深度分析!深入浅出总结一下手撕springMVC的要点,建议收藏起来慢慢看!

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1、创建过程与文件目录

1.1、创建Maven工程

2、pom依赖与配置文件

2.1、pom依赖

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.zhz</groupId>
    <artifactId>simulation-springmvc</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <name>simulation-springmvc Maven Webapp</name>
    <!-- FIXME change it to the project's website -->
    <url>http://www.example.com</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.7</maven.compiler.source>
        <maven.compiler.target>1.7</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>dom4j</groupId>
            <artifactId>dom4j</artifactId>
            <version>1.6.1</version>
        </dependency>

        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.5</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.1</version>
        </dependency>
    </dependencies>

    <build>
        <finalName>simulation-springmvc</finalName>
        <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
            <plugins>
                <plugin>
                    <artifactId>maven-clean-plugin</artifactId>
                    <version>3.1.0</version>
                </plugin>
                <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging -->
                <plugin>
                    <artifactId>maven-resources-plugin</artifactId>
                    <version>3.0.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.8.0</version>
                </plugin>
                <plugin>
                    <artifactId>maven-surefire-plugin</artifactId>
                    <version>2.22.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-war-plugin</artifactId>
                    <version>3.2.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-install-plugin</artifactId>
                    <version>2.5.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-deploy-plugin</artifactId>
                    <version>2.8.2</version>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>
</project>

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2.2、springmvc配置类

<?xml version="1.0" encoding="UTF-8" ?>
<beans>
    <!--配置创建容器时要扫描的包-->
    <component-scan base-package="com.zhz.controller,com.zhz.service"></component-scan>
</beans>

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2.3、web.xml

<!DOCTYPE web-app PUBLIC
        "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
        "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>

  <!--配置前端控制器-->
  <servlet>
    <servlet-name>DispatcherServlet</servlet-name>
    <servlet-class>com.zhz.springmvc.servlet.DispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:springmvc.xml</param-value>
    </init-param>
    <!--Web服务器一旦启动,Servlet就会实例化创建对象,然后初始化(预备创建对象)-->
    <load-on-startup>1</load-on-startup>
  </servlet>

  <servlet-mapping>
    <servlet-name>DispatcherServlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

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3、实体类(User)

实体类:User.java

package com.zhz.bean;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * @author :zhz
 * @date :Created in 2021/01/04
 * @version: V1.0
 * @slogan: 天下风云出我辈,一入代码岁月催
 * @description: 实体类
 **/
@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {
   private Integer id;
   private String name;
   private String password;
}

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4、控制器(UserController)

package com.zhz.controller;

import com.zhz.bean.User;
import com.zhz.service.UserService;
import com.zhz.springmvc.annotation.Autowired;
import com.zhz.springmvc.annotation.Controller;
import com.zhz.springmvc.annotation.RequestMapping;
import com.zhz.springmvc.annotation.ResponseBody;

/**
 * @author :zhz
 * @date :Created in 2021/01/03
 * @version: V1.0
 * @slogan: 天下风云出我辈,一入代码岁月催
 * @description: 控制器
 **/
@Controller
public class UserController {

    @Autowired(value = "userService")
    private UserService userService;

    @RequestMapping("/listUsers")
    public String listUsers(){
        userService.listUsers();
        return "forward:/success.jsp";
    }

    @RequestMapping("/getData")
    @ResponseBody  //返回json格式的数据
    public User getData(){
        //调用服务层
        return userService.getUser();
    }
}

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5、业务处理类与实现类(UserService,UserServiceImpl)

package com.zhz.service;

import com.zhz.bean.User;

/**
 * @author :zhz
 * @date :Created in 2021/01/03
 * @version: V1.0
 * @slogan: 天下风云出我辈,一入代码岁月催
 * @description:
 **/
public interface UserService {
    void listUsers();

    User getUser();
}

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package com.zhz.service.impl;

import com.zhz.bean.User;
import com.zhz.service.UserService;
import com.zhz.springmvc.annotation.Service;

/**
 * @author :zhz
 * @date :Created in 2021/01/03
 * @version: V1.0
 * @slogan: 天下风云出我辈,一入代码岁月催
 * @description:
 **/
@Service("userService")
public class UserServiceImpl implements UserService {

