装逼必备！手写springMVC（附详解）

程序员文章站 2024-03-19 08:08:22

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之前提到过的ssm流程原理装逼必备！手写springMVC（附详解）
今天就从底层解开ssm的面纱
首先准备几个常用的annotation（也就是注解）：
1.Hcontroller（controller）

package annotation;

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

@Target(ElementType.TYPE)//表示注解运行在哪里
@Retention(RetentionPolicy.RUNTIME)//用来说明该注解类的生命周期
@Documented
public @interface HController {
    /**
     * 表示给controller注册别名
     * @author hxz
     * @return
     */
    String value() default "";

}

2.HRequestMapping(RequestMapping)

package annotation;

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

@Target({ElementType.TYPE,ElementType.METHOD})//表示注解运行在哪里
@Retention(RetentionPolicy.RUNTIME)//用来说明该注解类的生命周期
@Documented
public @interface HRequestMapping {
    /**
     * 表示访问该方法的url
     * @author hxz
     * @return
     */
    String value() default "";

}

3.HRequestParam(RequestParam)

package annotation;

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

@Target({ElementType.TYPE,ElementType.METHOD})//表示注解运行在哪里
@Retention(RetentionPolicy.RUNTIME)//用来说明该注解类的生命周期
@Documented
public @interface HRequestMapping {
    /**
     * 表示访问该方法的url
     * @author hxz
     * @return
     */
    String value() default "";

}

这里只用了三个，当然还有很多，这里不祥解
最重要的！
最重要的！
最重要的！
MyDispatcherServlet（spring MVC核心DispatcherServlet）

package servlet;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import annotation.HController;
import annotation.HRequestMapping;

public class MyDispatcherServlet extends HttpServlet{

    private Properties properties = new Properties();

    private List<String> classNames = new ArrayList<String>();

    private Map<String, Object> ioc = new HashMap<String, Object>();

    private Map<String, Method> handlerMapping = new  HashMap<String, Method>();

    private Map<String, Object> controllerMap  =new HashMap<String, Object>();

    @Override
    public void init(ServletConfig config) throws ServletException {

        //1.加载配置文件
        doLoadConfig(config.getInitParameter("contextConfigLocation"));

        //2.初始化所有相关联的类,扫描用户设定的包下面所有的类
        doScanner(properties.getProperty("scanPackage"));

        //3.拿到扫描到的类,通过反射机制,实例化,并且放到ioc容器中(k-v  beanName-bean) beanName默认是首字母小写
        doInstance();

        //4.初始化HandlerMapping(将url和method对应上)
        initHandlerMapping();

    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        try {
            //处理请求
            doDispatch(req,resp);
        } catch (Exception e) {
            resp.getWriter().write("500!! Server Exception");
        }

    }

    private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception {
        if(handlerMapping.isEmpty()){
            return;
        }

        String url =req.getRequestURI();
        String contextPath = req.getContextPath();

        url=url.replace(contextPath, "").replaceAll("/+", "/");

        if(!this.handlerMapping.containsKey(url)){
            resp.getWriter().write("404 NOT FOUND!");
            return;
        }

        Method method =this.handlerMapping.get(url);

        //获取方法的参数列表
        Class<?>[] parameterTypes = method.getParameterTypes();

        //获取请求的参数
        Map<String, String[]> parameterMap = req.getParameterMap();

        //保存参数值
        Object [] paramValues= new Object[parameterTypes.length];

        //方法的参数列表
        for (int i = 0; i<parameterTypes.length; i++){  
            //根据参数名称，做某些处理  
            String requestParam = parameterTypes[i].getSimpleName();  

            if (requestParam.equals("HttpServletRequest")){  
                //参数类型已明确，这边强转类型  
                paramValues[i]=req;
                continue;  
            }  
            if (requestParam.equals("HttpServletResponse")){  
                paramValues[i]=resp;
                continue;  
            }
            if(requestParam.equals("String")){
                for (Entry<String, String[]> param : parameterMap.entrySet()) {
                    String value =Arrays.toString(param.getValue()).replaceAll("\\[|\\]", "").replaceAll(",\\s", ",");
                    paramValues[i]=value;
                }
            }
        }  
        //利用反射机制来调用
        try {
            method.invoke(this.controllerMap.get(url), paramValues);//第一个参数是method所对应的实例 在ioc容器中
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void  doLoadConfig(String location){
        //把web.xml中的contextConfigLocation对应value值的文件加载到流里面
        InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream(location);
        try {
            //用Properties文件加载文件里的内容
            properties.load(resourceAsStream);
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            //关流
            if(null!=resourceAsStream){
                try {
                    resourceAsStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    private void doScanner(String packageName) {
        //把所有的.替换成/
        URL url  =this.getClass().getClassLoader().getResource("/"+packageName.replaceAll("\\.", "/"));
        File dir = new File(url.getFile());
        for (File file : dir.listFiles()) {
            if(file.isDirectory()){
                //递归读取包
                doScanner(packageName+"."+file.getName());
            }else{
                String className =packageName +"." +file.getName().replace(".class", "");
                classNames.add(className);
            }
        }
    }

