MVC结构化程序上的java.lang.NullPointerException
每当我试图在我的项目上运行一个特定的jsp时，我总是会遇到这个错误 我已经做了我能想到的一切（包括重新创建它需要的数据库，检查并重新检查我认为有故障的行，MVC结构化程序上的java.lang.NullPointerException,java,jsp,exception,servlets,javabeans,Java,Jsp,Exception,Servlets,Javabeans,每当我试图在我的项目上运行一个特定的jsp时，我总是会遇到这个错误 我已经做了我能想到的一切（包括重新创建它需要的数据库，检查并重新检查我认为有故障的行，Projectbean.java，更具体地说是publicint rowCount（）函数的prepared语句部分） 如果有人能为我指出正确的方向，我将不胜感激 Projectservlet.java: import project.Projectbean; import java.io.IOException; i
Projectbean.javaint rowCount（） import project.Projectbean;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
*
* @author REY
*/
@WebServlet(name = "Projectservlet", urlPatterns = {"/Projectservlet"})
public class Projectservlet extends HttpServlet {
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
try {
/* TODO output your page here. You may use following sample code. */
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet Projectservlet</title>");
out.println("</head>");
out.println("<body>");
out.println("<h1>Servlet Projectservlet at " + request.getContextPath() + "</h1>");
out.println("</body>");
out.println("</html>");
} finally {
out.close();
}
}
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String option=request.getParameter("menu");
if(option == null || option.equals("menu"))
{
RequestDispatcher dr = request.getRequestDispatcher("Menu.jsp");
dr.forward(request, response);
}
else if(option.equals("stud"))
{
RequestDispatcher dr = request.getRequestDispatcher("Student.jsp");
dr.forward(request, response);
}
else if(option.equals("book"))
{
RequestDispatcher dr = request.getRequestDispatcher("Book.jsp");
dr.forward(request, response);
}
else if(option.equals("cat"))
{
RequestDispatcher dr = request.getRequestDispatcher("Category.jsp");
dr.forward(request, response);
}
else if(option.equals("Borrow"))
{
RequestDispatcher dr = request.getRequestDispatcher("Borrow.jsp");
dr.forward(request, response);
}
else if(option.equals("Return"))
{
RequestDispatcher dr = request.getRequestDispatcher("Return.jsp");
dr.forward(request, response);
}
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
PrintWriter out = response.getWriter();
String option = request.getParameter("option");
//STUDENT CONTROLLER
if (option.equals("Add Student"))
{
RequestDispatcher dr = request.getRequestDispatcher("AddStudent.jsp");
dr.include(request, response);
}
else if (option.equals("addedS"))
{
String id = request.getParameter("Studid");
int a = Integer.parseInt(id);
Projectbean addCustomer = new Projectbean();
addCustomer.setStudid(a);
addCustomer.setFname(request.getParameter("Fname"));
addCustomer.setLname(request.getParameter("Lname"));
addCustomer.setCourse(request.getParameter("Course"));
addCustomer.AddStudent();
RequestDispatcher dr = request.getRequestDispatcher("AddStudtConfirm.jsp");
dr.include(request, response);
}
else if (option.equals("Edit Student"))
{
RequestDispatcher dr = request.getRequestDispatcher("EditCustomer.jsp");
dr.include(request, response);
}
else if (option.equals("editS"))
{
String Studid = request.getParameter("edit");
request.setAttribute("Studid", Studid);
RequestDispatcher dr = request.getRequestDispatcher("EditedStudent.jsp");
dr.include(request, response);
}
else if (option.equals("editedC"))
{
Projectbean edit = new Projectbean();
int id = Integer.parseInt(request.getParameter("Studid"));
edit.setStudid(id);
edit.setFname(request.getParameter("Fname"));
edit.setLname(request.getParameter("Lname"));
edit.setCourse(request.getParameter("Course"));
edit.EditStudent();
RequestDispatcher dr = request.getRequestDispatcher("EditStudConfirm.jsp");
