简单实现mini版的springMVC框架

创建maven工程，依赖什么的，根据下面需要自己可以到maven仓库找
1、定义注解ExtController、ExtRequestMapping，这两个注解用在controller类上

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface ExtController {
}

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface ExtRequestMapping {
    String value() default "";
}

2、定义一个controller层并创建一个controller类，使用到了刚刚的两个注解

@ExtController
@ExtRequestMapping("/user")
public class IndexController {

    @ExtRequestMapping("/index")
    public String index() {
        return "index";
    }
}

3、定义ExtDispatcherServlet，这个是核心

public class ExtDispatcherServlet extends HttpServlet {
	//这个map用来存放类的，key是类名的小写，value的类的实例
    private ConcurrentHashMap<String, Object> springmvcBeans = new ConcurrentHashMap<>();
    //这个map用来存放路径和类实例，key是路径，如上面的/user/index,value是存放类的实例
    private ConcurrentHashMap<String, Object> urlBeans = new ConcurrentHashMap<>();
    //这个map用来存放路径和方法名，key是路径，value是方法名
    private ConcurrentHashMap<String, Object> urlMethods = new ConcurrentHashMap<>();

    @Override
    public void init() {
        //获取当前包下的所有类
        List<Class<?>> classes = ClassUtil.getClasses("com.zeny.mvc.controller");
        //将扫包范围所有的类，注入到springmvc容器里面，存放在map集合中key为默认类名小写， value为对象
        try {
            findClassMVCAnnotation(classes);
            handlerMapping();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void findClassMVCAnnotation(List<Class<?>> classes) throws Exception {
        for (Class<?> classInfo : classes) {
            ExtController extController = classInfo.getAnnotation(ExtController.class);
            if (extController != null) {
            	//注解存在的类，保存在springmvcBeans
                String beanId = ClassUtil.toLowerCaseFristOne(classInfo.getSimpleName());
                springmvcBeans.put(beanId, classInfo.newInstance());
            }
        }
    }

    public void handlerMapping() {
    	//遍历类springmvcBeans进行映射
        for (Map.Entry entry : springmvcBeans.entrySet()) {
            Object object = entry.getValue();
            Class<?> classInfo = object.getClass();
            //先看类上是否有ExtRequestMapping 注解
            ExtRequestMapping extRequestMapping = classInfo.getAnnotation(ExtRequestMapping.class);
            String url = "";
            if (extRequestMapping != null) {
                String value = extRequestMapping.value();
                url += value;
            }
            Method[] methods = classInfo.getDeclaredMethods();
            for (Method method : methods) {
            	//再看类上是否有ExtRequestMapping 注解
                ExtRequestMapping declaredAnnotation = method.getDeclaredAnnotation(ExtRequestMapping.class);
                if (declaredAnnotation != null) {
                    String baseUrl = url + declaredAnnotation.value();
                    urlBeans.put(baseUrl, object);
                    urlMethods.put(baseUrl, method.getName());
                }

