Servlet 3 + Spring MVC零配置：去除所有xml

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>

下一步是去除web.xml文件，用Java代码代替它。

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 */@Overridepublic 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());}}

此时便可删除web.xml。

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<bean>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 {@Beanpublic 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.Driverjdbc.url=jdbc:mysql://localhost:3306/mydbjdbc.username=rootjdbc.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，Java代码也可以这样写：

@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编码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。