手写Spring+demo+思路

我在学习Spring的时候，感觉Spring是很难的，通过学习后，发现Spring没有那么难，只有你去学习了，你才会发现，你才会进步

1、手写Spring思路：

分为配置、初始化、运行三个阶段如下图

第一个阶段

配置阶段  web.xml配置，如下图

<?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>HandWriting Web Application</display-name>

    <servlet>
        <servlet-name>HandWriting MVC</servlet-name>
        <servlet-class>com.wbg.framework.webmvc.servlet.HandWritingServlet</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>HandWriting MVC</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>
</web-app>

 在resources写properties文件

内容是需要扫描的包的路径

scanPackage=com.wbg.demo

第二、三个阶段

1、在初始化前，将注解自定义，我现在写了5个常用的注解，这些注解都是自定仪，如下图：

HandWritingAutowired

package com.wbg.framework.webmvc.annotation;

import java.lang.annotation.*;

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

HandWritingController

package com.wbg.framework.webmvc.annotation;

import java.lang.annotation.*;

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

HandWritingRequestMapping

package com.wbg.framework.webmvc.annotation;

import java.lang.annotation.*;

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

HandWritingRequestParam

package com.wbg.framework.webmvc.annotation;

import java.lang.annotation.*;

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

HandWritingService

package com.wbg.framework.webmvc.annotation;

import java.lang.annotation.*;

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

2、初始化阶段  init（ServletConfig config）

继承HttpServlet,重写init

3、运行阶段 doGet、doPost

继承HttpServlet,重写doGet、doPost

我这里创建一个 HandWritingServlet类继承HttpServlet

package com.wbg.framework.webmvc.servlet;

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.IOException;

public class HandWritingServlet extends HttpServlet {

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

    }

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

    }

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
    }
}

• 1、加载配置文件 获取web.xml文件的的param-name

• 2、扫描所有相关联的类 //配置文件的scanPackage = com...

• 3、初始化所有相关的类，并且将其保存到IOC容器之中

• 4、执行依赖注入（把加了@Autoidwired注解的字段赋值）

• 5、构造HandlerMapping,将URL和Method进行关联

运行阶段(doGet/doPost)

• 1、通过request获得url，然后再去HandlerMapping
• 2、用反射调用Method
• 3、response.writer()

代码如下

package com.wbg.framework.webmvc.servlet;

import com.wbg.framework.webmvc.annotation.*;

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.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class HandWritingServlet extends HttpServlet {
    //配置文件
    private Properties contextConfig = new Properties();
    //存配置文件 scanPackage=com.wbg.demo 下所有的类名
    private List<String> classNames = new ArrayList<String>();
    //IOC容器
    private Map<String, Object> ioc = new HashMap<String, Object>();
    //保存所有的URL和方法的映射关系
    private List<Handler> handlerMapping = new ArrayList<Handler>();

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
        this.doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
        try {
            doDispatch(req, resp);
        } catch (Exception e) {
            try {
                resp.getWriter().write("500 =========" + e);
            } catch (IOException e1) {
                e1.printStackTrace();
            }
        }
    }

    /**
     * 初始化，加载配置
     * @param config 配置文件
     */
    @Override
    public void init(ServletConfig config) {

        System.out.println("======初始化配置文件======");
        //1、加载配置文件  获取web.xml文件的的param-name
        doLoadConfig(config.getInitParameter("contextConfigLocation"));
        //2、扫描所有相关联的类 //配置文件的scanPackage = com...
        doScanner(contextConfig.getProperty("scanPackage"));
        //3、初始化所有相关的类，并且将其保存到IOC容器之中
        doInstance();
        //4、执行依赖注入（把加了@Autoidwired注解的字段赋值）
        doAutoWired();

        //-------------------------Spring的核心功能已经完成  IOC  DI注入

        //5、构造HandlerMapping,将URL和Method进行关联
        initHandlerMapping();

        System.out.println("=========启动完毕============");

    }

    /**
     * 构造HandlerMapping,将URL和Method进行关联
     */
    private void initHandlerMapping() {
        if (ioc.isEmpty()) {
            return;
        }
        for (Map.Entry<String, Object> entry : ioc.entrySet()) {

            Class<?> clazz = entry.getValue().getClass();
            //如果该类上没有Controller  下一个
            if (!clazz.isAnnotationPresent(HandWritingController.class)) {
                continue;
            }

            String baseUrl = "";
            //如果该类上有RequestMapping注解
            if (clazz.isAnnotationPresent(HandWritingRequestMapping.class)) {
                HandWritingRequestMapping requestMapping = clazz.getAnnotation(HandWritingRequestMapping.class);
                //获取RequestMapping注解的值
                baseUrl = requestMapping.value();
            }
            //获取该类的所有方法
            Method[] methods = clazz.getMethods();

            for (Method method : methods) {
                //如果该方法上面没有RequestMapping 下一个
                if (!method.isAnnotationPresent(HandWritingRequestMapping.class)) {
                    continue;
                }

