这是我的Servlet：
public class UpdateProductServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
String productID = (String) request.getParameter("productID");
String productName = (String) request.getParameter("productName");
String priceString = (String) request.getParameter("price");
String description = (String) request.getParameter("description");
double price;
try {
price = Double.parseDouble(priceString);
} catch (Exception e) {
price = 0;
}
HttpSession session = request.getSession();
Product p = (Product) session.getAttribute("Product");
p.setProductID(productID);
p.setProductName(productName);
p.setPrice(price);
p.setDescription(description);
String message = "";
if (p.getPrice() <= 0) {
message = "You must enter a positive number for the price without any currency symbols.";
}
if (p.getDescription().length() == 0) {
message = "You must enter all required fields.";
}
if (p.getProductID().length() == 0) {
message = "You must enter all required fields.";
}
if (p.getProductName().length() == 0) {
message = "You must enter all required fields.";
}
request.setAttribute("message", message);
String url = "";
if (message.length() == 0) {
if (UserDB.exists(p.getProductID())) {
UserDB.update(p);
} else {
UserDB.insertProduct(p);
}
url = "/return_user_details.jsp"; //display products
} else {
url = "/return_user_details.jsp"; //products??
}
RequestDispatcher dispatcher
= getServletContext().getRequestDispatcher(url);
dispatcher.forward(request, response);
}
}
这是我的UserDB中的一段代码：
public static int update(Product product) {
ConnectionPool pool = ConnectionPool.getInstance();
Connection connection = pool.getConnection();
PreparedStatement ps = null;
ResultSet rs = null;
//This method updates the record with a matching email address.
//It returns a value of 0 if the email address can't be found.
String query = "UPDATE Product SET "
+ "ProductID = ?, "
+ "ProductName = ?,"
+ "ProductPrice = ?, "
+ "ProductDescription = ? "
+ "WHERE ProductID = ?";
try {
ps = connection.prepareStatement(query);
ps.setString(1, product.getProductID());
ps.setString(2, product.getProductName());
ps.set
Double(3, product.getPrice());
ps.setString(4, product.getDescription());
return ps.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
return 0;
} finally {
DBUtil.closeResultSet(rs);
DBUtil.closePreparedStatement(ps);
pool.freeConnection(connection);
}
}
最后这是堆栈跟踪：
Warning: StandardWrapperValve[UpdateProductServlet]: Servlet.service() for servlet UpdateProductServlet threw exception
java.lang.NullPointerException
at admin.UpdateProductServlet.doPost(UpdateProductServlet.java:34)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:416)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:283)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:206)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:180)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:283)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:200)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:132)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:111)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:536)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
at java.lang.Thread.run(Thread.java:745)
显然问题出在p.setProductID(productID);
我得到的错误是java.lang.NullPointerException / HTTP Status 500 - Internal Server Error。我尝试调试代码，然后我看到这些值被插入到productID productName price和description中，所以我不知道这个问题是什么。
我已经完全插入产品了。我一直试图解决这一整天，我无法找到解决方案。如果有人能指出我哪里出错我会受到赞赏
我的连接池：
public class ConnectionPool
{
private static ConnectionPool pool = null;
private static DataSource dataSource = null;
public synchronized static ConnectionPool getInstance()
{
if (pool == null)
{
pool = new ConnectionPool();
}
return pool;
}
private ConnectionPool()
{
try
{
InitialContext ic = new InitialContext();
dataSource = (DataSource) ic.lookup("jdbc/onlineuserdb");
}
catch(Exception e)
{
e.printStackTrace();
}
}
public Connection getConnection()
{
try
{
return dataSource.getConnection();
}
catch (SQLException sqle)
{
sqle.printStackTrace();
return null;
}
}
public void freeConnection(Connection c)
{
try
{
c.close();
}
catch (SQLException sqle)
{
sqle.printStackTrace();
}
}
}