SpringBoot-基础(servlet3+springMVC去除所有的xml)

- 日理万妓 2021-06-22 15:36 298阅读 0赞

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("/");
        }
    }