微头条项目实战：新增RequestHeader注解

1、RequestHeader

package com.csdn.mymvc.annotation;
import java.lang.annotation.*;
@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Inherited
public @interface RequestHeader {
}

2、DispatcherServlet

package com.csdn.mymvc.core;
import com.csdn.mymvc.annotation.RequestBody;
import com.csdn.mymvc.annotation.RequestHeader;
import com.csdn.mymvc.util.RequestUtil;
import com.csdn.mymvc.util.ResponseUtil;
import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import com.csdn.headline.common.Result;
import java.io.IOException;
import java.lang.annotation.Annotation;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.util.Arrays;
import java.util.Map;
@WebServlet("/*")
public class DispatcherServlet extends HttpServlet {private final String BEAN_FACTORY = "beanFactory" ;private final String CONTROLLER_BEAN_MAP = "controllerBeanMap" ;@Overrideprotected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String[] staticResourceSuffixes={".html",".jsp",".jpg",".png",".gif",".css",".js",".ico"};//index.htmlString uri = request.getRequestURI();if(Arrays.stream(staticResourceSuffixes).anyMatch(uri::endsWith)){RequestDispatcher defaultDispatcher = request.getServletContext().getNamedDispatcher("default");defaultDispatcher.forward(request,response);}else{// uri:    /fruit/indexString[] arr = uri.split("/") ;if(arr==null || arr.length!=3){throw new RuntimeException(uri+"非法！");}//  [, fruit, index]String requestMapping = "/"+arr[1] ;  //   /fruitString methodMapping = "/"+arr[2];    //   /indexServletContext application = getServletContext();ControllerDefinition controllerDefinition = ((Map<String,ControllerDefinition>)application.getAttribute(CONTROLLER_BEAN_MAP)).get(requestMapping);if(controllerDefinition==null){throw new RuntimeException(requestMapping+"对应的controller组件不存在！");}//获取请求方式，例如：get或者postString requestMethodStr = request.getMethod().toLowerCase();//get_/indexMethod method = controllerDefinition.getMethodMappingMap().get(requestMethodStr+"_"+methodMapping) ;Object controllerBean = controllerDefinition.getControllerBean();try {//第1步：参数处理//获取method方法上的参数Parameter[] parameters = method.getParameters();Object[] parameterValues = new Object[parameters.length];for(int i = 0 ; i< parameters.length;i++){Parameter parameter = parameters[i];//获取参数名称//JDK8之前，通过反射获取到参数对象(Parameter对象)//然后通过parameter.getName()方法是得不到形参的名称的，返回的是arg0,arg1,arg2....//JDK8开始，反射技术得到的Class中可以包含方法形参的名称，不过需要做一个额外的设置：java compiler 中添加一个参数：-parametersString paramName = parameter.getName();Object parameterValue = null ;//获取当前这个参数上的所有注解Annotation[] annotations = parameter.getDeclaredAnnotations();if (Arrays.stream(annotations).anyMatch(annotation -> annotation instanceof RequestBody)) {parameterValue = RequestUtil.readObject(request,parameter.getType());} else if (Arrays.stream(annotations).anyMatch(annotation -> annotation instanceof RequestHeader)) {parameterValue = request.getHeader(paramName);} else{String paramValueStr = request.getParameter(paramName);if(paramValueStr!=null){//获取参数的类型，例如： java.lang.Integer,java.lang.StringString parameterTypeName = parameter.getType().getName();parameterValue = switch (parameterTypeName){case "java.lang.String"->paramValueStr;case "java.lang.Integer"->Integer.parseInt(paramValueStr);default -> null;};}}parameterValues[i]=parameterValue;}//第2步：方法调用//调用controllerBean对象中的method方法method.setAccessible(true);//第3步：结果集处理Object returnObj = method.invoke(controllerBean,parameterValues);if(returnObj!=null && returnObj instanceof Result){Result result = (Result) returnObj ;ResponseUtil.print(response,result);}} catch (IllegalAccessException e) {e.printStackTrace();throw new RuntimeException(e);} catch (InvocationTargetException e) {e.printStackTrace();throw new RuntimeException(e);}}}
}