手写 Spring MVC

学习自《Spring 5核心原理与30个类手写实战》作者 Tom 老师

手写 Spring MVC

不多说，简历装 X 必备。不过练好还是需要求一定的思维能力。

一、整体思路

思路要熟练背下来

1）配置阶段

配置 web.xml：
- <sevlet>
- XDispatchServlet
- 设定 init-param： contextConfigLocation = applicationContext.properties
- <servlet-mapping>
- 设定 url-pattern： /*
配置 Annotation： @XController @XService @XAutowired @XRequestMapping

2）初始化阶段

IOC：
- 调用 init() 方法： 加载配置文件
- IOC 容器初始化： Map<String, Object>
- 扫描相关的类： scan-package=“com.xiaopengwei”
- 创建实例化并保存到容器： 同过反射机制将类实例化放入 IOC 容器中
DI：
- 进行 DI 操作： 扫描 IOC 容器中的实例，给没有赋值的属性自动赋值
MVC：
- 初始化 HandlerMapping： 将一个 URL 和一个 Method 进行一对一的关联映射 Map<String, Method>

3）运行阶段

调用 doGet() / doPost() 方法： Web 容器调用 doGet() / doPost() 方法，获得 request/response 对象
匹配 HandleMapping： 从 request 对象中获得用户输入的 url，找到其对应的 Method
反射调用 method.invoker()： 利用反射调用方法并返回结果
response.getWrite().write()： 将返回结果输出到浏览器

二、源代码

GitHub：https://github.com/xpwi/spring-custom

项目结构：

源代码：

（1）在 pom.xml 引入一个 jar 包

<dependency><groupId>javax.servlet</groupId><artifactId>javax.servlet-api</artifactId><version>3.1.0</version>
</dependency>

（2）web.xml 文件：

<!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><servlet><servlet-name>xmvc</servlet-name><servlet-class>com.xiaopengwei.xspring.servlet.XDispatchServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><!--you can't use classpath*: --><param-value>application.properties</param-value></init-param></servlet><servlet-mapping><servlet-name>xmvc</servlet-name><url-pattern>/*</url-pattern></servlet-mapping>
</web-app>

（3）application.properties 文件：

scan-package=com.xiaopengwei

（4）自定义注解 XAutowired：

package com.xiaopengwei.xspring.annotation;
import java.lang.annotation.*;
/*** <p>** @author XiaoPengwei* @since 2019-07-19*/
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface XAutowired {String value() default "";
}

（5）自定义注解 XController：

package com.xiaopengwei.xspring.annotation;
import java.lang.annotation.*;
/*** <p>** @author XiaoPengwei* @since 2019-07-19*/
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface XController {String value() default "";
}

（6）自定义注解 XRequestMapping：

package com.xiaopengwei.xspring.annotation;
import java.lang.annotation.*;
/*** <p>** @author XiaoPengwei* @since 2019-07-19*/
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface XRequestMapping {String value() default "";
}

（7）自定义注解 XService：

package com.xiaopengwei.xspring.annotation;
import java.lang.annotation.*;
/*** <p>** @author XiaoPengwei* @since 2019-07-19*/
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface XService {String value() default "";
}

