<?xml version="1.0" encoding="UTF-8"?>
<web-app>
    <servlet>
        <servlet-name>HelloServlet</servlet-name>
        <servlet-class>cn.how2j.javaweb.HelloServlet</servlet-class>
        <init-param>
            <param-name>author</param-name>
            <param-value>how2j(servlet)</param-value>
        </init-param>
        <init-param>
            <param-name>site</param-name>
            <param-value>http://how2j.cn(servlet)</param-value>
        </init-param>
    </servlet>

    <servlet-mapping>
        <servlet-name>HelloServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

package cn.how2j.javaweb;

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

public class HelloServlet extends HttpServlet {
    public HelloServlet(){
        System.out.println(this + " 的构造方法");
    }

    public void init(ServletConfig config){
        String author = config.getInitParameter("author");
        String site = config.getInitParameter("site");

        System.out.println(this + " 的初始化方法 init");
        System.out.println("获取到了参数 author:" + author);
        System.out.println("获取到了参数 site:" + site);
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response){
        try {
            System.out.println(this + " 的doGet() 方法");
            response.getWriter().println("Hello DIY Tomcat from HelloServlet@javaweb " + this);
        } catch (Exception e) {
            e.printStackTrace();

        }
    }
    
    public void destroy(){
        System.out.println(this + " 被销毁");
    }

}

package cn.how2j.diytomcat.catalina;

import cn.how2j.diytomcat.classloader.WebappClassLoader;
import cn.how2j.diytomcat.exception.WebConfigDuplicatedException;
import cn.how2j.diytomcat.http.ApplicationContext;
import cn.how2j.diytomcat.http.StandardServletConfig;
import cn.how2j.diytomcat.util.ContextXMLUtil;
import cn.how2j.diytomcat.watcher.ContextFileChangeWatcher;
import cn.hutool.core.date.DateUtil;
import cn.hutool.core.date.TimeInterval;
import cn.hutool.core.io.FileUtil;
import cn.hutool.core.util.StrUtil;
import cn.hutool.log.LogFactory;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import java.io.File;
import java.util.*;

public class Context {
    private String path;
    private String docBase;
    private File contextWebXmlFile;

    private Map<String, String> url_servletClassName;
    private Map<String, String> url_ServletName;
    private Map<String, String> servletName_className;
    private Map<String, String> className_servletName;
    private Map<String, Map<String, String>> servlet_className_init_params;

    private WebappClassLoader webappClassLoader;

    private Host host;
    private boolean reloadable;
    private ContextFileChangeWatcher contextFileChangeWatcher;

    private ServletContext servletContext;
    private Map<Class<?>, HttpServlet> servletPool;

    public Context(String path, String docBase, Host host, boolean reloadable) {
        TimeInterval timeInterval = DateUtil.timer();
        this.host = host;
        this.reloadable = reloadable;

        this.path = path;
        this.docBase = docBase;
        this.contextWebXmlFile = new File(docBase, ContextXMLUtil.getWatchedResource());

        this.url_servletClassName = new HashMap<>();
        this.url_ServletName = new HashMap<>();
        this.servletName_className = new HashMap<>();
        this.className_servletName = new HashMap<>();
        this.servlet_className_init_params = new HashMap<>();

        this.servletContext = new ApplicationContext(this);

        ClassLoader commonClassLoader = Thread.currentThread().getContextClassLoader();
        this.webappClassLoader = new WebappClassLoader(docBase, commonClassLoader);

        this.servletPool = new HashMap<>();

        LogFactory.get().info("Deploying web application directory {}", this.docBase);
        deploy();
        LogFactory.get().info("Deployment of web application directory {} has finished in {} ms", this.docBase,timeInterval.intervalMs());
    }

    public void reload() {
        host.reload(this);
    }

    private void deploy() {
        init();

        if(reloadable){
            contextFileChangeWatcher = new ContextFileChangeWatcher(this);
            contextFileChangeWatcher.start();
        }
    }

    private void init() {
        if (!contextWebXmlFile.exists())
            return;

        try {
            checkDuplicated();
        } catch (WebConfigDuplicatedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return;
        }

