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" ;
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String[] staticResourceSuffixes={".html",".jsp",".jpg",".png",".gif",".css",".js",".ico"};
        //index.html
        String uri = request.getRequestURI();
        if(Arrays.stream(staticResourceSuffixes).anyMatch(uri::endsWith)){
            RequestDispatcher defaultDispatcher = request.getServletContext().getNamedDispatcher("default");
            defaultDispatcher.forward(request,response);
        }else{
            // uri:    /fruit/index
            String[] arr = uri.split("/") ;

            if(arr==null || arr.length!=3){
                throw new RuntimeException(uri+"非法！");
            }
            //  [, fruit, index]
            String requestMapping = "/"+arr[1] ;  //   /fruit
            String methodMapping = "/"+arr[2];    //   /index

            ServletContext application = getServletContext();
            ControllerDefinition controllerDefinition = ((Map)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post
            String requestMethodStr = request.getMethod().toLowerCase();
            //get_/index
            Method 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：-parameters
                    String 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.String
                            String 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);
            }
        }
    }
}