[Spring] 30个类手写 Spring Mini 版本系列（二）

/*
 * @ProjectName: 编程学习
 * @Copyright:   2019 HangZhou Ashe Dev, Ltd. All Right Reserved.
 * @address:     https://yiyuery.github.io/NoteBooks/
 * @date:        2020/4/12 5:30 下午
 * @description: 本内容仅限于编程技术学习使用，转发请注明出处.
 */
package com.yido.mvcframework.v2.servlet;

import com.yido.mvcframework.annotation.*;

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.annotation.Annotation;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.*;

/**
 * <p>
 * 手写一个 请求转发器 DispatchServlet
 * - 代码重构，流程清晰化
 * </p>
 *
 * @author Helios
 * @date 2020/4/12 5:30 下午
 */
public class XDispatchServlet extends HttpServlet {

    /**
     * 配置
     */
    private Properties contextConfig = new Properties();

    //享元模式，缓存
    private List<String> classNames = new ArrayList<String>();

    //IoC容器，key默认是类名首字母小写，value就是对应的实例对象
    private Map<String, Object> ioc = new HashMap<String, Object>();
    //URL 和 Method 映射关系
    private Map<String, Method> handlerMapping = new HashMap<String, Method>();

    /**
     * Get 请求处理转发
     *
     * @param req
     * @param resp
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doPost(req, resp);
    }

    /**
     * Post请求处理转发
     *
     * @param req
     * @param resp
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        try {
            //【运行阶段】
            //6. 委派：根据 URL 找到一个对应的 Method ，并通过 response 返回
            doDispatch(req, resp);
        } catch (Exception e) {
            e.printStackTrace();
            //出现异常，返回堆栈信息
            resp.getWriter().write("500 Exception, Detail:  " + Arrays.toString(e.getStackTrace()));
        }
    }

    /**
     * 根据 URL 找到一个对应的 Method ，并通过 response 返回
     *
     * @param req
     * @param resp
     */
    private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws IOException, InvocationTargetException, IllegalAccessException {
        //1. 获取参数和请求路径
        String url = req.getRequestURI();
        String contextPath = req.getContextPath();
        //替换请求上下文
        url = url.replace(contextPath, "")
                //替换多余 '/'
                .replaceAll("/+", "/");
        // 2. 获取请求处理器
        if (!this.handlerMapping.containsKey(url)) {
            resp.getWriter().write("404 Not Found!");
            return;
        }

        Map<String, String[]> params = req.getParameterMap();

        Method method = this.handlerMapping.get(url);
        // 3. 解析参数
        //3.1 获取形参列表
        Class<?>[] parameterTypes = method.getParameterTypes();
        Object[] paramValues = new Object[parameterTypes.length];
        boolean directReturn = true;
        for (int i = 0; i < parameterTypes.length; i++) {
            Class<?> parameterType = parameterTypes[i];
            if (parameterType == HttpServletRequest.class) {
                paramValues[i] = req;
            } else if (parameterType == HttpServletResponse.class) {
                paramValues[i] = resp;
                directReturn = false;
            } else if (parameterType == String.class) {
                //通过运行时状态去获取
                Annotation[][] parameterAnnotations = method.getParameterAnnotations();
                for (int j = 0; j < parameterAnnotations.length; j++) {
                    for (Annotation annotation : parameterAnnotations[j]) {
                        if (annotation instanceof XRequestParam) {
                            String paramName = ((XRequestParam) annotation).value();
                            if (!"".equals(paramName.trim())) {
                                paramValues[i] = Arrays.toString(params.get(paramName))
                                        .replaceAll("\\[|\\]", "")
                                        .replaceAll("\\s+", ",");
                            }
                        }
                    }
                }
            }
        }
        //暂时硬编码
        String beanName = toLowerFirstCase(method.getDeclaringClass().getSimpleName());
        //赋值实参列表
        Object result = method.invoke(ioc.get(beanName), paramValues);
        //方法入参没有 resp 时 & 方法返回值部不为 void 直接返回
        if (!"void".equals(method.getReturnType().getName()) && directReturn) {
            resp.getWriter().write(Arrays.toString(new Object[]{result}).replaceAll("\\[|\\]", ""));
        }

    }


    /**
     * 加载配置并缓存 Controller 实例和 初始化请求对应的 Method映射
     *
     * @param config
     * @throws ServletException
     */
    @Override
    public void init(ServletConfig config) throws ServletException {
        //【初始化阶段】
        //====== 初始化加载 =====
        //1. 读取配置文件
        doLoadConfig(config.getInitParameter("contextConfigLocation"));
        //2. 扫描
        doScanner(contextConfig.getProperty("scanPackage"));
        //====== IOC 容器 =====
        //3. 初始化 IOC 容器，将扫描到的相关类实例化，保存到 IOC 容器
        doInstance();
        //AOP 生成新的代理对象
        //====== DI =====
        //4. 完成依赖注入
        doAutoWired();
        //====== MVC =====
        //5. 初始化 HandlerMapping
        doInitHandlerMapping();
        System.out.println("XSpring MVC Framework has been initialed");
    }

