手撸一个简易Spring框架（五）
目录
- 前言
- DispatcherServlet
- HandlerMapping
- HandlerAdapter
- ViewResolver
- doDispatch
- 成果展示
- 最后
前言
这次我们来完成MVC的模块，最终目标需要达到用户能够使用Controller，浏览器能够显示模板引擎渲染的结果。为了能够解析前端的HTTP协议请求，需要在项目POM中引入Servlet。
<dependency>
<groupId>javax.servletgroupId>
<artifactId>servlet-apiartifactId>
<version>${servlet.api.version}version>
<scope>providedscope>
dependency>
DispatcherServlet
DispatcherServlet继承自HttpServlet，必然需要重写doGet和doPost来接收和处理用户的前端请求。又因为DispatcherServlet在初始化的时候就要先初始化ApplicationContext以及MVC九大组件(为了达成目的只需实现其中三个即可)，因此还要重写父类init()方法。
package com.lqb.springframework.webmvc.servlet;
import com.lqb.springframework.annotation.Controller;
import com.lqb.springframework.annotation.RequestMapping;
import com.lqb.springframework.context.support.DefaultApplicationContext;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.lang.reflect.Method;
import java.util.regex.Pattern;
public class DispatcherServlet extends HttpServlet {
/**配置文件地址，从web.xml中获取*/
private static final String CONTEXT_CONFIG_LOCATION = "contextConfigLocation";
private DefaultApplicationContext context;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
@Override
public void init(ServletConfig config) throws ServletException {
//1、初始化ApplicationContext
context = new DefaultApplicationContext(config.getInitParameter(CONTEXT_CONFIG_LOCATION));
//2、初始化Spring MVC 九大组件
initStrategies(context);
}
//初始化策略
protected void initStrategies(DefaultApplicationContext context) {
//多文件上传的组件
//初始化本地语言环境
//初始化模板处理器
//handlerMapping，必须实现
initHandlerMappings(context);
//初始化参数适配器，必须实现
initHandlerAdapters(context);
//初始化异常拦截器
//初始化视图预处理器
//初始化视图转换器，必须实现
initViewResolvers(context);
//参数缓存器
}
}
下面我们先来实现这三个组件HandlerMapping、HandlerAdapter以及ViewResolver
HandlerMapping
HandlerMapping保存了用户写的Controller实例、所有浏览器能访问到的方法，以及使用@RequestMapping定义的URL表达式
package com.lqb.springframework.webmvc.servlet;
import lombok.Data;
import java.lang.reflect.Method;
import java.util.regex.Pattern;
@Data
public class HandlerMapping {
//保存方法对应的实例
private Object controller;
//保存映射的方法
private Method method;
//URL的正则匹配
private Pattern pattern;
public HandlerMapping(Object controller, Method method, Pattern pattern) {
this.controller = controller;
this.method = method;
this.pattern = pattern;
}
}
填充到DispatcherServlet的流程中，代码逻辑如下：
- 遍历容器中的Bean，找到被@Controller注解的
- 遍历Controller的所有方法，找到被@RequestMapping注解的
- 获取URL表达式，编译成正则
- 将HandlerMapping添加到集合中保存起来
private List<HandlerMapping> handlerMappings = new ArrayList<>();
private void initHandlerMappings(DefaultApplicationContext context) {
String[] beanNames = context.getBeanDefinitionNames();
try {
for (String beanName : beanNames) {
Object controller = context.getBean(beanName);
Class<?> clazz = controller.getClass();
if (!clazz.isAnnotationPresent(Controller.class)) {
continue;
}
String baseUrl = "";
//获取Controller的url配置
if (clazz.isAnnotationPresent(RequestMapping.class)) {
RequestMapping requestMapping = clazz.getAnnotation(RequestMapping.class);
baseUrl = requestMapping.value();
}
//获取Method的url配置
Method[] methods = clazz.getMethods();
for (Method method : methods) {
//没有加RequestMapping注解的直接忽略
if (!method.isAnnotationPresent(RequestMapping.class)) {
continue;
}
//映射URL
RequestMapping requestMapping = method.getAnnotation(RequestMapping.class);
String regex = ("/" + baseUrl + "/" + requestMapping.value().replaceAll("\\*", ".*")).replaceAll("/+", "/");
Pattern pattern = Pattern.compile(regex);
