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手写 spring mvc 基于注解

author: huifer

前置知识

在 spring 中我们会有如下几个注解来帮助我们定义 web-mvc 的语义
1. Controller
2. Service
3. RequestParam
4. Autowired
5. RequestMapping
这些注解相比大家都使用过在这里就不具体展开描述了. 在后面的开发中我们再来细说

配置篇

web.xml 的配置
在 web.xml 中我们需要配置
1. servlet-class
2. spring的配置(伪)
3. url-pattern
spring 配置这里简化为一个包的扫描路径. component-scan
配置详情
web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
  version="4.0">
  <display-name>HuiFer web application</display-name>
  <servlet>
    <servlet-name>HuiFer mvc</servlet-name>
    <servlet-class>org.huifer.spring.servlet.v1.HFDispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath*:application.properties</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>HuiFer mvc</servlet-name>
    <url-pattern>/*</url-pattern>
  </servlet-mapping>
</web-app>

application.properties

scanPackage=org.huifer.spring

注解篇

HFAutowired

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

@Target({ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD,
    ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface HFAutowired {

  String value() default "";

}

HFController

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 HFController {

}

HFRequestMapping

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface HFRequestMapping {

  String name() default "";
}

HFRequestParam

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 HFRequestParam {

  String name() default "";
}

HFService

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 HFService {

  String name() default "";

}

注解篇没什么可以多说的. 只是定义一些语义标记. 接下来就是具体的实现了

servlet 篇

开发流程
1. 读取web.xml中的配置,读取包扫描路径
2. 根据包扫描路径加载类命.
3. 实例化类.(service注解)
  1. 根据名称注入
  2. 根据类型注入
4. 读取 requestMapping 注解
  1. key: url , value: method
5. 执行http请求
首先继承 javax.servlet.http.HttpServlet
重写的方法
1. init
2. doPost
3. doGet
主要部分都在init方法中, 按照行为拆分如下几个方法
1. doLoadConfig 读取配置
2. doScan 进行包扫描
3. instance 实例化
4. autowired 注入
5. initHandlerMapping url和method映射关系

读取配置文件. 通过 getServletConfig 获取 servlet 的配置, 并读取 resource 文件夹中的配置.

/**
   * 从 web.xml 读取contextConfigLocation <br> 把 {@code classpath*:application.properties} 载入配置
   */
  private void doLoadConfig() {
    InputStream resourceAsStream = null;
    try {

      // 获取servlet的配置
      ServletConfig servletConfig = this.getServletConfig();
      String configInitParameter = servletConfig.getInitParameter(CONTEXT_CONFIG_LOCATION)
          .replace("classpath*:", "");
      // 读取配置文件
      resourceAsStream = this.getClass().getClassLoader()
          .getResourceAsStream(configInitParameter);
      SPRING_CONTEXT_CONFIG.load(resourceAsStream);

    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      if (resourceAsStream != null) {
        try {
          resourceAsStream.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
    }
  }

包扫描. 递归的扫描基本路径下的class. 放入类名字列表

/**
   * 包扫描
   */
  private void doScan(String scanPackage) {

    // 类路径
    URL resource = this.getClass().getClassLoader()
        .getResource("/" + scanPackage.replaceAll("//.", "/"));

    File classPath = new File(resource.getFile());

    for (File file : classPath.listFiles()) {
      if (file.isDirectory()) {
        doScan(scanPackage + "." + file.getName());
      }
      else {
        if (!file.getName().endsWith(".class")) {
          continue;
        }
        else {
          String className = (scanPackage + "." + file.getName()).replace(".class", "");
          classNameList.add(className);
        }
      }
    }
  }

实例化.
- 那些类需要实例化. 带有 spring 注解的类需要初始化. 在spring里面是 @Component 这里做例子就直接写死了几个需要初始化的标记接口
  1. HFController
  2. HFService
- 实例化后的存储
  1. Map 结构毋庸置疑
    - 在spring中我们注入有 byName 和 byType. 我们这个简单的ioc容器也会有
      - byName 的存储方式: key: beanName value: object
    - 通过反射方法 getInterfaces 我们可以获取这个类实现了那些接口. 因此可以直接进行注入
      - byType 的存储方式: key: interfaceName value:Object

/**
   * 实例化
   */
  private void instance() {
    if (this.classNameList.isEmpty()) {
      return;
    }
    try {

      for (String clazz : this.classNameList) {
        Class<?> aClass = Class.forName(clazz);

        // 1. 接口的实现类初始化
        if (!aClass.isInterface()) {
          System.out.println(clazz);
          Object o = aClass.newInstance();
          // 1. 带有注解的初始化
          if (aClass.isAnnotationPresent(HFController.class)) {
            IOC_NAME.put(aClass.getSimpleName(), o);
          }
          else if (aClass.isAnnotationPresent(HFService.class)) {
            HFService annotation = aClass.getAnnotation(HFService.class);
            // 名字注入
            if (annotation.name().equals("")) {
              IOC_NAME.put(aClass.getSimpleName(), o);
            }
            else {
              IOC_NAME.put(annotation.name(), o);
            }

