Spring與Web環境集成

1.Spring與Web環境集成

1.1自定義監聽器將Spring集成到web環境

1_需求:將spring集成到web開發環境中,將所有的bean對象創建交給spring,除了servlet,servlet可以理解為一個測試類.在servlet中獲取ApplicationContext,獲取對應的bean

環境搭建,這個是自己一步步取實現的,其實spring有提供簡單的方法完成1.1的操作

<!--在pom文件中引入所需的依賴-->
    <!--Spring坐標-->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>5.0.5.RELEASE</version>
    </dependency>
    <!--SpringMVC坐標-->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>5.0.5.RELEASE</version>
    </dependency>
    <!--Servlet坐標-->
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>servlet-api</artifactId>
      <version>2.5</version>
    </dependency>
    <!--Jsp坐標-->
    <dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>jsp-api</artifactId>
      <version>2.0</version>
    </dependency>

//1.創建dao層接口和實現類
//dao接口 IUserDao
public interface IUserDao{
    void save();
}
//UserDaoImpl實現類
public class UserDaoImpl implements IUserDao{
    @Override
    public void save(){
        System.out.printLn("正在保存...");
    }
}

//2.創建service業務層接口和實現類
public interface IUserService{
    void save();
}
//UserServletImpl實現類
public class UserServiceImpl implements IUserService{
    private IUserDao userDao;
    //為依賴注入提供set方法
    public void setUserDao(IUserDao userDao){this userDao=userDao;}
    @Override
    public void save(){
        userDao.save();
    }
}

<!--applicationContext.xml文件中配置Dao,service交給spring管理-->
<?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">
    <!--配置Dao-->
    <bean class="cn.ppvir.dao.impl.UserDaoImpl" id="userDao"></bean>

    <!--配置service-->
    <bean class="cn.ppvir.service.impl.UserServiceImpl" id="userService">
        <property name="userDao" ref="userDao"></property>
    </bean>
    
</beans>    

/*web包下創建UserServlet類 內部功能:調Spring容器,創建service對象,調sava()方法*/
public class UserServlet extends HttpServlet{
    @Override//復寫doGet方法
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{
        //通過配置文件獲取上下文
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        //獲取bean,因為只有一個UserServiceImpl,可以使用字節碼的方法獲取
        UserServiceImpl userService = context.getBean(UserServiceImpl.class);
        //調用save方法
        userService.save();
    }
}

<!--在web.xml中配置 servlet-->
<servlet>
    <servlet-name>userServlet</servlet-name>
    <servlet-class>cn.ppvir.web.UserServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>userServlet</servlet-name>
    <url-pattern>/userServlet</url-pattern>
</servlet-mapping>

最后配置tomcat,啟動測試
http://localhost:80/userServlet

2_問題描述:
spring在web開發環境下,每個servlet都需要new ClassPathXmlApplicationContext("applicationContext.xml")
因為配置文件會加載多次,所以會造成性能浪費

3_改進一:
將ApplicationContext對象的創建交給監聽器創建,監聽器將創建好的對象存入ServletContext域對象中,在servlet中直接獲取該對象.

• 編寫監聽器代碼

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class ContextLoaderListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        //獲取上下文
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        //將spring獲取到的應用上下文,保存到servletContext域中
        ServletContext servletContext = servletContextEvent.getServletContext();
        servletContext.setAttribute("context",context);
        //之后去web.xml配置listener監聽器和改寫servlet代碼
    }

• 監聽器配置

web.xml
<!--配置servlet-->

<!--配置自己實現的監聽器-->
  <listener>
    <listener-class>cn.ppvir.listener.ContextLoaderListener</listener-class>
  </listener>

• servlet代碼改寫

public class UserServlet extends HttpServlet {
    /**
     * 改進一:
     * 將ApplicationContext對象的創建交給監聽器創建,監聽器將創建好的對象存入ServletContext域對象中,在servlet中直接取該對象即可
     *
     * @param req
     * @param resp
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //獲取servletContext域對象
        ServletContext servletContext = this.getServletContext();
        //從ServletContext域對象中,獲取監聽器創建的應用上下文,強轉為ApplicationContext
        ApplicationContext context = (ApplicationContext) servletContext.getAttribute("context");
        UserServiceImpl userService = context.getBean(UserServiceImpl.class);
        userService.save();
    }
}

重啟tomcat完成測試.

