跟我一起造轮子 手写springmvc

　　原创地址：https://www.cnblogs.com/xrog/p/9820168.html

　　作为java程序员，项目中使用到的主流框架多多少少和spring有关联，在面试的过程难免会问一些spring springmvc spring boot的东西，比如设计模式的使用、 怎么实现springioc 怎么实现springmvc诸如此类的问题，今天我们就来探寻spring mvc的实现，然后自己实现一个简单的spring mvc

一. 了解spring mvc的基本运行流程

　　ps: 网上一大堆关于springmvc的详细讲解，在这里就不累赘了

　　

　　小结：spring mvc的核心是DispatcherServlet，DispatcherServlet继承于HttpServlet，可以说spring mvc是基于Servlet的一个实现，DispatcherServlet负责协调和组织不同组件以完成请求处理并返回响应的工作，实现了MVC模式。

二. 梳理简单SpringMVC的设计思路

　　1. 初始化容器 

　　　　　　　1.1 读取配置文件

　　　　　　　　　　1.1.1.加载配置文件信息到DispatcherServlet

　　　　　　　1.2  根据配置扫描包、初始化容器和组件

　　　　　　　　　　1.2.1.根据配置信息递归扫描包

　　　　　　　　　　1.2.2.把包下的类实例化 并且扫描注解

　　　　　　　　　　1.2.3.根据类的方法和注解，初始化HandlerMapping

　　2. 处理业务请求

　　　　　　2.1 处理请求业务

　　　　　　　　2.2.1 首先拿到请求URI 

　　　　　　　 　   2.2.2 根据URI，在HandlerMapping中查找和URI对应的Handler

　　　　　　　        2.2.3 根据Handler里面的method中的参数名称和http中的请求参数匹配，填充method参数，反射调用

三. 没时间解释了，快上车

　　　　ps ：环境基于maven idea tomat（端口8080） servlet

　　1.搭建一个基本web项目，并导入idea配置servlet 和javassist pom依赖 如下

　　　　创建命令: mvn archetype:generate -DgroupId=com.adminkk -DartifactId=adminkk-mvc -DpackageName=com.adminkk -Dversion=1.0

             

 pom依赖

<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.adminkk</groupId>
  <artifactId>adminkk-mvc</artifactId>
  <version>1.0-SNAPSHOT</version>
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>8</source>
          <target>8</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
  <packaging>war</packaging>

  <name>adminkk-mvc</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-->
      <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.0.1</version>
        <scope>provided</scope>
      </dependency>

    <!-- asm -->
    <dependency>
      <groupId>asm</groupId>
      <artifactId>asm</artifactId>
      <version>3.3.1</version>
    </dependency>

    <!-- javassist -->
    <dependency>
      <groupId>org.javassist</groupId>
      <artifactId>javassist</artifactId>
      <version>3.23.1-GA</version>
    </dependency>


  </dependencies>
</project>

　　　　

2.创建mvc的注解 Controller RequestMapping 和统一异常处理类、方法参数工具类ParameterNameUtils　　 

package com.adminkk.annotation;

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

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface Controller {

    public String value() default "";

    public String description() default "";
}

package com.adminkk.annotation;

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})
@Retention(RetentionPolicy.RUNTIME)
public @interface RequestMapping {

    public String value() default "";

    public String method() default "";

    public String description() default "";
}

package com.adminkk.exception;

public  final  class MvcException extends RuntimeException{

    public MvcException() {
        super();
    }

    public MvcException(String message) {
        super(message);
    }


}

package com.adminkk.tools;

import javassist.*;
import javassist.bytecode.CodeAttribute;
import javassist.bytecode.LocalVariableAttribute;
import javassist.bytecode.MethodInfo;

import java.lang.reflect.Method;


public final class ParameterNameUtils {


    public final static String[] getParameterNamesByJavassist(final Class<?> clazz, final Method method) {

        ClassPool pool = ClassPool.getDefault();
        try {
            CtClass ctClass = pool.get(clazz.getName());
            CtMethod ctMethod = ctClass.getDeclaredMethod(method.getName());

