SpringMVC学习笔记

Posted 2021-05-30 芜湖男酮

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SpringMVC学习笔记

资源

官方文档：Web on Servlet Stack (spring.io)

中文文档：Spring Framework 4.3.21.RELEASE 中文文档 - 22. Web MVC 框架 | Docs4dev

SpringMVC工作流程（重点）

HelloSpringMVC

文件结构

pom.xml

<dependencies>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>servlet-api</artifactId>
        <version>2.5</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.13</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet.jsp</groupId>
        <artifactId>jsp-api</artifactId>
        <version>2.1</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>5.3.6</version>
    </dependency>
</dependencies>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <!--注册DispatchServlet-->
    <servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <!--关联springmvc配置文件-->
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc-servlet.xml</param-value>
        </init-param>
        <!--设置启动级别为1级-->
        <load-on-startup>1</load-on-startup>
    </servlet>
    <!-- /   匹配所有请求，浏览器地址栏，不包括.jsp -->
    <!-- /*  匹配所有请求，包括.jsp  -->
    <servlet-mapping>
        <servlet-name>springmvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

springmvc-servlet.xml

处理器映射器、处理器适配器、视图解析器

<?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">

    <!--注册处理器映射器-->
    <bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping"/>
    <!--注册处理器适配器-->
    <bean class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter"/>
    <!--视图解析器ModeAndView-->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver" id="internalResourceViewResolver">
        <!--前缀-->
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <!--后缀-->
        <property name="suffix" value=".jsp"/>
    </bean>

    <!--BeanNameUrlHandlerMapping：bean 处理/hello请求跳转到Controller-->
    <bean class="com.wll.controller.HelloSpringmvc" id="/hello"/>
</beans>

HelloSpringmvc

/**
 * @author wulele
 */
public class HelloSpringmvc implements Controller {
    @Override
    public ModelAndView handleRequest(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception {
        //ModelAndView  模型和视图
        ModelAndView view = new ModelAndView();
        
     	//业务层   
        
        //封装对象
        view.addObject("msg","Hello SpringMVC");
        //  /WEB-INF/jsp/hello.jsp
        view.setViewName("hello");
        return view;
    }
}

hello.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
    <head>
        <title>Title</title>
    </head>
    <body>
        ${msg}
    </body>
</html>

运行测试
注意点

如果页面404，打开idea项目配置，在工件（artifact）选项添加lib目录添加jar包

使用注解

springmvc-servlet.xml

<?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:mvc="http://www.springframework.org/schema/mvc"
       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
                           http://www.springframework.org/schema/mvc
                           http://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <!--包扫描-->
    <context:component-scan base-package="com.wll.controller"/>
    <!--将静态资源转交servlet处理，如果不是静态资源则由DispatcherServlet处理-->
    <mvc:default-servlet-handler/>
    <!--注解驱动开启-->
    <mvc:annotation-driven/>

    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver" id="internalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
</beans>

HelloSpringmvc

/**
 * @author wulele
 */
//这个类被spring接管，方法返回值为String、有具体视图跳转就会被解析
@Controller
@RequestMapping("/hello")
public class HelloSpringmvc {
    /**
     * localhost:80/hello/spring
     */
    @RequestMapping("/spring")
    public String Hello(Model model){
        model.addAttribute("msg","Hello SpringMVC");
        //  /WEB-INF/jsp/hello.jsp
        return "hello";
    }
}

运行结果同上

接收请求参数

浏览器地址栏参数名与Controller中函数参数名相同

当使用@RequestParam("参数名")时，浏览器地址栏参数名必须与注解中设置的参数名一样

Controller中函数参数为一个对象（实体类），地址栏传参必须与实体类的字段名一致

字符过滤（乱码问题）

自定义过滤器，自写继承自Filter的类，注册filter，详见smbms学习笔记（服务器端） - 芜湖男酮 - 博客园 (cnblogs.com)

使用SpringMVC提供的字符过滤，配置在web.xml

<filter>
    <filter-name>encoding</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
        <param-name>encoding</param-name>
        <param-value>utf-8</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>encoding</filter-name>
    <!--包括.jsp-->
    <url-pattern>/*</url-pattern>
</filter-mapping>

