代码实现SpringMvc

　　偶然看到一篇100多行实现SpringMvc的博客，阅读后整理加实现出来。大家共勉！（纸上得来终觉浅，绝知此事要躬行。）

　　实现Spring的部分。

Bean工厂，统一创建Bean；
IOC，实现Bean的依赖注入；
DispatchServlet，SpringMVC的路径映射。

　　代码解析如下：

　　1、首先创建Servelt，继承HttpServlet。覆盖init/doGet/doPost方法。

    @Override

    public void init() throws ServletException {

		 try {

			// 初始化配置文件

			 initConfig(super.getServletConfig().getInitParameter(CONFIG_NAME));

			 // 扫描类

			 doScanPackage(configProperties.getProperty("packageScan"));

			 // 加载类

			 initBeanInitializing();

			 // 依赖注入

			 initBeanAutowired();

			 // 路径映射

			 initServletDispatch();

		} catch (Exception e) {

			e.printStackTrace();

		}

		 System.out.println("====>beanFactory:\n"+beanFactory);

		 System.out.println("====>requestMap:\n"+requestMap);

    }

	@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{

		doDispatch(req,resp);

	}

　　2、配置web.xml

    <servlet>

  	<servlet-name>cwDispatchServlet</servlet-name>

  	<servlet-class>com.cw.servlets.CWDispatchServlet</servlet-class>

  	<init-param>

  		<param-name>dispatchConfig</param-name>

  		<param-value>config.properties</param-value>

  	</init-param>

  	<load-on-startup>1</load-on-startup>

  </servlet>

  <servlet-mapping>

  	<servlet-name>cwDispatchServlet</servlet-name>

  	<url-pattern>*.htm</url-pattern>

  </servlet-mapping>

　　2.1、配置文件config.properties在根目录，如下

# 设置配置文件

packageScan=com.cw.demo

　　3、定义支持的注入，如

　　Autowired

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.FIELD)

@Inherited

public @interface CWAutowired {

	String value() default "";

}

　　Controller

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.TYPE)

@Inherited

public @interface CWController {

	String value() default "";

}

　　RequestMapping

@Retention(RetentionPolicy.RUNTIME)

@Target({ElementType.TYPE,ElementType.METHOD})

@Inherited

public @interface CWRequestMapping {

	String value() default "";

}

　　Service

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.TYPE)

@Inherited

public @interface CWService {

	String value() default "";

}

　　4、在Servlet的init方法中，依次实现

　　4.1、加载配置文件

private void initConfig(String configName){

		InputStream inputStream = null;

		try {

			System.out.println("------->configName:"+configName);

			inputStream = this.getClass().getClassLoader().getResourceAsStream(configName);

			configProperties.load(inputStream);

		} catch (Exception e) {

			e.printStackTrace();

		}finally {

			if(null != inputStream) {

				try {

					inputStream.close();

				} catch (IOException e) {

					e.printStackTrace();

				}

			}

		}

	}

　　4.1、扫描所有Java类

        /**

	 * 扫描类

	 * @Title: doScanPackage

	 * @param packagePath

	 * @return void

	 */

	private void doScanPackage(String packagePath) {

		System.out.println("path:"+packagePath.replaceAll("\\.", "/"));

		URL url = this.getClass().getClassLoader().getResource("/"+packagePath.replaceAll("\\.", "/"));

		File file = new File(url.getFile());

		for(File sub:file.listFiles()) {

			if(sub.isDirectory()) {

				doScanPackage(packagePath+"."+sub.getName());

			}else {

				String clsName = packagePath+"."+sub.getName().replace(".class","");

				this.clsList.add(clsName);

			}

		}

	}

　　4.3、初始化类

　　　　　　private void initBeanInitializing() throws ClassNotFoundException, InstantiationException, IllegalAccessException {

		for(String clsName:clsList) {

			Class cls = Class.forName(clsName);

			if(cls.isAnnotationPresent(CWController.class)) {

				String name = cls.getSimpleName();

				beanFactory.put(lowerFirstChar(name) , cls.newInstance());

			}else if(cls.isAnnotationPresent(CWService.class)) {

				CWService service = (CWService) cls.getAnnotation(CWService.class);

				String defaultName = service.value();

				if(!"".equals(defaultName)) {

					beanFactory.put(defaultName, cls.newInstance());

