Tomcat半通用回显分析

public class Myservlet extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {        try{            Field WRAP_SAME_OBJECT_FIELD = Class.forName("org.apache.catalina.core.ApplicationDispatcher").getDeclaredField("WRAP_SAME_OBJECT");            Field RequestField = ApplicationFilterChain.class.getDeclaredField("lastServicedRequest");            Field ResponseField = ApplicationFilterChain.class.getDeclaredField("lastServicedResponse");
            //取消Final属性            Field modifiersField = Field.class.getDeclaredField("modifiers");            modifiersField.setAccessible(true);            modifiersField.setInt(WRAP_SAME_OBJECT_FIELD,WRAP_SAME_OBJECT_FIELD.getModifiers()&~Modifier.FINAL);            modifiersField.setInt(RequestField,RequestField.getModifiers()&~Modifier.FINAL);            modifiersField.setInt(ResponseField,ResponseField.getModifiers()&~Modifier.FINAL);
            WRAP_SAME_OBJECT_FIELD.setAccessible(true);            RequestField.setAccessible(true);            ResponseField.setAccessible(true);
            //获取ServletRequest和ServletResponse 用作后面的回显            ThreadLocal<ServletRequest> requests = (ThreadLocal<ServletRequest>) RequestField.get(null);            ThreadLocal<ServletResponse> responses = (ThreadLocal<ServletResponse>) ResponseField.get(null);
            //如果为null，则通过反射进行初始化            if(requests==null || responses==null){                WRAP_SAME_OBJECT_FIELD.set(null,true);                RequestField.set(null,new ThreadLocal<>());                ResponseField.set(null,new ThreadLocal<>());            }else{                    responses.get().getWriter().write("By Met32");            }
        }catch(Exception e){            e.printStackTrace();        }    }}

       if (ApplicationDispatcher.WRAP_SAME_OBJECT) {                    lastServicedRequest.set((Object)null);                    lastServicedResponse.set((Object)null);              }