spring boot(1)--基础(servlet3+springMVC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，本文的目标是消除这些xml文件，使用代码和注解替代。由于本文是基于servlet3，所以首先采用的servlet3的容器，例如tomcat7以上版本、jetty8及以上版本。

消除web.xml

下面是一个典型的web.xml,包涵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>

下一步去除web.xml文件，使用java代码替代下。
Spring MVC提供了一个接口WebApplicationInitializer，用于替代web.xml文件。实现这个借口的类会在Servlet容器启动的时候自动加载并运行。
将以上代码替换为Java代码:

public class MyWebInitializer implements WebApplicationInitializer {

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

    //初始化参数
    servletContext.setInitParameter("contextConfigLocation","classpath:applicationContext" +
                                    ".xml");

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

    //添加监听
    servletContext.addListener(new ContextLoaderListener());
  }
}

此时便可以删除web.xml。

去除spring mvc的配置文件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:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    <mvc:annotation-driven/>

    <context:component-scan base-package="org.wuqinghua.web"/>

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

Spring提供了@Configuration注解替代xml配置文件，@Bean注解可以替代xml中的来创建bean。将以上xml配置文件转换为Java代码。

@Configuration
@EnableWebMvc  //开启支持mvc
@ComponentScan(basePackages = "org.wuqinghua.web")
public class SpringMVCConfig {

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

去除spring配置文件applicationContext.xml

spring配置文件中的配置比较多，根据不同的项目还有不同的配置，一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:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       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="org.wuqinghua">
    <context:exclude-filter type="annotation"
                            expression="org.springframework.stereotype.Controller"></context:exclude-filter>
  </context:component-scan>

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

  <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="${jdbc.driver}"/>
    <property name="url" value="${jdbc.url}"/>
    <property name="username" value="${jdbc.username}"/>
    <property name="password" value="${jdbc.password}"/>
  </bean>
</beans>

其中的配置文件dataSource.properties文件

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1:3306/taotao?useUnicode=true&characterEncoding=utf-8
jdbc.username=root
jdbc.password=root

将以上代码转换为java代码为

@Configuration
@ComponentScan(basePackages = "org.wuqinghua", excludeFilters = {@ComponentScan.Filter(value =
        Controller.class)})
public class SpringConfig {

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

    @Bean
    public DataSource dataSource() {
        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName(driver);
        dataSource.setUrl(url);
        dataSource.setUsername(username);
        dataSource.setPassword(password);
        return dataSource;
    }

    /**
     * 必须添加static
     *
     * @return
     */
    @Bean
    public static PropertyPlaceholderConfigurer loadProperties() {
        PropertyPlaceholderConfigurer placeholderConfigurer = new PropertyPlaceholderConfigurer();
        ClassPathResource resource = new ClassPathResource("dataSource.properties");
        placeholderConfigurer.setLocation(resource);
        return placeholderConfigurer;
    }
}

修改MyWebAppInitializer.java

public class MyWebInitializer implements WebApplicationInitializer {

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

        AnnotationConfigWebApplicationContext rootContext = new AnnotationConfigWebApplicationContext();
        rootContext.register(SpringConfig.class);

        servletContext.addListener(new ContextLoaderListener(rootContext));

        AnnotationConfigWebApplicationContext webContext = new
                AnnotationConfigWebApplicationContext();
        webContext.register(SpringMVCConfig.class);

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

    }
}