spring学习笔记（25）——spring基本思路

野性酷女 2022-08-08 09:17 108阅读 0赞

# spring基本思路 #

spring在web应用中的配置与使用的基本思路：

*  需要加入额外的jar包  
    
    
     *  spring-web-4.0.0.RELEASE.jar
     *  spring-webmvc-4.0.0.RELEASE.jar
 *  配置文件和在java应用中一样配置
 *  如何创建IOC容器
    
     *  在非WEB应用中，使用ApplicationContext接口直接创建
     *  在WEB应用中，应该在应用启动时就创建
 *  WEB应用中其他组件（如Servlet）如何访问IOC容器  
    
    
     *  创建IOC容器后，将其放到ServletContext域中

# 模拟测试 #

现在我们根据上面所说的思路，建一个WEB应用

*  先写一个实体类

package com.spring.beans;
    
    public class Person { 
        private String name;
        public void setName(String name) {
            this.name = name;
        }
        @Override
        public String toString() {
            return "Person [name=" + name + "]";
        }
    
    }

*  配置文件中配置该Bean

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    
        <bean id="person" class="com.spring.beans.Person">
            <property name="name" value="tom"></property>
        </bean>
    </beans>

*  如何创建IOC容器？使用ServletContextListener 接口

package com.spring.listener;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletContextEvent;
    import javax.servlet.ServletContextListener;
    import javax.servlet.annotation.WebListener;
    
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    import com.spring.beans.Person;
    
    /** * Application Lifecycle Listener implementation class SpringServletContextListener * */
    @WebListener
    public class SpringServletContextListener implements ServletContextListener { 
    
        /** * Default constructor. */
        public SpringServletContextListener() {
            // TODO Auto-generated constructor stub
        }
    
        /** * @see ServletContextListener#contextInitialized(ServletContextEvent) */
        public void contextInitialized(ServletContextEvent arg0) {
            //得到在web.xml中配置的spring配置文件的位置
    // <context-param>
    // <param-name>configLocation</param-name>
    // <param-value>classpath:applicationContext.xml</param-value>
    // </context-param>
            ServletContext servletContext = arg0.getServletContext();
            String config = servletContext.getInitParameter("configLocation");
            //初始化IOC容器
            ApplicationContext ctx = new ClassPathXmlApplicationContext(config);
            //将IOC容器放到ApplicationContext域中,因此在servlet中就能使用IOC容器
            servletContext.setAttribute("ApplicationContext", ctx);
        }
    
        /** * @see ServletContextListener#contextDestroyed(ServletContextEvent) */
        public void contextDestroyed(ServletContextEvent arg0) {
            // TODO Auto-generated method stub
        }
    
    }

*  如何让这个Listener起作用？在web.xml中注册

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
      <display-name>spring4</display-name>
      
      <context-param>
        <param-name>configLocation</param-name>
        <param-value>classpath:applicationContext.xml</param-value>
      </context-param>
      
      <listener>
        <listener-class>com.spring.listener.SpringServletContextListener</listener-class>
      </listener>
    
    </web-app>

*  准备工作做好了。现在写个Servlet看看能不能成功地使用IOC容器

package com.spring.servlet;
    
    import java.io.IOException;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    import org.springframework.context.ApplicationContext;
    
    import com.spring.beans.Person;
    
    /** * Servlet implementation class TestServlet */
    @WebServlet("/TestServlet")
    public class TestServlet extends HttpServlet { 
        private static final long serialVersionUID = 1L;
    
        /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            //从域中得到ApplicationContext（IOC容器）
            ServletContext servletContext = getServletContext();
            ApplicationContext ctx = (ApplicationContext) servletContext.getAttribute("ApplicationContext");
            Person person = (Person) ctx.getBean("person");
            System.out.println(person);
        }
    
    }

> 访问这个Servlet，确实可以成功地得到IOC容器并使用

# spring自带的Listener #

上面其中一个步骤是使用ServletContextListener 接口创建IOC容器，其实spring已经帮我们实现这个接口，并创建IOC容器，我们可以直接使用。

<context-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:applicationContext.xml</param-value>
        </context-param>
    
        
        <listener>
            <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
        </listener>

*  在这种情况下，我们就不用自己去写`SpringServletContextListener implements ServletContextListener`
 *  如果要在servlet中使用IOC容器，使用`WebApplicationContextUtils`

package com.spring.servlet;
    
    import java.io.IOException;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    import org.springframework.context.ApplicationContext;
    import org.springframework.web.context.support.WebApplicationContextUtils;
    
    import com.spring.beans.Person;
    
    /** * Servlet implementation class TestServlet */
    @WebServlet("/TestServlet")
    public class TestServlet extends HttpServlet { 
        private static final long serialVersionUID = 1L;
    
        /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            ServletContext servletContext = getServletContext();
            ApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(servletContext);
            //ApplicationContext ctx = (ApplicationContext) servletContext.getAttribute("ApplicationContext");
            Person person = (Person) ctx.getBean("person");
            System.out.println(person);
        }
    
    }

# 总结：在web项目中使用spring #

*  在web.xml中配置Listener
 *  配置spring配置文件
 *  如果需要获取IOC容器，可以用`WebApplicationContextUtils`，不过一般情况下我们是不需要获取IOC容器的