手写 Spring MVC

向右看齐 2021-12-03 05:23 230阅读 0赞

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][https_github.com_xpwi_spring-custom]

**项目结构：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9pY29kZS5ibG9nLmNzZG4ubmV0_size_16_color_FFFFFF_t_70][]

**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>
 
 <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.*;
 /** * * * @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.*;
 /** * * * @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.*;
 /** * * * @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.*;
 /** * * * @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.*;
 
 /** * * 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("/+", "/");
 
 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：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 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("/" + 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;
 
 /** * * 前置控制器 * * @author XiaoPengwei * @since 2019-07-19 */
 @XController
 @XRequestMapping("/test")
 public class TestController { 
 
 @XAutowired
 ITestXService 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;
 /** * * 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;
 
 /** * * 业务实现类 * * @author XiaoPengwei * @since 2019-07-19 */
 @XService
 public class TestXServiceImpl implements ITestXService { 
 
 @Override
 public 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

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9pY29kZS5ibG9nLmNzZG4ubmV0_size_16_color_FFFFFF_t_70 1]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9pY29kZS5ibG9nLmNzZG4ubmV0_size_16_color_FFFFFF_t_70 2]

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

[https_github.com_xpwi_spring-custom]: https://github.com/xpwi/spring-custom
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