javaweb 网页 反射问题

Question

这是运行时的报错

java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.atguigu.myssm.myspringmvc.DispatcherServlet.service(DispatcherServlet.java:132)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:502)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1104)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2508)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2497)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException
    at com.atguigu.fruit.controllers.FruitController.index(FruitController.java:49)
    ... 27 more

网页是水果库存系统，初学javaweb。目前不是数据库问题

这是ViewBaseServlet.class文件

package com.atguigu.myssm.myspringmvc;

import org.thymeleaf.TemplateEngine;
import org.thymeleaf.context.WebContext;
import org.thymeleaf.templatemode.TemplateMode;
import org.thymeleaf.templateresolver.ServletContextTemplateResolver;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ViewBaseServlet extends HttpServlet {

    private TemplateEngine templateEngine;

    @Override
    public void init() throws ServletException {

        // 1.获取ServletContext对象
        ServletContext servletContext = this.getServletContext();

        // 2.创建Thymeleaf解析器对象
        ServletContextTemplateResolver templateResolver = new ServletContextTemplateResolver(servletContext);

        // 3.给解析器对象设置参数
        // ①HTML是默认模式，明确设置是为了代码更容易理解
        templateResolver.setTemplateMode(TemplateMode.HTML);

        // ②设置前缀
        String viewPrefix = servletContext.getInitParameter("view-prefix");

        templateResolver.setPrefix(viewPrefix);

        // ③设置后缀
        String viewSuffix = servletContext.getInitParameter("view-suffix");

        templateResolver.setSuffix(viewSuffix);

        // ④设置缓存过期时间（毫秒）
        templateResolver.setCacheTTLMs(60000L);

        // ⑤设置是否缓存
        templateResolver.setCacheable(true);

        // ⑥设置服务器端编码方式
        templateResolver.setCharacterEncoding("utf-8");

        // 4.创建模板引擎对象
        templateEngine = new TemplateEngine();

        // 5.给模板引擎对象设置模板解析器
        templateEngine.setTemplateResolver(templateResolver);

    }

    protected void processTemplate(String templateName, HttpServletRequest req, HttpServletResponse resp) throws IOException {
        // 1.设置响应体内容类型和字符集
        resp.setContentType("text/html;charset=UTF-8");

        // 2.创建WebContext对象
        WebContext webContext = new WebContext(req, resp, getServletContext());

        // 3.处理模板数据
        templateEngine.process(templateName, webContext, resp.getWriter());
    }
}

这是DispatcherServlet文件

package com.atguigu.myssm.myspringmvc;

import com.atguigu.myssm.util.StringUtil;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.util.HashMap;
import java.util.Map;

@WebServlet("*.do")
public class DispatcherServlet extends ViewBaseServlet{

    private Map<String,Object> beanMap = new HashMap<>();

    public DispatcherServlet(){
    }

    public void init() throws ServletException {
        super.init();
        try {
            InputStream inputStream = getClass().getClassLoader().getResourceAsStream("applicationContext.xml");
            //1.创建DocumentBuilderFactory
            DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
            //2.创建DocumentBuilder对象
            DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder() ;
            //3.创建Document对象
            Document document = documentBuilder.parse(inputStream);

            //4.获取所有的bean节点
            NodeList beanNodeList = document.getElementsByTagName("bean");
            for(int i = 0 ; i<beanNodeList.getLength() ; i++){
                Node beanNode = beanNodeList.item(i);
                if(beanNode.getNodeType() == Node.ELEMENT_NODE){
                    Element beanElement = (Element)beanNode ;
                    String beanId =  beanElement.getAttribute("id");
                    String className = beanElement.getAttribute("class");
                    Class controllerBeanClass = Class.forName(className);
                    Object beanObj = controllerBeanClass.newInstance() ;
                    beanMap.put(beanId , beanObj) ;
                }
            }
        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置编码
        request.setCharacterEncoding("UTF-8");
        //假设url是：  http://localhost:8080/pro15/hello.do
        //那么servletPath是：    /hello.do
        // 我的思路是：
        // 第1步： /hello.do ->   hello   或者  /fruit.do  -> fruit
        // 第2步： hello -> HelloController 或者 fruit -> FruitController
        String servletPath = request.getServletPath();
        servletPath = servletPath.substring(1);
        int lastDotIndex = servletPath.lastIndexOf(".do") ;
        servletPath = servletPath.substring(0,lastDotIndex);

        Object controllerBeanObj = beanMap.get(servletPath);

        String operate = request.getParameter("operate");
        if(StringUtil.isEmpty(operate)){
            operate = "index" ;
        }

        try {
            Method[] methods = controllerBeanObj.getClass().getDeclaredMethods();
            for(Method method : methods){
                if(operate.equals(method.getName())){
                    //1.统一获取请求参数