    private void doInstance() {
        if (classNames.isEmpty()) {
            return;
        }   
        for (String className : classNames) {
            try {
                //把类搞出来,反射来实例化(只有加@MyController需要实例化)
                Class<?> clazz =Class.forName(className);
               if(clazz.isAnnotationPresent(HController.class)){
                    ioc.put(toLowerFirstWord(clazz.getSimpleName()),clazz.newInstance());
                }else{
                    continue;
                }

            } catch (Exception e) {
                e.printStackTrace();
                continue;
            }
        }
    }

    private void initHandlerMapping(){
        if(ioc.isEmpty()){
            return;
        }
        try {
            for (Entry<String, Object> entry: ioc.entrySet()) {
                Class<? extends Object> clazz = entry.getValue().getClass();
                if(!clazz.isAnnotationPresent(HController.class)){
                    continue;
                }

                //拼url时,是controller头的url拼上方法上的url
                String baseUrl ="";
                if(clazz.isAnnotationPresent(HRequestMapping.class)){
                    HRequestMapping annotation = clazz.getAnnotation(HRequestMapping.class);
                    baseUrl=annotation.value();
                }
                Method[] methods = clazz.getMethods();
                for (Method method : methods) {
                    if(!method.isAnnotationPresent(HRequestMapping.class)){
                        continue;
                    }
                    HRequestMapping annotation = method.getAnnotation(HRequestMapping.class);
                    String url = annotation.value();

                    url =(baseUrl+"/"+url).replaceAll("/+", "/");
                    handlerMapping.put(url,method);
                    controllerMap.put(url,clazz.newInstance());
                    System.out.println(url+","+method);
                }

            }

        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    /**
     * 把字符串的首字母小写
     * @param name
     * @return
     */
    private String toLowerFirstWord(String name){
        char[] charArray = name.toCharArray();
        charArray[0] += 32;
        return String.valueOf(charArray);
    }

}

还有web.xml和一个jar包依赖：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	version="3.0">
	<!-- 拦截器 拦截所有请求至MVC——dispatcherServlet -->
	<servlet>
		<servlet-name>MySpringMVC</servlet-name>
		<servlet-class>com.liugh.servlet.MyDispatcherServlet</servlet-class>
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>application.properties</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>MySpringMVC</servlet-name>
		<url-pattern>/*</url-pattern>
	</servlet-mapping>

</web-app>

<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>springmvc</groupId>
	<artifactId>springmvc</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>springmvc</name>
	<url>http://maven.apache.org</url>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
	</properties>

	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>3.8.1</version>
			<scope>test</scope>
		</dependency>
		<!-- servlet依赖 -->
		<dependency>
			<groupId>javax.servlet</groupId>
			<artifactId>javax.servlet-api</artifactId>
			<version>3.0.1</version>
			<scope>provided</scope>
		</dependency>
	</dependencies>
</project>

application.properties：

scanPackage=controller

这是我的整个项目结构
装逼必备！手写springMVC（附详解）
流程详解
⑴ 用户发送请求至前端控制器MyDispatcherServlet（xml拦截所有请求）
⑵ DispatcherServlet收到前台发出的请求调用HandlerMapping映射器。
⑶ 处理器映射器根据请求url找到具体的映射器，生成处理器对象及处理器拦截器(如果有则生成)一并返回给DispatcherServlet。
⑷ DispatcherServlet通过HandlerAdapter处理器适配器调用处理器
⑸ 执行处理器(HController，也叫后端控制器)。
⑹ HController执行完成返回ModelAndView
⑺ HandlerAdapter将Hcontroller执行结果ModelAndView返回给MyDispatcherServlet
⑻ MyDispatcherServlet将ModelAndView传给ViewReslover视图解析器
⑼ ViewReslover解析后返回具体View
⑽ MyDispatcherServlet对View进行渲染视图（即将数据填充至视图中）。
⑾ MyDispatcherServlet返回响应给用户。

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