用300行代码手写1个Spring框架，麻雀虽小五脏俱全 javaspring源码

本文节选自《Spring 5核心原理》

1 自定义配置 1.1 配置application.properties文件
为了解析方便，我们用application.properties来代替application.xml文件，具体配置内容如下：

scanPackage=com.tom.demo

1.2 配置web.xml文件
大家都知道，所有依赖于Web容器的项目都是从读取web.xml文件开始的。我们先配置好web.xml中的内容：

Gupao Web Applicationgpmvc com.tom.mvcframework.v1.servlet.GPDispatcherServlet contextConfigLocationapplication.properties 1gpmvc /*

其中的GPDispatcherServlet是模拟Spring实现的核心功能类。
1.3 自定义注解
@GPService注解如下：

package com.tom.mvcframework.annotation; import java.lang.annotation.*; @Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface GPService { String value() default ""; }

@GPAutowired注解如下：

package com.tom.mvcframework.annotation; import java.lang.annotation.*; @Target({ElementType.FIELD}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface GPAutowired { String value() default ""; }

@GPController注解如下：

package com.tom.mvcframework.annotation; import java.lang.annotation.*; @Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface GPController { String value() default ""; }

@GPRequestMapping注解如下：

package com.tom.mvcframework.annotation; import java.lang.annotation.*; @Target({ElementType.TYPE,ElementType.METHOD}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface GPRequestMapping { String value() default ""; }

@GPRequestParam注解如下：

package com.tom.mvcframework.annotation; import java.lang.annotation.*; @Target({ElementType.PARAMETER}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface GPRequestParam { String value() default ""; }

1.4 配置注解
配置业务实现类DemoService：

package com.tom.demo.service.impl; import com.tom.demo.service.IDemoService; import com.tom.mvcframework.annotation.GPService; /** * 核心业务逻辑 */ @GPService public class DemoService implements IDemoService{ public String get(String name) { return "My name is " + name; } }

配置请求入口类DemoAction：

package com.tom.demo.mvc.action; import java.io.IOException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.tom.demo.service.IDemoService; import com.tom.mvcframework.annotation.GPAutowired; import com.tom.mvcframework.annotation.GPController; import com.tom.mvcframework.annotation.GPRequestMapping; import com.tom.mvcframework.annotation.GPRequestParam; @GPController @GPRequestMapping("/demo") public class DemoAction { @GPAutowired private IDemoService demoService; @GPRequestMapping("/query") public void query(HttpServletRequest req, HttpServletResponse resp, @GPRequestParam("name") String name){ String result = demoService.get(name); try { resp.getWriter().write(result); } catch (IOException e) { e.printStackTrace(); } } @GPRequestMapping("/add") public void add(HttpServletRequest req, HttpServletResponse resp, @GPRequestParam("a") Integer a, @GPRequestParam("b") Integer b){ try { resp.getWriter().write(a + "+" + b + "=" + (a + b)); } catch (IOException e) { e.printStackTrace(); } } @GPRequestMapping("/remove") public void remove(HttpServletRequest req,HttpServletResponse resp, @GPRequestParam("id") Integer id){ } }

