我目前是 java ee 的新手。我需要有关如何将我的数据从 jsp 传递到我的 servlet 以填写我的查询的帮助。每当我运行时，都会捕获错误并打印出异常。它说java.null.exception ..我找不到我的错误在哪里..请帮助我...谢谢..
这是我的代码：
更新ProductServlet.java
try {
String description = request.getParameter("description");
float price = Float.parseFloat(request.getParameter("price"));
String size = request.getParameter("size");
int aisle_id = Integer.parseInt(request.getParameter("aisle"));
int id = Integer.parseInt(request.getParameter("id"));
ProductsDao productsDao = new ProductsDao();
productsDao.updateProduct(description, price, size, aisle_id, id);
} catch (Exception e) {
out.println(e);
}
和我的 ProductDao.java
public void updateProduct(String description, float price, String size, int aisle_id, int id)
throws ClassNotFoundException, SQLException {
Connection conn = null;
PreparedStatement stmt = null;
String sql = "UPDATE products "
+ "SET description = ?, price = ?, size = ?, aisle_id = ? "
+ "WHERE id = ? ";
try {
conn = ConnectionFactory.getConnection();
stmt = conn.prepareStatement(sql);
stmt.setString(1, description);
stmt.setFloat(2, price);
stmt.setString(3, size);
stmt.setInt(4, aisle_id);
stmt.setInt(5, id);
stmt.executeUpdate();
} finally {
if (conn != null) {
conn.close();
}
if (stmt != null){
stmt.close();
}
}
}
这是我的 ProductById.jsp
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
<script>
function functionEdit()
{
document.getElementById("edit").type="hidden";
document.getElementById("update").type="button";
document.getElementById("delete").type="hidden";
document.getElementById("cancel").type="button";
document.getElementById("description").disabled="";
document.getElementById("size").disabled="";
document.getElementById("price").disabled="";
document.getElementById("select").disabled="";
}
function functionUpdateRecord(){
if(confirm('Update existing record?')){
document.location.href="/MachineProblemWebApp/UpdateProductServlet";
alert('Update success!');
document.location.href="/MachineProblemWebApp/GetAllProductsServlet";
}else{
alert('No changes have been made!');
}
}
</script>
</head>
<body>
<table border="0">
<tr>
<td>id: </td>
<td><input type="text" name="id" id="id" value="${product.id}" disabled="disabled"></td>
</tr>
<tr>
<td>Description: </td>
<td><input type="text" name="description" id="description" value="${product.description}" disabled="disabled"></td>
</tr>
<tr>
<td>Aisle </td>
<td><select name="aisle" disabled="disabled" id="select">
<c:forEach var="aisle" items="${aisles}" >
<option value="${aisle.id}" ${(aisle.id==product.aisle.id)?"selected" : ""}>${aisle.description}</option>
</c:forEach>
</select></td>
</tr>
<tr>
<td>Size: </td>
<td><input type="text" name="size" id="size" value="${product.size}" disabled="disabled"></td>
</tr>
<tr>
<td>Price: </td>
<td><input type="text" name="price" id="price" value="${product.price}" disabled="disabled"></td>
</tr>
<tr>
<td><input type="button" name="edit" id="edit" onClick="functionEdit()" value="Edit" >
<input type="hidden" name="update" id="update" onClick="functionUpdateRecord()"value="Update">
<input type="button" name="delete" id="delete" value="Delete">
<input type="hidden" name="cancel" id="cancel" value="Cancel"></td>
</tr>
</table>
</body>
这是堆栈跟踪吗？张贴在 Apache Tomcat 日志中？
Dec 10, 2012 7:38:13 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [UpdateProductServlet] in context with path [/MachineProblemWebApp] threw exception
java.lang.NullPointerException
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1008)
at java.lang.Float.parseFloat(Float.java:452)
at grocerific.ui.UpdateProductServlet.processRequest(UpdateProductServlet.java:45)
at grocerific.ui.UpdateProductServlet.doGet(UpdateProductServlet.java:75)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)
Dec 10, 2012 9:36:40 PM org.apache.catalina.core.ApplicationContext log
INFO: SessionListener: contextDestroyed()
Dec 10, 2012 9:36:40 PM org.apache.catalina.core.ApplicationContext log
INFO: ContextListener: contextDestroyed()
Dec 10, 2012 9:36:46 PM org.apache.catalina.core.ApplicationContext log
INFO: ContextListener: contextInitialized()
Dec 10, 2012 9:36:46 PM org.apache.catalina.core.ApplicationContext log
INFO: SessionListener: contextInitialized()
Dec 10, 2012 9:36:46 PM org.apache.catalina.core.ApplicationContext log
INFO: ContextListener: attributeAdded('org.apache.jasper.compiler.TldLocationsCache', 'org.apache.jasper.compiler.TldLocationsCache@8a47d9')