手撕源码之代码手写mvc
1.首先附上代码地址
https://gitee.com/cqut__lin/hand-tear-source-code
实现思路
Spring主要也是通过DispatcherServlet实现了Servlet这个接口，又叫前端控制器，来自前端的请求会先到达这里，它负责到后台去匹配合适的handler。DispatcherServlet的主要工作流程如下：
前端请求到达DispatcherServlet。
前端控制器请求HandlerMappering 查找Handler。
如果查找到存在的处理器，进一步去调用service和dao层
返回结果再到controller层，渲染具体的视图，返回结果给页面。
通过手写mvc基础httpservlet实现了spring与springmvc的一些初级功能。
2.手写框架基础关系
3.代码结构
web.xml
读取WEB-INF下的web.xml，获取servlet的实现类位置
声明了一个名为mymvc的servlet
位置在com.myspringmvc.mvcframework.DispatcherServlet
参数contextConfigLocation，值是application.properties
所有的/*请求都被映射到名称为mymvc的servlet
<?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/j2ee" xmlns:javaee="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/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
version="2.4">
<display-name>MySpringMVC Web Application</display-name>
<servlet>
<servlet-name>mymvc</servlet-name>
<servlet-class>com.myspringmvc.mvcframework.DispatcherServlet</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>mymvc</servlet-name>
<url-pattern>/*
简单模拟application.properties
scanPackage=com.myspringmvc.demo
jdbc.driver = oracle.jdbc.driver.OracleDriver
jdbc.url = jdbc:oracle:thin:@172.25.1.196:1521:mldn
HttpServletBean
读取配置文件
public abstract class HttpServletBean extends HttpServlet {
//保存application.properties配置文件中的内容
protected Properties contextConfig = new Properties();
//加载配置文件
public void doLoadConfig(String contextConfigLocation) {
//直接从类路径下找到Spring主配置文件所在的路径
//并且将其读取出来放到Properties对象中
//相对于scanPackage=com.gupaoedu.demo 从文件中保存到了内存中
InputStream fis = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation);
try {
contextConfig.load(fis);
} catch (IOException e) {
e.printStackTrace();
}finally {
if(null != fis){
try {
fis.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
FrameworkServlet
使用策略模式进行init
public abstract class FrameworkServlet extends HttpServletBean{
//保存扫描的所有的类名
private List<String> classNames = new ArrayList<String>();
//映射处理器
protected List<Handler> handlerMapping = new ArrayList<Handler>();
//传说中的IOC容器，我们来揭开它的神秘面纱
//为了简化程序，暂时不考虑ConcurrentHashMap
// 主要还是关注设计思想和原理
private Map<String,Object> ioc = new HashMap<String,Object>();
//初始化阶段
@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"));
//3、初始化扫描到的类，并且将它们放入到ICO容器之中
doInstance();
//4、完成依赖注入
doAutowired();
//5、初始化HandlerMapping
initHandlerMapping();
System.out.println("GP Spring framework is init.");
}
//初始化url和Method的一对一对应关系
private void initHandlerMapping() {
if(ioc.isEmpty()){ return; }
for (Map.Entry<String, Object> entry : ioc.entrySet()) {
Class<?> clazz = entry.getValue().getClass();
if(!clazz.isAnnotationPresent(Controller.class)){continue;}
//保存写在类上面的@GPRequestMapping("/demo")
String baseUrl = "";
if(clazz.isAnnotationPresent(RequestMapping.class)){
RequestMapping requestMapping = clazz.getAnnotation(RequestMapping.class);
baseUrl = requestMapping.value();
}
//默认获取所有的public方法
for (Method method : clazz.getMethods()) {
if(!method.isAnnotationPresent(RequestMapping.class)){continue;}
RequestMapping requestMapping = method.getAnnotation(RequestMapping.class);
//优化
// //demo///query
String regex = ("/" + baseUrl + "/" + requestMapping.value())
.replaceAll("/+","/");
Pattern pattern = Pattern.compile(regex);
this.handlerMapping.add(new Handler(pattern,entry.getValue(),method));
// handlerMapping.put(url,method);
System.out.println("Mapped :" + pattern + "," + method);