                    //1-1.获取当前方法的参数，返回参数数组
                    Parameter[] parameters = method.getParameters();
                    //1-2.parameterValues 用来承载参数的值
                    Object[] parameterValues = new Object[parameters.length];
                    for (int i = 0; i < parameters.length; i++) {
                        Parameter parameter = parameters[i];
                        String parameterName = parameter.getName() ;
                        //如果参数名是request,response,session 那么就不是通过请求中获取参数的方式了
                        if("request".equals(parameterName)){
                            parameterValues[i] = request ;
                        }else if("response".equals(parameterName)){
                            parameterValues[i] = response ;
                        }else if("session".equals(parameterName)){
                            parameterValues[i] = request.getSession() ;
                        }else{
                            //从请求中获取参数值
                            String parameterValue = request.getParameter(parameterName);
                            String typeName = parameter.getType().getName();

                            Object parameterObj = parameterValue ;

                            if(parameterObj!=null) {
                                if ("java.lang.Integer".equals(typeName)) {
                                    parameterObj = Integer.parseInt(parameterValue);
                                }
                            }

                            parameterValues[i] = parameterObj ;
                        }
                    }
                    //2.controller组件中的方法调用
                    method.setAccessible(true);
                    Object returnObj = method.invoke(controllerBeanObj,parameterValues);

                    //3.视图处理
                    String methodReturnStr = (String)returnObj ;
                    if(methodReturnStr.startsWith("redirect:")){        //比如：  redirect:fruit.do
                        String redirectStr = methodReturnStr.substring("redirect:".length());
                        response.sendRedirect(redirectStr);
                    }else{
                        super.processTemplate(methodReturnStr,request,response);    // 比如：  "edit"
                    }
                }
            }

            /*
            }else{
                throw new RuntimeException("operate值非法!");
            }
            */
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
    }
}

这是FruitController文件

package com.atguigu.fruit.controllers;

import com.atguigu.fruit.dao.FruitDAO;
import com.atguigu.fruit.dao.impl.FruitDAOImpl;
import com.atguigu.fruit.pojo.Fruit;
import com.atguigu.myssm.util.StringUtil;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.util.List;

public class FruitController {
    private FruitDAO fruitDAO = new FruitDAOImpl();

    private String update(Integer fid , String fname , Integer price , Integer fcount , String remark ){
        //3.执行更新
        fruitDAO.updateFruit(new Fruit(fid,fname, price ,fcount ,remark ));
        //4.资源跳转
        return "redirect:fruit.do";
    }

    private String edit(Integer fid , HttpServletRequest request){
        if(fid!=null){
            Fruit fruit = fruitDAO.getFruitByFid(fid);
            request.setAttribute("fruit",fruit);
            //super.processTemplate("edit",request,response);
            return "edit";
        }
        return "error" ;
    }

    private String del(Integer fid  ){
        if(fid!=null){
            fruitDAO.delFruit(fid);
            return "redirect:fruit.do";
        }
        return "error";
    }

    private String add(String fname , Integer price , Integer fcount , String remark ) {
        Fruit fruit = new Fruit(0,fname , price , fcount , remark ) ;
        fruitDAO.addFruit(fruit);
        return "redirect:fruit.do";
    }

    private String index(String oper , String keyword , Integer pageNo , HttpServletRequest request ) {
        HttpSession session = request.getSession() ;

        if(pageNo==null){
            pageNo = 1;
        }
        if(StringUtil.isNotEmpty(oper) && "search".equals(oper)){
            pageNo = 1 ;
            if(StringUtil.isEmpty(keyword)){
                keyword = "" ;
            }
            session.setAttribute("keyword",keyword);
        }else{
            Object keywordObj = session.getAttribute("keyword");
            if(keywordObj!=null){
                keyword = (String)keywordObj ;
            }else{
                keyword = "" ;
            }
        }

        // 重新更新当前页的值
        session.setAttribute("pageNo",pageNo);

        FruitDAO fruitDAO = new FruitDAOImpl();
        List<Fruit> fruitList = fruitDAO.getFruitList(keyword , pageNo);
        session.setAttribute("fruitList",fruitList);

        //总记录条数
        int fruitCount = fruitDAO.getFruitCount(keyword);
        //总页数
        int pageCount = (fruitCount+5-1)/5 ;
        session.setAttribute("pageCount",pageCount);

        return "index" ;
    }
}

这是web.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <context-param>
        <param-name>view-prefix</param-name>
        <param-value>/</param-value>
    </context-param>
    <context-param>
        <param-name>view-suffix</param-name>
        <param-value>.html</param-value>
    </context-param>

</web-app>

Answer 1

要设置thymeleaf

# 配置模板存放路径
spring.thymeleaf.prefix=classpath:/templates/
#配置模板后缀
spring.thymeleaf.suffix=.html