至此，配置全部完成。
2 容器初始化1.0版本所有的核心逻辑全部写在init()方法中，代码如下：

package com.tom.mvcframework.v1.servlet; import com.tom.mvcframework.annotation.GPAutowired; import com.tom.mvcframework.annotation.GPController; import com.tom.mvcframework.annotation.GPRequestMapping; import com.tom.mvcframework.annotation.GPService; 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.Method; import java.net.URL; import java.util.*; public class GPDispatcherServlet extends HttpServlet { private Map mapping = new HashMap(); @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 {}@Override public void init(ServletConfig config) throws ServletException { InputStream is = null; try{ Properties configContext = new Properties(); is = this.getClass().getClassLoader().getResourceAsStream(config.getInitParameter ("contextConfigLocation")); configContext.load(is); String scanPackage = configContext.getProperty("scanPackage"); doScanner(scanPackage); for (String className : mapping.keySet()) { if(!className.contains(".")){continue; } Class clazz = Class.forName(className); if(clazz.isAnnotationPresent(GPController.class)){ mapping.put(className,clazz.newInstance()); String baseUrl = ""; if (clazz.isAnnotationPresent(GPRequestMapping.class)) { GPRequestMapping requestMapping = clazz.getAnnotation (GPRequestMapping.class); baseUrl = requestMapping.value(); } Method[] methods = clazz.getMethods(); for (Method method : methods) { if(!method.isAnnotationPresent(GPRequestMapping.class)){continue; } GPRequestMapping requestMapping = method.getAnnotation (GPRequestMapping.class); String url = (baseUrl + "/" + requestMapping.value()).replaceAll("/+", "/"); mapping.put(url, method); System.out.println("Mapped " + url + "," + method); } }else if(clazz.isAnnotationPresent(GPService.class)){ GPService service = clazz.getAnnotation(GPService.class); String beanName = service.value(); if("".equals(beanName)){beanName = clazz.getName(); } Object instance = clazz.newInstance(); mapping.put(beanName,instance); for (Class i : clazz.getInterfaces()) { mapping.put(i.getName(),instance); } }else {continue; } } for (Object object : mapping.values()) { if(object == null){continue; } Class clazz = object.getClass(); if(clazz.isAnnotationPresent(GPController.class)){ Field [] fields = clazz.getDeclaredFields(); for (Field field : fields) { if(!field.isAnnotationPresent(GPAutowired.class)){continue; } GPAutowired autowired = field.getAnnotation(GPAutowired.class); String beanName = autowired.value(); if("".equals(beanName)){beanName = field.getType().getName(); } field.setAccessible(true); try { field.set(mapping.get(clazz.getName()),mapping.get(beanName)); } catch (IllegalAccessException e) { e.printStackTrace(); } } } } } catch (Exception e) { }finally { if(is != null){ try {is.close(); } catch (IOException e) { e.printStackTrace(); } } } System.out.print("GP MVC Framework is init"); } private void doScanner(String scanPackage) { URL url = this.getClass().getClassLoader().getResource("/" + scanPackage.replaceAll ("\\.","/")); File classDir = new File(url.getFile()); for (File file : classDir.listFiles()) { if(file.isDirectory()){ doScanner(scanPackage + "." +file.getName()); }else { if(!file.getName().endsWith(".class")){continue; } String clazzName = (scanPackage + "." + file.getName().replace(".class","")); mapping.put(clazzName,null); } } } }

3 请求执行重点实现doGet()和doPost()方法，实际上就是在doGet()和doPost()方法中调用doDispatch()方法，具体代码如下：

public class GPDispatcherServlet extends HttpServlet { private Map mapping = new HashMap(); @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 { doDispatch(req,resp); } catch (Exception e) { resp.getWriter().write("500 Exception " + Arrays.toString(e.getStackTrace())); } } private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception { String url = req.getRequestURI(); String contextPath = req.getContextPath(); url = url.replace(contextPath, "").replaceAll("/+", "/"); if(!this.mapping.containsKey(url)){resp.getWriter().write("404 Not Found!!"); return; } Method method = (Method) this.mapping.get(url); Map params = req.getParameterMap(); method.invoke(this.mapping.get(method.getDeclaringClass().getName()),new Object[]{req,resp,params.get("name")[0]}); } @Override public void init(ServletConfig config) throws ServletException { ... }}

4 优化并实现2.0版本在1.0版本上进行优化，采用常用的设计模式（工厂模式、单例模式、委派模式、策略模式），将init()方法中的代码进行封装。按照之前的实现思路，先搭基础框架，再“填肉注血”，具体代码如下：

//初始化阶段 @Override public void init(ServletConfig config) throws ServletException {//1. 加载配置文件 doLoadConfig(config.getInitParameter("contextConfigLocation")); //2. 扫描相关的类 doScanner(contextConfig.getProperty("scanPackage")); //3. 初始化扫描到的类，并且将它们放入IoC容器中 doInstance(); //4. 完成依赖注入 doAutowired(); //5. 初始化HandlerMapping initHandlerMapping(); System.out.println("GP Spring framework is init."); }

声明全局成员变量，其中IoC容器就是注册时单例的具体案例：

//保存application.properties配置文件中的内容 private Properties contextConfig = new Properties(); //保存扫描的所有的类名 private List classNames = new ArrayList(); //传说中的IoC容器，我们来揭开它的神秘面纱 //为了简化程序，暂时不考虑ConcurrentHashMap //主要还是关注设计思想和原理 private Map ioc = new HashMap(); //保存url和Method的对应关系 private Map handlerMapping = new HashMap();

