在一些基于Spring/Spring MVC的Java Web项目中,总是会有一些xml配置文件,如web.xml、applicationContext.xml等,本文的目标即消灭这些xml配置文件,用代码和注解来代替。

由于本文是基于Servlet 3,所以首先需要准备支持Servlet 3的容器,例如Tomcat 7.0及以上版本、Jetty 8及以上版本。

1、去除web.xml

下面是一个典型的web.xml,包含Spring/Spring MVC的配置:

<?xml version="1.0" encoding="UTF-8"?>  
<web-app xmlns="http://java.sun.com/xml/ns/javaee"  
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
 version="3.0">

 <context-param>
 <param-name>contextConfigLocation</param-name>
 <param-value>classpath:applicationContext.xml</param-value>
 </context-param>
 <servlet>
 <servlet-name>dispatcher</servlet-name>
 <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
 <init-param>
 <param-name>contextConfigLocation</param-name>
 <param-value>classpath:dispatcher-servlet.xml</param-value>
 </init-param>
 <load-on-startup>1</load-on-startup>
 </servlet>
 <servlet-mapping>
 <servlet-name>dispatcher</servlet-name>
 <url-pattern>/</url-pattern>
 </servlet-mapping>
 <listener>
 <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
 </listener>

</web-app>  

Spring MVC提供了一个接口WebApplicationInitializer,用于替代web.xml配置文件。实现该接口的类会在Servlet容器启动时自动加载并运行。

将以上xml文件转换成Java代码:

public class MyWebAppInitializer implements WebApplicationInitializer {

 /**
 * Servlet容器启动时会自动运行该方法
 */
 @Override
 public void onStartup(ServletContext servletContext) throws ServletException {

 servletContext.setInitParameter("contextConfigLocation", "classpath:applicationContext.xml");

 ServletRegistration.Dynamic registration = servletContext.addServlet("dispatcher", new DispatcherServlet());
 registration.setLoadOnStartup(1);
 registration.addMapping("/");
 registration.setInitParameter("contextConfigLocation", "classpath:dispatcher-servlet.xml");

 servletContext.addListener(new ContextLoaderListener());
 }
}

此时即可删除web.xml文件,程序同样可以运行。

2、去除Spring MVC配置文件dispatcher-servlet.xml

一个典型的Spring MVC配置文件如下:

<?xml version="1.0" encoding="UTF-8"?>  
<beans xmlns="http://www.springframework.org/schema/beans"  
 xmlns:context="http://www.springframework.org/schema/context"
 xmlns:mvc="http://www.springframework.org/schema/mvc"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="
 http://www.springframework.org/schema/beans
 http://www.springframework.org/schema/beans/spring-beans.xsd
 http://www.springframework.org/schema/context
 http://www.springframework.org/schema/context/spring-context.xsd
 http://www.springframework.org/schema/mvc
 http://www.springframework.org/schema/mvc/spring-mvc.xsd">

 <mvc:annotation-driven />

 <context:component-scan base-package="com.xxg.controller" />

 <bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
 <property name="prefix" value="/WEB-INF/jsp/" />
 <property name="suffix" value=".jsp" />
 </bean>

</beans>  

Spring提供了@Configuration注解用于替代xml配置文件,@Bean注解可以替代xml中的来创建bean。

将以上xml配置文件转换成Java代码:

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.xxg.controller")
public class WebConfig {

 @Bean
 public InternalResourceViewResolver internalResourceViewResolver() {
 InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
 viewResolver.setPrefix("/WEB-INF/jsp/");
 viewResolver.setSuffix(".jsp");
 return viewResolver;
 }
}

3、去除Spring配置文件applicationContext.xml

Spring的配置文件中内容可能会比较多,并且不同的项目会有不同的配置,以下提供了一个简单的配置:

<?xml version="1.0" encoding="UTF-8"?>  
<beans xmlns="http://www.springframework.org/schema/beans"  
 xmlns:context="http://www.springframework.org/schema/context"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://www.springframework.org/schema/beans
 http://www.springframework.org/schema/beans/spring-beans.xsd
 http://www.springframework.org/schema/context
 http://www.springframework.org/schema/context/spring-context.xsd">