            // 使用javassist的反射方法的参数名
            MethodInfo methodInfo = ctMethod.getMethodInfo();
            CodeAttribute codeAttribute = methodInfo.getCodeAttribute();
            LocalVariableAttribute attr = (LocalVariableAttribute) codeAttribute
                    .getAttribute(LocalVariableAttribute.tag);
            if (attr != null) {

                String[] rtv = new String[ctMethod.getParameterTypes().length];
                int len = ctMethod.getParameterTypes().length;
                // 非静态的成员函数的第一个参数是this
                int pos = Modifier.isStatic(ctMethod.getModifiers()) ? 0 : 1;
                for (int i = 0; i < len; i++) {
                    rtv[i] = attr.variableName(i + pos);
                }
                return rtv;
            }
        } catch (NotFoundException e) {
            System.out.println("获取异常"+ e.getMessage());
        }
        return new String[0];
    }



}

3.创建 HandlerMapping类 主要是两个方法  doInit初始化 doService处理请求 相关代码如下

package com.adminkk.handler;

import com.adminkk.scan.FileScaner;
import com.adminkk.scan.Scaner;
import com.adminkk.scan.XmlScaner;
import com.adminkk.tools.ParameterNameUtils;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.PrintWriter;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public final  class HandlerMapping {


    private static  final Map<String,Handler> handlerMapping = new HashMap<String, Handler>();

    private static  final List<Scaner> scaners = new ArrayList<>(2);
    static {
        scaners.add(new XmlScaner());
        scaners.add(new FileScaner());
    }

    public  static void scanPackage(String scanUrl) throws RuntimeException, IllegalAccessException, InstantiationException, ClassNotFoundException {

        for (Scaner scaner : scaners) {
            scaner.doScane(scanUrl);
        }

    }




    public static void doInit(String scanUrl) throws IllegalAccessException, ClassNotFoundException, InstantiationException {
        scanPackage(scanUrl);
    }



    public static void doService(HttpServletRequest request, HttpServletResponse response) {

        String requestURI = request.getRequestURI();
        System.out.println("请求地址是="+ requestURI);
        Handler handler = handlerMapping.get(requestURI);
        if(handler == null){
            System.out.println("请求地址是="+ requestURI+" 没有配置改路径");
            return;
        }
        Method method = handler.getMethod();
        Object instance = handler.getInstance();
        response.setCharacterEncoding("UTF-8");
        //response.setContentType("application/json; charset=utf-8");
        PrintWriter writer = null;

        try {

            //这里是简单的解析 可以像springmvc那样解析处理
            Map<String, String[]> parameterMap = request.getParameterMap();
            String[] parameters = ParameterNameUtils.getParameterNamesByJavassist(instance.getClass(),method);
            Object[]  parameter = new Object[parameters.length];
            if(parameters != null && parameters.length > 0){
                for (int i = 0; i < parameters.length; i++) {
                    final String simpleName = parameters[i];
                    StringBuilder parameterSb = new  StringBuilder();
                    final String[] parameterStr = parameterMap.get(simpleName);
                    if(parameterStr != null){
                        for (int j = 0; j < parameterStr.length; j++) {
                            parameterSb.append(parameterStr[j]);
                        }
                    }
                    parameter[i] = parameterSb.toString();
                }
            }

            writer = response.getWriter();
            String result = (String) method.invoke(instance,parameter);
            writer.print(result);
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("请求地址是="+ requestURI+" 执行异常");
            writer.print("业务执行异常");
        }finally {
            writer.flush();
            writer.close();
        }
    }

    public static Handler addHandlerMapping(String url,Handler handler) {
        return handlerMapping.put(url,handler);
    }

    public static Handler getHandlerMapping(String url) {
        return handlerMapping.get(url);
    }