实现doLoadConfig()方法：

//加载配置文件 private void doLoadConfig(String contextConfigLocation) { //直接通过类路径找到Spring主配置文件所在的路径 //并且将其读取出来放到Properties对象中 //相当于将scanPackage=com.tom.demo保存到了内存中 InputStream fis = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation); try { contextConfig.load(fis); } catch (IOException e) { e.printStackTrace(); }finally { if(null != fis){ try { fis.close(); } catch (IOException e) { e.printStackTrace(); } } } }

实现doScanner()方法：

//扫描相关的类 private void doScanner(String scanPackage) { //scanPackage = com.tom.demo ，存储的是包路径 //转换为文件路径，实际上就是把.替换为/ URL url = this.getClass().getClassLoader().getResource("/" + scanPackage.replaceAll ("\\.","/")); File classPath = new File(url.getFile()); for (File file : classPath.listFiles()) { if(file.isDirectory()){ doScanner(scanPackage + "." + file.getName()); }else{ if(!file.getName().endsWith(".class")){ continue; } String className = (scanPackage + "." + file.getName().replace(".class","")); classNames.add(className); } } }

实现doInstance()方法，doInstance()方法就是工厂模式的具体实现：

private void doInstance() { //初始化，为DI做准备 if(classNames.isEmpty()){return; }try { for (String className : classNames) { Class clazz = Class.forName(className); //什么样的类才需要初始化呢？ //加了注解的类才初始化，怎么判断？ //为了简化代码逻辑，主要体会设计思想，只用@Controller和@Service举例， //@Componment等就不一一举例了 if(clazz.isAnnotationPresent(GPController.class)){ Object instance = clazz.newInstance(); //Spring默认类名首字母小写 String beanName = toLowerFirstCase(clazz.getSimpleName()); ioc.put(beanName,instance); }else if(clazz.isAnnotationPresent(GPService.class)){ //1. 自定义的beanName GPService service = clazz.getAnnotation(GPService.class); String beanName = service.value(); //2. 默认类名首字母小写 if("".equals(beanName.trim())){ beanName = toLowerFirstCase(clazz.getSimpleName()); }Object instance = clazz.newInstance(); ioc.put(beanName,instance); //3. 根据类型自动赋值，这是投机取巧的方式 for (Class i : clazz.getInterfaces()) { if(ioc.containsKey(i.getName())){ throw new Exception("The “" + i.getName() + "” is exists!!"); } //把接口的类型直接当成key ioc.put(i.getName(),instance); } }else { continue; }} }catch (Exception e){ e.printStackTrace(); }}

为了处理方便，自己实现了toLowerFirstCase()方法，来实现类名首字母小写，具体代码如下：

//将类名首字母改为小写 private String toLowerFirstCase(String simpleName) { char [] chars = simpleName.toCharArray(); //之所以要做加法，是因为大、小写字母的ASCII码相差32 //而且大写字母的ASCII码要小于小写字母的ASCII码 //在Java中，对char做算术运算实际上就是对ASCII码做算术运算 chars[0] += 32; return String.valueOf(chars); }

实现doAutowired()方法：

//自动进行依赖注入 private void doAutowired() { if(ioc.isEmpty()){return; }for (Map.Entry entry : ioc.entrySet()) { //获取所有的字段，包括private、protected、default类型的 //正常来说，普通的OOP编程只能获得public类型的字段 Field[] fields = entry.getValue().getClass().getDeclaredFields(); for (Field field : fields) { if(!field.isAnnotationPresent(GPAutowired.class)){continue; } GPAutowired autowired = field.getAnnotation(GPAutowired.class); //如果用户没有自定义beanName，默认就根据类型注入 //这个地方省去了对类名首字母小写的情况的判断，这个作为课后作业请“小伙伴们”自己去实现 String beanName = autowired.value().trim(); if("".equals(beanName)){ //获得接口的类型，作为key，稍后用这个key到IoC容器中取值 beanName = field.getType().getName(); }//如果是public以外的类型，只要加了@Autowired注解都要强制赋值 //反射中叫作暴力访问 field.setAccessible(true); try { //用反射机制动态给字段赋值 field.set(entry.getValue(),ioc.get(beanName)); } catch (IllegalAccessException e) { e.printStackTrace(); }}}}

