Spring与Web环境集成

1.Spring与Web环境集成

1.1自定义监听器将Spring集成到web环境

1_需求:将spring集成到web开发环境中,将所有的bean对象创建交给spring,除了servlet,servlet可以理解为一个测试类.在servlet中获取ApplicationContext,获取对应的bean

环境搭建,这个是自己一步步取实现的,其实spring有提供简单的方法完成1.1的操作

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

//1.创建dao层接口和实现类
//dao接口 IUserDao
public interface IUserDao{
    void save();
}
//UserDaoImpl实现类
public class UserDaoImpl implements IUserDao{
    @Override
    public void save(){
        System.out.printLn("正在保存...");
    }
}

//2.创建service业务层接口和实现类
public interface IUserService{
    void save();
}
//UserServletImpl实现类
public class UserServiceImpl implements IUserService{
    private IUserDao userDao;
    //为依赖注入提供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交给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包下创建UserServlet类 内部功能:调Spring容器,创建service对象,调sava()方法*/
public class UserServlet extends HttpServlet{
    @Override//复写doGet方法
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{
        //通过配置文件获取上下文
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        //获取bean,因为只有一个UserServiceImpl,可以使用字节码的方法获取
        UserServiceImpl userService = context.getBean(UserServiceImpl.class);
        //调用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,启动测试
http://localhost:80/userServlet

2_问题描述:
spring在web开发环境下,每个servlet都需要new ClassPathXmlApplicationContext("applicationContext.xml")
因为配置文件会加载多次,所以会造成性能浪费

3_改进一:
将ApplicationContext对象的创建交给监听器创建,监听器将创建好的对象存入ServletContext域对象中,在servlet中直接获取该对象.

• 编写监听器代码

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) {
        //获取上下文
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        //将spring获取到的应用上下文,保存到servletContext域中
        ServletContext servletContext = servletContextEvent.getServletContext();
        servletContext.setAttribute("context",context);
        //之后去web.xml配置listener监听器和改写servlet代码
    }

• 监听器配置

web.xml
<!--配置servlet-->

<!--配置自己实现的监听器-->
  <listener>
    <listener-class>cn.ppvir.listener.ContextLoaderListener</listener-class>
  </listener>

• servlet代码改写

public class UserServlet extends HttpServlet {
    /**
     * 改进一:
     * 将ApplicationContext对象的创建交给监听器创建,监听器将创建好的对象存入ServletContext域对象中,在servlet中直接取该对象即可
     *
     * @param req
     * @param resp
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取servletContext域对象
        ServletContext servletContext = this.getServletContext();
        //从ServletContext域对象中,获取监听器创建的应用上下文,强转为ApplicationContext
        ApplicationContext context = (ApplicationContext) servletContext.getAttribute("context");
        UserServiceImpl userService = context.getBean(UserServiceImpl.class);
        userService.save();
    }
}

重启tomcat完成测试.

4.优化二:

• 1_在web.xml文件中配置要加载的applicationContext.xml文件

web.xml
<!--改进二: 之前的基础上添加配置-->
  <!--全局初始化参数-->
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext.xml</param-value>
  </context-param>

• 2.改写ContextLoaderListener监听器类,获取全局初始化参数

public class ContextLoaderListener implements ServletContextListener {
    /**
     * 优化二: 获取全局初始化参数
     *
     * @param servletContextEvent
     */
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        //获取域对象
        ServletContext servletContext = servletContextEvent.getServletContext();
        //从配置文件中获取applicationContext
        /*
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:applicationContext.xml</param-value>
         */
        String contextConfigLocation = servletContext.getInitParameter("contextConfigLocation");
        //获取应用上下文
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(contextConfigLocation);
        //将Spring的应用上下文 存储到ServletContext域对象中
        servletContext.setAttribute("context",context);
        System.out.println("spring容器创建完毕...");
    }
}

• 3.优化强转ApplicationContext,使用工具类直接从servletContext域对象中获取applicationContext对象.

//创建工具类
package cn.ppvir.listener;
import org.springframework.context.ApplicationContext;
import javax.servlet.ServletContext;
/**
 * 工具类,强转context上下文为ApplicationContext
 */
public class WebApplicationContextUtils {
    /**
     * @param servletContext 参数是域对象
     * @return  返回值是强转后的对象ApplicationContext
     */
    public static ApplicationContext getWebapplicationContext(ServletContext servletContext){
        return (ApplicationContext)servletContext.getAttribute("context");
    }
}

• 4.修改UserServlet类使用WebApplicationContextUtils优化强转context

public class ContextLoaderListener implements ServletContextListener {
     /**
     * 优化二: 使用WebApplicationContextUtils工具类,简化强转上下文对象的操作
     * @param req
     * @param resp
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       //获取域对象
        ServletContext servletContext = this.getServletContext();
        ApplicationContext context = WebApplicationContextUtils.getWebapplicationContext(servletContext);
        UserServiceImpl userService = context.getBean(UserServiceImpl.class);
        userService.save();
    }
}

重启tomcat完成测试

1.2使用spring提供的监听器将spring集成到web环境

UserDao和UserService层与上面一样

• 导入依赖

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

• 配置Spring提供的监听器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">
  <!--全局参数-->
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext.xml</param-value>
  </context-param>
  <!--监听器-->
  <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配置让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中通过工具获得应用上下文对象

public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取servletContext域对象
        ServletContext servletContext = this.getServletContext();
        //使用spring框架自带的WebApplicationContextUtils工具,获取上下文对象
        WebApplicationContext context = WebApplicationContextUtils.getWebApplicationContext(servletContext);
        UserServiceImpl userService = context.getBean(UserServiceImpl.class);
        userService.save();
    }
}

1.3小结:

1.web环境中集成spring只需要配置监听器即可
2.Spring负责管理处=除了controller以外的所有bean对象

来源：https://www.cnblogs.com/ppvir/p/11403064.html