}

 扫描包

package com.adminkk.scan;

public interface Scaner {

    void doScane(String scanUrl) throws IllegalAccessException, InstantiationException, ClassNotFoundException;
}

package com.adminkk.scan;

import com.adminkk.exception.MvcException;
import com.adminkk.factory.BeanPostProcessor;
import com.adminkk.factory.MvcBeanPostProcessor;
import com.adminkk.factory.ServiceBeanPostProcessor;
import com.adminkk.handler.HandlerMapping;
import javassist.ClassClassPath;
import javassist.ClassPool;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

public final  class FileScaner implements Scaner{

    public FileScaner() {
    }

    public static final List<BeanPostProcessor> beanPostProcessorList = new ArrayList<>();
    static {
        beanPostProcessorList.add(new MvcBeanPostProcessor());
        beanPostProcessorList.add(new ServiceBeanPostProcessor());
    }

    @Override
    public void doScane(String scanUrl) throws IllegalAccessException, InstantiationException, ClassNotFoundException {
        if(scanUrl == null || scanUrl.length() == 0){
            throw new MvcException("容器基础扫描路径为空，请检查参数配置");
        }
        String baseUrl = HandlerMapping.class.getResource("/").getPath();
        String codeUrl = scanUrl.replaceAll("\.", "/");
        String path =  baseUrl + codeUrl;
        File file = new File(path);
        if(file == null || !file.exists()){
            throw new MvcException("找不到对应扫描路径，请检查参数配置");
        }
        recursionRedFile(scanUrl,file);
    }

    //递归读取文件
    private  void recursionRedFile(String scanUrl,File file) throws MvcException, ClassNotFoundException, IllegalAccessException, InstantiationException {

        if(!file.exists()){
            return;
        }

        //读取java文件
        if(file.isFile()){

            String beanName = scanUrl.replaceAll(".class","");
            Class<?> forName = Class.forName(beanName);
            //放到Javassist容器里面
            ClassPool pool = ClassPool.getDefault();
            ClassClassPath classPath = new ClassClassPath(forName);
            pool.insertClassPath(classPath);
            if(forName.isAnnotation() || forName.isEnum() || forName.isInterface() ){
                return;
            }
            Object newInstance = forName.newInstance();

            //前置执行
            for (int i = 0; i < beanPostProcessorList.size() ; i++) {
                BeanPostProcessor beanPostProcessor = beanPostProcessorList.get(i);
                beanPostProcessor.postProcessBeforeInitialization(newInstance,beanName);
            }

            //后置执行
            for (int i = beanPostProcessorList.size()-1; i > 0  ; i--) {
                BeanPostProcessor beanPostProcessor = beanPostProcessorList.get(i);
                beanPostProcessor.postProcessAfterInitialization(newInstance,beanName);
            }
            return;
        }

        //文件夹下面的文件都递归处理
        if(file.isDirectory()){
            File[] files = file.listFiles();
            if(files != null && files.length >0){
                for (int i = 0; i < files.length; i++) {
                    File targetFile = files[i];
                    recursionRedFile(scanUrl+"."+targetFile.getName(),targetFile);
                }
            }
        }

    }
}

package com.adminkk.scan;

public final class XmlScaner implements Scaner{

    public XmlScaner() {
    }

    @Override
    public void doScane(String scanUrl) {
        //可自行扩展
    }


}

　　扫描bean

package com.adminkk.factory;

import com.adminkk.exception.MvcException;

public interface BeanPostProcessor {

    Object postProcessBeforeInitialization(Object object, String beanName) throws MvcException;

    Object postProcessAfterInitialization(Object object, String beanName) throws MvcException;
}

package com.adminkk.factory;

import com.adminkk.annotation.Controller;
import com.adminkk.annotation.RequestMapping;
import com.adminkk.exception.MvcException;
import com.adminkk.handler.Handler;
import com.adminkk.handler.HandlerMapping;

import java.lang.reflect.Method;

public class MvcBeanPostProcessor implements BeanPostProcessor{


    //扫描Controller业务
    @Override
    public Object postProcessBeforeInitialization(Object object, String beanName) throws MvcException {

