Servlet3 + SpringMVC零配置：去除所有的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>

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());
	}
}

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>

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;
	}
}

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>

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

@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;
    }
}

@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;
    }
}

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("/");
    }
}