手写一个SpringMVC框架(转)

一：梳理SpringMVC的设计思路

　　本文只实现自己的@Controller、@RequestMapping、@RequestParam注解起作用，其余SpringMVC功能读者可以尝试自己实现。　

1、读取配置

　　SpringMVC本质上是一个Servlet,这个 Servlet 继承自 HttpServlet。FrameworkServlet负责初始化SpringMVC的容器，并将Spring容器设置为父容器。因为本文只是实现SpringMVC，对于Spring容器不做过多讲解。

　　为了读取web.xml中的配置，我们用到ServletConfig这个类，它代表当前Servlet在web.xml中的配置信息。通过web.xml中加载我们自己写的MyDispatcherServlet和读取配置文件。

2、初始化阶段

加载配置文件
扫描用户配置包下面所有的类
拿到扫描到的类，通过反射机制，实例化。并且放到ioc容器中(Map的键值对 beanName-bean) beanName默认是首字母小写
初始化HandlerMapping，这里其实就是把url和method对应起来放在一个k-v的Map中,在运行阶段取出

3、运行阶段　

　　每一次请求将会调用doGet或doPost方法，所以统一运行阶段都放在doDispatch方法里处理，它会根据url请求去HandlerMapping中匹配到对应的Method，然后利用反射机制调用Controller中的url对应的方法，并得到结果返回。按顺序包括以下功能：

异常的拦截
获取请求传入的参数并处理参数
通过初始化好的handlerMapping中拿出url对应的方法名，反射调用

二、实现自己的SpringMVC框架

　　工程文件及目录：

用到javax.servlet.jar

web.xml:

<?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" id="WebApp_ID" version="3.0">
  <display-name>web01</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
    <servlet>
           <servlet-name>MySpringMVC</servlet-name>
           <servlet-class>com.gdut.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>

application.properties文件中只是配置要扫描的包到SpringMVC容器中。application.properties文件内容为：

创建自己的Controller注解，它只能标注在类上面：

package com.gdut.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

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

RequestMapping注解，可以在类和方法上：

package com.gdut.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@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 "";

}

RequestParam注解,只能注解在参数上

package com.gdut.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

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

}

然后创建MyDispatcherServlet这个类，去继承HttpServlet，重写init方法、doGet、doPost方法，以及加上我们第二步分析时要实现的功能：

package com.gdut.servlet;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.gdut.annotation.MyController;
import com.gdut.annotation.MyRequestMapping;

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);

        // 用Properties文件加载文件里的内容
        try {
            properties.load(resourceAsStream);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (resourceAsStream != null) {
                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 {
                Class<?> clazz = Class.forName(className);
                if (clazz.isAnnotationPresent(MyController.class)) {
                    ioc.put(toLowerFirstWord(clazz.getSimpleName()),
                            clazz.newInstance());
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    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);
    }
}

这里我们就开发完了自己的SpringMVC，现在我们测试一下：

package com.gdut.core;

import java.io.IOException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.gdut.annotation.MyController;
import com.gdut.annotation.MyRequestMapping;
import com.gdut.annotation.MyRequestParam;

@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();
        }
    }
}

访问http://localhost:8080/web01/test/doTest?param=liugh如下：

访问一个不存在的试试：

转自：https://www.cnblogs.com/java1024/p/8556519.html