dr.include(request, response);
}
else if (option.equals("Delete Student"))
{
RequestDispatcher dr = request.getRequestDispatcher("DeleteStudent.jsp");
dr.include(request, response);
}
else if (option.equals("deleteS"))
{
String ID = request.getParameter("delete");
int custID = Integer.parseInt(ID);
Projectbean delete = new Projectbean();
delete.DeleteStudent(custID);
RequestDispatcher dr = request.getRequestDispatcher("DeleteStudConfirm.jsp");
dr.include(request, response);
}
else if (option.equals("Search Student"))
{
RequestDispatcher dr = request.getRequestDispatcher("SearchStudent.jsp");
dr.include(request, response);
}
else if (option.equals("searchS"))
{
String search = request.getParameter("search");
request.setAttribute("search", search);
RequestDispatcher dr = request.getRequestDispatcher("SearchedStudent.jsp");
dr.include(request, response);
}
//CATEGORY CONTROLLER
else if (option.equals("Add Category"))
{
RequestDispatcher dr = request.getRequestDispatcher("AddCategory.jsp");
dr.include(request, response);
}
else if (option.equals("addedCat"))
{
String id = request.getParameter("Catid");
int a = Integer.parseInt(id);
Projectbean addCategory = new Projectbean();
addCategory.setCatid(a);
addCategory.setCatname(request.getParameter("Catname"));
addCategory.AddCategory();
RequestDispatcher dr = request.getRequestDispatcher("AddCatConfirm.jsp");
dr.include(request, response);
}
else if (option.equals("Edit Category"))
{
RequestDispatcher dr = request.getRequestDispatcher("EditCategory.jsp");
dr.include(request, response);
}
else if (option.equals("editCat"))
{
String catID = request.getParameter("catedit");
request.setAttribute("Catid", catID);
out.println (catID);
RequestDispatcher dr = request.getRequestDispatcher("EditedCategory.jsp");
dr.forward(request, response);
}
else if (option.equals("editedCat"))
{
Projectbean editcat = new Projectbean();
int id = Integer.parseInt(request.getParameter("Catid"));
editcat.setCatid(id);
editcat.setCatname(request.getParameter("Catname"));
editcat.EditCategory();
RequestDispatcher dr = request.getRequestDispatcher("EditCatConfirm.jsp");
dr.include(request, response);
}
else if (option.equals("Delete Category"))
{
RequestDispatcher dr = request.getRequestDispatcher("DeleteCategory.jsp");
dr.include(request, response);
}
else if (option.equals("delCat"))
{
String ID = request.getParameter("catdelete");
int Catid = Integer.parseInt(ID);
Projectbean catdelete = new Projectbean();
catdelete.DeleteCategory(Catid);
RequestDispatcher dr = request.getRequestDispatcher("DeleteCatConfirm.jsp");
dr.include(request, response);
}
else if (option.equals("Search Category"))
{
RequestDispatcher dr = request.getRequestDispatcher("SearchCategory.jsp");
dr.include(request, response);
}
else if (option.equals("searchCat"))
{
String search = request.getParameter("search");
request.setAttribute("search", search);
RequestDispatcher dr = request.getRequestDispatcher("SearchedCategory.jsp");
dr.include(request, response);
}
//PRODUCT CONTROLLER
else if (option.equals("Add Book"))
{
RequestDispatcher dr = request.getRequestDispatcher("AddBook.jsp");
dr.include(request, response);
}
else if (option.equals("addedBook"))
{
String id = request.getParameter("Bookid");
String Catid = request.getParameter("edit");
int catID = Integer.parseInt (Catid);
int Bookid = Integer.parseInt(id);
//int numavail = Integer.parseInt(request.getParameter("availNo"));
//double price = Double.parseDouble(request.getParameter("prodPrice"));
Projectbean addProduct = new Projectbean();
addProduct.setBookid(Bookid);
addProduct.setTitle(request.getParameter("Title"));