				}else {

					Class[] interfaces = cls.getInterfaces();

					Object instance = cls.newInstance();

					for(Class inter:interfaces) {

						beanFactory.put(lowerFirstChar(inter.getSimpleName()), instance);

					}

				}

			}else  if(cls.isAnnotationPresent(CWComponent.class)){

				String name = cls.getName();

				beanFactory.put(lowerFirstChar(name), cls.newInstance());

			}

		}

	}

　　4.4、完成类的依赖注入

　　　　　　private void initBeanAutowired() throws IllegalArgumentException, IllegalAccessException {

		for(Map.Entry<String, Object> entry:beanFactory.entrySet()) {

			Object bean = entry.getValue();

			Field[] fields = bean.getClass().getDeclaredFields();

			if(null == fields || fields.length ==0 ) {

				continue;

			}

			for(Field field:fields) {

				if(field.isAnnotationPresent(CWAutowired.class)) {

					String fieldTypeName = field.getType().getSimpleName();

					field.setAccessible(true);

					field.set(bean, beanFactory.get(this.lowerFirstChar(fieldTypeName)));

				}

			}

		}

	}

　　4.5、完成request的路径映射

　　　　　　private void initServletDispatch() {

		for(Map.Entry<String, Object> entry:beanFactory.entrySet()) {

			Object bean = entry.getValue();

			System.out.println(entry.getKey()+":"+entry.getValue());

			if(!bean.getClass().isAnnotationPresent(CWController.class)) {

				continue;

			}

			// 基本路径

			String basePath = "";

			if(bean.getClass().isAnnotationPresent(CWRequestMapping.class)) {

				basePath = ((CWRequestMapping)bean.getClass().getAnnotation(CWRequestMapping.class)).value();

			}

			System.out.println("=========>basePath:"+basePath);

			// 方法路径

			Method[] methods = bean.getClass().getMethods();

			for(Method method:methods) {

				if(method.isAnnotationPresent(CWRequestMapping.class)) {

					String path = ((CWRequestMapping)method.getAnnotation(CWRequestMapping.class)).value();

					requestMap.put(("/"+basePath +"/"+path).replaceAll("/+", "/"), method);

				}

			}

		}

	}

　　5、处理页面请求

        private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws UnsupportedEncodingException, IOException {

		String url = req.getRequestURI();

		String contextPath = req.getContextPath();

		url = url.replace(contextPath, "").replaceAll("/+", "/");

		System.out.println("=========>request url:"+url);

		Method method = this.requestMap.get(url);

		if(null == method) {

			resp.getOutputStream().write("404 not found!".getBytes("UTF-8"));

			return;

		}

		String beanName = this.lowerFirstChar(method.getDeclaringClass().getSimpleName());

		try {

			method.invoke(beanFactory.get(beanName), req,resp);

		}catch (Exception e) {

			e.printStackTrace();

			resp.getOutputStream().write("404 not found!".getBytes("UTF-8"));

		}

	}

　　6、添加测试类了

　　HelloWorldAction.java

@CWController

@CWRequestMapping("/h")

public class HelloWorldAction {

	@CWAutowired

	private IUserService userService;

	@CWRequestMapping("/hello.htm")

	public void hello(HttpServletRequest request,HttpServletResponse response) {

		try {

			System.out.println(userService.getUserNameById(1L));

			response.getWriter().write("hello World!");

			response.flushBuffer();

		} catch (IOException e) {

			e.printStackTrace();

		}

	}

}

　　IUserService.java

public interface IUserService {

	public String getUserNameById(Long id);

}

　　UserServiceImpl.java

@CWService

public class UserServiceImpl implements IUserService {

	@Override

	public String getUserNameById(Long id) {

		return "master";

	}

}

　　7、tomcat启动，大功告成

　　http:127.0.0.1:8080/h/hello.htm

总结：

　　1、看别人的代码，很简单，自己实现就发现很多坑。关键还是要自己实践。实践！实践！实践！

备注:

　　1、参考来源

　　https://www.toutiao.com/i6636629045259796995/

　　2、工程源码

　　https://pan.baidu.com/s/1F0el_nwDJ99-AYueeH0esw

巴特西

代码实现SpringMvc

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