    /**
     * 读取配置文件
     *
     * @param contextConfigLocation
     */
    private void doLoadConfig(String contextConfigLocation) {
        try (InputStream is = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation)) {
            contextConfig.load(is);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void doScanner(String scanPackage) {
        URL url = this.getClass().getClassLoader().getResource("/" + scanPackage.replaceAll("\\.", "/"));
        File rootDir = new File(url.getFile());
        for (File file : rootDir.listFiles()) {
            if (file.isDirectory()) {
                doScanner(scanPackage + "." + file.getName());
            } else {
                if (!file.getName().endsWith(".class")) {
                    continue;
                }
                String clazzName = scanPackage + "." + file.getName().replace(".class", "");
                classNames.add(clazzName);
            }
        }
    }

    /**
     * 完成依赖注入
     */
    private void doAutoWired() {
        if (ioc.isEmpty()) {
            return;
        }
        Collection<Object> values = ioc.values();
        for (Object value : values) {
            if (null == value) {
                continue;
            }
            Class clazz = value.getClass();
            if (clazz.isAnnotationPresent(XController.class)) {
                Field[] fields = clazz.getDeclaredFields();
                for (Field field : fields) {
                    if (!field.isAnnotationPresent(XAutowired.class)) {
                        continue;
                    }
                    XAutowired autowired = field.getAnnotation(XAutowired.class);
                    String beanName = autowired.value();
                    if ("".equals(beanName)) {
                        beanName = toLowerFirstCase(field.getType().getSimpleName());
                    }
                    //注入依赖实例
                    field.setAccessible(true);
                    try {
                        field.set(value, ioc.get(beanName));
                    } catch (IllegalAccessException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
        //Spring 实例平铺后只需要再次扫描进行一次 DI 操作即可解决依赖注入的问题,此处演示未涉及，暂不做此处理
    }

    /**
     * 初始化 IOC 容器，将扫描到的相关类实例化，保存到 IOC 容器
     */
    private void doInstance() {
        if (classNames.isEmpty()) {
            return;
        }
        try {
            for (String clazzName : classNames) {
                if (!clazzName.contains(".")) {
                    continue;
                }
                Class<?> clazz = Class.forName(clazzName);
                // 1. 处理 XController
                if (clazz.isAnnotationPresent(XController.class)) {
                    ioc.put(toLowerFirstCase(clazz.getSimpleName()), clazz.newInstance());
                    // 2. 处理 XService
                } else if (clazz.isAnnotationPresent(XService.class)) {
                    //2.1 在多个包下出现相同的类名，只能（自己）起一个全局唯一的名字
                    //自定义命名
                    XService service = clazz.getAnnotation(XService.class);
                    String beanName = service.value();
                    //2.2 默认的类名首字母小写
                    if ("".equals(beanName)) {
                        beanName = toLowerFirstCase(clazz.getSimpleName());
                    }
                    //2.3 如果是接口
                    //判断有多少个实现类，如果有多个重名实例，只能抛异常
                    Object instance = clazz.newInstance();
                    ioc.put(beanName, instance);
                    for (Class<?> i : clazz.getInterfaces()) {
                        if (ioc.containsKey(toLowerFirstCase(i.getSimpleName()))) {
                            //不允许一个接口映射多个实例，默认取第一个
                            throw new Exception("The " + i.getName() + " is exists!!");
                        }
                        ioc.put(toLowerFirstCase(i.getSimpleName()), instance);
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 首字母小写
     *
     * @param name
     * @return
     */
    private String toLowerFirstCase(String name) {
        char[] chars = name.toCharArray();
        chars[0] += 32;
        return String.valueOf(chars);
    }

    /**
     * 初始化 HandlerMapping
     */
    private void doInitHandlerMapping() {
        if (classNames.isEmpty()) {
            return;
        }
        try {
            for (Map.Entry<String, Object> entry : ioc.entrySet()) {
                Class<?> clazz = entry.getValue().getClass();
                if (!clazz.isAnnotationPresent(XController.class)) {
                    continue;
                }
                String baseUrl = "";
                // 1. 处理 XController 中方法映射
                if (clazz.isAnnotationPresent(XController.class)) {
                    // 1.1 解析请求路径前缀
                    if (clazz.isAnnotationPresent(XRequestMapping.class)) {
                        XRequestMapping requestMapping = clazz.getAnnotation(XRequestMapping.class);
                        baseUrl = requestMapping.value();
                    }
                    // 1.2 解析public方法
                    Method[] methods = clazz.getMethods();
                    for (Method method : methods) {
                        if (method.isAnnotationPresent(XRequestMapping.class)) {
                            XRequestMapping annotation = method.getAnnotation(XRequestMapping.class);
                            //替换多/为单/
                            String url = ("/" + baseUrl + "/" + annotation.value()).replaceAll("/+", "/");
                            handlerMapping.put(url, method);
                            System.out.println("> Mapped--------->url: " + url + "," + method.getName());
                        }
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

   /**
     * support:
     * spring-v1
     * spring-v2
     *
     * @param name
     * @return
     */
    @XRequestMapping("/v2/welcome")
    public String welcome2(@XRequestParam(value = "name") String name) {
        return helloService.welcome(name);
    }

    /**
     * support:
     * spring-v1
     * spring-v2
     *
     * @param name
     * @return
     */
    @XRequestMapping("/v3/welcome")
    public String welcome3(@XRequestParam(value = "name") String name, @XRequestParam("nick") String nick) {
        return helloService.welcome(nick + " " + name);
    }