经是一等公民了,可以实现任何原先只能在xml文件中配置的功能,并具有简洁,静态检查及重构友好等优点。总体上来讲spring提供的“魔法”还是太多了,尤其是跟hibernate,事务,open session in view等机制结合在一起的时候,简洁代码的背后隐藏着太多的依赖关系,如果程序出了问题,排除这些魔法,一层一层地还原程序的本来面目,将是一件很需要耐心的事情