this.handlerMappings.add(new HandlerMapping(controller, method, pattern));
System.out.println("Mapped " + regex + "," + method);
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
HandlerAdapter
HandlerAdapter简单讲就是负责接收用户的请求，然后将参数填充到Controller中的方法中调用。
package com.lqb.springframework.webmvc.servlet;
import com.lqb.springframework.annotation.RequestParam;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.lang.annotation.Annotation;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
public class HandlerAdapter {
ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
HandlerMapping handlerMapping = (HandlerMapping) handler;
//把方法的形参列表和request的参数列表所在顺序进行一一对应
Map<String, Integer> paramIndexMapping = new HashMap<>();
//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 = handlerMapping.getMethod().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 = handlerMapping.getMethod().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);
}
}
//获得方法的形参列表
Map<String, String[]> params = request.getParameterMap();
//controller的方法实参列表
Object[] paramValues = new Object[paramsTypes.length];
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] = parseStringValue(value, paramsTypes[index]);
}
//填充HttpServletRequest参数
if (paramIndexMapping.containsKey(HttpServletRequest.class.getName())) {
int reqIndex = paramIndexMapping.get(HttpServletRequest.class.getName());
paramValues[reqIndex] = request;
}
//填充HttpServletResponse参数
if (paramIndexMapping.containsKey(HttpServletResponse.class.getName())) {
int respIndex = paramIndexMapping.get(HttpServletResponse.class.getName());
paramValues[respIndex] = response;
}
//反射调用controller的方法
Object result = handlerMapping.getMethod().invoke(handlerMapping.getController(), paramValues);
if (result == null || result instanceof Void) {
return null;
}
//解析controller的方法返回
Class<?> returnType = handlerMapping.getMethod().getReturnType();
boolean isModelAndView = returnType == ModelAndView.class;
if (isModelAndView) {
return (ModelAndView) result;
} else if (returnType == Void.class) {
return null;
} else if (returnType == String.class) {
//return (String) result;
}
return null;
}
/**
* request中接收的参数都是string类型的，需要转换为controller中实际的参数类型
* 暂时只支持string、int、double类型
*/
private Object parseStringValue(String value, Class<?> paramsType) {
if (String.class == paramsType) {
return value;
}
if (Integer.class == paramsType) {
return Integer.valueOf(value);
} else if (Double.class == paramsType) {
return Double.valueOf(value);
} else {
if (value != null) {
return value;
}
return null;
}
//还有，继续加if
//其他类型在这里暂时不实现，希望小伙伴自己来实现
}
}
ModelAndView是Controller方法返回的类型，封装了模板引擎名称和参数
package com.lqb.springframework.webmvc.servlet;
import java.util.Map;
public class ModelAndView {
//模板名字
private String viewName;
//模板中填充的参数
private Map<String, ?> model;
public ModelAndView(String viewName) {
this.viewName = viewName;
}
public ModelAndView(String viewName, Map<String, ?> model) {
this.viewName = viewName;
this.model = model;
}
public String getViewName() {
return viewName;
}
public Map<String, ?> getModel() {
return model;
}
}
填充创建HandlerAdapter逻辑到DispatcherServlet的流程中
private Map<HandlerMapping, HandlerAdapter> handlerAdapters = new HashMap<>();
private void initHandlerAdapters(DefaultApplicationContext context) {
//一个HandlerMapping对应一个HandlerAdapter
for (HandlerMapping handlerMapping : this.handlerMappings) {
this.handlerAdapters.put(handlerMapping, new HandlerAdapter());