4.優化二:

• 1_在web.xml文件中配置要加載的applicationContext.xml文件

web.xml
<!--改進二: 之前的基礎上添加配置-->
  <!--全局初始化參數-->
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext.xml</param-value>
  </context-param>

• 2.改寫ContextLoaderListener監聽器類,獲取全局初始化參數

public class ContextLoaderListener implements ServletContextListener {
    /**
     * 優化二: 獲取全局初始化參數
     *
     * @param servletContextEvent
     */
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        //獲取域對象
        ServletContext servletContext = servletContextEvent.getServletContext();
        //從配置文件中獲取applicationContext
        /*
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:applicationContext.xml</param-value>
         */
        String contextConfigLocation = servletContext.getInitParameter("contextConfigLocation");
        //獲取應用上下文
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(contextConfigLocation);
        //將Spring的應用上下文 存儲到ServletContext域對象中
        servletContext.setAttribute("context",context);
        System.out.println("spring容器創建完畢...");
    }
}

• 3.優化強轉ApplicationContext,使用工具類直接從servletContext域對象中獲取applicationContext對象.

//創建工具類
package cn.ppvir.listener;
import org.springframework.context.ApplicationContext;
import javax.servlet.ServletContext;
/**
 * 工具類,強轉context上下文為ApplicationContext
 */
public class WebApplicationContextUtils {
    /**
     * @param servletContext 參數是域對象
     * @return  返回值是強轉后的對象ApplicationContext
     */
    public static ApplicationContext getWebapplicationContext(ServletContext servletContext){
        return (ApplicationContext)servletContext.getAttribute("context");
    }
}

• 4.修改UserServlet類使用WebApplicationContextUtils優化強轉context

public class ContextLoaderListener implements ServletContextListener {
     /**
     * 優化二: 使用WebApplicationContextUtils工具類,簡化強轉上下文對象的操作
     * @param req
     * @param resp
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       //獲取域對象
        ServletContext servletContext = this.getServletContext();
        ApplicationContext context = WebApplicationContextUtils.getWebapplicationContext(servletContext);
        UserServiceImpl userService = context.getBean(UserServiceImpl.class);
        userService.save();
    }
}

重啟tomcat完成測試

1.2使用spring提供的監聽器將spring集成到web環境

UserDao和UserService層與上面一樣

• 導入依賴

pom.xml
 <!--spring-web坐標-->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>5.0.5.RELEASE</version>
    </dependency>

• 配置Spring提供的監聽器ContextLoaderListener

web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" 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">
  <!--全局參數-->
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext.xml</param-value>
  </context-param>
  <!--監聽器-->
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  <!--配置servlet-->
  <servlet>
    <servlet-name>service</servlet-name>
    <servlet-class>web.UserServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>service</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

• applicationContext.xml配置讓spring管理注入

applicationContext.xml
<bean class="dao.impl.UserDaoImpl" id="userDao"></bean>

    <bean class="service.impl.UserServiceImpl" id="userService">
        <property name="userDao" ref="userDao"></property>
    </bean>

• servlet中通過工具獲得應用上下文對象

public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //獲取servletContext域對象
        ServletContext servletContext = this.getServletContext();
        //使用spring框架自帶的WebApplicationContextUtils工具,獲取上下文對象
        WebApplicationContext context = WebApplicationContextUtils.getWebApplicationContext(servletContext);
        UserServiceImpl userService = context.getBean(UserServiceImpl.class);
        userService.save();
    }
}

1.3小結:

1.web環境中集成spring只需要配置監聽器即可
2.Spring負責管理處=除了controller以外的所有bean對象