手动实现SpringMVC框架

前言：

SpringMVC最核心的就是DispatchServlet,所以要先对Servlet有一定的认识，然后就是反射注解ioc等相关知识，

思路：

主要的核心编码是在Servlet初始化里面扫描所有需要的包并将被@Controller,@Service注解修饰的对象实例化放在一个容IOC器里面管理（k-v，className as key ），属性值注入：遍历IOC里面所有的bean对象，遍历每个对象里面的属性，利用反射机制将value映射给它，同时将所有被@RequestMapping修饰的控制器或者方法也放在一个容器里面管理（k-v）, Servlet拦截并截取对应的uri 根据uri这个key获取相应的控制器与方法执行invoke操作

代码：

创建一个maven项目 添加依赖 然后转成web项目

  <dependency>
        <groupId>javax.servlet</groupId> 
      <artifactId>javax.servlet-api</artifactId> 
      <version>3.0.1</version> 
      <scope>provided</scope>
   </dependency>

1.实现几个常用的注解@Controller,@Service,@RequestMapping @Autowired，我这边以LP打头命名

项目结构图

@LPAutowired

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

@LPController

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

@LPRequestMapping

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

@LPService

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

控制器TestController

@LPController
@LPRequestMapping("/test")
public class TestController {

	@LPAutowired
	LoginService loginService1;
	
	@LPRequestMapping("/login")
	public void login(HttpServletRequest req, HttpServletResponse resp,String account,String pwd) throws IOException{
		loginService1.login(account, pwd);
		resp.getWriter().write("request success,param:"+account+"-"+pwd);
	}
	
}

LoginService

public interface LoginService {
	
	public void login(String account,String password);
	
}

LoginServiceImpl

@LPService("loginService")//key的规则：Interface Name 首字母小写当做ioc的key
public class LoginServiceImpl implements LoginService {

	public void login(String account, String password) {
		// TODO Auto-generated method stub
		System.out.println("账号"+account+" 密码:"+password);
	}

}

application.properties 配置需要扫描的包路径

scanPackage=com.mvc.custom

以上基本实现的springmvc的用法，但是他只是一个空壳，核心在下面

LPDispatchServlet 核心工作

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
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 com.mvc.custom.annotation.LPAutowired;
import com.mvc.custom.annotation.LPController;
import com.mvc.custom.annotation.LPRequestMapping;
import com.mvc.custom.annotation.LPService;

/**
 * 
 * @版权：弹指支付 版权所有 (c) 2017
 * @ClassName:LPDispatchServlet
 * @author linpeng<br/>
 * @email [email protected]
 * @version Revision 1.0.0
 * @since JDK 1.7
 * @创建日期：2018年7月21日下午1:43:50 @功能说明：
 * 
 */
public class LPDispatchServlet 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();
		// 5。属性注入
		doAutoWired();
	}

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		System.out.println("doGet");
		this.doPost(req, resp);
	}

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		System.out.println("doPost");
		// super.doPost(req, resp);
		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[] paramValue = param.getValue();
					String value = Arrays.toString(paramValue).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.controllerMap.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 {
			// 用Properties文件加载文件里的内容
			properties.load(resourceAsStream);
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			// 关流
			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()) {
				// 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 {
				// 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(LPController.class)) {
					ioc.put(toLowerFirstWord(clazz.getSimpleName()), clazz.newInstance());
				}else if (clazz.isAnnotationPresent(LPService.class)) {
					Object instance = clazz.newInstance();
					LPService service = (LPService) clazz.getAnnotation(LPService.class);
					String key = service.value();
					ioc.put(key, instance);

				} else {
					continue;
				}

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

	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(LPController.class)) {
					continue;
				}
				Object instance = entry.getValue();
				// 拼url时,是controller头的url拼上方法上的url
				String baseUrl = "";
				if (clazz.isAnnotationPresent(LPRequestMapping.class)) {
					LPRequestMapping annotation = clazz.getAnnotation(LPRequestMapping.class);
					baseUrl = annotation.value();
				}
				Method[] methods = clazz.getMethods();
				for (Method method : methods) {
					if (!method.isAnnotationPresent(LPRequestMapping.class)) {
						continue;
					}
					LPRequestMapping annotation = method.getAnnotation(LPRequestMapping.class);
					String url = annotation.value();

					url = (baseUrl + "/" + url).replaceAll("/+", "/");
					handlerMapping.put(url, method);
					controllerMap.put(url,  instance);
					System.out.println(url + "," + method);
				}
			


			}

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

	}

	/**
	 * 给被AutoWired注解的属性注入值
	 */
	private void doAutoWired() {
		if (ioc.isEmpty()) {
			return;
		}
		// 遍历所有被托管的对象
		for (Map.Entry<String, Object> entry : ioc.entrySet()) {
			// 查找所有被Autowired注解的属性
			// getFields()获得某个类的所有的公共（public）的字段，包括父类;
			// getDeclaredFields()获得某个类的所有申明的字段，即包括public、private和proteced，但是不包括父类的申明字段。
			Object instance = entry.getValue();
			Field[] fields = entry.getValue().getClass().getDeclaredFields();
			for (Field field : fields) {
				// 没加autowired的不需要注值
				if (!field.isAnnotationPresent(LPAutowired.class)) {
					continue;
				}
				String beanName;
				// 获取AutoWired上面写的值，譬如@Autowired("abc")
				LPAutowired autowired = field.getAnnotation(LPAutowired.class);
				if ("".equals(autowired.value())) {
					// 例 searchService。注意，此处是获取属性的类名的首字母小写，与属性名无关，可以定义@Autowired
					// SearchService abc都可以。
					beanName = toLowerFirstWord(field.getType().getSimpleName());
				} else {
					beanName = autowired.value();
				}
				// 将私有化的属性设为true,不然访问不到
				field.setAccessible(true);
				// 去映射中找是否存在该beanName对应的实例对象
				if (ioc.get(beanName) != null) {
					try {
						field.set(instance, ioc.get(beanName));
					} catch (IllegalAccessException 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);
	}

web.xml 配置servlety与拦截规则以及属性文件等

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:web="http://java.sun.com/xml/ns/javaee" 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.mvc.custom.servlet.LPDispatchServlet</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>

运行：

http://localhost:8080/linp/test/login?account=linp&pwd=123456

大功告成，基本已经实现了一个极其简单的Springmvc的框架，这里只是简单的一个demo,还有涉及静态资源，线程安全等都还没有实现，所以说spring还是非常强大的！ 以上代码如果运行有错误 可以私聊一起调！