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
4.0.0 com.adminkk adminkk-mvc 1.0-SNAPSHOT org.apache.maven.plugins maven-compiler-plugin 8 8 war adminkk-mvc http://maven.apache.org</url> UTF-8 junit junit 3.8.1 test javax.servlet javax.servlet-api 3.0.1 provided asm asm 3.3.1 org.javassist javassist 3.23.1-GA
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 {
publicString value()default"";
publicString 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 {
publicString value()default"";
publicString method()default"";
publicString 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;importjavassist.*;import javassist.bytecode.CodeAttribute;import javassist.bytecode.LocalVariableAttribute;import javassist.bytecode.MethodInfo;import java.lang.reflect.Method;publicfinalclass ParameterNameUtils {
publicfinalstaticString[] getParameterNamesByJavassist(finalClass 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];
intlen = ctMethod.getParameterTypes().length;
// 非静态的成员函数的第一个参数是thisintpos = Modifier.isStatic(ctMethod.getModifiers()) ? 0 : 1;
for(inti = 0; i < len; i++) {
rtv[i] = attr.variableName(i + pos);
}
return rtv;
}
} catch (NotFoundException e) {
System.out.println("获取异常"+ e.getMessage());
}
returnnewString[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;publicfinalclass HandlerMapping {
privatestaticfinalMap handlerMapping =newHashMap();
privatestaticfinalList scaners =newArrayList<>(2);
static {
scaners.add(new XmlScaner());
scaners.add(new FileScaner());
}
publicstaticvoidscanPackage(String scanUrl)throws RuntimeException, IllegalAccessException, InstantiationException, ClassNotFoundException {
for (Scaner scaner : scaners) {
scaner.doScane(scanUrl);
}
}
publicstaticvoiddoInit(String scanUrl)throws IllegalAccessException, ClassNotFoundException, InstantiationException {
scanPackage(scanUrl);
}
publicstaticvoid 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 parameterMap = request.getParameterMap();
String[] parameters = ParameterNameUtils.getParameterNamesByJavassist(instance.getClass(),method);
Object[] parameter =new Object[parameters.length];
if(parameters !=null&& parameters.length > 0){
for(inti = 0; i < parameters.length; i++) {
finalString simpleName = parameters[i];
StringBuilder parameterSb =new StringBuilder();
finalString[] parameterStr = parameterMap.get(simpleName);
if(parameterStr !=null){
for(intj = 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();
}
}
publicstatic Handler addHandlerMapping(String url,Handler handler) {
return handlerMapping.put(url,handler);
}
publicstatic Handler getHandlerMapping(String url) {
return handlerMapping.get(url);
}
}
扫描包
package com.adminkk.scan;publicinterface Scaner {
voiddoScane(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 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;publicinterface 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;publicclassMvcBeanPostProcessorimplements BeanPostProcessor{
//扫描Controller业务 @Override
publicObject 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(inti = 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 {
thrownewMvcException("请求路径"+ url + "已经存在容器中");
}
}
}
}
}
return object;
}
@Override
publicObject postProcessAfterInitialization(Object object, String beanName)throws MvcException {
returnnull;
}
}
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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