    @Override
    public void listUsers() {
        System.out.println("===调用===UserServiceImpl===listUser===");
    }

    @Override
    public User getUser() {
        return new User(1,"zhz","123456");
    }
}

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6、手撕mvc具体代码

6.1、核心annotation注解

package com.zhz.springmvc.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * @Retention注解表示Annotation的保留策略 RetentionPolicy.Class:运行时不保留,不可以通过反射读取。
 * RetentionPolicy.RUNTIME:运行是保留,可以通过反射读取。
 * RetentionPolicy.SOURCE:丢弃。
 */
@Target(value = ElementType.FIELD)  //作用在属性上
@Retention(value = RetentionPolicy.RUNTIME)
public @interface Autowired {
    String value();
}

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package com.zhz.springmvc.annotation;

import java.lang.annotation.*;

@Target(ElementType.TYPE)  //  //作用在类上
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Controller {

    String value() default "";
}

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package com.zhz.springmvc.annotation;

import java.lang.annotation.*;

@Target(ElementType.METHOD)    //作用在方法上
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface RequestMapping {

    String value() default "";
}

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package com.zhz.springmvc.annotation;

import java.lang.annotation.*;

/**
 * @BelongsProject: SpringMvc
 */
@Target(ElementType.METHOD)    //作用在方法上
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ResponseBody {
}

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package com.zhz.springmvc.annotation;

import java.lang.annotation.*;

/**
 * @Description: 自定义注解
 */
@Target(ElementType.TYPE)  //作用在类上
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Service {

    String value();
}

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6.2、context上下文(SpringMVC容器)

package com.zhz.springmvc.context;

import com.zhz.springmvc.annotation.Autowired;
import com.zhz.springmvc.annotation.Controller;
import com.zhz.springmvc.annotation.Service;
import com.zhz.springmvc.xml.XmlParse;

import java.io.File;
import java.lang.reflect.Field;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * @author :zhz
 * @date :Created in 2021/01/03
 * @version: V1.0
 * @slogan: 天下风云出我辈,一入代码岁月催
 * @description: SpringMVC容器
 **/
public class WebApplicationContext {

    //classpath:springmvc.xml
    String contextConfigLocation;

    //定义集合  用于存放 bean 的权限名|包名.类名
    List<String> classNameList = new ArrayList<>();

    //创建Map集合用于扮演IOC容器:  key存放bean的名字   value存放bean实例
    public Map<String, Object> iocMap = new ConcurrentHashMap<>();

    public WebApplicationContext() {
    }

    public WebApplicationContext(String contextConfigLocation) {
        this.contextConfigLocation = contextConfigLocation;
    }

    /**
     * 初始化Spring容器
     */
    public void onRefresh() {
        //1、进行解析spring mvc配置文件操作  ==》 com.zhz.controller,com.zhz.service
        String basePackage = XmlParse.getBasePackage(contextConfigLocation.split(":")[1]);
        //通过","来分割com.zhz.controller,com.zhz.service 获得对应的包名
        String[] packs = basePackage.split(",");
        //2、进行包扫描
        for (String pack : packs) {
            executeScanPackage(pack);
        }
        //3、实例化容器中的bean
        executeInstance();

        //4、进行自动注入操作
        executeAutowired();
    }

    /**
     * 进行包扫描
     *
     * @param pack
     */
    private void executeScanPackage(String pack) {
        //1、把com.zhz.controller====>com/zhz/controller   com.zhz.service====>com/zhz/controller
        URL url = this.getClass().getClassLoader().getResource("/" + pack.replaceAll("\\.", "/"));
        String path = url.getFile();
        //2、/com/zhz/service
        File dir = new File(path);
        for (File file : dir.listFiles()) {
            if (file.isDirectory()) {//说明是com.zhz.service.impl层
                executeScanPackage(pack + "." + file.getName());
            } else {
                //文件目录下文件  获取全路径   UserController.class  ==> com.zhz.controller.UserController
                String className = pack + "." + file.getName().replaceAll(".class", "");
                classNameList.add(className);
            }
        }