}
}
}
//自动依赖注入
private void doAutowired() {
if(ioc.isEmpty()){return;}
for (Map.Entry<String, Object> entry : ioc.entrySet()) {
//Declared 所有的，特定的 字段，包括private/protected/default
//正常来说，普通的OOP编程只能拿到public的属性
Field[] fields = entry.getValue().getClass().getDeclaredFields();
for (Field field : fields) {
if(!field.isAnnotationPresent(Autowired.class)){continue;}
Autowired autowired = field.getAnnotation(Autowired.class);
//如果用户没有自定义beanName，默认就根据类型注入
//这个地方省去了对类名首字母小写的情况的判断，这个作为课后作业
//小伙伴们自己去完善
String beanName = autowired.value().trim();
if("".equals(beanName)){
//获得接口的类型，作为key待会拿这个key到ioc容器中去取值
beanName = field.getType().getName();
}
//如果是public以外的修饰符，只要加了@Autowired注解，都要强制赋值
//反射中叫做暴力访问， 强吻
field.setAccessible(true);
try {
//用反射机制，动态给字段赋值
field.set(entry.getValue(),ioc.get(beanName));
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
}
private void doInstance() {
//初始化，为DI做准备
if(classNames.isEmpty()){return;}
try {
for (String className : classNames) {
Class<?> clazz = Class.forName(className);
//什么样的类才需要初始化呢？
//加了注解的类，才初始化，怎么判断？
//为了简化代码逻辑，主要体会设计思想，只举例 @Controller和@Service,
// @Componment...就一一举例了
if(clazz.isAnnotationPresent(Controller.class)){
Object instance = clazz.newInstance();
//Spring默认类名首字母小写
String beanName = toLowerFirstCase(clazz.getSimpleName());
ioc.put(beanName,instance);
}else if(clazz.isAnnotationPresent(Service.class)){
//1、自定义的beanName
Service service = clazz.getAnnotation(Service.class);
String beanName = service.value();
//2、默认类名首字母小写
if("".equals(beanName.trim())){
beanName = toLowerFirstCase(clazz.getSimpleName());
}
Object instance = clazz.newInstance();
ioc.put(beanName,instance);
//3、根据类型自动赋值,投机取巧的方式
for (Class<?> i : clazz.getInterfaces()) {
if(ioc.containsKey(i.getName())){
throw new Exception("The “" + i.getName() + "” is exists!!");
}
//把接口的类型直接当成key了
ioc.put(i.getName(),instance);
}
}else {
continue;
}
}
}catch (Exception e){
e.printStackTrace();
}
}
//如果类名本身是小写字母，确实会出问题
//但是我要说明的是：这个方法是我自己用，private的
//传值也是自己传，类也都遵循了驼峰命名法
//默认传入的值，存在首字母小写的情况，也不可能出现非字母的情况
//为了简化程序逻辑，就不做其他判断了，大家了解就OK
//其实用写注释的时间都能够把逻辑写完了
private String toLowerFirstCase(String simpleName) {
char [] chars = simpleName.toCharArray();
//之所以加，是因为大小写字母的ASCII码相差32，
// 而且大写字母的ASCII码要小于小写字母的ASCII码
//在Java中，对char做算学运算，实际上就是对ASCII码做算学运算
chars[0] += 32;
return String.valueOf(chars);
}
//扫描出相关的类
private void doScanner(String scanPackage) {
//scanPackage = com.gupaoedu.demo ，存储的是包路径
//转换为文件路径，实际上就是把.替换为/就OK了
//classpath
URL url = this.getClass().getClassLoader().getResource("/" + scanPackage.replaceAll("\\.","/"));
File classPath = new File(url.getFile());
for (File file : classPath.listFiles()) {
if(file.isDirectory()){
doScanner(scanPackage + "." + file.getName());
}else{
if(!file.getName().endsWith(".class")){ continue;}
String className = (scanPackage + "." + file.getName().replace(".class",""));
classNames.add(className);
}
}
}
}
DispatcherServlet
设计Dispatcher
public class DispatcherServlet extends FrameworkServlet{
@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 {
//6、调用，运行阶段
try {
doDispatch(req,resp);
} catch (Exception e) {
e.printStackTrace();
resp.getWriter().write("500 Exection,Detail : " + Arrays.toString(e.getStackTrace()));
}
}
private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception {
Handler handler = getHandler(req);
if(handler == null){
resp.getWriter().write("404 Not Found!!!");