终极方案：使用网上大神写好的自定义过滤器

Jackson使用及JsonUtils（Json工具类）的书写

pom.xml

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.12.3</version>
</dependency>

springmvc-servlet.xml

<!--注解驱动开启 json乱码处理-->
<mvc:annotation-driven>
    <mvc:message-converters register-defaults="true">
        <bean class="org.springframework.http.converter.StringHttpMessageConverter">
            <constructor-arg value="UTF-8"/>
        </bean>
        <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
            <property name="objectMapper">
                <bean class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
                    <property name="failOnEmptyBeans" value="false"/>
                </bean>
            </property>
        </bean>
    </mvc:message-converters>
</mvc:annotation-driven>

给前端返回一个对象

/**
 * @author wulele
 * @RestController 不走视图解析器，直接返回字符串，作用于类
 * @ResponseBody   不走视图解析器，直接返回字符串，作用于方法
 */
@Controller
public class Hello {
    @RequestMapping("/json")
    @ResponseBody
    public String testJson(){
        String value = null;
        User user = new User("杰克", 12, "123123");
        ObjectMapper mapper = new ObjectMapper();
        try {
            value = mapper.writeValueAsString(user);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        return value;
    }
}

给前端返回一个对象列表

@RequestMapping("/json1")
@ResponseBody
public String testJson1() throws JsonProcessingException {
    List<User> userList = new ArrayList<>();
    User user1 = new User("杰克", 12, "123123");
    User user2 = new User("汤姆", 12, "123123");
    User user3 = new User("皮克", 12, "123123");
    userList.add(user1);
    userList.add(user2);
    userList.add(user3);
    ObjectMapper mapper = new ObjectMapper();
    String s = mapper.writeValueAsString(userList);
    return s;
}

给前端返回时间

@RequestMapping("/json2")
@ResponseBody
public String testJson2() throws JsonProcessingException {
    Date date = new Date();
    ObjectMapper mapper = new ObjectMapper();
    //关闭ObjectMapper默认日期格式为时间戳方式
    mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);
    mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
    String s = mapper.writeValueAsString(date);

    //将时间戳格式化为指定格式
    //SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    //String s = dateFormat.format(date);

    return s;
}

封装为Json工具类

/**
 * @author wulele
 */
public class JsonUtil {

    public static String getJson(Object object){
        return getJson(object,new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
    }

    public static String getJson(Object object, SimpleDateFormat simpleDateFormat){
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);
        mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
        try {
            return mapper.writeValueAsString(object);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        return null;
    }
}

举例优化返回给前端一个对象、时间

//返回一个对象
@RequestMapping("/json")
@ResponseBody
public String testJson(){
    String value = null;
    User user = new User("杰克", 12, "123123");
    //ObjectMapper mapper = new ObjectMapper();
    //try {
    //    value = mapper.writeValueAsString(user);
    //} catch (JsonProcessingException e) {
    //    e.printStackTrace();
    //}
    return JsonUtil.getJson(user);
}
//返回时间
@RequestMapping("/json3")
@ResponseBody
public String testJson3() throws JsonProcessingException {
    return JsonUtil.getJson(new Date());
}

FastJson使用

@RequestMapping("/json4")
@ResponseBody
public String testJson4(){
    //返回对象列表
    //List<User> userList = new ArrayList<>();
    //User user1 = new User("杰克", 12, "123123");
    //User user2 = new User("汤姆", 12, "123123");
    //User user3 = new User("皮克", 12, "123123");
    //userList.add(user1);
    //userList.add(user2);
    //userList.add(user3);
    //String s = JSON.toJSONString(userList);
    //返回时间
    String s = JSON.toJSONString(new Date(),SerializerFeature.DisableCircularReferenceDetect, SerializerFeature.WriteDateUseDateFormat);
    return s;
}

HandlerInterceptor

实现HandlerInterceptor接口的方法（不是必须实现），类比Filtersmbms学习笔记（服务器端） - 芜湖男酮 - 博客园 (cnblogs.com)

/**
 * @author wulele
 */
public class MyInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("before");
        //true请求继续执行，false则相反
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("after");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("clear");
    }
}

springmvc-servlet.xml

<mvc:interceptors>
    <mvc:interceptor>
         <!--过滤所有请求-->
        <mvc:mapping path="/**"/>
        <bean class="com.wll.filter.LoginInterceptor"/>
    </mvc:interceptor>
</mvc:interceptors>

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