            // 类型注入
            Class<?>[] interfaces = aClass.getInterfaces();
            for (Class<?> anInterface : interfaces) {
              if (!IOC_NAME.containsKey(anInterface.getName())) {
                IOC_NAME.put(anInterface.getName(), o);
              }
            }
          }

          else {
            continue;
          }
        }

      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

自动注入
- 从ico容器中获取实例化的对象并且强制设置属性
  1. 那些字段需要呗强制设置? 带有 HFAutowired 注解的字段

private void autowired() {

    if (IOC_NAME.isEmpty()) {
      return;
    }

    for (Entry<String, Object> entry : IOC_NAME.entrySet()) {
      try {

        String k = entry.getKey();
        Object v = entry.getValue();
        Field[] declaredFields = v.getClass().getDeclaredFields();
        for (Field declaredField : declaredFields) {
          // 是否又自动注入的注解
          if (declaredField.isAnnotationPresent(HFAutowired.class)) {
            HFAutowired annotation = declaredField.getAnnotation(HFAutowired.class);
            String beanName = annotation.value().trim();
            // byType 获取具体的实现类
            if (beanName.equals("")) {
              beanName = declaredField.getType().getName();
            }
            declaredField.setAccessible(true);
            declaredField.set(v, IOC_NAME.get(beanName));
          }
          else {
            continue;
          }
        }
      } catch (Exception e) {
        e.printStackTrace();

      }
    }

  }

绑定url和执行方法
- 先找到 HFController. 再找到 HFRequestMapping 反射获取所有 method 判断method是否有 HFRequestMapping. 最终组装, 类上面的HFRequestMapping和方法上的HFRequestMapping属性值拼接起来就是url

private void initHandlerMapping() {
    if (IOC_NAME.isEmpty()) {
      return;
    }

    for (Entry<String, Object> entry : IOC_NAME.entrySet()) {
      Class<?> clazz = entry.getValue().getClass();

      if (clazz.isAnnotationPresent(HFController.class)) {
        if (clazz.isAnnotationPresent(HFRequestMapping.class)) {
          HFRequestMapping annotation = clazz.getAnnotation(HFRequestMapping.class);
          String baseUri = annotation.name();

          for (Method method : clazz.getMethods()) {
            HFRequestMapping annotation1 = method.getAnnotation(HFRequestMapping.class);
            if (annotation1 != null) {

              String uri = ("/" + baseUri + "/" + annotation1.name()).replaceAll("/+", "/");
              HandlerMapping.put(uri, method);
            }
          }
        }
      }


    }

  }

运行时

处理请求
1. 从请求的url转换为method
2. 参数匹配
  1. 读取method的参数列表,类型列表
  2. 根据类型我们有两个可以直接设置HttpServletRequest,HttpServletResponse
  3. 获取参数的注解. HFRequestParam . 从url中获取对应的名称. 放入参数列表.
  4. method.invoke 执行.
  5. 获取method的执行结果. response 写出

private void dispath(HttpServletRequest req, HttpServletResponse resp) throws Exception {
    String requestURI = req.getRequestURI();
    String contextPath = req.getContextPath();
    requestURI = requestURI.replaceAll(contextPath, "").replaceAll("/+", "/");
    if (!HandlerMapping.containsKey(requestURI)) {
      throw new RuntimeException("不存在的url");
    }

    Method method = HandlerMapping.get(requestURI);
    if (method != null) {

      // 获取 method 所在的class
      String simpleName = method.getDeclaringClass().getSimpleName();
      Object o = IOC_NAME.get(simpleName);

      // 请求参数
      Map<String, String[]> parameterMap = req.getParameterMap();
      // 参数动态赋值
      Class<?>[] parameterTypes = method.getParameterTypes();
      Object[] paramValues = new Object[parameterTypes.length];

      for (int i = 0; i < paramValues.length; i++) {
        // 获取 controller 中的参数类型
        Class<?> parameterType = parameterTypes[i];
        if (parameterType.equals(req.getClass())) {
          paramValues[i] = req;
        }
        else if (parameterType.equals(resp.getClass())) {
          paramValues[i] = resp;
        }
        // todo: 2020/7/25 参数内容的设置
        else if (parameterType.equals(String.class)) {
          Annotation[][] parameterAnnotations = method.getParameterAnnotations();
          for (Annotation a : parameterAnnotations[i]) {
            if (a instanceof HFRequestParam) {
              String paramName = ((HFRequestParam) a).name();
              if (!"".equals(paramName.trim())) {
                String value = Arrays.toString(parameterMap.get(paramName))
                    .replaceAll("//[|//]", "").replaceAll("//s", ",");
                paramValues[i] = value;
              }