            }
        }
    }


    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //处理请求
        //获取URL地址
        String contextPath = request.getContextPath();
        String requestURI = request.getRequestURI();
        String url = requestURI.replace(contextPath, "");
        System.out.println(url);
        //根据路径查找类
        Object bean = urlBeans.get(url);
        //根据路径查找方法名
        String method = (String) urlMethods.get(url);
        if (bean == null || (method == null || method.equals(""))) {
        	//响应404
            response.getWriter().println(responsePage());
            return;
        }
        //找到对应的方法，类调用该方法
        Class<?> classInfo = bean.getClass();
        try {
        	//通过urlBeans根据URL找到类，通过urlMethods根据URL找到方法名，然后调用该方法，获得返回值，然后解析到页面
            Method classInfoMethod = classInfo.getMethod(method);
            String str = (String) classInfoMethod.invoke(bean);
            extResourceViewResolver(str, request, response);
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    private void extResourceViewResolver(String pageName, HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String prefix = "/static/";  //在webapp下创建static文件夹来存放页面，也可以换成自己的
        String suffix = ".jsp";
        request.getRequestDispatcher(prefix + pageName + suffix).forward(request, response);
    }
	//404响应页面
    private String responsePage() {
        return "<!doctype html>\n" +
                "<html lang=\"en\">\n" +
                "<head><title>HTTP Status 404 Not Found</title>\n" +
                "    <style type=\"text/css\">H1 {\n" +
                "        font-family: Tahoma, Arial, sans-serif;\n" +
                "        color: white;\n" +
                "        background-color: #525D76;\n" +
                "        font-size: 22px;\n" +
                "    }\n" +
                "\n" +
                "    H2 {\n" +
                "        font-family: Tahoma, Arial, sans-serif;\n" +
                "        color: white;\n" +
                "        background-color: #525D76;\n" +
                "        font-size: 16px;\n" +
                "    }\n" +
                "\n" +
                "    H3 {\n" +
                "        font-family: Tahoma, Arial, sans-serif;\n" +
                "        color: white;\n" +
                "        background-color: #525D76;\n" +
                "        font-size: 14px;\n" +
                "    }\n" +
                "\n" +
                "    BODY {\n" +
                "        font-family: Tahoma, Arial, sans-serif;\n" +
                "        color: black;\n" +
                "        background-color: white;\n" +
                "    }\n" +
                "\n" +
                "    B {\n" +
                "        font-family: Tahoma, Arial, sans-serif;\n" +
                "        color: white;\n" +
                "        background-color: #525D76;\n" +
                "    }\n" +
                "\n" +
                "    P {\n" +
                "        font-family: Tahoma, Arial, sans-serif;\n" +
                "        background: white;\n" +
                "        color: black;\n" +
                "        font-size: 12px;\n" +
                "    }\n" +
                "\n" +
                "    A {\n" +
                "        color: black;\n" +
                "    }\n" +
                "\n" +
                "    A.name {\n" +
                "        color: black;\n" +
                "    }\n" +
                "\n" +
                "    HR {\n" +
                "        color: #525D76;\n" +
                "    }</style>\n" +
                "</head>\n" +
                "<body><h1>HTTP Status 404 - Not Found</h1>\n" +
                "<hr class=\"line\"/>\n" +
                "<p><b>Type</b> Status Report</p>\n" +
                "<p><b>Message</b> sorry your url is wrong</p>\n" +
                "<p><b>Description</b> The origin server did not find a current representation for the target resource or is not willing\n" +
                "    to disclose that one exists.</p>\n" +
                "<hr class=\"line\"/>\n" +
                "\n" +
                "</html>";
    }
}

4、在web.xml文件中配置ExtDispatcherServlet，具体路径换成自己的

    <servlet>
        <servlet-name>extDispatcherServlet</servlet-name>
        <servlet-class>com.zeny.mvc.servlet.ExtDispatcherServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>extDispatcherServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

5、部署在Tomcat中测试

成功了！！！！！！

附上:ClassUtil

public class ClassUtil {

	/**
	 * 取得某个接口下所有实现这个接口的类
	 */
	public static List<Class> getAllClassByInterface(Class c) {
		List<Class> returnClassList = null;

		if (c.isInterface()) {
			// 获取当前的包名
			String packageName = c.getPackage().getName();
			// 获取当前包下以及子包下所以的类
			List<Class<?>> allClass = getClasses(packageName);
			if (allClass != null) {
				returnClassList = new ArrayList<Class>();
				for (Class classes : allClass) {
					// 判断是否是同一个接口
					if (c.isAssignableFrom(classes)) {
						// 本身不加入进去
						if (!c.equals(classes)) {
							returnClassList.add(classes);
						}
					}
				}
			}
		}

		return returnClassList;
	}

	/*
	 * 取得某一类所在包的所有类名 不含迭代
	 */
	public static String[] getPackageAllClassName(String classLocation, String packageName) {
		// 将packageName分解
		String[] packagePathSplit = packageName.split("[.]");
		String realClassLocation = classLocation;
		int packageLength = packagePathSplit.length;
		for (int i = 0; i < packageLength; i++) {
			realClassLocation = realClassLocation + File.separator + packagePathSplit[i];
		}
		File packeageDir = new File(realClassLocation);
		if (packeageDir.isDirectory()) {
			String[] allClassName = packeageDir.list();
			return allClassName;
		}
		return null;
	}

	/**
	 * 从包package中获取所有的Class
	 * 
	 * @param pack
	 * @return
	 */
	public static List<Class<?>> getClasses(String packageName) {

