[刘阳Java]_Spring整合Servlet补充_第14讲

Posted 2020-09-11 刘阳Java

这篇内容我们给大家介绍一下Spring框架如何整合Servlet。光看表面现象这个问题感觉没有什么太大难度，但是实际在整合过程中不是那么轻松

既然是以补充的方式来介绍，那么我们就直接上一个案例来说明整合实现的步骤

1. 案例要求

• 通过Spring框架注解方式来打通控制层，业务逻辑层，数据访问层之间的依赖关系
• 控制层采用Servlet来完成对用户请求与相应的处理
• 然后在Servlet中通过@Autowired方式来依赖注入业务逻辑层
• 业务逻辑层也是通过@Autowired方式来依赖注入数据访问层
• 数据访问层采用Spring对JDBC支持方式来获取数据，编辑数据等操作

2. 技术难点

• 如何让Servlet被Spring框架管理
• 如何让Tomcat服务器加载Spring框架（即：如何加载Spring的配置文件）
• 一旦Servlet被Spring框架管理，但是@Autowired注解是不能自动依赖注入业务逻辑层中的对象，这个该如何解决

3. Tomcat服务器加载Spring配置文件的实现步骤

• 导入spring-web.jar包
• 在web.xml文件中添加<listener.../>监听标签
• 利用Spring框架的ContextLoaderListener来加载Spring的配置文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>spring</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <context-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:com/gxa/spring/day02/spring-controller.xml</param-value>
  </context-param>
  
  <listener>
      <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
</web-app>

4. 在Spring配置文件中使用<context:componet-scan .../>来扫描注解类

<?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:p="http://www.springframework.org/schema/p"
    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="com.gxa.spring.day02"></context:component-scan>
        
</beans> 

 5. 创建UserServlet，通过覆盖HttpServlet中init方法来测试UserServlet是否被Spring框架所管理。因为@Autowired在Servlet中会失效，所以我们需要加入Spring框架中AutowireCapableBeanFactory来让@Autowired起作用。这一步非常重要

package com.gxa.spring.day02;

import java.io.IOException;

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.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
import org.springframework.stereotype.Controller;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

@Controller
@WebServlet("/user.do")
public class UserServlet extends HttpServlet {
    
    /**
     * Servlet和Spring框架整合时候, Servlet本身是不能自动依赖注入
     * 解决方案：
     * 1. Spring框架提供的接口, AutowireCapableBeanFactory
     * 2. 就可以完成Servlet中依赖对象的自动装配
     */
    @Autowired
    private UserService userService;
    
    @Override
    public void init() throws ServletException {
        /**
         * 利用init方法来调用Spring容器BeanFactory
         * 看看UserServlet是否能够通过Spring容器获取对象
         */
        WebApplicationContext wc = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext()); //通过Web容器去得到BeanFactory对象
        AutowireCapableBeanFactory autowireCapableBeanFactory = wc.getAutowireCapableBeanFactory();
        autowireCapableBeanFactory.autowireBean(this);
    }
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
    }
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        userService.getUser();
    }
}

6. 创建业务逻辑层接口和实现类

• 注意：由于这篇文章是对Spring整合Servlet的一个补充，我就没有进行MVC的分包。所以后面创建的业务层代码和Dao层都和Controller在同一个包里面
• 业务逻辑层实现类中要定义好注解的bean id名称，这样子Servlet通过@Autowired才能找到依赖的bean。不然会出现NoSuchDefinitionException

package com.gxa.spring.day02;

public interface UserService {
    public void getUser();
}

package com.gxa.spring.day02;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service("userService")
public class UserServiceImpl implements UserService {
    
    @Autowired
    private UserDao userDao;

    @Override
    public void getUser() {
        userDao.getUser();
    }

}

7. 创建Dao层接口和它的实现类。因为想Dao层能够获取到数据库中数据，所以这里用了JdbcTemplate来搞定数据查询

 

<?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:p="http://www.springframework.org/schema/p"
    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="com.gxa.spring.day02"></context:component-scan>
    <context:property-placeholder location="classpath:com/gxa/spring/day02/jdbc.properties"/>
    
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
        <property name="driverClassName" value="${mysql.driver}"></property>
        <property name="url" value="${mysql.url}"></property>
        <property name="username" value="${mysql.username}"></property>
        <property name="password" value="${mysql.password}"></property>
    </bean>
    
    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"></property>
    </bean>
        
</beans> 

package com.gxa.spring.day02;

public interface UserDao {
    public void getUser();
}

package com.gxa.spring.day02;

import java.util.List;
import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Repository;

@Repository("userDao")
public class UserDaoImpl implements UserDao {
    
    @Autowired
    private JdbcTemplate jdbcTemplate;

    @Override
    public void getUser() {
        String sql = "select * from student";
        List<Map<String,Object>> list = jdbcTemplate.queryForList(sql);
        System.out.println(list);
    }

}