（8）核心 XDispatchServlet：

package com.xiaopengwei.xspring.servlet;
import com.xiaopengwei.xspring.annotation.XAutowired;
import com.xiaopengwei.xspring.annotation.XController;
import com.xiaopengwei.xspring.annotation.XRequestMapping;
import com.xiaopengwei.xspring.annotation.XService;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.*;/*** <p>* XSpring** @author XiaoPengwei* @since 2019-07-19*/
public class XDispatchServlet extends HttpServlet {/*** 属性配置文件*/private Properties contextConfig = new Properties();private List<String> classNameList = new ArrayList<>();/*** IOC 容器*/Map<String, Object> iocMap = new HashMap<String, Object>();Map<String, Method> handlerMapping = new HashMap<String, Method>();@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {this.doPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//7、运行阶段try {doDispatch(req, resp);} catch (Exception e) {e.printStackTrace();resp.getWriter().write("500 Exception Detail:\n" + Arrays.toString(e.getStackTrace()));}}/*** 7、运行阶段，进行拦截，匹配** @param req  请求* @param resp 响应*/private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws InvocationTargetException, IllegalAccessException {String url = req.getRequestURI();String contextPath = req.getContextPath();url = url.replaceAll(contextPath, "").replaceAll("/+", "/");System.out.println("[INFO-7] request url-->" + url);if (!this.handlerMapping.containsKey(url)) {try {resp.getWriter().write("404 NOT FOUND!!");return;} catch (IOException e) {e.printStackTrace();}}Method method = this.handlerMapping.get(url);System.out.println("[INFO-7] method-->" + method);String beanName = toLowerFirstCase(method.getDeclaringClass().getSimpleName());System.out.println("[INFO-7] iocMap.get(beanName)->" + iocMap.get(beanName));// 第一个参数是获取方法，后面是参数，多个参数直接加，按顺序对应method.invoke(iocMap.get(beanName), req, resp);System.out.println("[INFO-7] method.invoke put {" + iocMap.get(beanName) + "}.");}@Overridepublic void init(ServletConfig servletConfig) throws ServletException {//1、加载配置文件doLoadConfig(servletConfig.getInitParameter("contextConfigLocation"));//2、扫描相关的类doScanner(contextConfig.getProperty("scan-package"));//3、初始化 IOC 容器，将所有相关的类实例保存到 IOC 容器中doInstance();//4、依赖注入doAutowired();//5、初始化 HandlerMappinginitHandlerMapping();System.out.println("XSpring FrameWork is init.");//6、打印数据doTestPrintData();}/*** 6、打印数据*/private void doTestPrintData() {System.out.println("[INFO-6]----data------------------------");System.out.println("contextConfig.propertyNames()-->" + contextConfig.propertyNames());System.out.println("[classNameList]-->");for (String str : classNameList) {System.out.println(str);}System.out.println("[iocMap]-->");for (Map.Entry<String, Object> entry : iocMap.entrySet()) {System.out.println(entry);}System.out.println("[handlerMapping]-->");for (Map.Entry<String, Method> entry : handlerMapping.entrySet()) {System.out.println(entry);}System.out.println("[INFO-6]----done-----------------------");System.out.println("====启动成功====");System.out.println("测试地址：http://localhost:8080/test/query?username=xiaopengwei");System.out.println("测试地址：http://localhost:8080/test/listClassName");}/*** 5、初始化 HandlerMapping*/private void initHandlerMapping() {if (iocMap.isEmpty()) {return;}for (Map.Entry<String, Object> entry : iocMap.entrySet()) {Class<?> clazz = entry.getValue().getClass();if (!clazz.isAnnotationPresent(XController.class)) {continue;}String baseUrl = "";if (clazz.isAnnotationPresent(XRequestMapping.class)) {XRequestMapping xRequestMapping = clazz.getAnnotation(XRequestMapping.class);baseUrl = xRequestMapping.value();}for (Method method : clazz.getMethods()) {if (!method.isAnnotationPresent(XRequestMapping.class)) {continue;}XRequestMapping xRequestMapping = method.getAnnotation(XRequestMapping.class);String url = ("/" + baseUrl + "/" + xRequestMapping.value()).replaceAll("/+", "/");handlerMapping.put(url, method);System.out.println("[INFO-5] handlerMapping put {" + url + "} - {" + method + "}.");}}}/*** 4、依赖注入*/private void doAutowired() {if (iocMap.isEmpty()) {return;}for (Map.Entry<String, Object> entry : iocMap.entrySet()) {Field[] fields = entry.getValue().getClass().getDeclaredFields();for (Field field : fields) {if (!field.isAnnotationPresent(XAutowired.class)) {continue;}System.out.println("[INFO-4] Existence XAutowired.");// 获取注解对应的类XAutowired xAutowired = field.getAnnotation(XAutowired.class);String beanName = xAutowired.value().trim();// 获取 XAutowired 注解的值if ("".equals(beanName)) {System.out.println("[INFO] xAutowired.value() is null");beanName = field.getType().getName();}// 只要加了注解，都要加载，不管是 private 还是 protectfield.setAccessible(true);try {field.set(entry.getValue(), iocMap.get(beanName));System.out.println("[INFO-4] field set {" + entry.getValue() + "} - {" + iocMap.get(beanName) + "}.");} catch (IllegalAccessException e) {e.printStackTrace();}}}}/*** 3、初始化 IOC 容器，将所有相关的类实例保存到 IOC 容器中*/private void doInstance() {if (classNameList.isEmpty()) {return;}try {for (String className : classNameList) {Class<?> clazz = Class.forName(className);if (clazz.isAnnotationPresent(XController.class)) {String beanName = toLowerFirstCase(clazz.getSimpleName());Object instance = clazz.newInstance();// 保存在 ioc 容器iocMap.put(beanName, instance);System.out.println("[INFO-3] {" + beanName + "} has been saved in iocMap.");} else if (clazz.isAnnotationPresent(XService.class)) {String beanName = toLowerFirstCase(clazz.getSimpleName());// 如果注解包含自定义名称XService xService = clazz.getAnnotation(XService.class);if (!"".equals(xService.value())) {beanName = xService.value();}Object instance = clazz.newInstance();iocMap.put(beanName, instance);System.out.println("[INFO-3] {" + beanName + "} has been saved in iocMap.");// 找类的接口for (Class<?> i : clazz.getInterfaces()) {if (iocMap.containsKey(i.getName())) {throw new Exception("The Bean Name Is Exist.");}iocMap.put(i.getName(), instance);System.out.println("[INFO-3] {" + i.getName() + "} has been saved in iocMap.");}}}} catch (Exception e) {e.printStackTrace();}}/*** 获取类的首字母小写的名称** @param className ClassName* @return java.lang.String*/private String toLowerFirstCase(String className) {char[] charArray = className.toCharArray();charArray[0] += 32;return String.valueOf(charArray);}/*** 2、扫描相关的类** @param scanPackage properties --> scan-package*/private void doScanner(String scanPackage) {// package's . ==> /URL resourcePath = this.getClass().getClassLoader().getResource("/" + scanPackage.replaceAll("\\.", "/"));if (resourcePath == null) {return;}File classPath = new File(resourcePath.getFile());for (File file : classPath.listFiles()) {if (file.isDirectory()) {System.out.println("[INFO-2] {" + file.getName() + "} is a directory.");// 子目录递归doScanner(scanPackage + "." + file.getName());} else {if (!file.getName().endsWith(".class")) {System.out.println("[INFO-2] {" + file.getName() + "} is not a class file.");continue;}String className = (scanPackage + "." + file.getName()).replace(".class", "");// 保存在内容classNameList.add(className);System.out.println("[INFO-2] {" + className + "} has been saved in classNameList.");}}}/*** 1、加载配置文件** @param contextConfigLocation web.xml --> servlet/init-param*/private void doLoadConfig(String contextConfigLocation) {InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation);try {// 保存在内存contextConfig.load(inputStream);System.out.println("[INFO-1] property file has been saved in contextConfig.");} catch (IOException e) {e.printStackTrace();} finally {if (null != inputStream) {try {inputStream.close();} catch (IOException e) {e.printStackTrace();}}}}
}