}
}
ViewResolver
ViewResolver需要根据模板名找到对应的模板，封装成View
package com.lqb.springframework.webmvc.servlet;
import java.io.File;
import java.util.Locale;
public class ViewResolver {
private final String DEFAULT_TEMPLATE_SUFFIX = ".html";
/**模板根目录*/
private File templateRootDir;
public ViewResolver(String templateRoot) {
String templateRootPath = this.getClass().getClassLoader().getResource(templateRoot).getFile();
templateRootDir = new File(templateRootPath);
}
public View resolveViewName(String viewName, Locale locale) throws Exception{
if(null == viewName || "".equals(viewName.trim())){return null;}
viewName = viewName.endsWith(DEFAULT_TEMPLATE_SUFFIX) ? viewName : (viewName + DEFAULT_TEMPLATE_SUFFIX);
File templateFile = new File((templateRootDir.getPath() + "/" + viewName).replaceAll("/+","/"));
return new View(templateFile);
}
}
View封装了模板，提供了渲染的功能
package com.lqb.springframework.webmvc.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.RandomAccessFile;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class View {
/**模板*/
private File viewFile;
/**占位符表达式*/
private Pattern pattern = Pattern.compile("#\\{[^\\}]+\\}", Pattern.CASE_INSENSITIVE);
public View(File viewFile) {
this.viewFile = viewFile;
}
/**
* 渲染
*/
public void render(Map<String, ?> model,
HttpServletRequest request,
HttpServletResponse response) throws Exception {
StringBuilder sb = new StringBuilder();
RandomAccessFile ra = new RandomAccessFile(this.viewFile, "r");
String line;
while (null != (line = ra.readLine())) {
line = new String(line.getBytes("ISO-8859-1"), "utf-8");
Matcher matcher = this.pattern.matcher(line);
//找到下一个占位符
while (matcher.find()) {
String paramName = matcher.group();
paramName = paramName.replaceAll("#\\{|\\}", "");
Object paramValue = model.get(paramName);
if (null == paramValue) {
continue;
}
//替换占位符为实际值
line = matcher.replaceFirst(makeStringForRegExp(paramValue.toString()));
//接着匹配下一个占位符
matcher = pattern.matcher(line);
}
sb.append(line);
}
response.setCharacterEncoding("utf-8");
//输出到response
response.getWriter().write(sb.toString());
}
//处理特殊字符
public static String makeStringForRegExp(String str) {
return str.replace("\\", "\\\\").replace("*", "\\*")
.replace("+", "\\+").replace("|", "\\|")
.replace("{", "\\{").replace("}", "\\}")
.replace("(", "\\(").replace(")", "\\)")
.replace("^", "\\^").replace("$", "\\$")
.replace("[", "\\[").replace("]", "\\]")
.replace("?", "\\?").replace(",", "\\,")
.replace(".", "\\.").replace("&", "\\&");
}
}
最后填充初始化ViewResolver的逻辑到DispatcherServlet的中
private List<ViewResolver> viewResolvers = new ArrayList<>();
private void initViewResolvers(DefaultApplicationContext context) {
//配置文件中拿到模板的存放目录
String templateRoot = context.getConfig().getProperty("templateRoot");
String templateRootPath = this.getClass().getClassLoader().getResource(templateRoot).getFile();
File templateRootDir = new File(templateRootPath);
String[] templates = templateRootDir.list();
for (int i = 0; i < templates.length; i ++) {
this.viewResolvers.add(new ViewResolver(templateRoot));
}
}
至此组件都初始化好了，接着利用这些组件来处理用户请求了。
doDispatch
在DispatcherServlet中，doGet和doPost需要调用doDispatch来处理用户请求
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
try {
this.doDispatch(req, resp);
} catch (Exception e) {
resp.getWriter().write("500 Exception,Details:\r\n"
+ Arrays.toString(e.getStackTrace()).replaceAll("\\[|\\]", "")
.replaceAll(",\\s", "\r\n"));