            }
          }
        }
        else if (parameterType.equals(Integer.class) || parameterType.equals(int.class)) {
          Annotation[][] parameterAnnotations = method.getParameterAnnotations();
          for (Annotation a : parameterAnnotations[i]) {
            if (a instanceof HFRequestParam) {
              String paramName = ((HFRequestParam) a).name();
              if (!"".equals(paramName.trim())) {
                String value = Arrays.toString(parameterMap.get(paramName))
                    .replaceAll("//[|//]", "").replaceAll("//s", ",");
                paramValues[i] = Integer.valueOf(value);
              }

            }
          }
        }
      }
      Object invoke = method.invoke(o, paramValues);
      resp.getWriter().write(invoke.toString());
    }

  }

完整的类

package org.huifer.spring.servlet.v1;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
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 org.huifer.spring.annotation.HFAutowired;
import org.huifer.spring.annotation.HFController;
import org.huifer.spring.annotation.HFRequestMapping;
import org.huifer.spring.annotation.HFRequestParam;
import org.huifer.spring.annotation.HFService;

public class HFDispatcherServlet extends HttpServlet {


  public static final String CONTEXT_CONFIG_LOCATION = "contextConfigLocation";
  public static final String SCAN_KEY = "scanPackage";
  private final Properties SPRING_CONTEXT_CONFIG = new Properties();
  private final List<String> classNameList = new ArrayList<>();
  private final Map<String, Method> HandlerMapping = new HashMap<>();
  /**
   *
   */
  Map<String, Object> IOC_NAME = new HashMap<>();

  @Override
  public void init() throws ServletException {
    // 配置读取
    doLoadConfig();
    // 注解扫描.
    doScan(this.SPRING_CONTEXT_CONFIG.getProperty(SCAN_KEY));
    // 初始化类
    instance();
    // 依赖注入
    autowired();
    // 初始化 handlerMapping
    initHandlerMapping();
    System.out.println();
  }

  private void initHandlerMapping() {
    if (IOC_NAME.isEmpty()) {
      return;
    }

    for (Entry<String, Object> entry : IOC_NAME.entrySet()) {
      Class<?> clazz = entry.getValue().getClass();

      if (clazz.isAnnotationPresent(HFController.class)) {
        if (clazz.isAnnotationPresent(HFRequestMapping.class)) {
          HFRequestMapping annotation = clazz.getAnnotation(HFRequestMapping.class);
          String baseUri = annotation.name();

          for (Method method : clazz.getMethods()) {
            HFRequestMapping annotation1 = method.getAnnotation(HFRequestMapping.class);
            if (annotation1 != null) {

              String uri = ("/" + baseUri + "/" + annotation1.name()).replaceAll("/+", "/");
              HandlerMapping.put(uri, method);
            }
          }
        }
      }


    }

  }

  private void autowired() {

    if (IOC_NAME.isEmpty()) {
      return;
    }

    for (Entry<String, Object> entry : IOC_NAME.entrySet()) {
      try {

        String k = entry.getKey();
        Object v = entry.getValue();
        Field[] declaredFields = v.getClass().getDeclaredFields();
        for (Field declaredField : declaredFields) {
          // 是否又自动注入的注解
          if (declaredField.isAnnotationPresent(HFAutowired.class)) {
            HFAutowired annotation = declaredField.getAnnotation(HFAutowired.class);
            String beanName = annotation.value().trim();
            // byType 获取具体的实现类
            if (beanName.equals("")) {
              beanName = declaredField.getType().getName();
            }
            declaredField.setAccessible(true);
            declaredField.set(v, IOC_NAME.get(beanName));
          }
          else {
            continue;
          }
        }
      } catch (Exception e) {
        e.printStackTrace();

      }
    }

  }

  /**
   * 实例化
   */
  private void instance() {
    if (this.classNameList.isEmpty()) {
      return;
    }
    try {

      for (String clazz : this.classNameList) {
        Class<?> aClass = Class.forName(clazz);

        // 1. 接口的实现类初始化
        if (!aClass.isInterface()) {
          System.out.println(clazz);
          Object o = aClass.newInstance();
          // 1. 带有注解的初始化
          if (aClass.isAnnotationPresent(HFController.class)) {
            IOC_NAME.put(aClass.getSimpleName(), o);
          }
          else if (aClass.isAnnotationPresent(HFService.class)) {
            HFService annotation = aClass.getAnnotation(HFService.class);
            // 名字注入
            if (annotation.name().equals("")) {
              IOC_NAME.put(aClass.getSimpleName(), o);
            }
            else {
              IOC_NAME.put(annotation.name(), o);
            }