        String xml = FileUtil.readUtf8String(contextWebXmlFile);
        Document d = Jsoup.parse(xml);
        parseServletMapping(d);
        parseServletInitParams(d);
    }

    private void parseServletMapping(Document d) {
        // url_ServletName
        Elements mappingurlElements = d.select("servlet-mapping url-pattern");
        for (Element mappingurlElement : mappingurlElements) {
            String urlPattern = mappingurlElement.text();
            String servletName = mappingurlElement.parent().select("servlet-name").first().text();
            url_ServletName.put(urlPattern, servletName);
        }
        // servletName_className / className_servletName
        Elements servletNameElements = d.select("servlet servlet-name");
        for (Element servletNameElement : servletNameElements) {
            String servletName = servletNameElement.text();
            String servletClass = servletNameElement.parent().select("servlet-class").first().text();
            servletName_className.put(servletName, servletClass);
            className_servletName.put(servletClass, servletName);
        }
        // url_servletClassName
        Set<String> urls = url_ServletName.keySet();
        for (String url : urls) {
            String servletName = url_ServletName.get(url);
            String servletClassName = servletName_className.get(servletName);
            url_servletClassName.put(url, servletClassName);
        }
    }

    private void checkDuplicated(Document d, String mapping, String desc) throws WebConfigDuplicatedException {
        Elements elements = d.select(mapping);
        // 判断逻辑是放入一个集合，然后把集合排序之后看两临两个元素是否相同
        List<String> contents = new ArrayList<>();
        for (Element e : elements) {
            contents.add(e.text());
        }

        Collections.sort(contents);

        for (int i = 0; i < contents.size() - 1; i++) {
            String contentPre = contents.get(i);
            String contentNext = contents.get(i + 1);
            if (contentPre.equals(contentNext)) {
                throw new WebConfigDuplicatedException(StrUtil.format(desc, contentPre));
            }
        }

    }

    private void checkDuplicated() throws WebConfigDuplicatedException {
        String xml = FileUtil.readUtf8String(contextWebXmlFile);
        Document d = Jsoup.parse(xml);

        checkDuplicated(d, "servlet-mapping url-pattern", "servlet url 重复,请保持其唯一性:{} ");
        checkDuplicated(d, "servlet servlet-name", "servlet 名称重复,请保持其唯一性:{} ");
        checkDuplicated(d, "servlet servlet-class", "servlet 类名重复,请保持其唯一性:{} ");
    }

    public String getServletClassName(String uri) {
        return url_servletClassName.get(uri);
    }

    public String getPath() {
        return path;
    }

    public void setPath(String path) {
        this.path = path;
    }

    public String getDocBase() {
        return docBase;
    }

    public void setDocBase(String docBase) {
        this.docBase = docBase;
    }

    public WebappClassLoader getWebappClassLoader() {
        return webappClassLoader;
    }

    public void stop() {
        webappClassLoader.stop();
        contextFileChangeWatcher.stop();

        destroyServlets();
    }

    public boolean isReloadable() {
        return reloadable;
    }

    public void setReloadable(boolean reloadable) {
        this.reloadable = reloadable;
    }

    public ServletContext getServletContext() {
        return servletContext;
    }

    public synchronized HttpServlet  getServlet(Class<?> clazz)
            throws InstantiationException, IllegalAccessException, ServletException {
        HttpServlet servlet = servletPool.get(clazz);

        if (null == servlet) {
            servlet = (HttpServlet) clazz.newInstance();
            ServletContext servletContext = this.getServletContext();

            String className = clazz.getName();
            String servletName = className_servletName.get(className);

            Map<String, String> initParameters = servlet_className_init_params.get(className);
            ServletConfig servletConfig = new StandardServletConfig(servletContext, servletName, initParameters);

            servlet.init(servletConfig);
            servletPool.put(clazz, servlet);
        }

        return servlet;
    }

    private void parseServletInitParams(Document d) {
        Elements servletClassNameElements = d.select("servlet-class");
        for (Element servletClassNameElement : servletClassNameElements) {
            String servletClassName = servletClassNameElement.text();

            Elements initElements = servletClassNameElement.parent().select("init-param");
            if (initElements.isEmpty())
                continue;

            Map<String, String> initParams = new HashMap<>();

            for (Element element : initElements) {
                String name = element.select("param-name").get(0).text();
                String value = element.select("param-value").get(0).text();
                initParams.put(name, value);
            }

            servlet_className_init_params.put(servletClassName, initParams);

        }

//		System.out.println("class_name_init_params:" + servlet_className_init_params);

    }
    private void destroyServlets() {
        Collection<HttpServlet> servlets = servletPool.values();
        for (HttpServlet servlet : servlets) {
            servlet.destroy();
        }
    }

}