    }

    /**
     * 实例化容器
     */
    private void executeInstance() {
        try {
            // com.zhz.controller.UserController      com.zhz.service.impl.UserServiceImpl
            for (String className : classNameList) {
                Class<?> clazz = Class.forName(className);
                if (clazz.isAnnotationPresent(Controller.class)) {
                    //控制层的bean,得到类的简写名称也就是UserController
                    String beanName = clazz.getSimpleName().substring(0, 1).toLowerCase()+clazz.getSimpleName().substring(1);//首位变为小写
                    iocMap.put(beanName, clazz.newInstance());
                } else if (clazz.isAnnotationPresent(Service.class)) {
                    //Service层,主要是为了获得他的value
                    Service service = clazz.getAnnotation(Service.class);
                    String beanName = service.value();
                    iocMap.put(beanName, clazz.newInstance());
                }
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        }
    }

    /**
     * 进行自动注入操作
     */
    private void executeAutowired() {
        try {
            //从容器中取出bean,然后判断bean中是否有属性上使用Autowired,如果使用了该注解,就需要进行自动注入操作
            for (Map.Entry<String, Object> entry : iocMap.entrySet()) {
                //取出容器中的bean
                Object bean = entry.getValue();
                //从bean中获取属性
                Field[] fields = bean.getClass().getDeclaredFields();
                for (Field field : fields) {
                    if (field.isAnnotationPresent(Autowired.class)) {
                        //获取注解中的value值,该值是bean的name
                        Autowired autowired = field.getAnnotation(Autowired.class);
                        String beanName = autowired.value();
                        ;
                        //取消检查机制
                        field.setAccessible(true);
                        field.set(bean, iocMap.get(beanName));
                    }
                }
            }
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    }
}

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6.3、映射处理(url与ccontroller之间的映射)

package com.zhz.springmvc.handler;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.lang.reflect.Method;

/**
 * @author :zhz
 * @date :Created in 2021/01/04
 * @version: V1.0
 * @slogan: 天下风云出我辈,一入代码岁月催
 * @description:
 **/
@Data
@AllArgsConstructor
@NoArgsConstructor
public class HandlerMapping {

    //请求URL地址
    private String url;
    //控制器
    private Object controller;
    //控制器的方法
    private Method method;
}

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6.4、前端处理器

package com.zhz.springmvc.servlet;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.zhz.springmvc.annotation.Controller;
import com.zhz.springmvc.annotation.RequestMapping;
import com.zhz.springmvc.annotation.ResponseBody;
import com.zhz.springmvc.context.WebApplicationContext;
import com.zhz.springmvc.handler.HandlerMapping;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * @author :zhz
 * @date :Created in 2021/01/03
 * @version: V1.0
 * @slogan: 天下风云出我辈,一入代码岁月催
 * @description: 前端控制器
 **/
public class DispatcherServlet extends HttpServlet {

    //指定SpringMvc容器
    private WebApplicationContext webApplicationContext;
    //创建集合,用于存放映射关系、映射地址与控制器.方法,用于发送请求直接从该集合中进行匹配
    List<HandlerMapping> handList = new ArrayList<>();

    @Override
    public void init() throws ServletException {
        //1、从web.xml中获得加载初始化参数contextConfigLocation的值classpath:springmvc.xml
        String configLocation = this.getServletConfig().getInitParameter("contextConfigLocation");
        //2、创建SpringMVC容器
        webApplicationContext = new WebApplicationContext(configLocation);

        //3、进行初始化操作
        webApplicationContext.onRefresh();

        //4、初始化请求映射关系   /findUser   ===》控制器.方法
        initHandlerMapping();
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //进行请求分发处理
        doDispatcher(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }

    /**
     * 初始化请求映射关系(获取链接地址0
     */
    private void initHandlerMapping() {
        //遍历map, key存放bean的名字   value存放bean实例
        for (Map.Entry<String, Object> entry : webApplicationContext.iocMap.entrySet()) {
            //获得bean的class类型
            Class<?> clazz = entry.getValue().getClass();
            if (clazz.isAnnotationPresent(Controller.class)) {
                //获取bean中所有的方法,为这些方法建立映射关系
                Method[] methods = clazz.getDeclaredMethods();
                for (Method method : methods) {
                    if (method.isAnnotationPresent(RequestMapping.class)) {
                        RequestMapping requestMapping = method.getAnnotation(RequestMapping.class);
                        //获取注解中的值
                        String url = requestMapping.value();
                        //建立映射地址,与控制器 方法
                        HandlerMapping handlerMapping = new HandlerMapping(url, entry.getValue(), method);
                        handList.add(handlerMapping);
                    }
                }
            }
        }
    }