addProduct.setAuthor(request.getParameter("Author"));
//addProduct.setProdAvail(numavail);
//addProduct.setProdPrice(price);
addProduct.setCatid(catID);
addProduct.AddBook();
RequestDispatcher dr = request.getRequestDispatcher("AddBookConfirm.jsp");
dr.include(request, response);
}
else if (option.equals("Edit Book"))
{
RequestDispatcher dr = request.getRequestDispatcher("EditBook.jsp");
dr.include(request, response);
}
else if (option.equals("editBook"))
{
String Bookid = request.getParameter("prodedit");
request.setAttribute("Bookid", Bookid);
out.println (Bookid);
RequestDispatcher dr = request.getRequestDispatcher("EditedBook.jsp");
dr.forward(request, response);
}
else if (option.equals("editedBook"))
{
Projectbean editprod = new Projectbean();
int id = Integer.parseInt(request.getParameter("Bookid"));
//int avail = Integer.parseInt (request.getParameter("prodavail"));
double price = Double.parseDouble(request.getParameter("prodprice"));
int catID = Integer.parseInt(request.getParameter("category"));
editprod.setBookid(id);
editprod.setTitle(request.getParameter("Title"));
editprod.setAuthor(request.getParameter("Author"));
//editprod.setProdAvail(avail);
//editprod.setProdPrice(price);
editprod.setCatid(catID);
editprod.EditBook();
RequestDispatcher dr = request.getRequestDispatcher("EditBookConfirm.jsp");
dr.include(request, response);
}
else if (option.equals("Delete Book"))
{
RequestDispatcher dr = request.getRequestDispatcher("DeleteBook.jsp");
dr.include(request, response);
}
else if (option.equals("delBook"))
{
String ID = request.getParameter("bookdel");
int prodID = Integer.parseInt(ID);
Projectbean catdelete = new Projectbean();
catdelete.DeleteBook(prodID);
RequestDispatcher dr = request.getRequestDispatcher("DeleteBookConfirm.jsp");
dr.include(request, response);
}
else if (option.equals("Search Book"))
{
RequestDispatcher dr = request.getRequestDispatcher("SearchBook.jsp");
dr.include(request, response);
}
else if (option.equals("searchBook"))
{
String id = request.getParameter("category");
String search = request.getParameter("search");
request.setAttribute("Catid",id);
request.setAttribute("search", search);
RequestDispatcher dr = request.getRequestDispatcher("SearchedBook.jsp");
dr.include(request, response);
}
}
@Override
public String getServletInfo() {
return "Short description";
}
}
connullnullpackage project;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class Projectbean {
private Connection con;
//student
int Studid;
String Fname;
String Lname;
String Course;
//book
int Bookid;
String Title;
String Author;
String Dborrowed;
String Dreturned;
int Fee;
//Category
int Catid;
String Catname;
//student setters
public void setStudid (int id)
{
Studid = id;
}
public void setFname (String val)
{
Fname = val;
}
public void setLname (String val)
{
Fname = val;
}
public void setCourse (String val)
{
Course = val;
}
//student getters
public int getStudid ()
{
return Studid ;
}
public String getFname ()
{
return Fname ;
}
public String getLname ()
{
return Lname ;
}
public String getCourse ()
{
return Course ;
}
//book setters
public void setBookid (int id)
{
Bookid = id;
}
public void setTitle (String val)
{
Title = val;
}
public void setAuthor (String val)
{
Author = val;
}
public void setDborrowed (String val)
{
Dborrowed = val;
}
public void setDreturned (String val)
{
Dreturned = val;
}
public void setFee (int fee)
{
Fee = fee;
}
//book getters
public int getBookid ()
{
return Bookid ;
}
public String getTitle ()
{
return Title ;
}
public String getAuthor ()
{
return Author ;
}
