学习手写简单的MVC框架

1. 学习手写简单的 MVC 框架的实现流程

2. 自定义注解

2.1.@LagouService注解

package com.lagou.edu.mvcframework.annotations;

import java.lang.annotation.*;

@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface LagouService {
    String value() default "";
}

2.2.@LagouRequestMapping注解

package com.lagou.edu.mvcframework.annotations;

import java.lang.annotation.*;

@Documented
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface LagouRequestMapping {
    String value() default "";
}

2.3.@LagouAutowired注解

package com.lagou.edu.mvcframework.annotations;

import java.lang.annotation.*;

@Documented
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface LagouAutowired {
    String value() default "";
}

2.4.@LagouController

package com.lagou.edu.mvcframework.annotations;

import java.lang.annotation.*;

@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface LagouService {
    String value() default "";
}

3. 运用注解写Demo代码

3.1 Service接口及其实现类（使用自定义注解@LagouService）

(1)IDemoService.java

package com.lagou.edu.demo.service;

public interface IDemoService {
    String get(String name);
}

(2)DemoServiceImpl.java

package com.lagou.edu.demo.service.impl;

import com.lagou.edu.demo.service.IDemoService;
import com.lagou.edu.mvcframework.annotations.LagouService;

@LagouService
public class DemoServiceImpl implements IDemoService {
    @Override
    public String get(String name) {
        System.out.println("service 实现类中的name参数：" + name);
        return name;
    }
}

3.2 Controller类 （使用自定义注解@LagouController,@LagouRequestMapping,@LagouAutowired）

DemoController.java

package com.lagou.edu.demo.controller;

import com.lagou.edu.demo.service.IDemoService;
import com.lagou.edu.mvcframework.annotations.LagouAutowired;
import com.lagou.edu.mvcframework.annotations.LagouController;
import com.lagou.edu.mvcframework.annotations.LagouRequestMapping;

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

@LagouController
@LagouRequestMapping("/demo")
public class DemoController {
    @LagouAutowired
    private IDemoService demoService;


    @LagouRequestMapping("/query")
    public String query(HttpServletRequest request, HttpServletResponse response, String name){
        return demoService.get(name);
    }
}

4. 实现自定义框架

4.1. src\main\resources\springmvc.properties 扫描包的配置

scanPackage=com.lagou.demo

4.2. src\main\webapp\WEB-INF\web.xml 的配置

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  
  <!-- 	配置DispatcherServlet前端控制器 -->
  <servlet>
    <servlet-name>lagoumvc</servlet-name>
    <servlet-class>com.lagou.edu.mvcframework.servlet.LgDispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>springmvc.properties</param-value>
    </init-param>
  </servlet>

  <servlet-mapping>
    <servlet-name>lagoumvc</servlet-name>
    <url-pattern>/*</url-pattern>
  </servlet-mapping>

</web-app>

4.3. 封装handler方法相关的信息

package com.lagou.edu.mvcframework.pojo;

import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
import java.util.regex.Pattern;

/**
 * 封装handler方法相关的信息
 */
public class Handler {
    private Object controller ; // method.invoke(object,)

    private Method method;

    private Pattern pattern; // spring中url是支持正则的

    // 参数顺序，为了进行参数绑定，key是参数，value代表是第几个参数<name,2>
    private Map<String, Integer> paramIndexMapping; 

    public Handler(Object controller, Method method, Pattern pattern){
        this.controller = controller;
        this.method = method;
        this.pattern = pattern;
        this.paramIndexMapping = new HashMap<>();
    }

    public Object getController() {
        return controller;
    }

    public void setController(Object controller) {
        this.controller = controller;
    }

    public Method getMethod() {
        return method;
    }

    public void setMethod(Method method) {
        this.method = method;
    }

    public Pattern getPattern() {
        return pattern;
    }

    public void setPattern(Pattern pattern) {
        this.pattern = pattern;
    }

    public Map<String, Integer> getParamIndexMapping() {
        return paramIndexMapping;
    }

    public void setParamIndexMapping(Map<String, Integer> paramIndexMapping) {
        this.paramIndexMapping = paramIndexMapping;
    }
}

4.4. LgDispatcherServlet.java 自定义 mvc 框架核心 java 实现

package com.lagou.edu.mvcframework.servlet;

import com.lagou.edu.demo.service.IDemoService;
import com.lagou.edu.mvcframework.annotations.LagouAutowired;
import com.lagou.edu.mvcframework.annotations.LagouController;
import com.lagou.edu.mvcframework.annotations.LagouRequestMapping;
import com.lagou.edu.mvcframework.annotations.LagouService;
import com.lagou.edu.mvcframework.pojo.Handler;
import org.apache.commons.lang3.StringUtils;

