老师，求助 添加分类提示空指针异常

老师，求助 添加分类提示空指针异常

package com.imooc.icake.global;

import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class GlobalController extends GenericServlet {

    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        /*
        .do
        /login.do              DefaultController login
        /Cake/detail.do        CakeController detail
        /admin/Cake/add.do     CakeController add
         */
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        String path=request.getServletPath();
        if (path.indexOf("/admin") != -1) {
            path=path.substring(7);
        } else {
            path=path.substring(1);
        }
        String className=null;
        String methodName=null;
        int index=path.indexOf("/");
        if (index != -1) {
            className = "com.imooc.icake.controller." + path.substring(0, index)+"Controller";
            methodName=path.substring(index+1, path.indexOf(".do"));
        } else {
            className="com.imooc.icake.controller."+"DefaultController";
            methodName=path.substring(0, path.indexOf(".do"));
        }
        try {
            Class cla = Class.forName(className);
            Object object = cla.newInstance();
            Method method = cla.getMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            method.invoke(object, request, response);
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

}


package com.imooc.icake.biz;

import com.imooc.icake.entity.Catalog;

import java.util.List;

public interface CatalogBiz {
    void add(List<Catalog> list);
    void remove(int id);
    Catalog getRoot();
}


package com.imooc.icake.biz.impl;

import com.imooc.icake.biz.CatalogBiz;
import com.imooc.icake.dao.CatalogDao;
import com.imooc.icake.entity.Catalog;
import com.imooc.icake.global.DaoFactory;

import java.util.List;

public class CatalogBizImpl implements CatalogBiz {
    CatalogDao catalogDao = DaoFactory.getInstance().getDao(CatalogDao.class);
    public void add(List<Catalog> list) {
        catalogDao.batchInsert(list);
    }

    public void remove(int id) {
        catalogDao.delete(id);
    }

    public Catalog getRoot() {
      return catalogDao.select(10000);
    }
}






package com.imooc.icake.dao;

import com.imooc.icake.entity.Catalog;
import org.apache.ibatis.annotations.*;

import java.util.List;

public interface CatalogDao {
    /**
     * 新增     * @param list
     */
    @Insert("<script>" +
            "insert into catalog(title,pid,info) values"+
            "<foreach connection='list' var='catalog' separator=','>" +
            "(#{catalog.title},#{catalog.pid},#{catalog.info})" +
            "</foreach>"+
            "</script>")
    @Options(useGeneratedKeys = true,keyProperty = "id")
    void batchInsert( List<Catalog> list);

    /**
     * 删除
     */
    @Delete("delete from catalog where id=#{id}")
    void delete(int id);

    /**
     * 查询所有分类
     */
    @Select("select * from catalog where id=#{id}")
    @Results(id = "all",value = {
            @Result(column = "id", property = "id", id = true),
            @Result(column = "title",property = "title"),
            @Result(column = "pid", property = "pid"),
            @Result(column = "info", property = "info"),
            @Result(column = "id",property = "children",many = @Many(select = "selectByPid"))
    })
    Catalog select(int id);
    @Select("select * from catalog where pid=#{pid}")
    @ResultMap("all")
    List<Catalog> selectByPid(int pid);
}

