public String getDborrowed ()
{
return Dborrowed ;
}
public String getDreturned ()
{
return Dreturned ;
}
public int getFee ()
{
return Fee ;
}
//Category setters
public void setCatid (int id)
{
Catid = id ;
}
public void setCatname(String val)
{
Catname = val;
}
//Category getters
public int getCatid()
{
return Catid;
}
public String getCatname()
{
return Catname;
}
public Projectbean(){
try{
Class.forName("org.apache.derby.jdbc.ClientDriver");
con = DriverManager.getConnection(
"jdbc:derby://localhost:1527/final",
"", "");
}catch(Exception e){
System.out.println("Exception" + e);
}
}
//student
public ResultSet GetStudent() throws SQLException, Exception{
Statement s = con.createStatement();
ResultSet rs = s.executeQuery("Select * from APP.STUDENT");
return rs;
}
//set student id
public int rowCount() throws SQLException{
PreparedStatement st= con.prepareStatement("SELECT STUDENTID FROM APP.STUDENT");
ResultSet rs = st.executeQuery();
//get the number of rows from the result set
int count = 0;
while (rs.next()){
count = rs.getInt(1);
}
return count;
}
//get specific student
public void GetSpecificStudent (String StudID) throws SQLException, Exception{
int id = Integer.parseInt(StudID);
Statement s = con.createStatement();
ResultSet rs = s.executeQuery("Select * from APP.STUDENT WHERE STUDID="+id+" ");
rs.next();
this.Studid = id;
Fname = rs.getString("FIRSTNAME");
Lname = rs.getString ("LASTNAME");
Course = rs.getString("COURSE");
}
//Add Student
public void AddStudent(){
String read = "insert into APP.STUDENT (STUDID,FIRSTNAME,LASTNAME,COURSE) values(?,?,?,?)";
PreparedStatement addrec;
try {
addrec = con.prepareStatement(read);
addrec.setInt(1, Studid);
addrec.setString(2, Fname);
addrec.setString(3, Lname);
addrec.setString(4, Course);
addrec.execute();
}
catch (SQLException e){
System.out.println ("Exception " + e);
}
}
//edit student
public void EditStudent(){
String read = "Update APP.STUDENT set STUDID=?, FIRSTNAME=?, LASTNAME=?, COURSE=? where ID="+Studid;
PreparedStatement editRec;
try{
editRec = con.prepareStatement(read);
editRec.setInt (1,Studid);
editRec.setString(2,Fname);
editRec.setString(3,Lname);
editRec.setString(4,Course);
editRec.execute();
}
catch (SQLException e){
System.out.println ("Exception " + e);
}
}
//Delete student
public void DeleteStudent (int id) {
try
{
Statement s = con.createStatement();
String read= "Delete FROM APP.STUDENT where STUDID = "+id+"";
s.executeUpdate(read);
}
catch(SQLException e)
{
System.out.println(e);
}
}
//search student
public ResultSet SearchStudent(String search) throws SQLException, Exception{
String[] split = search.split("\\s+");
int count = split.length;
Statement s = con.createStatement();
ResultSet rs = s.executeQuery("Select * from APP.STUDENT WHERE FIRSTNAME= '"+split[0]+"' OR LASTNAME= '"+split[count-1]+"' ");
return rs;
}
//BOOK
public ResultSet GetBook() throws SQLException, Exception{
Statement s = con.createStatement();
ResultSet rs = s.executeQuery("Select * from APP.BOOK");
return rs;
}
//set book id
public int BookrowCount() throws SQLException{
PreparedStatement st= con.prepareStatement("SELECT BOOKID FROM APP.BOOK");
ResultSet rs = st.executeQuery();
//get the number of rows from the result set
int count = 0;
while (rs.next()){
count = rs.getInt(1);
}
return count;
}
//get specific book
public void GetSpecificBook (String BookID) throws SQLException, Exception{
int id = Integer.parseInt(BookID);
Statement s = con.createStatement();
ResultSet rs = s.executeQuery("Select * from APP.BOOK WHERE custID="+id+" ");
rs.next();
this.Bookid = id;
Title = rs.getString("TITLE");
