1.新建maven项目
2.到pom中添加servlet依赖
<groupId>com.justin.springmvc</groupId>
<artifactId>springmvc</artifactId>
<version>1.0-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>
3.新建web.xml文件（src下main下webapp下WEB-INF下）
<?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"
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.justin.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>
4.新建application.properties文件（resources下）
配置待扫描的包
scanPackage=com.justin.core
5.新建包com.justin.annotation
6.创建自己的controller注解
package com.justin.annotation;
import java.lang.annotation.*;
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyController {
/**
* 给MyController注册别名
*
* @return 别名
*/
String value() default "";
}
7.创建自己的MyRequestMapping注解
package com.justin.annotation;
import java.lang.annotation.*;
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyRequestMapping {
/**
* 访问该方法的url
*
* @return url
*/
String value() default "";
}
8.创建自己的MyRequestParam
package com.justin.annotation;
import java.lang.annotation.*;
@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyRequestParam {
/**
* 参数的别名，必填
*
* @return 别名
*/
String value();
}
9.新建com.justin.servlet包
10.新建MyDispatcherServlet
package com.justin.servlet;
import com.justin.annotation.MyController;
import com.justin.annotation.MyRequestMapping;
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.io.InputStream;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.*;
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> conntrollerMap = new HashMap<>();
@Override
public void init(ServletConfig config) throws ServletException {
//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 (Map.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 {
//第一个参数是method所对应的实例 在ioc容器中
method.invoke(this.conntrollerMap.get(url), paramValues);
} 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 {
properties.load(resourceAsStream);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (null != 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()) {
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 (Map.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);
conntrollerMap.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 代转字符串
* @return 转出结果
*/
private String toLowerFirstWord(String name) {
char[] charArray = name.toCharArray();
charArray[0] += 32;
return String.valueOf(charArray);
}
}
11.新建com.justin.core.controller
12.新建TestController
package com.justin.core.controller;
import com.justin.annotation.MyController;
import com.justin.annotation.MyRequestMapping;
import com.justin.annotation.MyRequestParam;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@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();
}
}
}
13.大功告成，通过tomcat或jetty启动项目
14.访问localhost:8080/test/doTest?param=justin
15.没报异常错误则说明构建成功，否则请根据异常自行检查！