            // 类型注入
            Class<?>[] interfaces = aClass.getInterfaces();
            for (Class<?> anInterface : interfaces) {
              if (!IOC_NAME.containsKey(anInterface.getName())) {
                IOC_NAME.put(anInterface.getName(), o);
              }
            }
          }

          else {
            continue;
          }
        }

      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }


  /**
   * 包扫描
   */
  private void doScan(String scanPackage) {

    // 类路径
    URL resource = this.getClass().getClassLoader()
        .getResource("/" + scanPackage.replaceAll("//.", "/"));

    File classPath = new File(resource.getFile());

    for (File file : classPath.listFiles()) {
      if (file.isDirectory()) {
        doScan(scanPackage + "." + file.getName());
      }
      else {
        if (!file.getName().endsWith(".class")) {
          continue;
        }
        else {
          String className = (scanPackage + "." + file.getName()).replace(".class", "");
          classNameList.add(className);
        }
      }
    }
  }

  /**
   * 从 web.xml 读取contextConfigLocation <br> 把 {@code classpath*:application.properties} 载入配置
   */
  private void doLoadConfig() {
    InputStream resourceAsStream = null;
    try {

      // 获取servlet的配置
      ServletConfig servletConfig = this.getServletConfig();
      String configInitParameter = servletConfig.getInitParameter(CONTEXT_CONFIG_LOCATION)
          .replace("classpath*:", "");
      // 读取配置文件
      resourceAsStream = this.getClass().getClassLoader()
          .getResourceAsStream(configInitParameter);
      SPRING_CONTEXT_CONFIG.load(resourceAsStream);

    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      if (resourceAsStream != null) {
        try {
          resourceAsStream.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
    }
  }

  @Override
  protected void doPost(HttpServletRequest req,
      HttpServletResponse resp) throws ServletException, IOException {
    try {

      dispath(req, resp);
    } catch (Exception e) {
      e.printStackTrace();
      resp.getWriter().write(Arrays.toString(e.getStackTrace()));

    }
  }

  private void dispath(HttpServletRequest req, HttpServletResponse resp) throws Exception {
    String requestURI = req.getRequestURI();
    String contextPath = req.getContextPath();
    requestURI = requestURI.replaceAll(contextPath, "").replaceAll("/+", "/");
    if (!HandlerMapping.containsKey(requestURI)) {
      throw new RuntimeException("不存在的url");
    }

    Method method = HandlerMapping.get(requestURI);
    if (method != null) {

      // 获取 method 所在的class
      String simpleName = method.getDeclaringClass().getSimpleName();
      Object o = IOC_NAME.get(simpleName);

      // 请求参数
      Map<String, String[]> parameterMap = req.getParameterMap();
      // 参数动态赋值
      Class<?>[] parameterTypes = method.getParameterTypes();
      Object[] paramValues = new Object[parameterTypes.length];

      for (int i = 0; i < paramValues.length; i++) {
        // 获取 controller 中的参数类型
        Class<?> parameterType = parameterTypes[i];
        if (parameterType.equals(req.getClass())) {
          paramValues[i] = req;
        }
        else if (parameterType.equals(resp.getClass())) {
          paramValues[i] = resp;
        }
        // todo: 2020/7/25 参数内容的设置
        else if (parameterType.equals(String.class)) {
          Annotation[][] parameterAnnotations = method.getParameterAnnotations();
          for (Annotation a : parameterAnnotations[i]) {
            if (a instanceof HFRequestParam) {
              String paramName = ((HFRequestParam) a).name();
              if (!"".equals(paramName.trim())) {
                String value = Arrays.toString(parameterMap.get(paramName))
                    .replaceAll("//[|//]", "").replaceAll("//s", ",");
                paramValues[i] = value;
              }

            }
          }
        }
        else if (parameterType.equals(Integer.class) || parameterType.equals(int.class)) {
          Annotation[][] parameterAnnotations = method.getParameterAnnotations();
          for (Annotation a : parameterAnnotations[i]) {
            if (a instanceof HFRequestParam) {
              String paramName = ((HFRequestParam) a).name();
              if (!"".equals(paramName.trim())) {
                String value = Arrays.toString(parameterMap.get(paramName))
                    .replaceAll("//[|//]", "").replaceAll("//s", ",");
                paramValues[i] = Integer.valueOf(value);
              }

            }
          }
        }
      }
      Object invoke = method.invoke(o, paramValues);
      resp.getWriter().write(invoke.toString());
    }

  }

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    try {

      dispath(req, resp);
    } catch (Exception e) {
      e.printStackTrace();
      resp.getWriter().write(Arrays.toString(e.getStackTrace()));

    }
  }
}

原文 https://segmentfault.com/a/1190000023380183

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