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大家好我是java和jsp的新手，老實說我沒有json的知識。但我有一些要求，我必須從數據庫中提取數據並顯示在jsp頁面上。但是標準是我必須使用Bootstrap Data Table，爲什麼我使用這種方法是因爲它提供了很多靈活性，如分頁過濾排序多列排序單個列過濾器。 我得到一個java.lang.NullPointerException在我的jsp 任何機構可以告訴我爲什麼我得到這個錯誤。 這是我的jsp頁面jsp中的java.lang.NullPointerException
dataTable.jsp
<%@page import="org.codehaus.jettison.json.JSONObject"%>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ page import ="java.util.*" %>
<%-- <%@ page import="com.varun.DataBase"%> --%>
<%@ page import="java.sql.*" %>
<%-- <%@ page import="org.json.*"%> --%>
<%@ page import ="net.sf.json.JSONArray" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>DataTable</title>
</head>
<body>
<h1>Lets display the data from database using dataTabel</h1>
<%
String[] cols = { "id","engine", "browser", "platform", "version", "grade" };
String table = "ajax";
JSONObject result = new JSONObject();
JSONArray arr = new JSONArray();
int amount = 10;
int start = 0;
int echo = 0;
int col = 0;
int id=0;
String engine = "";
String browser = "";
String platform = "";
String version = "";
String grade = "";
String dir = "asc";
String sStart = request.getParameter("iDisplayStart");
String sAmount = request.getParameter("iDisplayLength");
String sEcho = request.getParameter("sEcho");
String sCol = request.getParameter("iSortCol_0");
String sdir = request.getParameter("sSortDir_0");
engine = request.getParameter("sSearch_0");
browser = request.getParameter("sSearch_1");
platform = request.getParameter("sSearch_2");
version = request.getParameter("sSearch_3");
grade = request.getParameter("sSearch_4");
List<String> sArray = new ArrayList<String>();
if (!engine.equals("")) {
String sEngine = " engine like '%" + engine + "%'";
sArray.add(sEngine);
//or combine the above two steps as:
//sArray.add(" engine like '%" + engine + "%'");
//the same as followings
}
if (!browser.equals("")) {
String sBrowser = " browser like '%" + browser + "%'";
sArray.add(sBrowser);
}
if (!platform.equals("")) {
String sPlatform = " platform like '%" + platform + "%'";
sArray.add(sPlatform);
}
if (!version.equals("")) {
String sVersion = " version like '%" + version + "%'";
sArray.add(sVersion);
}
if (!grade.equals("")) {
String sGrade = " grade like '%" + grade + "%'";
sArray.add(sGrade);
}
String individualSearch = "";
if(sArray.size()==1){
individualSearch = sArray.get(0);
}else if(sArray.size()>1){
for(int i=0;i<sArray.size()-1;i++){
individualSearch += sArray.get(i)+ " and ";
}
individualSearch += sArray.get(sArray.size()-1);
}
if (sStart != null) {
start = Integer.parseInt(sStart);
if (start < 0)
start = 0;
}
if (sAmount != null) {
amount = Integer.parseInt(sAmount);
if (amount < 10 || amount > 100)
amount = 10;
}
if (sEcho != null) {
echo = Integer.parseInt(sEcho);
}
if (sCol != null) {
col = Integer.parseInt(sCol);
if (col < 0 || col > 5)
col = 0;
}
if (sdir != null) {
if (!sdir.equals("asc"))
dir = "desc";
}
String colName = cols[col];
int total = 0;
Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl","system","admin");
try {
String sql = "SELECT count(*) FROM "+table;
PreparedStatement ps = conn.prepareStatement(sql);
ResultSet rs = ps.executeQuery();
if(rs.next()){
total = rs.getInt("count(*)");
}
}catch(Exception e){
}
int totalAfterFilter = total;
//result.put("sEcho",echo);
try {
String searchSQL = "";
String sql = "SELECT * FROM "+table;
String searchTerm = request.getParameter("sSearch");
String globeSearch = " where (engine like '%"+searchTerm+"%'"
+ " or browser like '%"+searchTerm+"%'"
+ " or platform like '%"+searchTerm+"%'"
+ " or version like '%"+searchTerm+"%'"
+ " or grade like '%"+searchTerm+"%')";
if(searchTerm!=""&&individualSearch!=""){
searchSQL = globeSearch + " and " + individualSearch;
}
else if(individualSearch!=""){
searchSQL = " where " + individualSearch;
}else if(searchTerm!=""){
searchSQL=globeSearch;
}
sql += searchSQL;
sql += " order by " + colName + " " + dir;
sql += " limit " + start + ", " + amount;
PreparedStatement ps = conn.prepareStatement(sql);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
// JSONArray ja = new JSONArray();
net.sf.json.JSONArray ja = new net.sf.json.JSONArray();
ja.add(rs.getInt("id"));
ja.add(rs.getString("engine"));
ja.add(rs.getString("browser"));
ja.add(rs.getString("platform"));
ja.add(rs.getString("version"));
ja.add(rs.getString("grade"));
arr.add(ja);
}
String sql2 = "SELECT count(*) FROM "+table;
if (searchTerm != "") {
sql2 += searchSQL;
PreparedStatement ps2 = conn.prepareStatement(sql2);
ResultSet rs2 = ps2.executeQuery();
if (rs2.next()) {
totalAfterFilter = rs2.getInt("count(*)");
}
}
result.put("iTotalRecords", total);
result.put("iTotalDisplayRecords", totalAfterFilter);
result.put("aaData", arr);
response.setContentType("application/json");
response.setHeader("Cache-Control", "no-store");
out.print(result);
conn.close();
} catch (Exception e) {
}
%>
</body>
</html>
堆棧跟蹤
11:26:50,224 ERROR [[jsp]] Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.dataTable_jsp._jspService(dataTable_jsp.java:114)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:369)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:322)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:249)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:190)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:92)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.process(SecurityContextEstablishmentValve.java:126)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:70)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:330)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:829)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:598)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Unknown Source)
您可以指向行號'114' – silentprogrammer
轉到翻譯的Servlet'dataTable_jsp.java'這個JSP文件，看看行不114.這將是下'工作'文件夾，如果你正在通過tomcat服務器運行它。 – Braj
可能會使用這個'http：// jquerygrid.net /' – Babel