手撸了一个 Spring MVC 框架（spring的mvc框架是围绕什么来设计的?）

protected void initStrategies(ApplicationContext context) {
//用于处理上传请求。处理方法是将普通的request包装成MultipartHttpServletRequest，后者可以直接调用getFile方法获取File.
initMultipartResolver(context);
//SpringMVC主要有两个地方用到了Locale：一是ViewResolver视图解析的时候；二是用到国际化资源或者主题的时候。
initLocaleResolver(context); 
//用于解析主题。SpringMVC中一个主题对应一个properties文件，里面存放着跟当前主题相关的所有资源、
//如图片、css样式等。SpringMVC的主题也支持国际化， 
initThemeResolver(context);
//用来查找Handler的。
initHandlerMappings(context);
//从名字上看，它就是一个适配器。Servlet需要的处理方法的结构却是固定的，都是以request和response为参数的方法。
//如何让固定的Servlet处理方法调用灵活的Handler来进行处理呢？这就是HandlerAdapter要做的事情
initHandlerAdapters(context);
//其它组件都是用来干活的。在干活的过程中难免会出现问题，出问题后怎么办呢？
//这就需要有一个专门的角色对异常情况进行处理，在SpringMVC中就是HandlerExceptionResolver。
initHandlerExceptionResolvers(context);
//有的Handler处理完后并没有设置View也没有设置ViewName，这时就需要从request获取ViewName了，
//如何从request中获取ViewName就是RequestToViewNameTranslator要做的事情了。
initRequestToViewNameTranslator(context);
//ViewResolver用来将String类型的视图名和Locale解析为View类型的视图。
//View是用来渲染页面的，也就是将程序返回的参数填入模板里，生成html（也可能是其它类型）文件。
initViewResolvers(context);
//用来管理FlashMap的，FlashMap主要用在redirect重定向中传递参数。
initFlashMapManager(context); 
}

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.liugh</groupId>
<artifactId>liughMVC</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>war</packaging>

<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
<java.version>1.8</java.version>
</properties>

<dependencies>
<dependency>
<groupId>javax.servlet</groupId> 
<artifactId>javax.servlet-api</artifactId> 
<version>3.0.1</version> 
<scope>provided</scope>
</dependency>
</dependencies>
</project>

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
version="3.0">
<servlet>
<servlet-name>MySpringMVC</servlet-name>
<servlet-class>com.liugh.servlet.MyDispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>application.properties</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>MySpringMVC</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping></web-app>

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyController {
/**
 * 表示给controller注册别名
 * @return
 */
String value() default "";

}

@Target({ElementType.TYPE,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyRequestMapping {
/**
 * 表示访问该方法的url
 * @return
 */
String value() default "";

}

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyRequestParam {
/**
 * 表示参数的别名，必填
 * @return
 */
String value();

}

public class MyDispatcherServlet extends HttpServlet{

private Properties properties = new Properties();
private List<String> classNames = new ArrayList<>();
private Map<String, Object> ioc = new HashMap<>();
private Map<String, Method> handlerMapping = new HashMap<>();
private Map<String, Object> controllerMap =new HashMap<>();

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

//1.加载配置文件
 doLoadConfig(config.getInitParameter("contextConfigLocation"));
//2.初始化所有相关联的类,扫描用户设定的包下面所有的类
 doScanner(properties.getProperty("scanPackage"));
//3.拿到扫描到的类,通过反射机制,实例化,并且放到ioc容器中(k-v beanName-bean) beanName默认是首字母小写
 doInstance();
//4.初始化HandlerMapping(将url和method对应上)
 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 {
//处理请求
 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);

//获取方法的参数列表
 Class<?>[] parameterTypes = method.getParameterTypes();

//获取请求的参数
 Map<String, String[]> parameterMap = req.getParameterMap();

//保存参数值
Object [] paramValues= new Object[parameterTypes.length];

//方法的参数列表
for (int i = 0; i<parameterTypes.length; i++){ 
//根据参数名称，做某些处理 
String requestParam = parameterTypes[i].getSimpleName(); 


if (requestParam.equals("HttpServletRequest")){ 
//参数类型已明确，这边强转类型 
 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;
 }
 }
 } 
//利用反射机制来调用
try {
 method.invoke(this.controllerMap.get(url), paramValues);//第一个参数是method所对应的实例 在ioc容器中
 } catch (Exception e) {
 e.printStackTrace();
 }
 }



private void doLoadConfig(String location){
//把web.xml中的contextConfigLocation对应value值的文件加载到流里面
 InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream(location);
try {
//用Properties文件加载文件里的内容
 properties.load(resourceAsStream);
 } catch (IOException e) {
 e.printStackTrace();
 }finally {
//关流
if(!=resourceAsStream){
try {
 resourceAsStream.close();
 } catch (IOException e) {
 e.printStackTrace();
 }
 }
 }

 }

private void doScanner(String packageName) {
//把所有的.替换成/
 URL url =this.getClass().getClassLoader().getResource("/"+packageName.replaceAll("\\.", "/"));
 File dir = new File(url.getFile());
for (File file : dir.listFiles()) {
if(file.isDirectory()){
//递归读取包
 doScanner(packageName+"."+file.getName());
 }else{
String className =packageName +"." +file.getName().replace(".class", "");
 classNames.add(className);
 }
 }
 }



private void doInstance() {
if (classNames.isEmpty()) {
return;
 } 
for (String className : classNames) {
try {
//把类搞出来,反射来实例化(只有加@MyController需要实例化)
 Class<?> clazz =Class.forName(className);
if(clazz.isAnnotationPresent(MyController.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(MyController.class)){
continue;
 }

//拼url时,是controller头的url拼上方法上的url
String baseUrl ="";
if(clazz.isAnnotationPresent(MyRequestMapping.class)){
 MyRequestMapping annotation = clazz.getAnnotation(MyRequestMapping.class);
 baseUrl=annotation.value();
 }
 Method[] methods = clazz.getMethods();
for (Method method : methods) {
if(!method.isAnnotationPresent(MyRequestMapping.class)){
continue;
 }
 MyRequestMapping annotation = method.getAnnotation(MyRequestMapping.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写
 * @param name
 * @return
 */
private String toLowerFirstWord(String name){
 char[] charArray = name.toCharArray();
 charArray[0] += 32;
return String.valueOf(charArray);
 }


}

@MyController
@MyRequestMapping("/test")
public class TestController {

@MyRequestMapping("/doTest")
 public void test1(HttpServletRequest request, HttpServletResponse response,
@MyRequestParam("param") String param){
System.out.println(param);
try {
response.getWriter().write( "doTest method success! param:"+param);
 } catch (IOException e) {
e.printStackTrace();
 }
 }

 @MyRequestMapping("/doTest2")
public void test2(HttpServletRequest request, HttpServletResponse response){
try {
response.getWriter().println("doTest2 method success!");
 } catch (IOException e) {
e.printStackTrace();
 }
 }
}