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.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class LgDispatcherServlet extends HttpServlet {


    private Properties properties = new Properties();

    private List<String> classNames = new ArrayList<>(); // 缓存扫描到的类的全限定类名

    // ioc容器
    private Map<String, Object> ioc = new HashMap<>();

    // handlerMapping
    //private Map<String, Method> handlerMapping = new HashMap<>(); // 存贮url和method之间的映射关系
    private List<Handler> handlerMapping = new ArrayList<>(); // 存贮url和method之间的映射关系


    @Override
    public void init(ServletConfig config) throws ServletException {
        // 1.加载配置文件 springmvc.properties
        String contextConfigLocation = config.getInitParameter("contextConfigLocation");
        doLoadCofig(contextConfigLocation);

        // 2.扫描相关的类，扫描注解
        doScan(properties.getProperty("scanPackage"));

        // 3.初始化bean对象（实现ioc容器，基于注解）
        doInstance();

        // 4.实现依赖注入
        doAutoWired();

        // 5.构造一个HandlerMapping处理器映射器，将配置好的url和Method建立映射关系
        initHandlerMapping();

       System.out.println("lagou mv 初始化完成");

    }

    /**
     * 构建一个HandlerMapping处理器映射器
     */
    private void initHandlerMapping() {
        if(ioc.isEmpty()) {return;}

        // 扫描ioc容器中
        for (Map.Entry<String, Object> entry : ioc.entrySet()) {

            // 获取ioc中当前遍历的对象的class类型
            Class<?> aClass = entry.getValue().getClass();

            if(!aClass.isAnnotationPresent(LagouController.class)) {continue;}

            String baseUrl = "";
            if(aClass.isAnnotationPresent(LagouRequestMapping.class)){
                LagouRequestMapping annotation = aClass.getAnnotation(LagouRequestMapping.class);
                baseUrl = annotation.value(); // 等同于/demo
            }

            // 获取方法
            Method[] methods = aClass.getMethods();
            for (Method method : methods) {

                // 方法没有标识 @LagouRequestMapping 就不处理
                if(!method.isAnnotationPresent(LagouRequestMapping.class)){continue;}

                // 如果标识就处理
                LagouRequestMapping annotation = method.getAnnotation(LagouRequestMapping.class);
                String methodUrl = annotation.value(); // 等同于/query
                String url = baseUrl + methodUrl;     // 计算出来的url /demo/query

                // 把method所有信息及url封装为要给Handler
                Handler handler = new Handler(entry.getValue(),method, Pattern.compile(url));

                // 处理计算参数位置信息 query(HttpServletRequest request, HttpServletResponse response, String name){
                Parameter[] parameters = method.getParameters();
                for (int i = 0; i < parameters.length; i++) {
                    Parameter parameter = parameters[i];
                    if(parameter.getType() == HttpServletRequest.class || parameter.getType() == HttpServletResponse.class){
                        // 如果是request和response对象，那么参数名称写HttpServletRequest和HttpServletResponse
                        handler.getParamIndexMapping().put(parameter.getType().getSimpleName(),i);
                    }else{
                        handler.getParamIndexMapping().put(parameter.getName(),i); // <name, 2>
                    }
                }
                //建立url和method之间的映射关系(map缓存起来)
                handlerMapping.add(handler);
            }
        }
    }

    /**
     * 实现依赖注入
     */
    private void doAutoWired()  {
        if(ioc.isEmpty()){return;}

        // 有对象， 再进行依赖注入处理

        // 遍历ioc中所有的对象，查看对象中的字段，是否有@LagouAutowired注解，如果有需要维护依赖注入关系
        for (Map.Entry<String, Object> entry : ioc.entrySet()) {
            // 获取bean对象中的字段信息
            Field[] declaredFields = entry.getValue().getClass().getDeclaredFields();
            // 遍历判断处理
            for (Field declaredField : declaredFields) {     // @LagouAutowired  private IDemoService demoService;
                if(!declaredField.isAnnotationPresent(LagouAutowired.class)){
                    continue;
                }else{
                    LagouAutowired annotation = declaredField.getAnnotation(LagouAutowired.class);
                    String beanName = annotation.value();
                    if("".equals(beanName)){
                        // 如果没有配置具体的bean id，那就需要根据当前字段类型注入（接口注入） IDemoService
                        beanName = declaredField.getType().getName();
                    }
                    // 开启赋值
                    declaredField.setAccessible(true);
                    try {
                        declaredField.set(entry.getValue(), ioc.get(beanName));
                    } catch (IllegalAccessException e) {
                        e.printStackTrace();
                    }
                }
            }
        }