Author = rs.getString ("AUTHOR");
Dborrowed = rs.getString("DATEBORROWED");
Dreturned = rs.getString("DATERETURNED");
Fee = rs.getInt("BORROWERSFEE");
}
//Add book
public void AddBook(){
String read = "insert into APP.BOOK (BOOKID,TITLE,AUTHOR,CATEGORYID) values(?,?,?)";
PreparedStatement addrec;
try {
addrec = con.prepareStatement(read);
addrec.setInt(1, Bookid);
addrec.setString(2, Title);
addrec.setString(3, Author);
addrec.setInt(4, Catid);
addrec.execute();
}
catch (SQLException e){
System.out.println ("Exception " + e);
}
}
//edit book
public void EditBook(){
String read = "Update APP.BOOK set BOOKID=?, TITLE=?, AUTHOR=?, CATEGORYID=? where BOOKID="+Bookid;
PreparedStatement editRec;
try{
editRec = con.prepareStatement(read);
editRec.setInt (1,Bookid);
editRec.setString(2,Title);
editRec.setString(3,Author);
editRec.setInt(4,Catid);
editRec.execute();
}
catch (SQLException e){
System.out.println ("Exception " + e);
}
}
//delete book
public void DeleteBook (int id) {
try
{
Statement s = con.createStatement();
String read= "Delete FROM APP.BOOK where BOOKID = "+id+"";
s.executeUpdate(read);
}
catch(SQLException e)
{
System.out.println(e);
}
}
//search book
public ResultSet SearchBook(String search) throws SQLException, Exception{
String[] split = search.split("\\s+");
int count = split.length;
Statement s = con.createStatement();
ResultSet rs = s.executeQuery("Select * from APP.book WHERE TITLE= '"+split[0]+"' OR AUTHOR= '"+split[count-1]+"' ");
return rs;
}
//CATEGORY
//Set Category ID
public int rowCountCat() throws SQLException{
PreparedStatement st= con.prepareStatement("SELECT CATEGORYID FROM APP.CATEGORY");
ResultSet rs = st.executeQuery();
//get the number of rows from the result set
int count1 = 0;
while (rs.next()){
count1 = rs.getInt(1);
}
return count1;
}
//Add Category
public void AddCategory (){
String read = "insert into APP.CATEGORY (CATEGORYID,CATEGORYNAME) values(?,?)";
PreparedStatement addrec;
try {
addrec = con.prepareStatement(read);
addrec.setInt(1, Catid);
addrec.setString(2, Catname);
addrec.execute();
}
catch (SQLException e){
System.out.println ("Exception " + e);
}
}
//Get List of Category
public ResultSet GetCategory () throws SQLException, Exception{
Statement s = con.createStatement();
ResultSet rs = s.executeQuery("Select * from APP.CATEGORY");
return rs;
}
//Get Specific Category
public void GetSpecificCategory (String catID) throws SQLException, Exception {
int id = Integer.parseInt(catID);
Statement s = con.createStatement();
ResultSet rs = s.executeQuery("Select * from APP.CATEGORY WHERE CATEGORYID="+id+" ");
rs.next();
this.Catid = id;
Catname = rs.getString("CATEGORYNAME");
}
//EDIT Category
public void EditCategory () {
String read = "Update APP.CATEGORY set CATEGORYID=?, CATEGORYNAME=? WHERE CATEGORYID="+Catid;
PreparedStatement editRec;
try{
editRec = con.prepareStatement(read);
editRec.setInt (1,Catid);
editRec.setString(2,Catname);
editRec.execute();
}
catch (SQLException e){
System.out.println ("Exception " + e);
}
}
//Delete Category
public void DeleteCategory (int id) {
try
{
Statement s = con.createStatement();
String read= "Delete FROM APP.CATEGORY where CATEGORYID = "+id+"";
s.executeUpdate(read);
}
catch(SQLException e)
{
System.out.println(e);
}
}
//Search Category
public ResultSet SearchCategory (String search) throws SQLException, Exception{
String[] split = search.split("\\s+");
int count = split.length;
Statement s = con.createStatement();
ResultSet rs = s.executeQuery("Select * from APP.CATEGORY WHERE CATEGORYNAME= '"+split[0]+"' OR CATEGORYNAME= '"+split[count-1]+"' ");
return rs;
}
}