实现initHandlerMapping()方法，HandlerMapping就是策略模式的应用案例：

//初始化url和Method的一对一关系 private void initHandlerMapping() { if(ioc.isEmpty()){ return; }for (Map.Entry entry : ioc.entrySet()) { Class clazz = entry.getValue().getClass(); if(!clazz.isAnnotationPresent(GPController.class)){continue; }//保存写在类上面的@GPRequestMapping("/demo") String baseUrl = ""; if(clazz.isAnnotationPresent(GPRequestMapping.class)){ GPRequestMapping requestMapping = clazz.getAnnotation(GPRequestMapping.class); baseUrl = requestMapping.value(); }//默认获取所有的public类型的方法 for (Method method : clazz.getMethods()) { if(!method.isAnnotationPresent(GPRequestMapping.class)){continue; }GPRequestMapping requestMapping = method.getAnnotation(GPRequestMapping.class); //优化 String url = ("/" + baseUrl + "/" + requestMapping.value()) .replaceAll("/+","/"); handlerMapping.put(url,method); System.out.println("Mapped :" + url + "," + method); }}}

到这里初始化的工作完成，接下来实现运行的逻辑，来看doGet()和doPost()方法的代码：

@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 {//运行阶段 try { doDispatch(req,resp); } catch (Exception e) { e.printStackTrace(); resp.getWriter().write("500 Exection,Detail : " + Arrays.toString(e.getStackTrace())); } }

doPost()方法中用了委派模式，委派模式的具体逻辑在doDispatch()方法中实现：

private void doDispatch(HttpServletRequest req, HttpServletResponse resp)throws Exception { String url = req.getRequestURI(); String contextPath = req.getContextPath(); url = url.replaceAll(contextPath,"").replaceAll("/+","/"); if(!this.handlerMapping.containsKey(url)){ resp.getWriter().write("404 Not Found!!"); return; } Method method = this.handlerMapping.get(url); //第一个参数：方法所在的实例 //第二个参数：调用时所需要的实参Map params = req.getParameterMap(); //投机取巧的方式 String beanName = toLowerFirstCase(method.getDeclaringClass().getSimpleName()); method.invoke(ioc.get(beanName),new Object[]{req,resp,params.get("name")[0]}); //System.out.println(method); }

在以上代码中，doDispatch()虽然完成了动态委派并进行了反射调用，但对url参数的处理还是静态的。要实现url参数的动态获取，其实有些复杂。我们可以优化doDispatch()方法的实现，代码如下：

private void doDispatch(HttpServletRequest req, HttpServletResponse resp)throws Exception { String url = req.getRequestURI(); String contextPath = req.getContextPath(); url = url.replaceAll(contextPath,"").replaceAll("/+","/"); if(!this.handlerMapping.containsKey(url)){ resp.getWriter().write("404 Not Found!!"); return; }Method method = this.handlerMapping.get(url); //第一个参数：方法所在的实例 //第二个参数：调用时所需要的实参 Map params = req.getParameterMap(); //获取方法的形参列表 Class [] parameterTypes = method.getParameterTypes(); //保存请求的url参数列表 Map parameterMap = req.getParameterMap(); //保存赋值参数的位置 Object [] paramValues = new Object[parameterTypes.length]; //根据参数位置动态赋值 for (int i = 0; i < parameterTypes.length; i ++){ Class parameterType = parameterTypes[i]; if(parameterType == HttpServletRequest.class){ paramValues[i] = req; continue; }else if(parameterType == HttpServletResponse.class){ paramValues[i] = resp; continue; }else if(parameterType == String.class){//提取方法中加了注解的参数 Annotation[] [] pa = method.getParameterAnnotations(); for (int j = 0; j < pa.length ; j ++) { for(Annotation a : pa[i]){ if(a instanceof GPRequestParam){ String paramName = ((GPRequestParam) a).value(); if(!"".equals(paramName.trim())){ String value = https://www.it610.com/article/Arrays.toString(parameterMap.get(paramName)) .replaceAll("\\[|\\]","") .replaceAll("\\s",","); paramValues[i] = value; } } } }} } //投机取巧的方式 //通过反射获得Method所在的Class，获得Class之后还要获得Class的名称 //再调用toLowerFirstCase获得beanName String beanName = toLowerFirstCase(method.getDeclaringClass().getSimpleName()); method.invoke(ioc.get(beanName),new Object[]{req,resp,params.get("name")[0]}); }

关注微信公众号『 Tom弹架构』回复“Spring”可获取完整源码。