我试图将数据库数据加载到表中，但每次（LEFTJOIN，JOIN）我这样做我得到空指针错误，我已经尝试了LEFT JOIN，JOIN和WHERE子句（没有JOIN）但是相同的查询一直都是错误的。我是否需要使用coloumn名称
rs.getString("p.Name")? Since the Name colomn is in Products table
这是我正在做的事情，请让我知道我错在哪里
---在JSP ---
<table class="table table-striped">
<thead>
<tr>
<th class="col-sm-1">Name</th>
<th class="col-sm-2">Price</th>
<th class="col-sm-2">Shipping Address</th>
<th class="col-sm-2">Order Date</th>
<th class="col-sm-2">Discount</th>
<th class="col-sm-1">Sales Tax</th>
<th class="col-sm-2">Quantity</th>
<th class="col-sm-2">Final Amount</th>
<th class="col-sm-2">Payment Status</th>
<th class="col-sm-2">User</th>
</tr>
</thead>
<tbody align="center">
<%ProductDAO s = new ProductDAO();
Sales_Details pr[] = s.getSalesDetails(); %>
<% int i=0;
while(i>pr.length){ %>
<tr>
<td class="col-sm-1"><%out.print(pr[i].getName());%></td>
<td class="col-sm-2"><%out.print(pr[i].getPrice());%></td>
<td class="col-sm-2"><%out.print(pr[i].getSales_Address());%></td>
<td class="col-sm-2"><%out.print(pr[i].getOrder_Date());%></td>
<td class="col-sm-2"><%out.print(pr[i].getDiscount());%></td>
<td class="col-sm-2"><%out.print(pr[i].getSales_Tax());%></td>
<td class="col-sm-2"><%out.print(pr[i].getQuantity());%></td>
<td class="col-sm-2"><%out.print(pr[i].getFinal_Amount());%></td>
<td class="col-sm-2"><%out.print(pr[i].getPayment_Status());%></td>
<td class="col-sm-2"><%out.print(pr[i].getUser());%></td>
<td class="col-sm-2"> <a href="ViewProducts.jsp?value=<%out.print(pr[i].getName());%>" class="btn btn-default">delete</a></td>
</tr>
<% i++; } %>
</tbody>
</table>
---在DAO ---
public Sales_Details[] getSalesDetails()
{
//List<String> obj = new ArrayList<String>();
String query = "SELECT s.*,d.*,p.* FROM sales_order s JOIN sales_order_details d on s.Order_No = d.Order_No JOIN products p on d.Products_ID = p.ID";
Sales_Details[] sd = new Sales_Details[500];
int i = 0;
try
{
ResultSet rs = stmt.executeQuery(query);
while (rs.next())
{
sd[i].setName(rs.getString("Product").toString());
sd[i].setPrice(rs.getString("Price").toString().toString());
sd[i].setSales_Address(rs.getString("Sales_Address").toString());
sd[i].setOrder_Date(rs.getString("Order_Date").toString());
sd[i].setDiscount(rs.getString("Discount").toString());
sd[i].setSales_Tax(rs.getString("Sales_Tax").toString());
sd[i].setQuantity(rs.getString("Quantity").toString());
sd[i].setFinal_Amount(rs.getString("Final_Amount").toString());
sd[i].setPayment_Status(rs.getString("Payment_Status").toString());
sd[i].setUser(rs.getString("User").toString());
i++;
}
}
catch(SQLException e)
{
System.out.println("Problem in Query");
e.printStackTrace();
}
return sd;
}
--- --- Sales_Details
public class Sales_Details {
private String Name;
private String Price;
private String Sales_Address;
private String Order_Date;
private String Discount;
private String Sales_Tax;
private String Quantity;
private String Final_Amount;
private String Payment_Status;
private String User;
//Getters, Setters and Constructors
栈跟踪
Aug 20, 2015 7:17:07 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [Servlets.Login] in context with path [/Final_Project] threw exception [java.lang.NullPointerException] with root cause
java.lang.NullPointerException
at DAO.ProductDAO.getSalesDetails(ProductDAO.java:151)
at org.apache.jsp.admin_jsp._jspService(admin_jsp.java:301)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:417)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:391)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:306)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:672)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:463)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:402)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:329)
at Servlets.Login.doPost(Login.java:71)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:306)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:541)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:383)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:243)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:166)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:288)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
答案 0 :(得分：0)
下面：
<%ProductDAO s = new ProductDAO();
Sales_Details pr[] = s.getSalesDetails(); %>
<% int i=0;
while(i>pr.length){ %>
这种情况while(i>pr.length)什么时候会成真？
另一点：
检查数据库中的查询。它是否返回任何数据？
在以html显示之前，请检查Sales_details数组的大小。如果它有数据，则处理显示数据的逻辑。否则，显示相应的消息。
编辑：
检查/ WEB-INF / lib是否包含jsp-api - * .jar等内容。如果是，则删除，重建，部署然后测试。
答案 1 :(得分：0)
谢谢大家，问题确实是我的病情错了
while(i>pr.length)
并且数组没有初始化，现在就开始工作了。