Catalog{id=0, title='生日', pid=10000, info='好吃', children=[]}
[Catalog{id=0, title='生日', pid=10000, info='好吃', children=[]}]
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.imooc.icake.global.GlobalController.service(GlobalController.java:44)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at com.imooc.icake.global.EncodingFilter.doFilter(EncodingFilter.java:21)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:748)
Caused by: org.apache.ibatis.exceptions.PersistenceException: 
### Error updating database.  Cause: java.lang.NullPointerException
### Cause: java.lang.NullPointerException
	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:200)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.insert(DefaultSqlSession.java:185)
	at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:57)
	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
	at com.sun.proxy.$Proxy14.batchInsert(Unknown Source)
	at com.imooc.icake.biz.impl.CatalogBizImpl.add(CatalogBizImpl.java:13)
	at com.imooc.icake.controller.CatalogController.add(CatalogController.java:52)
	... 30 more
Caused by: java.lang.NullPointerException
	at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:936)
	at org.apache.ibatis.scripting.xmltags.OgnlCache.parseExpression(OgnlCache.java:51)
	at org.apache.ibatis.scripting.xmltags.OgnlCache.getValue(OgnlCache.java:44)
	at org.apache.ibatis.scripting.xmltags.ExpressionEvaluator.evaluateIterable(ExpressionEvaluator.java:43)
	at org.apache.ibatis.scripting.xmltags.ForEachSqlNode.apply(ForEachSqlNode.java:55)
	at org.apache.ibatis.scripting.xmltags.MixedSqlNode.apply(MixedSqlNode.java:33)
	at org.apache.ibatis.scripting.xmltags.DynamicSqlSource.getBoundSql(DynamicSqlSource.java:41)
	at org.apache.ibatis.mapping.MappedStatement.getBoundSql(MappedStatement.java:292)
	at org.apache.ibatis.executor.statement.BaseStatementHandler.<init>(BaseStatementHandler.java:64)
	at org.apache.ibatis.executor.statement.PreparedStatementHandler.<init>(PreparedStatementHandler.java:40)
	at org.apache.ibatis.executor.statement.RoutingStatementHandler.<init>(RoutingStatementHandler.java:46)
	at org.apache.ibatis.session.Configuration.newStatementHandler(Configuration.java:545)
	at org.apache.ibatis.executor.SimpleExecutor.doUpdate(SimpleExecutor.java:48)
	at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:117)
	at org.apache.ibatis.executor.CachingExecutor.update(CachingExecutor.java:76)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:198)
	... 36 more
指尖板命狂敲 2019-03-05
源自：项目：商品信息管理   3-2 分类管理表现层
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提问者 指尖板命狂敲 2019-03-05 19:52:48 
package com.imooc.icake.controller;

import com.imooc.icake.biz.CatalogBiz;
import com.imooc.icake.biz.impl.CatalogBizImpl;
import com.imooc.icake.entity.Catalog;

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

public class CatalogController {
    private CatalogBiz catalogBiz=new CatalogBizImpl();

    /**
     * 列表页
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    //     /admin/Catalog/list.do
    public void list(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Catalog root=catalogBiz.getRoot();
        request.setAttribute("root", root);
        request.getRequestDispatcher("/WEB-INF/pages/admin/catalog_list.jsp").forward(request,response);
    }
    //   /admin/Catalog/toAdd.do
    public void toAdd(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Catalog root=catalogBiz.getRoot();
        request.setAttribute("root", root);
        request.getRequestDispatcher("/WEB-INF/pages/admin/catalog_add.jsp").forward(request,response);
    }

    //    /admin/Catalog/add.do
    public void add(HttpServletRequest request, HttpServletResponse response) throws IOException {
        String[] titles = request.getParameterValues("title");
        String[] pids = request.getParameterValues("pid");
        String[] infos = request.getParameterValues("info");
        List<Catalog> catalogs = new ArrayList<Catalog>();
        for (int i = 0; i < titles.length; i++) {
            Catalog catalog=new Catalog();
            catalog.setTitle(titles[i]);
            catalog.setPid(Integer.parseInt(pids[i]));
            catalog.setInfo(infos[i]);
            System.out.println(catalog);
            catalogs.add(catalog);
        }
        System.out.println(catalogs);
        catalogBiz.add(catalogs);
        response.sendRedirect("list.do");
    }

    // /admin/Catalog/remove.do
    public void remove(HttpServletRequest request, HttpServletResponse response) throws IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        catalogBiz.remove(id);
        response.sendRedirect("list.do");
    }
}



老师，我debug了一遍还是没找到原因


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好帮手慕阿满 2019-03-05 19:30:18

同学你好，从同学的报错信息上看，

http://img1.sycdn.imooc.com//climg/5c7e5cc5000165b407590264.jpg

空指针出现在如上类中的add方法处，建议同学自己查看空指针出现的地方。如果问题没解决，请将这两处的代码贴一下。祝：学习愉快~

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  • 提问者 指尖板命狂敲 #1
    老师，我debug了一遍还是没找到原因求助
    2019-03-05 19:53:31
  • 提问者 指尖板命狂敲 #2
    谢谢老师，我找到问题了
    2019-03-06 11:13:36
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