SSM框架流程及原理分析

package servlet;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import annotation.HController;
import annotation.HRequestMapping;

/**
 * 手寫SpringMVC
 * 
 * @author hxz
 * @description TODO
 * @data 2020年1月2日 上午9:39:57
 */
public class MyDispatcherServlet extends HttpServlet {
   //加載屬性文件
	private Properties properties = new Properties();
    //裝載beanname
	private List<String> classNames = new ArrayList<String>();
	//ioc容器
	private Map<String, Object> ioc = new HashMap<String, Object>();
    //類似於以前自定義的cache緩存容器，這裡也是起到一個容器的作用
    //用於加載各個mapping
	private Map<String, Method> handlerMapping = new HashMap<String, Method>();
    //容器加載所有的controller
	private Map<String, Object> controllerMap = new HashMap<String, Object>();

	@Override
	public void init(ServletConfig config) throws ServletException {

		// 1.加載配置文件
		doLoadConfig(config.getInitParameter("contextConfigLocation"));

		// 2.初始化所有相關聯的類,掃描用戶設定的包下面所有的類
		doScanner(properties.getProperty("scanPackage"));

		// 3.拿到掃描到的類,通過反射機制,實例化,並且放到ioc容器中beanName默認是首字母小寫
		doInstance();

		// 4.初始化HandlerMapping(將url和method對應上)
		initHandlerMapping();

	}

	@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 {
			// 處理請求
			doDispatch(req, resp);
		} catch (Exception e) {
			resp.getWriter().write("500!! Server Exception");
		}

	}

	private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception {
		if (handlerMapping.isEmpty()) {
			return;
		}

		String url = req.getRequestURI();
		String contextPath = req.getContextPath();

		url = url.replace(contextPath, "").replaceAll("/+", "/");

		if (!this.handlerMapping.containsKey(url)) {
			resp.getWriter().write("404 NOT FOUND!");
			return;
		}

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

		// 獲取方法的參數列表
		Class<?>[] parameterTypes = method.getParameterTypes();

		// 獲取請求的參數
		Map<String, String[]> parameterMap = req.getParameterMap();

		// 保存參數值
		Object[] paramValues = new Object[parameterTypes.length];

		// 方法的參數列表
		for (int i = 0; i < parameterTypes.length; i++) {
			// 根據參數名稱，做某些處理
			String requestParam = parameterTypes[i].getSimpleName();

			if (requestParam.equals("HttpServletRequest")) {
				// 參數類型已明確，這邊強轉類型
				paramValues[i] = req;
				continue;
			}
			if (requestParam.equals("HttpServletResponse")) {
				paramValues[i] = resp;
				continue;
			}
			if (requestParam.equals("String")) {
				for (Entry<String, String[]> param : parameterMap.entrySet()) {
					String value = Arrays.toString(param.getValue()).replaceAll("\\[|\\]", "").replaceAll(",\\s", ",");
					paramValues[i] = value;
				}
			}
		}
		// 利用反射機制來調用
		try {
			method.invoke(this.controllerMap.get(url), paramValues);// 第一個參數是method所對應的實例
																	// 在ioc容器中
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	private void doLoadConfig(String location) {
		// 把web.xml中的contextConfigLocation對應value值的文件加載到流裡面
		InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream(location);
		try {
			// 用Properties文件加載文件裡的內容
			properties.load(resourceAsStream);
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			// 關流
			if (null != resourceAsStream) {
				try {
					resourceAsStream.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}

	}

	private void doScanner(String packageName) {
		// 把所有的.替換成/
		URL url = this.getClass().getClassLoader().getResource("/" + packageName.replaceAll("\\.", "/"));
		File dir = new File(url.getFile());
		for (File file : dir.listFiles()) {
			if (file.isDirectory()) {
				// 遞歸讀取包
				doScanner(packageName + "." + file.getName());
			} else {
				String className = packageName + "." + file.getName().replace(".class", "");
				classNames.add(className);
			}
		}
	}
	//利用java的反射機制
	private void doInstance() {
		if (classNames.isEmpty()) {
			return;
		}
		for (String className : classNames) {
			try {
				// 把類搞出來,反射來實例化
				Class<?> clazz = Class.forName(className);
				if (clazz.isAnnotationPresent(HController.class)) {
					ioc.put(toLowerFirstWord(clazz.getSimpleName()), clazz.newInstance());
				} else {
					continue;
				}

			} catch (Exception e) {
				e.printStackTrace();
				continue;
			}
		}
	}

	private void initHandlerMapping() {
		if (ioc.isEmpty()) {
			return;
		}
		try {
		    
			for (Entry<String, Object> entry : ioc.entrySet()) {
				Class<? extends Object> clazz = entry.getValue().getClass();
				if (!clazz.isAnnotationPresent(HController.class)) {
					continue;
				}

				// 拼url時,是controller頭的url拼上方法上的url
				String baseUrl = "";
				if (clazz.isAnnotationPresent(HRequestMapping.class)) {
					HRequestMapping annotation = clazz.getAnnotation(HRequestMapping.class);
					baseUrl = annotation.value();
				}
				Method[] methods = clazz.getMethods();
				for (Method method : methods) {
					if (!method.isAnnotationPresent(HRequestMapping.class)) {
						continue;
					}
					HRequestMapping annotation = method.getAnnotation(HRequestMapping.class);
					String url = annotation.value();

					url = (baseUrl + "/" + url).replaceAll("/+", "/");
					handlerMapping.put(url, method);
					controllerMap.put(url, clazz.newInstance());
					System.out.println(url + "," + method);
				}

			}

		} catch (Exception e) {
			e.printStackTrace();
		}

	}

	/**
	 * 把字符串的首字母小寫
	 * 
	 * @param name
	 * @return
	 */
	private String toLowerFirstWord(String name) {
		char[] charArray = name.toCharArray();
		charArray[0] += 32;
		return String.valueOf(charArray);
	}

}

 protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);