e.printStackTrace();
}
}
private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception {
//1、通过从request中拿到URL，去匹配一个HandlerMapping
HandlerMapping handler = getHandler(req);
if (handler == null) {
//没有找到handler返回404
processDispatchResult(req, resp, new ModelAndView("404"));
return;
}
//2、准备调用前的参数
HandlerAdapter ha = getHandlerAdapter(handler);
//3、真正的调用controller的方法
ModelAndView mv = ha.handle(req, resp, handler);
//4、渲染页面输出
processDispatchResult(req, resp, mv);
}
第一步通过用户访问的URL，拿到HandlerMapping
private HandlerMapping getHandler(HttpServletRequest req) throws Exception {
if (this.handlerMappings.isEmpty()) {
return null;
}
String url = req.getRequestURI();
String contextPath = req.getContextPath();
url = url.replace(contextPath, "").replaceAll("/+", "/");
for (HandlerMapping handler : this.handlerMappings) {
try {
Matcher matcher = handler.getPattern().matcher(url);
//如果没有匹配上继续下一个匹配
if (!matcher.matches()) {
continue;
}
return handler;
} catch (Exception e) {
throw e;
}
}
return null;
}
第二步，根据HandlerMapping拿到HandlerAdapter
private HandlerAdapter getHandlerAdapter(HandlerMapping handler) {
if (this.handlerAdapters.isEmpty()) {
return null;
}
HandlerAdapter ha = this.handlerAdapters.get(handler);
return ha;
}
最后，调用完Controller方法渲染模板输出到用户
private void processDispatchResult(HttpServletRequest req, HttpServletResponse resp, ModelAndView mv) throws Exception {
if (null == mv) {
return;
}
if (this.viewResolvers.isEmpty()) {
return;
}
for (ViewResolver viewResolver : this.viewResolvers) {
//根据模板名拿到View
View view = viewResolver.resolveViewName(mv.getViewName(), null);
//开始渲染
view.render(mv.getModel(), req, resp);
return;
}
}
至此，MVC模块已经搞定，下面来展示成果。
成果展示
先mvn install发布到本地仓库，然后在src/main/webapp/WEB-INF目录下新建web.xml
<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>My Web Applicationdisplay-name>
<servlet>
<servlet-name>mymvcservlet-name>
<servlet-class>com.lqb.springframework.webmvc.servlet.DispatcherServletservlet-class>
<init-param>
<param-name>contextConfigLocationparam-name>
<param-value>application.propertiesparam-value>
init-param>
<load-on-startup>1load-on-startup>
servlet>
<servlet-mapping>
<servlet-name>mymvcservlet-name>
<url-pattern>/*url-pattern>
servlet-mapping>
web-app>
配置文件application.properties中指定模板位置
# 模板目录
templateRoot=layouts
在resource目录下新建layouts文件夹，然后我们创建一个叫test.html的模板，包含两个占位符“data1”和“data2”
<html lang="zh-cn">
<head>
<meta charset="utf-8">
<title>手写一个Springtitle>
head>
<center>
<h1>#{data1}大家好，我是#{data2}h1>
center>
html>
再创建一个叫404的模板
<html lang="zh-cn">
<head>
<meta charset="utf-8">
<title>页面去火星了title>
head>
<body>
<font size='25' color='red'>404 Not Foundfont><br/>
body>
html>
创建一个Controller
package com.lqb.demo;
import com.lqb.springframework.annotation.Controller;
import com.lqb.springframework.annotation.RequestMapping;
import com.lqb.springframework.webmvc.servlet.ModelAndView;
import java.util.HashMap;
@Controller
public class HelloController {
@RequestMapping("/hello")
public ModelAndView hello() {
HashMap<String, Object> model = new HashMap<>();
model.put("data1", "hello");
model.put("data2", "world");
return new ModelAndView("test", model);
}
}
因为我们是一个Web项目，因此需要启动Web Server，我这里是启动了Jetty
打开浏览器，地址栏输入http://localhost:8080/hello，成功输入模板引擎的内容
最后
《手撸一个简易Spring框架》系列正式结束了。通过手写简易Spring我们应该要掌握Spring的IOC启动流程、DI依赖注入以及AOP代理创建过程，另外就是涉及到的设计模式，如AOP中的责任链。
Github源码
系列：
手撸一个简易Spring框架（一）
手撸一个简易Spring框架（二）
手撸一个简易Spring框架（三）
手撸一个简易Spring框架（四）