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>();

    @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;

/**
 * <p>
 * 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;
/**
 * <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 {

    @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

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