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
- 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
- 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
- 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>
- 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>
- 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();
}
}
- 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();
}
}
- 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);
}
}
