nosum-spring/src/main/java/cn/nosum/framework/mvc/v2/servlet/DispatcherServlet.java

package cn.nosum.framework.mvc.v2.servlet;

import cn.nosum.framework.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.IOException;
import java.io.InputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.*;
import java.io.File;

public class DispatcherServlet extends HttpServlet {
    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>();

    // 保存 URL 与对应执行方法的映射
    private 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 {
        try {
            //6、委派,根据URL去找到一个对应的Method并通过response返回
            doDispatch(req,resp);
        } catch (Exception e) {
            e.printStackTrace();
            resp.getWriter().write("500 Exception,Detail : " + Arrays.toString(e.getStackTrace()));
        }

    }

    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;
        }

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

        Method method = this.handlerMapping.get(url);

        //获取形参列表
        Class<?> [] parameterTypes = method.getParameterTypes();
        Object [] paramValues = new Object[parameterTypes.length];

        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;
            }else if(parameterType == String.class){
                // 需要通过运行时的状态才可以拿到
                Annotation[] [] pa = method.getParameterAnnotations();
                for (int j = 0; j < pa.length ; j ++) {
                    for(Annotation annotation : pa[i]){
                        if(annotation instanceof RequestParam){
                            String paramName = ((RequestParam) annotation).value();
                            if(!"".equals(paramName.trim())){
                               String value = Arrays.toString(params.get(paramName))
                                       .replaceAll("\\[|\\]","")
                                       .replaceAll("\\s+",",");
                                paramValues[i] = value;
                            }
                        }
                    }
                }
            }
        }
        // 通过 method 获取对应的类
        String beanName = toLowerFirstCase(method.getDeclaringClass().getSimpleName());
        // 从 ioc 中获取对应的类并且执行
        method.invoke(ioc.get(beanName),paramValues);

    }

    @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"));

        //==============IoC部分==============
        //3、初始化IoC容器，将扫描到的相关的类实例化，保存到IcC容器中
        doInstance();

        //AOP，新生成的代理对象

        //==============DI部分==============
        //4、完成依赖注入
        doAutowired();

        //==============MVC部分==============
        //5、初始化HandlerMapping
        doInitHandlerMapping();

        System.out.println("Spring framework is init.");
    }

    private void doInitHandlerMapping() {
        if(ioc.isEmpty()){ return;}
        for (Map.Entry<String,Object> entry : ioc.entrySet()) {
            Class<?> clazz = entry.getValue().getClass();
            if(!clazz.isAnnotationPresent(Controller.class)){ continue; }
            String baseUrl = "";
            if(clazz.isAnnotationPresent(RequestMapping.class)){
                // 取得类配置的 url
                RequestMapping requestMapping = clazz.getAnnotation(RequestMapping.class);
                baseUrl = requestMapping.value();
            }

            // 只获取 public 的方法
            for (Method method : clazz.getMethods()) {
                if(!method.isAnnotationPresent(RequestMapping.class)){continue;}
                // 提取每个方法配置的 url
                RequestMapping requestMapping = method.getAnnotation(RequestMapping.class);
                String url = ("/" + baseUrl + "/" + requestMapping.value()).replaceAll("/+","/");
                handlerMapping.put(url,method);
                System.out.println("Mapped : " + url + "," + method);
            }
        }
    }

    private void doAutowired() {
        if(ioc.isEmpty()){return;}
        for (Map.Entry<String,Object> entry : ioc.entrySet()) {
            // 把所有 private/protected/default/public 修饰字段都取出来
            for (Field field : entry.getValue().getClass().getDeclaredFields()) {
                if(!field.isAnnotationPresent(Autowired.class)){ continue; }

                Autowired autowired = field.getAnnotation(Autowired.class);

                // 没有自定义的beanName，根据类型注入
                String beanName = autowired.value().trim();
                if("".equals(beanName)){
                    beanName = field.getType().getName();
                }
                // 赋值
                try {
                    field.setAccessible(true);
                    field.set(entry.getValue(),ioc.get(beanName));
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private void doInstance() {
        if(classNames.isEmpty()){return;}

        try {
            for (String className : classNames) {
                Class<?> clazz = Class.forName(className);

                if(clazz.isAnnotationPresent(Controller.class)) {
                    String beanName = toLowerFirstCase(clazz.getSimpleName());
                    Object instance = clazz.newInstance();
                    ioc.put(beanName, instance);
                }else if(clazz.isAnnotationPresent(Service.class)){
                    // 获取自定义的名称
                    String beanName = clazz.getAnnotation(Service.class).value();
                    if("".equals(beanName.trim())){
                        beanName = toLowerFirstCase(clazz.getSimpleName());
                    }
                    Object instance = clazz.newInstance();
                    ioc.put(beanName, instance);

                    // 如果是接口，只能有一个实现，否则抛出异常
                    for (Class<?> i : clazz.getInterfaces()) {
                        if(ioc.containsKey(i.getName())){
                            throw new Exception("The " + i.getName() + " is exists!!");
                        }
                        ioc.put(i.getName(),instance);
                    }
                }else{
                    continue;
                }
            }
        }catch (Exception e){
            e.printStackTrace();
        }

    }

    private void doScanner(String scanPackage) {
        URL url = this.getClass().getClassLoader().getResource("/" + scanPackage.replaceAll("\\.","/"));
        File classPath = new File(url.getFile());

        //当成是一个 ClassPath 文件夹
        for (File file : classPath.listFiles()) {
            if(file.isDirectory()){
                doScanner(scanPackage + "." + file.getName());
            }else {
                if(!file.getName().endsWith(".class")){continue;}
                // 全类名 = 包名.类名
                String className = (scanPackage + "." + file.getName().replace(".class", ""));
                classNames.add(className);
            }
        }
    }

    private void doLoadConfig(String contextConfigLocation) {
        InputStream is = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation);
        try {
            contextConfig.load(is);
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(null != is){
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private String toLowerFirstCase(String simpleName) {
        char [] chars = simpleName.toCharArray();
        chars[0] += 32;
        return String.valueOf(chars);
    }
}