        Class<?> objectClass = object.getClass();
        if(objectClass.getAnnotation(Controller.class) != null){
            RequestMapping calssRequestMappingAnnotation = objectClass.getAnnotation(RequestMapping.class);
            StringBuilder urlSb = new StringBuilder();
            if(calssRequestMappingAnnotation != null){
                urlSb.append(calssRequestMappingAnnotation.value());
            }
            Method[] methods = objectClass.getMethods();
            if(methods != null && methods.length > 0 ){
                for (int i = 0; i < methods.length; i++) {
                    Method method = methods[i];
                    RequestMapping methodAnnotation = method.getAnnotation(RequestMapping.class);
                    if(methodAnnotation != null){
                        String methodValue = methodAnnotation.value();
                        String url = new StringBuilder().append(urlSb).append(methodValue).toString();
                        Handler handler = HandlerMapping.getHandlerMapping(url);
                        if(handler == null){
                            handler = new Handler();
                            handler.setMethod(method);
                            handler.setInstance(object);
                            HandlerMapping.addHandlerMapping(url,handler);
                        }else {
                            throw new MvcException("请求路径"+ url + "已经存在容器中");
                        }
                    }
                }

            }
        }

        return object;
    }

    @Override
    public Object postProcessAfterInitialization(Object object, String beanName) throws MvcException {
        return null;
    }
}

package com.adminkk.factory;

import com.adminkk.exception.MvcException;

public class ServiceBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object object, String beanName) throws MvcException {
        //可自行扩展
        return null;
    }

    @Override
    public Object postProcessAfterInitialization(Object object, String beanName) throws MvcException {
        //可自行扩展
        return null;
    }
}

　　

5.创建 DispatcherServlet

package com.adminkk.servlet;

import com.adminkk.handler.HandlerMapping;

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 java.io.IOException;

@WebServlet(name = "DispatcherServlet",loadOnStartup=1,urlPatterns={"/"})
public final  class DispatcherServlet extends HttpServlet {



    public static final String BASE_SCAN_URL = "com.adminkk";

    //初始化容器
    @Override
    public void init() throws ServletException {
        doInit();
    }

    //处理业务请求
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doService(req,resp);
    }

    private void doService(HttpServletRequest req, HttpServletResponse resp) throws ServletException {
        try {
            HandlerMapping.doService(req,resp);
        }catch (Exception e){
            e.printStackTrace();
            throw new ServletException(e.getMessage());
        }
    }

    private void doInit() throws ServletException {
        try {     
            HandlerMapping.doInit(this.BASE_SCAN_URL);
        }catch (Exception e){
            e.printStackTrace();
            throw new ServletException(e.getMessage());
        }

    }
}

　　

　　好了，目前为止我们就写好了简版的springmvc 下面开始测试

package com.adminkk.controller;

import com.adminkk.annotation.Controller;
import com.adminkk.annotation.RequestMapping;


@Controller
@RequestMapping("/mvc")
public class MvcController {


    @RequestMapping("/index")
    public String index(){
        return  "adminkk-mvc system is running";
    }


    @RequestMapping("/arg")
    public String parameter(String argOne, String argTwo){
        return  "argOne = " + argOne + " argTwo = " + argTwo;
    }
}

　　

　　　　　　访问地址 http://localhost:8080/mvc/index

　　　　　　

　　　　　　访问地址: http://localhost:8080/mvc/arg?argOne=argOne&argTwo=argTwo

　　　　　　

总结：整体实现简单的springmvc，设计上还可以扩展更多，难点在于method 获取方法上的参数名称，由于jdk1.8以前是不支持的，需要借用第三方工具 比如 asm javassist黑科技工具包来帮助实现，spring-core使用的是LocalVariableTableParameterNameDiscoverer底层是调用asm,我们这里使用的是javassist。延用这套思路还可以和spring项目结合，写一个 基于spring的springmvc项目

源代码 ： https://gitee.com/chenchenche/mvc

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