    }

    /**
     * ioc 容器
     * 基于classNames缓存的全限定类名，以及反射技术，完成对象创建和管理
     */
    private void doInstance() {

        try {
            if (classNames.size() == 0) {
                return;
            }
            for (String className : classNames) { // com.lagou.edu.controller.DemoController

                // 反射
                Class<?> aClass = Class.forName(className);
                // 区分controller， 区分service
                if(aClass.isAnnotationPresent(LagouController.class)){
                    // controller的id此处不做过多处理，不去value了，就拿类的首字母小写作为id，保存到ioc中
                    String simpleName = aClass.getSimpleName(); // DemoController
                    String lowerFirstSimpleName = lowerFirst(simpleName);// demoController

                    Object o = aClass.newInstance();
                    ioc.put(lowerFirstSimpleName,o);

                } else  if(aClass.isAnnotationPresent(LagouService.class)){
                     LagouService annotation = aClass.getAnnotation(LagouService.class);
                     // 获取注解value的值
                    String beanName = annotation.value();

                    // 如果制定了id，就医指定的为准
                    if(!"".equals(beanName)){
                        ioc.put(beanName, aClass.newInstance());
                    }else{
                        // 如果没有指定， 就以类名首字母小写
                        beanName = lowerFirst(aClass.getSimpleName());
                        ioc.put(beanName,aClass.newInstance());
                    }
                    // service层往往是有接口的， 面向接口开发，此时再以接口名为id， 放入一份对象到ioc容器中， 便于后期根据接口类型注入
                    Class<?>[] interfaces = aClass.getInterfaces();
                    for (Class<?> anInterface : interfaces) {
                        // 以接口的全限定类名作为id放入
                        ioc.put(anInterface.getName(),aClass.newInstance());
                    }

                }else{
                    continue;
                }
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    }

    /**
     * 首字母小写方法
     */
    public String lowerFirst(String str){
        char[] chars = str.toCharArray();
        if(chars[0] >= 'A' && chars[0] <= 'Z'){
            chars[0] += 32;
        }
        // return chars.toString();
        return String.valueOf(chars);
    }


    /**
   * 扫描类
     * scanPackage: com.lagou.demo package----> 磁盘上的文件(file)  com/lagou/demo
     */
    private void doScan(String scanPackage) {
        // 拿到classpath路径
        String scanPackagePath = Thread.currentThread().getContextClassLoader().getResource("").getPath()  + scanPackage.replaceAll("\\.", "/");
        File pack = new File(scanPackagePath);

        File[] files = pack.listFiles();
        for (File file : files) {
            if(file.isDirectory()){ // 子package则递归调用
                // 递归
                doScan(scanPackage + "." + file.getName());
            }else if(file.getName().endsWith(".class")){ // class则添加到缓存中
                String className = scanPackage + "." + file.getName().replaceAll(".class", "");
                classNames.add(className);
            }
        }
    }

    /**
     * 加载配置文件
     * @param contextConfigLocation
     */
    private void doLoadCofig(String contextConfigLocation) {

        InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation);
        try {
            properties.load(resourceAsStream);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }


    // 接收处理请求
    @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 {
        // 处理请求:根据url，找到对应的Method方法，进行调用
        // 获取uri
//        String requestURI = req.getRequestURI();
//        Method method = handlerMapping.get(requestURI);
//        // 反射调用，需要对象，需要传入参数，此处无法完成调用，没有把对象缓存起来，也没有参数！
//        method.invoke()

        // 根据uri获取到当前请求的handler，（从handlerMapping（list)中获取）
        Handler handler = getHandler(req);
        if(handler == null){
            resp.getWriter().write("404 not found");
            return;
        }

        // 参数绑定
        // 获取所有参数类型数组，这个数组的长度就是我们最后要出啊如的args数组的长度
        Class<?>[] parameterTypes = handler.getMethod().getParameterTypes();
        // 根据上述数组的长度创建一个新的数组（参数数组，是要传入反射调用的）
        Object[] paraValues = new Object[parameterTypes.length];

        // 以下就是为了想参数数组中塞值，而且还要保证参数的顺序和方法中形参顺序一致

        Map<String, String[]> parameterMap = req.getParameterMap();// 拿到参数集合

        // 遍历request中的所有参数 (填充除了request，response之外的参数）
        for (Map.Entry<String, String[]> param : parameterMap.entrySet()) {
            // name=1&name=2  name [1,2]
            String value = StringUtils.join(param.getValue(),",");

            // 如果参数和方法中的参数匹配上了，填充数据
            if(!handler.getParamIndexMapping().containsKey(param.getKey())){continue;}

            // 方法形参确实有参数，找到对应的index，对应的把参数值放入paraValues
            Integer index = handler.getParamIndexMapping().get(param.getKey());
            paraValues[index] = value;
        }

