Day22SSM之Spring web模块(了解)

SpringAutowired与Qualifier

  • (1)@Autowired:Spring会自动创建实现类对象,并且将实现类对象赋值给dao
    如果项目中有该接口只有一个实现类,可以使用Autowired
    但是,接口有两个或者两个以上的实现类,此时抛异常
    如:PersonDaoImpl StudentDaoImp
  • (2)@Qualifier:可以手动指定将哪一个实现类的对象赋值给IPersonDao接口
  • (3)两个必须合在一起使用
public class A{
     
@Autowired
@Qualifier("id值")  默认类名首字母小写
 private B b;
}
@Repository
public class PersonDaoImpl implements IPersonDao {
     
    public boolean findByUserNameAndPassword(Person person) {
     
        return true;
    }
}

@Repository
public class StudentDaoImpl implements IPersonDao {
     
    public boolean findByUserNameAndPassword(Person person) {
     
        return true;
    }
}

因为接口有两个实现类

//类跟接口是实现关系
@Service
public class PersonServiceImpl implements IPersonService {
     

    //private IPersonDao dao = new PersonDaoImpl();
    @Autowired
    @Qualifier("personDaoImpl")
    private IPersonDao dao;

Spring和web结合-代码实现

  • (1)复制一个模块
  • (2)依赖配置
  • (3)编写LoginServlet
 
    <dependency>
        <groupId>jstlgroupId>
        <artifactId>jstlartifactId>
        <version>1.2version>
        <scope>providedscope>
    dependency>

        <dependency>
            <groupId>javax.servletgroupId>
            <artifactId>javax.servlet-apiartifactId>
            <version>3.1.0version>
            <scope>providedscope>
        dependency>
        <dependency>
            <groupId>javax.servlet.jspgroupId>
            <artifactId>javax.servlet.jsp-apiartifactId>
            <version>2.2.1version>
            <scope>providedscope>
        dependency>

LoginServlet

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
     
    private static final Logger logger = LoggerFactory.getLogger(LoginServlet.class);
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
     
            doGet(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
     
        //获取账号密码
        String username=request.getParameter("username");
        String password=request.getParameter("password");
        logger.debug(username);
        logger.debug(password);
        //调用登录方法
        ClassPathXmlApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");
        IPersonService personService = (IPersonService) context.getBean("personServiceImpl");
        Person person = new Person(username,password);

        boolean flag = personService.login(person);
        logger.debug(flag+" doGet ");
        //结果
        response.getWriter().println(flag?"success":"error");
    }
}

Spring和web结合-代码优化1

PersonServiceImpl service = (PersonServiceImpl) context.getBean(“PersonServiceImpl”));

  • (1)代码中有没有使用接口?
  • (2)代码中写死配置信息? 如:实现类
    》info.properties
    》Properties
    》getProperty(key)
   //从配置文件中取数据 .properties  Properties
        Properties p = new Properties();
        InputStream is = LoginServlet.class.getClassLoader().getResourceAsStream("info.properties");
        p.load(is);
        //调用登录方法

        ClassPathXmlApplicationContext context=new ClassPathXmlApplicationContext(p.getProperty("config"));
        IPersonService personService = (IPersonService) context.getBean(p.getProperty("serviceId"));

Spring和web结合-代码优化2

  • (1)doGet或者doPost什么时候执行?引起什么问题?
  • (2)一个程序只有一个实例
    》单例模式
    》ServletContext有什么用?
    支持多个Servlet共享数据且整个项目只有一个实例

ContextLoaderListener介绍

  • (1)ContextLoaderListener是什么?
    》Spring编写了一个监听器,该监听器监听ServletContext对象的创建
  • (2)ContextLoaderListener有什么用?
    会自动读取contextConfigLocation配置 ,并创建IOC容器
    将IOC容器保存在ServletContext中
  • (3)如何使用?
    》》依赖spring-web
    》》在web.xml中配置监听器
    Day22SSM之Spring web模块(了解)_第1张图片

pom.xml

 <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <version>5.2.9.RELEASE</version>
        </dependency>

web.xml

  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext.xml</param-value>
  </context-param>

  <listener>
    <!--
      监听ServletContext对象创建,然后将spring容器放到该ServletContext中缓存起来
    -->
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>

LoginServlet

  // ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(p.getProperty("config"));
        //1:从ServletContext域对象获取Spring容器
        WebApplicationContext context = (WebApplicationContext) getServletContext().getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);

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