		// 第一个class类的集合
		List<Class<?>> classes = new ArrayList<Class<?>>();
		// 是否循环迭代
		boolean recursive = true;
		// 获取包的名字 并进行替换
		String packageDirName = packageName.replace('.', '/');
		// 定义一个枚举的集合 并进行循环来处理这个目录下的things
		Enumeration<URL> dirs;
		try {
			dirs = Thread.currentThread().getContextClassLoader().getResources(packageDirName);
			// 循环迭代下去
			while (dirs.hasMoreElements()) {
				// 获取下一个元素
				URL url = dirs.nextElement();
				// 得到协议的名称
				String protocol = url.getProtocol();
				// 如果是以文件的形式保存在服务器上
				if ("file".equals(protocol)) {
					// 获取包的物理路径
					String filePath = URLDecoder.decode(url.getFile(), "UTF-8");
					// 以文件的方式扫描整个包下的文件 并添加到集合中
					findAndAddClassesInPackageByFile(packageName, filePath, recursive, classes);
				} else if ("jar".equals(protocol)) {
					// 如果是jar包文件
					// 定义一个JarFile
					JarFile jar;
					try {
						// 获取jar
						jar = ((JarURLConnection) url.openConnection()).getJarFile();
						// 从此jar包 得到一个枚举类
						Enumeration<JarEntry> entries = jar.entries();
						// 同样的进行循环迭代
						while (entries.hasMoreElements()) {
							// 获取jar里的一个实体 可以是目录 和一些jar包里的其他文件 如META-INF等文件
							JarEntry entry = entries.nextElement();
							String name = entry.getName();
							// 如果是以/开头的
							if (name.charAt(0) == '/') {
								// 获取后面的字符串
								name = name.substring(1);
							}
							// 如果前半部分和定义的包名相同
							if (name.startsWith(packageDirName)) {
								int idx = name.lastIndexOf('/');
								// 如果以"/"结尾 是一个包
								if (idx != -1) {
									// 获取包名 把"/"替换成"."
									packageName = name.substring(0, idx).replace('/', '.');
								}
								// 如果可以迭代下去 并且是一个包
								if ((idx != -1) || recursive) {
									// 如果是一个.class文件 而且不是目录
									if (name.endsWith(".class") && !entry.isDirectory()) {
										// 去掉后面的".class" 获取真正的类名
										String className = name.substring(packageName.length() + 1, name.length() - 6);
										try {
											// 添加到classes
											classes.add(Class.forName(packageName + '.' + className));
										} catch (ClassNotFoundException e) {
											e.printStackTrace();
										}
									}
								}
							}
						}
					} catch (IOException e) {
						e.printStackTrace();
					}
				}
			}
		} catch (IOException e) {
			e.printStackTrace();
		}

		return classes;
	}

	/**
	 * 以文件的形式来获取包下的所有Class
	 * 
	 * @param packageName
	 * @param packagePath
	 * @param recursive
	 * @param classes
	 */
	public static void findAndAddClassesInPackageByFile(String packageName, String packagePath, final boolean recursive,
			List<Class<?>> classes) {
		// 获取此包的目录 建立一个File
		File dir = new File(packagePath);
		// 如果不存在或者 也不是目录就直接返回
		if (!dir.exists() || !dir.isDirectory()) {
			return;
		}
		// 如果存在 就获取包下的所有文件 包括目录
		File[] dirfiles = dir.listFiles(new FileFilter() {
			// 自定义过滤规则 如果可以循环(包含子目录) 或则是以.class结尾的文件(编译好的java类文件)
			public boolean accept(File file) {
				return (recursive && file.isDirectory()) || (file.getName().endsWith(".class"));
			}
		});
		// 循环所有文件
		for (File file : dirfiles) {
			// 如果是目录 则继续扫描
			if (file.isDirectory()) {
				findAndAddClassesInPackageByFile(packageName + "." + file.getName(), file.getAbsolutePath(), recursive,
						classes);
			} else {
				// 如果是java类文件 去掉后面的.class 只留下类名
				String className = file.getName().substring(0, file.getName().length() - 6);
				try {
					// 添加到集合中去
					classes.add(Class.forName(packageName + '.' + className));
				} catch (ClassNotFoundException e) {
					e.printStackTrace();
				}
			}
		}
	}
    public static String toLowerCaseFristOne(String str) {
        if (Character.isLowerCase(str.charAt(0))) {
            return str;
        } else {
            return (Character.toLowerCase(str.charAt(0))) + str.substring(1);
        }
    }
}