        // 放入req
        int requestIndex = handler.getParamIndexMapping().get(HttpServletRequest.class.getSimpleName());
        paraValues[requestIndex] = req;

        // 放入resp
        int responseIndex = handler.getParamIndexMapping().get(HttpServletResponse.class.getSimpleName());
        paraValues[responseIndex] = resp;

        // 最终调用handler的mathod属性
        try {
            handler.getMethod().invoke(handler.getController(),paraValues);
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }

    }

    private Handler getHandler(HttpServletRequest req) {
        if (handlerMapping.isEmpty()) {
            return null;
        }

        String url = req.getRequestURI();
        for (Handler handler : handlerMapping) {
            Matcher matcher = handler.getPattern().matcher(url);
            if (!matcher.matches()) {
                continue;
            }
            return handler;
        }
        return null;
    }
}

4.4. pom.xml

<?xml version="1.0" encoding="UTF-8"?>

<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>org.example</groupId>
  <artifactId>mvc</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>

  <name>mvc Maven Webapp</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>11</maven.compiler.source>
    <maven.compiler.target>11</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
    </dependency>

    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>3.1.0</version>
      <scope>provided</scope>
    </dependency>

    <dependency>
      <groupId>org.apache.commons</groupId>
      <artifactId>commons-lang3</artifactId>
      <version>3.11</version>
    </dependency>

  </dependencies>

  <build>
    <plugins>

      <plugin>
        <!-- 编译插件定义编译细节 -->
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.8.1</version>
        <configuration>
          <source>11</source>
          <target>11</target>
          <encoding>utf-8</encoding>
          <!-- 告诉编译器编译的时候记录一下形参的真实名字 -->
          <compilerArgs>
            <arg>-parameters</arg>
          </compilerArgs>
        </configuration>
      </plugin>

      <!-- tomcat 插件 -->
      <plugin>
        <groupId>org.apache.tomcat.maven</groupId>
        <artifactId>tomcat7-maven-plugin</artifactId>
        <version>2.2</version>
        <configuration>
          <port>8080</port>
          <path>/</path>
        </configuration>
      </plugin>
    </plugins>
  </build>

</project>

5. 小知识

1.学会自定义注解的定义方法，实际用法，以及其他的一些跟反射相关的技术

// 判断如果类上面没有标注@LagouController就不处理
if(!aClass.isAnnotationPresent(LagouController.class)) {continue;}

// 方法没有标识 @LagouRequestMapping 就不处理
if(!method.isAnnotationPresent(LagouRequestMapping.class)){continue;}

// 字段没有标注@LagouAutowired 就不处理
if(!declaredField.isAnnotationPresent(LagouAutowired.class)){continue;}

// 获取方法的参数
Parameter[] parameters = method.getParameters();

// 获取方法的所有参数类型
Class<?>[] parameterTypes = handler.getMethod().getParameterTypes();

// 获取类的所有接口
Class<?>[] interfaces = aClass.getInterfaces();

// service层往往是有接口的， 面向接口开发，此时再以接口名为id， 放入一份对象到ioc容器中， 便于后期根据接口类型注入
Class<?>[] interfaces = aClass.getInterfaces();
for (Class<?> anInterface : interfaces) {
    // 以接口的全限定类名作为id放入
    ioc.put(anInterface.getName(),aClass.newInstance());
}
                    
// 获取参数的属性名字
parameter.getType().getSimpleName()

// 获取对象的所有字段
Field[] declaredFields = entry.getValue().getClass().getDeclaredFields();

// 获取自读类型的名字
beanName = declaredField.getType().getName();

// 开启赋值并赋值
declaredField.setAccessible(true);
declaredField.set(entry.getValue(), ioc.get(beanName));

// 从web.xml中获取 <param-name>contextConfigLocation</param-name>对应的<param-value>的值
String contextConfigLocation = config.getInitParameter("contextConfigLocation");

// 拿到classpath路径
String scanPackagePath = Thread.currentThread().getContextClassLoader().getResource("").getPath() 

// 通过路径生成一个File对象
File pack = new File(scanPackagePath);
// 获取File对象的文件一览
File[] files = pack.listFiles();

// 获取属性配置文件的输入流，然后加载属性配置文件
InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation);
private Properties properties = new Properties();
properties.load(resourceAsStream);

// 想resp中写入"404 not found")
resp.getWriter().write("404 not found");

2.通过maven-compiler-plugin插件定义编译细节，不定义的话无法保留参数的名字

<!-- 告诉编译器编译的时候记录一下形参的真实名字 -->
<compilerArgs>
  <arg>-parameters</arg>
</compilerArgs>

3. 通过scope定义provided避免运行时冲突

    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>3.1.0</version>
      <scope>provided</scope>
    </dependency>