老师，我什么我使用new Integer()这种方式会报错，说空指针异常，但是用setObject的方式却不会可以
删除成功，麻烦老师帮忙看一下

	private void delete(HttpServletRequest request, HttpServletResponse response) throws IOException {
		//1.接收参数
		Integer cid =Integer.parseInt(request.getParameter("cid"));
		//2.处理数据
		CategoryService categoryService = new CategoryServiceImpl();
		categoryService.delete(cid);
		//3.页面跳转
		response.sendRedirect(request.getContextPath()+"/CategoryServlet?method=findAll");
	}
------------------------------
	//删除分类接口的实现类
	@Override
	public void delete(Integer cid) {
		//在删除分类之前，先将所属改分类的商品先处理一下
		ProductDao productDao = new ProductDaoImpl();
		List<Product> list = productDao.findByCid(cid);
		//将cid置为空 并且重新设置product
		for(Product product:list) {
			product.getCategory().setCid(null);
			//修改的时候要注意，我们分类的cid是int类型，int类型获取不到null
			//所以我们这里要获取到的null要进行强转成Integer，因为包装类才有null
			//或者我们在set的时候不用setInt去set cid 而是直接SetObject
			productDao.update(product);
		}
----------------------------------------------------------------
	//修改商品：修改商品的信息
	@Override
	public void update(Product product) {
		Connection conn = null;
		PreparedStatement pstmt = null;
		
		try {
			//获得连接
			conn = JDBCUtils.getConnection();
			//编写SQL
			String sql = "UPDATE product set pname=?,author=?,price=?,description=?,filename=?,path=?,cid=? WHERE pid=?";
			//预编译SQL
			pstmt = conn.prepareStatement(sql);
			//设置值
			pstmt.setString(1, product.getPname());
			pstmt.setString(2, product.getAuthor());
			pstmt.setDouble(3, product.getPrice());
			pstmt.setString(4, product.getDescription());
			pstmt.setString(5, product.getFilename());
			pstmt.setString(6, product.getPath());
			//修改的时候要注意，我们分类的cid是int类型，int类型获取不到null
			//所以我们这里要获取到的null要进行强转成Integer，因为包装类才有null
			//或者我们在set的时候不用setInt去set cid 而是直接SetObject
			pstmt.setInt(7,new Integer(product.getCategory().getCid()));
			pstmt.setInt(8, product.getPid());
			//执行SQL
			pstmt.executeUpdate();
		}catch(Exception e) {
			e.printStackTrace();
		}finally {
			//释放资源
			JDBCUtils.release(pstmt, conn);
		}
		
	}

java.lang.NullPointerException
	at com.zhou.dao.impl.ProductDaoImpl.update(ProductDaoImpl.java:168)
	at com.zhou.service.impl.CategoryServiceImpl.delete(CategoryServiceImpl.java:59)
	at com.zhou.web.action.CategoryServlet.delete(CategoryServlet.java:64)
	at com.zhou.web.action.CategoryServlet.doGet(CategoryServlet.java:44)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	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.zhou.web.filter.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:27)
	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:199)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:528)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:798)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:810)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	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:745)
java.lang.NullPointerException
	at com.zhou.dao.impl.ProductDaoImpl.update(ProductDaoImpl.java:168)
	at com.zhou.service.impl.CategoryServiceImpl.delete(CategoryServiceImpl.java:59)
	at com.zhou.web.action.CategoryServlet.delete(CategoryServlet.java:64)
	at com.zhou.web.action.CategoryServlet.doGet(CategoryServlet.java:44)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	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.zhou.web.filter.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:27)
	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:199)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:528)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:798)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:810)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	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:745)
java.lang.NullPointerException
	at com.zhou.dao.impl.ProductDaoImpl.update(ProductDaoImpl.java:168)
	at com.zhou.service.impl.CategoryServiceImpl.delete(CategoryServiceImpl.java:59)
	at com.zhou.web.action.CategoryServlet.delete(CategoryServlet.java:64)
	at com.zhou.web.action.CategoryServlet.doGet(CategoryServlet.java:44)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	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.zhou.web.filter.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:27)
	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:199)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:528)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:798)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:810)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	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:745)
java.lang.NullPointerException
	at com.zhou.dao.impl.ProductDaoImpl.update(ProductDaoImpl.java:168)
	at com.zhou.service.impl.CategoryServiceImpl.delete(CategoryServiceImpl.java:59)
	at com.zhou.web.action.CategoryServlet.delete(CategoryServlet.java:64)
	at com.zhou.web.action.CategoryServlet.doGet(CategoryServlet.java:44)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	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.zhou.web.filter.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:27)
	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:199)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:528)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:798)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:810)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	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:745)
com.mysql.jdbc.exceptions.MySQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`shop`.`product`, CONSTRAINT `fk_0001` FOREIGN KEY (`cid`) REFERENCES `category` (`cid`))
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:931)
	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2870)
	at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1573)
	at com.mysql.jdbc.ServerPreparedStatement.serverExecute(ServerPreparedStatement.java:1169)
	at com.mysql.jdbc.ServerPreparedStatement.executeInternal(ServerPreparedStatement.java:693)
	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1404)
	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1318)
	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1303)
	at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeUpdate(NewProxyPreparedStatement.java:105)
	at com.zhou.dao.impl.CategoryDaoImpl.delete(CategoryDaoImpl.java:182)
	at com.zhou.service.impl.CategoryServiceImpl.delete(CategoryServiceImpl.java:64)
	at com.zhou.web.action.CategoryServlet.delete(CategoryServlet.java:64)
	at com.zhou.web.action.CategoryServlet.doGet(CategoryServlet.java:44)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	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.zhou.web.filter.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:27)
	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:199)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:528)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:798)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:810)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	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:745)