（9）示例：TestController：

package com.xiaopengwei.demo.xcontroller;
import com.xiaopengwei.demo.xservice.ITestXService;
import com.xiaopengwei.xspring.annotation.XAutowired;
import com.xiaopengwei.xspring.annotation.XController;
import com.xiaopengwei.xspring.annotation.XRequestMapping;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;/*** <p>* 前置控制器** @author XiaoPengwei* @since 2019-07-19*/
@XController
@XRequestMapping("/test")
public class TestController {@XAutowiredITestXService testXService;/*** 测试方法 /test/query** @param req  请求体* @param resp 响应体*/@XRequestMapping("/query")public void query(HttpServletRequest req, HttpServletResponse resp) {if (req.getParameter("username") == null) {try {resp.getWriter().write("param username is null");} catch (IOException e) {e.printStackTrace();}} else {String paramName = req.getParameter("username");try {resp.getWriter().write("param username is " + paramName);} catch (IOException e) {e.printStackTrace();}System.out.println("[INFO-req] New request param username-->" + paramName);}}/*** 测试方法 /test/listClassName** @param req  请求体* @param resp 响应体*/@XRequestMapping("/listClassName")public void listClassName(HttpServletRequest req, HttpServletResponse resp) {String str = testXService.listClassName();System.out.println("testXService----------=-=-=>" + str);try {resp.getWriter().write(str);} catch (IOException e) {e.printStackTrace();}}
}

（10）示例接口：ITestXService：

package com.xiaopengwei.demo.xservice;
/*** <p>* 接口** @author XiaoPengwei* @since 2019-07-19*/
public interface ITestXService {String listClassName();
}

（11）示例实现类 TestXServiceImpl：

package com.xiaopengwei.demo.xservice.impl;
import com.xiaopengwei.demo.xservice.ITestXService;
import com.xiaopengwei.xspring.annotation.XService;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.ArrayList;
import java.util.List;/*** <p>* 业务实现类** @author XiaoPengwei* @since 2019-07-19*/
@XService
public class TestXServiceImpl implements ITestXService {@Overridepublic String listClassName() {// 假装来自数据库return "123456TestXServiceImpl";}
}

（12）测试：

配置 Tomcat 后，访问：

http://localhost:8080/test/query?username=xiaopengwei

和

http://localhost:8080/test/listClassName

https://github.com/xpwi/spring-custom