return;
}
//获得方法的形参列表
Class<?> [] paramTypes = handler.getParamTypes();
Object [] paramValues = new Object[paramTypes.length];
Map<String, Integer> paramIndexMapping =handler.getParamIndexMapping();
Map<String,String[]> params = req.getParameterMap();
for (Map.Entry<String, String[]> parm : params.entrySet()) {
String value = Arrays.toString(parm.getValue()).replaceAll("\\[|\\]","")
.replaceAll("\\s",",");
if(!paramIndexMapping.containsKey(parm.getKey())){continue;}
int index = paramIndexMapping.get(parm.getKey());
paramValues[index] = convert(paramTypes[index],value);
}
if(paramIndexMapping.containsKey(HttpServletRequest.class.getName())) {
int reqIndex = paramIndexMapping.get(HttpServletRequest.class.getName());
paramValues[reqIndex] = req;
}
if(paramIndexMapping.containsKey(HttpServletResponse.class.getName())) {
int respIndex = paramIndexMapping.get(HttpServletResponse.class.getName());
paramValues[respIndex] = resp;
}
Object returnValue = handler.getMethod().invoke(handler.getController(),paramValues);
if(returnValue == null || returnValue instanceof Void){ return; }
resp.getWriter().write(returnValue.toString());
}
private Handler getHandler(HttpServletRequest req) {
if(handlerMapping.isEmpty()){return null;}
//绝对路径
String url = req.getRequestURI();
//处理成相对路径
String contextPath = req.getContextPath();
url = url.replaceAll(contextPath,"").replaceAll("/+","/");
for (Handler handler : this.handlerMapping) {
Matcher matcher = handler.getPattern().matcher(url);
if(!matcher.matches()){ continue;}
return handler;
}
return null;
}
//url传过来的参数都是String类型的，HTTP是基于字符串协议
//只需要把String转换为任意类型就好
private Object convert(Class<?> type,String value){
//如果是int
if(Integer.class == type){
return Integer.valueOf(value);
}
else if(Double.class == type){
return Double.valueOf(value);
}
//如果还有double或者其他类型，继续加if
//这时候，我们应该想到策略模式了
//在这里暂时不实现，希望小伙伴自己来实现
return value;
}
}
映射处理器Handler
public class Handler {
//必须把url放到HandlerMapping才好理解吧
private Pattern pattern; //正则
private Method method;
private Object controller;
private Class<?>[] paramTypes;
//形参列表
//参数的名字作为key,参数的顺序，位置作为值
private Map<String, Integer> paramIndexMapping;
public Handler(Pattern pattern, Object controller, Method method) {
this.pattern = pattern;
this.method = method;
this.controller = controller;
paramTypes = method.getParameterTypes();
paramIndexMapping = new HashMap<String, Integer>();
putParamIndexMapping(method);
}
private void putParamIndexMapping(Method method) {
//提取方法中加了注解的参数
//把方法上的注解拿到，得到的是一个二维数组
//因为一个参数可以有多个注解，而一个方法又有多个参数
Annotation[][] pa = method.getParameterAnnotations();
for (int i = 0; i < pa.length; i++) {
for (Annotation a : pa[i]) {
if (a instanceof RequestParam) {
String paramName = ((RequestParam) a).value();
if (!"".equals(paramName.trim())) {
paramIndexMapping.put(paramName, i);
}
}
}
}
//提取方法中的request和response参数
Class<?>[] paramsTypes = method.getParameterTypes();
for (int i = 0; i < paramsTypes.length; i++) {
Class<?> type = paramsTypes[i];
if (type == HttpServletRequest.class ||
type == HttpServletResponse.class) {
paramIndexMapping.put(type.getName(), i);
}
}
}
public Pattern getPattern() {
return pattern;
}
public Method getMethod() {
return method;
}
public Object getController() {
return controller;
}
public Class<?>[] getParamTypes() {
return paramTypes;
}
public Map<String, Integer> getParamIndexMapping() {
return paramIndexMapping;
}
}