 <context:component-scan base-package="com.xxg">
 <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller" />
 </context:component-scan>

 <context:property-placeholder location="classpath:config.properties"/>

 <bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
 <property name="driverClassName" value="${jdbc.driverClassName}"/>
 <property name="url" value="${jdbc.url}"/>
 <property name="username" value="${jdbc.username}"/>
 <property name="password" value="${jdbc.password}"/>
 </bean>

</beans>  

其中数据库的相关配置从config.properties配置文件读取:

jdbc.driverClassName=com.mysql.jdbc.Driver  
jdbc.url=jdbc:mysql://localhost:3306/mydb  
jdbc.username=root  
jdbc.password=123456  

将以上xml配置转换成Java代码:

@Configuration
@ComponentScan(basePackages = "com.xxg", excludeFilters = {@Filter(value = Controller.class)})
public class AppConfig {

 @Value("${jdbc.driverClassName}")
 private String driverClassName;

 @Value("${jdbc.url}")
 private String url;

 @Value("${jdbc.username}")
 private String username;

 @Value("${jdbc.password}")
 private String password;

 @Bean(destroyMethod = "close")
 public DataSource dataSource() {
 BasicDataSource dataSource = new BasicDataSource();
 dataSource.setDriverClassName(driverClassName);
 dataSource.setUrl(url);
 dataSource.setUsername(username);
 dataSource.setPassword(password);
 return dataSource;
 }

 /**
 * 必须加上static
 */
 @Bean
 public static PropertyPlaceholderConfigurer loadProperties() {
 PropertyPlaceholderConfigurer configurer = new PropertyPlaceholderConfigurer();
 ClassPathResource resource = new ClassPathResource("config.properties");
 configurer.setLocations(resource);
 return configurer;
 }
}

除了上面的方法外,加载properties配置文件还可以使用@PropertySource注解:

@Configuration
@ComponentScan(basePackages = "com.xxg", excludeFilters = {@Filter(value = Controller.class)})
@PropertySource("classpath:config.properties")
public class AppConfig {

 @Value("${jdbc.driverClassName}")
 private String driverClassName;

 @Value("${jdbc.url}")
 private String url;

 @Value("${jdbc.username}")
 private String username;

 @Value("${jdbc.password}")
 private String password;

 @Bean(destroyMethod = "close")
 public DataSource dataSource() {
 BasicDataSource dataSource = new BasicDataSource();
 dataSource.setDriverClassName(driverClassName);
 dataSource.setUrl(url);
 dataSource.setUsername(username);
 dataSource.setPassword(password);
 return dataSource;
 }

 /**
 * 必须加上static
 */
 @Bean
 public static PropertySourcesPlaceholderConfigurer loadProperties() {
 PropertySourcesPlaceholderConfigurer configurer = new PropertySourcesPlaceholderConfigurer();
 return configurer;
 }
}

以上两种Java实现方式选择其中一种即可。

4、修改MyWebAppInitializer.java

完成以上步骤后,就可以去掉dispatcher-servlet.xml和applicationContext.xml等Spring配置文件,用Java代码替代了。

此时,第1步中的MyWebAppInitializer.java需要修改,不再读取xml配置文件,而是加载@Configuration注解的Java代码来配置Spring:

public class MyWebAppInitializer implements WebApplicationInitializer {

 /**
 * Servlet容器启动时会自动运行该方法
 */
 @Override
 public void onStartup(ServletContext servletContext) throws ServletException {

 AnnotationConfigWebApplicationContext rootContext = new AnnotationConfigWebApplicationContext();
 rootContext.register(AppConfig.class);
 servletContext.addListener(new ContextLoaderListener(rootContext));

 AnnotationConfigWebApplicationContext webContext = new AnnotationConfigWebApplicationContext();
 webContext.register(WebConfig.class);
 ServletRegistration.Dynamic registration = servletContext.addServlet("dispatcher", new DispatcherServlet(webContext));
 registration.setLoadOnStartup(1);
 registration.addMapping("/");
 }
}

至此,便完成了Java程序替换xml配置文件所有工序。

原文:http://xxgblog.com/2015/07/09/spring-zero-xml/