SSM学习day04_MVC_Spring集成web环境

目录

• 一、 Spring与Web环境集成
  • 搭建环境
  • 1.1 ApplicationContext应用上下文获取方式
  • 优化##

一、 Spring与Web环境集成

搭建环境

1. 新建maven的Module，勾选Create from archetype，找到maven-archetype-webapp，勾选上并创建
2. main下新建java和resources文件夹
3. pom.xml中添加依赖文件，除了之前都有的，还要新加jakarta.servlet.jsp-api和jakarta.servlet-api
4. 新建dao、service、web层，前两层与之前一样，web层中创建UserServlet
5. web.xml中配置servlet
6. 配置Tomcat，选中此项目，运行

pom.xml

    <dependency>
      <groupId>jakarta.servlet.jsp</groupId>
      <artifactId>jakarta.servlet.jsp-api</artifactId>
      <version>3.0.0</version>
    </dependency>
    <dependency>
      <groupId>jakarta.servlet</groupId>
      <artifactId>jakarta.servlet-api</artifactId>
      <version>5.0.0</version>
    </dependency>

web.xml

  <servlet>
    <servlet-name>UserServlet</servlet-name>
    <servlet-class>com.hf.web.UserServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>UserServlet</servlet-name>
    <url-pattern>/userServlet</url-pattern>
  </servlet-mapping>

UserServlet.java

public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml");
        UserService userService = app.getBean(UserService.class);
        userService.save();
    }
}

1.1 ApplicationContext应用上下文获取方式

采用new ClasspathXmlApplicationContext方式获取Spring配置文件会导致每次从容器获得Bean都要编写这一句，配置文件被加载很多次且应用上下文对象被创建很多次。

在Web项目中，可以用ServletContextListener监听Web应用启动，在Web对象启动时就加载Spring的配置文件，创建应用上下文对象ApplicationContext，将其存储到最大的域servletContext中，这样就可以在任意位置从域中获取ApplicationContext对象。

创建监听器类Listener.ContextLoaderListener

public class ContextLoaderListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {

        ApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml");

        //将Spring的应用上下文对象存储到ServiceContext域中
        ServletContext servletContext = sce.getServletContext();
        servletContext.setAttribute("app",app);
        System.out.println("Spring容器创建完毕");

    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {

    }
}

修改UserServlet.java

        //ApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml");
        ServletContext servletContext = req.getServletContext();
        ApplicationContext app = (ApplicationContext) servletContext.getAttribute("app");
        UserService userService = app.getBean(UserService.class);
        userService.save();

优化##

1. 对于读取配置文件进行解耦合，将这一步写到web.xml文件中，利用全局初始化参数
   web.xml

<!--  全局初始化参数-->
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>applicationContext.xml</param-value>
  </context-param>

修改ContextLoaderListener.java中的初始化函数

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        ServletContext servletContext = sce.getServletContext();
        //读取web.xml中的全局参数

        String contextConfigLocation = servletContext.getInitParameter("contextConfigLocation");

        ApplicationContext app = new ClassPathXmlApplicationContext(contextConfigLocation);

        //将Spring的应用上下文对象存储到ServiceContext域中
        servletContext.setAttribute("app",app);
        System.out.println("Spring容器创建完毕");

    }

2. 工具类通过名称获取上下文，改为通过工具类
   创建工具类WebApplicationContextUtils.java

public class WebApplicationContextUtils {

    public static ApplicationContext getWebApplicationContext(ServletContext servletContext){
        return (ApplicationContext) servletContext.getAttribute("app");
    }
}

修改UserServlet.java

//ApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml");

        ServletContext servletContext = req.getServletContext();
        //ApplicationContext app = (ApplicationContext) servletContext.getAttribute("app");
        ApplicationContext app = WebApplicationContextUtils.getWebApplicationContext(servletContext);
        UserService userService = app.getBean(UserService.class);
        userService.save();