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
*/
@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 {
@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，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。