手写 Spring

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： XDispatchServlet

设定 init-param： contextConfigLocation = classpath:application.xml

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

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>(); @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 { //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("/+", "http://www.likecs.com/"); 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) + "}."); } @Override public 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 HandlerMapping initHandlerMapping(); 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：:8080/test/query?username=xiaopengwei"); System.out.println("测试地址：: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 = ("http://www.likecs.com/" + baseUrl + "http://www.likecs.com/" + xRequestMapping.value()).replaceAll("/+", "http://www.likecs.com/"); 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 protect field.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("http://www.likecs.com/" + scanPackage.replaceAll("\\.", "http://www.likecs.com/")); 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(); } } } } }