                HandWritingRequestMapping requestMapping = method.getAnnotation(HandWritingRequestMapping.class);
                //获取RequestMapping注解的值
                String regex = requestMapping.value();
                //将 类上、方法上 的RequestMapping 注解相加  得到一个url
                regex = (baseUrl + regex).replaceAll("/+", "/");
                Pattern pattern = Pattern.compile(regex);
                handlerMapping.add(new Handler(pattern, entry.getValue(), method));
                System.out.println("handlerMapping：" + regex);
            }

        }

    }

    /**
     * 执行依赖注入 将加了AutoWired注解的字段进行赋值
     * 注入的意思就是把所有IOC容器中加了@Autowired注解的字段全部赋值
     */
    private void doAutoWired() {
        if (ioc.isEmpty()) {
            return;
        }
        for (Map.Entry<String, Object> entry : ioc.entrySet()) {
            //获取该类的声明字段 包过私有的字段
            Field[] fields = entry.getValue().getClass().getDeclaredFields();
            //循环加入IOC容器
            for (Field field : fields) {
                //如果字段不加Autowired注解  下一个
                if (!field.isAnnotationPresent(HandWritingAutowired.class)) {
                    continue;
                }
                //获取这个字段上的Autowired注解
                HandWritingAutowired autowired = field.getAnnotation(HandWritingAutowired.class);
                //获取注解上的value
                String beanName = autowired.value().trim();
                //如果为空
                if ("".equals(beanName)) {
                    //获取这个字段的名字
                    beanName = field.getType().getName();
                }
                //如果这个字段是私有的字段，强制访问
                field.setAccessible(true);
                try {
                    //赋值
                    field.set(entry.getValue(), ioc.get(beanName));
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 初始化所有相关的类
     * 加了注解的才初始化
     */
    private void doInstance() {
        if (classNames.isEmpty()) {
            return;
        }
        for (String className : classNames) {
            try {
                Class<?> clazz = Class.forName(className);
                //只有加了注解的  才初始化
                if (clazz.isAnnotationPresent(HandWritingController.class)) {
                    Object instance = clazz.newInstance();
                    String beanName = lowerFirstClass(clazz.getSimpleName());
                    ioc.put(beanName, instance);
                } else if (clazz.isAnnotationPresent(HandWritingService.class)) {
                    HandWritingService service = clazz.getAnnotation(HandWritingService.class);
                    //2、自定义命名，优先使用自定义命名
                    String beanName = service.value();
                    //1、默认类名首字母小写
                    if ("".equals(beanName.trim())) {
                        beanName = lowerFirstClass(clazz.getSimpleName());
                    }
                    Object instance = clazz.newInstance();
                    ioc.put(beanName, instance);

                    // 3、自动类型匹配（例如将实现类赋值给接口）
                    Class<?>[] instances = clazz.getInterfaces();
                    for (Class<?> i : instances) {
                        ioc.put(i.getName(), instance);
                    }
                } else {
                    continue;
                }

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

    /**
     * 将字符串的首字母变成小写  利用ASCII转换
     * @param simpleName
     * @return
     */
    private String lowerFirstClass(String simpleName) {
        char[] c = simpleName.toCharArray();
        c[0] += 32;
        return String.valueOf(c);
    }

    protected void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception {
        Handler handler = getHandler(req);
        //如果为空  没有这个请求路径
        if (handler == null) {
            resp.getWriter().write("=========handWritingSpring=============404==========");
            return;
        }
        try {
            //获取方法的参数列表
            Class<?>[] paramTypes = handler.method.getParameterTypes();
            //保存所有需要自动赋值的参数值
            Object[] paramValues = new Object[paramTypes.length];
            //获取方法上的参数
            Map<String, String[]> params = req.getParameterMap();
            for (Map.Entry<String, String[]> param : params.entrySet()) {
                //转换为String 去掉数组[]两边 去掉字符的空白
                String value = Arrays.toString(param.getValue()).replaceAll("\\[|\\]", "").replaceAll("\\s", "");
                //如果找到匹配的对象，则开始填充参数值
                if (!handler.paramIndexMapping.containsKey(param.getKey())) {
                    continue;
                }
                int index = handler.paramIndexMapping.get(param.getKey());
                paramValues[index] = convert(paramTypes[index], value);
            }
            int reqIndex = handler.paramIndexMapping.get(HttpServletRequest.class.getName());
            paramValues[reqIndex] = req;
            int respIndex = handler.paramIndexMapping.get(HttpServletResponse.class.getName());
            paramValues[respIndex] = resp;
            handler.method.invoke(handler.controller, paramValues);
        } catch (Exception e) {
            throw e;
        }
    }

    private Handler getHandler(HttpServletRequest req) throws Exception {
        if (handlerMapping.isEmpty()) {
            return null;
        }
        String url = req.getRequestURI();
        String contextPath = req.getContextPath();
        url = url.replaceAll(contextPath, "").replaceAll("/+", "/");
        for (Handler handler : handlerMapping) {
            try {
                Matcher matcher = handler.pattern.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;
    }

    /**
     * 转换类型Integer
     * @param type
     * @param value
     * @return
     */
    private Object convert(Class<?> type, String value) {
        if (Integer.class == type) {
            return Integer.valueOf(value);
        }
        return value;
    }