    /**
     * 进行请求分发处理
     *
     * @param request
     * @param response
     */
    private void doDispatcher(HttpServletRequest request, HttpServletResponse response) {
        try {
            //根据用户的请求地址(/listUsers)查找Controller
            HandlerMapping handlerMapping = getHandler(request);

            if (handlerMapping == null) {
                response.getWriter().print("<h1>404 NOT  FOUND!</h1>");
            } else {
                //调用处理方法之前 进行参数的注入

                //调用目标方法---》获得方法的返回值类型
                Object result = handlerMapping.getMethod().invoke(handlerMapping.getController());
                if (result instanceof String){
                    //跳转到JSP中
                    String viewName = (String)result;
                    //forward:/success.jsp重定向
                    if (viewName.contains(":")){
                        String viewType=viewName.split(":")[0];//也就是forward或者redirect
                        String viewPage=viewName.split(":")[1];//跳转的页面
                        if (viewType.equals("forward")){//请求转发
                            request.getRequestDispatcher(viewPage).forward(request,response);
                        }else{//重定向
                            response.sendRedirect(viewPage);
                        }
                    }else{
                        //默认请求转发
                        request.getRequestDispatcher(viewName).forward(request,response);
                    }
                }else{
                    //返回JSON格式数据
                    Method method=handlerMapping.getMethod();
                    if (method.isAnnotationPresent(ResponseBody.class)){
                        //将返回值转换成 json格式数据
                        ObjectMapper objectMapper = new ObjectMapper();
                        String json = objectMapper.writeValueAsString(result);
                        response.setContentType("text/html;charset=utf-8");
                        PrintWriter writer= response.getWriter();
                        writer.print(json);
                        writer.flush();
                        writer.close();
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (ServletException e) {
            e.printStackTrace();
        }
    }

    /**
     * 根据用户请求查找对应的Handler======>获取请求对应的handler(也就是从handList中取出)
     *
     * @param request
     * @return
     */
    private HandlerMapping getHandler(HttpServletRequest request) {
        String requestURI = request.getRequestURI();
        for (HandlerMapping handlerMapping : handList) {
            //从容器的Handle取出URL  和  用户的请求地址进行匹配,找到满足条件的Handler(controller)
            if (handlerMapping.getUrl().equals(requestURI)) {
                return handlerMapping;
            }
        }
        return null;
    }

}

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6.5、解析XML

package com.zhz.springmvc.xml;

import lombok.val;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

import java.io.File;
import java.io.InputStream;

/**
 * @author :zhz
 * @date :Created in 2021/01/04
 * @version: V1.0
 * @slogan: 天下风云出我辈,一入代码岁月催
 * @description: 解析spring mvc.xml
 **/
public class XmlParse {

    public static String getBasePackage(String xml){
        try {
            SAXReader saxReader=new SAXReader();
            // 通过reader对象的read方法加载spring mvc.xml文件,获取docuemnt对象。
            InputStream inputStream = XmlParse.class.getClassLoader().getResourceAsStream(xml);
            Document document = saxReader.read(inputStream);
            // 通过document对象获取根节点beans
            Element rootElement = document.getRootElement();
            // 通过element对象的返回给定本地名称和任何名称空间的第一个元素
            Element componentScan = rootElement.element("component-scan");
            //返回componentScan的参数
            Attribute attribute = componentScan.attribute("base-package");
            //返回base-package的值
            String basePackage = attribute.getText();
            return basePackage;
        } catch (DocumentException e) {
            e.printStackTrace();
        }
        return "";
    }
}

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7、前端页面

7.1、index.jsp

<html>
<body>
<h2>Hello World!</h2>
</body>
</html>

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7.2、succes.jsp

<html>
<body>
<h2>Hello World!</h2>
   跳转至success.jsp页面
</body>
</html>

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总结

这篇关于手撕springMVC的文章就先更到这里了,感谢你看到这里,文章有什么不足还请指正,觉得文章对你有帮助的话记得给我点个赞,每天都会分享java相关技术文章或行业资讯,欢迎大家关注和转发文章! springMVC其实并不算是一个很难的知识点,用点心多看就很简单,最后点击这里即可领取Java架构大礼包哦!!!

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