servlet数量太多，搞个轻量级springmvc

这两天用jsp+servlet+MySQL开发了一个企业网站，后台和前台都有，功能已经实现了，现在总结发现，servlet是真的多，我这个系统有7个表，后台实现一遍增删改查，就得有28个servlet，而且还有前台的部分，servlet的数量真的太多了，想想看springmvc，其实是可以写一个轻量级的springmvc的。

在Servlet中实现类似Spring的@Controller注解功能，主要是通过自定义注解和一个中央处理器（如Servlet过滤器或一个集中的Servlet）来解析这些注解并将请求映射到相应的方法。下面是一个简单的示例：

自定义注解 - Controller 和 RequestMapping

java">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)
public @interface Controller {
}

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface RequestMapping {
    String value();
}

自定义控制器类

java">@Controller
public class MyController {

    @RequestMapping(value = "/hello")
    public void hello(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.getWriter().write("Hello, World!");
    }
}

创建一个过滤器来处理请求映射

java">import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

public class DispatcherFilter implements Filter {

    private Map<String, Method> handlerMapping = new HashMap<>();

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // 扫描所有带有@Controller注解的类，并将它们注册到handlerMapping中
        // 这里需要使用反射或类路径扫描库（如ClassGraph）
        // 以下代码仅为示例，实际应用中需要根据项目结构进行调整
        Class<MyController> clazz = MyController.class;
        for (Method method : clazz.getDeclaredMethods()) {
            if (method.isAnnotationPresent(RequestMapping.class)) {
                RequestMapping annotation = method.getAnnotation(RequestMapping.class);
                handlerMapping.put(annotation.value(), method);
            }
        }
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        String uri = request.getRequestURI();
        Method method = handlerMapping.get(uri);
        if (method != null) {
            try {
                method.invoke(method.getDeclaringClass().newInstance(), request, response);
            } catch (Exception e) {
                throw new ServletException(e);
            }
        } else {
            response.sendError(HttpServletResponse.SC_NOT_FOUND);
        }
    }

    @Override
    public void destroy() {
    }
}

在web.xml中配置过滤器

<filter>
    <filter-name>dispatcher</filter-name>
    <filter-class>com.example.DispatcherFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>dispatcher</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>