    /**
     * 扫描basePackage路径下所以的类
     * @param basePackage
     */
    private void doScanner(String basePackage) {
        //获取路径
        URL url = this.getClass().getClassLoader().getResource("/" + basePackage.replaceAll("\\.", "/"));
        File dir = new File(url.getFile());
        for (File file : dir.listFiles()) {
            //如果是一个文件夹
            if (file.isDirectory()) {
                //递归
                doScanner(basePackage + "." + file.getName());
            } else {
                //获取类名
                String className = basePackage + "." + file.getName().replace(".class", "");
                //将所有项目所有类存起来
                classNames.add(className);
            }
        }
    }

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

        InputStream is = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation);
        try {
            contextConfig.load(is);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (null != is) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * Handler记录Controller中的RequestMapping和Method对应的关系
     */
    private class Handler {
        protected Object controller; //保存方法对应的实例
        protected Method method; //保存映射的方法
        protected Pattern pattern;  //RequestMapping存的URL
        protected Map<String, Integer> paramIndexMapping; //参数顺序

        /**
         * 基本参数
         * @param pattern
         * @param controller
         * @param method
         */
        protected Handler(Pattern pattern, Object controller, Method method) {
            this.pattern = pattern;
            this.controller = controller;
            this.method = method;
            paramIndexMapping = new HashMap<String, Integer>();
            putParamIndexMapping(method);

        }

        /**
         * 保存RequestParam注解的参数值
         * @param method 类的方法
         */
        private void putParamIndexMapping(Method method) {
            //获取方法中加了注解的参数
            Annotation[][] pa = method.getParameterAnnotations();
            for (int i = 0; i < pa.length; i++) {
                for (Annotation annotation : pa[i]) {
                    //如果使用到了HandWritingRequestParam注解
                    if (annotation instanceof HandWritingRequestParam) {
                        //获取该注解的值
                        String paramName = ((HandWritingRequestParam) annotation).value();
                        //如果这个值不为空
                        if (!"".equals(paramName.trim())) {
                            //保存参数
                            paramIndexMapping.put(paramName, i);
                        }
                    }
                }
            }
            //提取方法中的request和response参数
            Class<?>[] paramsTypes = method.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);
                }
            }

        }

    }
}

以上代码完成后Spring就ok了，现在开始使用，我写的demo如下：

1、首先创建接口  DemoService

public interface DemoService {
    String get(String name);
    String sum(int a,int b);
    String remove(String id);
}

2、在类上使用刚刚自定义的注解  @HandWritingService  调用DemoService

@HandWritingService
public class DemoServiceImp implements DemoService {
    public String get(String name) {
        return "My name is " + name;
    }

    public String sum(int a,int b) {
        return "a + b = " + (a+b);
    }

    public String remove(String id) {
        return "remove id = " + id;
    }
}

3、开始写Controll控制器

1、在类上使用 @HandWritingController 相当于 Controlle

　　　　@HandWritingRequestMapping 相当于RequestMapping

2、字段 注入   @HandWritingAutowired  相当于 Autowired

3、方法上使用 @HandWritingRequestMapping("/sum.json") 和类上一样，当然可以写一个注解 GetRequestMapping  get请求

4、参数上使用 @HandWritingRequestParam("name")  相当于 RequestParam

代码如下：

package com.wbg.demo.mvc.action;

import com.wbg.demo.service.DemoService;
import com.wbg.framework.webmvc.annotation.HandWritingAutowired;
import com.wbg.framework.webmvc.annotation.HandWritingController;
import com.wbg.framework.webmvc.annotation.HandWritingRequestMapping;
import com.wbg.framework.webmvc.annotation.HandWritingRequestParam;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@HandWritingController
@HandWritingRequestMapping("/demo")
public class DemoAction {
    @HandWritingAutowired
    private DemoService demoService;

    @HandWritingRequestMapping("/query.json")
    public void query(HttpServletRequest req, HttpServletResponse resp, @HandWritingRequestParam("name")String name){
        String result =  demoService.get(name);
        try{
            resp.getWriter().write(result);
        }catch (IOException e){
            e.printStackTrace();
        }
    }
    @HandWritingRequestMapping("/sum.json")
    public void sum(HttpServletRequest req, HttpServletResponse resp, @HandWritingRequestParam("a") Integer a, @HandWritingRequestParam("b") Integer b){
        String result =  demoService.sum(a,b);
        try{
            resp.getWriter().write(result);
        }catch (IOException e){
            e.printStackTrace();
        }
    }
    @HandWritingRequestMapping("/remove.json")
    public void remove(HttpServletRequest req, HttpServletResponse resp, @HandWritingRequestParam("id") String id){
        String result =  demoService.remove(id);
        try{
            resp.getWriter().write(result);
        }catch (IOException e){
            e.printStackTrace();
        }
    }
}

现在启动服务，验证一下，如下图

项目demo：https://github.com/weibanggang/handwritingspring

对你有帮助，麻烦点下星，谢谢